Discussion:
LTE-Lite module
(too old to reply)
S. Jackson via time-nuts
2014-10-17 18:32:49 UTC
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Raw Message
Hello Jim,
let me answer through Time Nuts as this may interest other parties as
well.
Yes, using a fast flip flop to generate 10MHz out of the 20MHz TCXO 3.0V
CMOS output from the LTE-Lite module will preserve the phase noise (actually
improve it by up to 6dB due to the 20log(n/m) noise improvement) and will
not add any spurs if you use the clean 3.0V output from the LTE-Lite module
or an external clean power supply (please note the LTE-Lite TCXO RF output
is 3.0V due to the internal 3.3V to 3.0V Low Noise regulator feeding the
TCXO and buffer).
Use fast logic such as 74AC74, 74FCT74, or the like. We do exactly that on
our ULN-2550 boards to generate 50MHz and 25MHz out of the 100MHz, and
using a fast CMOS divider will result in additive phase noise that will be
below the crystal oscillator phase noise floor.
That will result in significantly better phase noise and much lower spurs
than using the synthesized 10MHz output from the board, and one 74' chip
can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite output. This is
exactly what we would do here if we needed a clean 10MHz from the 20MHz
LTE-Lite board.
I believe you can order low-noise divide-by-2 blue-top boxes from Wenzel
already packaged-up and connectorized as well.
Hope that helps,
Said
Hi Said
I was one of those looking for 10Mhz but I just thought again now that it
might be just as well to divide the standard 20Mhz output by 2 using a FF.
I think that would preserve all the desirable characteristics of the 20Mhz
signal which I understand to just be square wave at CMOS 3.3v levels
anyway. Is that correct?
Thanks
Jim
Jim Sanford
2014-10-17 20:37:46 UTC
Permalink
Raw Message
I have emailed Wenzel about pricing and whether or not they will sell
small quantities. Will advise.

Jim
wb4gcs-***@public.gmane.org

On 10/17/2014 2:32 PM, S. Jackson via time-nuts wrote:
>
> Hello Jim,
> let me answer through Time Nuts as this may interest other parties as
> well.
> Yes, using a fast flip flop to generate 10MHz out of the 20MHz TCXO 3.0V
> CMOS output from the LTE-Lite module will preserve the phase noise (actually
> improve it by up to 6dB due to the 20log(n/m) noise improvement) and will
> not add any spurs if you use the clean 3.0V output from the LTE-Lite module
> or an external clean power supply (please note the LTE-Lite TCXO RF output
> is 3.0V due to the internal 3.3V to 3.0V Low Noise regulator feeding the
> TCXO and buffer).
> Use fast logic such as 74AC74, 74FCT74, or the like. We do exactly that on
> our ULN-2550 boards to generate 50MHz and 25MHz out of the 100MHz, and
> using a fast CMOS divider will result in additive phase noise that will be
> below the crystal oscillator phase noise floor.
> That will result in significantly better phase noise and much lower spurs
> than using the synthesized 10MHz output from the board, and one 74' chip
> can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite output. This is
> exactly what we would do here if we needed a clean 10MHz from the 20MHz
> LTE-Lite board.
> I believe you can order low-noise divide-by-2 blue-top boxes from Wenzel
> already packaged-up and connectorized as well.
> Hope that helps,
> Said
> Hi Said
> I was one of those looking for 10Mhz but I just thought again now that it
> might be just as well to divide the standard 20Mhz output by 2 using a FF.
> I think that would preserve all the desirable characteristics of the 20Mhz
> signal which I understand to just be square wave at CMOS 3.3v levels
> anyway. Is that correct?
> Thanks
> Jim
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>


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S. Jackson via time-nuts
2014-10-17 20:40:29 UTC
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Hi there,

I don't know how much the Wenzel units are, but if someone is not able to,
or willing to build one on their own then this could be a viable
alternative.

I will look into writing a short appnote describing how a low-noise
div-by-2 can be built at home with minimal components using a surface mount '74
chip and a couple of passives.

Lastly the 20MHz LTE-Lite boards do generate a 10MHz output of course, and
if you feed that into a standard counter (5370B, 53132A etc etc) I think
the noise floor of the counter would be higher than the noise floor of the
synthesized 10MHz output, so you would not see any difference between using
the noisier synthesized output and the low-noise 10MHz TCXO divided output..

Bye,
Said


In a message dated 10/17/2014 13:19:08 Pacific Daylight Time,
gigneil-***@public.gmane.org writes:

How much would we guess that Wenzel blue-top would run you?


Relative to the low cost GPSDO, my understanding is the Wenzel parts are
priced appropriately to their quality.






On Fri, Oct 17, 2014 at 11:32 AM, S. Jackson via time-nuts
<_time-nuts-***@public.gmane.org_ (mailto:time-nuts-***@public.gmane.org) > wrote:


Hello Jim,
let me answer through Time Nuts as this may interest other parties as
well.
Yes, using a fast flip flop to generate 10MHz out of the 20MHz TCXO 3.0V
CMOS output from the LTE-Lite module will preserve the phase noise
(actually
improve it by up to 6dB due to the 20log(n/m) noise improvement) and will
not add any spurs if you use the clean 3.0V output from the LTE-Lite
module
or an external clean power supply (please note the LTE-Lite TCXO RF output
is 3.0V due to the internal 3.3V to 3.0V Low Noise regulator feeding the
TCXO and buffer).
Use fast logic such as 74AC74, 74FCT74, or the like. We do exactly that on
our ULN-2550 boards to generate 50MHz and 25MHz out of the 100MHz, and
using a fast CMOS divider will result in additive phase noise that will be
below the crystal oscillator phase noise floor.
That will result in significantly better phase noise and much lower spurs
than using the synthesized 10MHz output from the board, and one 74' chip
can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite output. This is
exactly what we would do here if we needed a clean 10MHz from the 20MHz
LTE-Lite board.
I believe you can order low-noise divide-by-2 blue-top boxes from Wenzel
already packaged-up and connectorized as well.
Hope that helps,
Said
Hi Said
I was one of those looking for 10Mhz but I just thought again now that it
might be just as well to divide the standard 20Mhz output by 2 using a FF.
I think that would preserve all the desirable characteristics of the 20Mhz
signal which I understand to just be square wave at CMOS 3.3v levels
anyway. Is that correct?
Thanks
Jim
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Jim Sanford
2014-10-17 21:06:40 UTC
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I look forward to the app note. Might be the incentive to get me to
actually USE the Express PCB software I have.....
Jim

On 10/17/2014 4:40 PM, S. Jackson via time-nuts wrote:
> Hi there,
>
> I don't know how much the Wenzel units are, but if someone is not able to,
> or willing to build one on their own then this could be a viable
> alternative.
>
> I will look into writing a short appnote describing how a low-noise
> div-by-2 can be built at home with minimal components using a surface mount '74
> chip and a couple of passives.
>
> Lastly the 20MHz LTE-Lite boards do generate a 10MHz output of course, and
> if you feed that into a standard counter (5370B, 53132A etc etc) I think
> the noise floor of the counter would be higher than the noise floor of the
> synthesized 10MHz output, so you would not see any difference between using
> the noisier synthesized output and the low-noise 10MHz TCXO divided output..
>
> Bye,
> Said
>
>
> In a message dated 10/17/2014 13:19:08 Pacific Daylight Time,
> gigneil-***@public.gmane.org writes:
>
> How much would we guess that Wenzel blue-top would run you?
>
>
> Relative to the low cost GPSDO, my understanding is the Wenzel parts are
> priced appropriately to their quality.
>
>
>
>
>
>
> On Fri, Oct 17, 2014 at 11:32 AM, S. Jackson via time-nuts
> <_time-nuts-***@public.gmane.org_ (mailto:time-nuts-***@public.gmane.org) > wrote:
>
>
> Hello Jim,
> let me answer through Time Nuts as this may interest other parties as
> well.
> Yes, using a fast flip flop to generate 10MHz out of the 20MHz TCXO 3.0V
> CMOS output from the LTE-Lite module will preserve the phase noise
> (actually
> improve it by up to 6dB due to the 20log(n/m) noise improvement) and will
> not add any spurs if you use the clean 3.0V output from the LTE-Lite
> module
> or an external clean power supply (please note the LTE-Lite TCXO RF output
> is 3.0V due to the internal 3.3V to 3.0V Low Noise regulator feeding the
> TCXO and buffer).
> Use fast logic such as 74AC74, 74FCT74, or the like. We do exactly that on
> our ULN-2550 boards to generate 50MHz and 25MHz out of the 100MHz, and
> using a fast CMOS divider will result in additive phase noise that will be
> below the crystal oscillator phase noise floor.
> That will result in significantly better phase noise and much lower spurs
> than using the synthesized 10MHz output from the board, and one 74' chip
> can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite output. This is
> exactly what we would do here if we needed a clean 10MHz from the 20MHz
> LTE-Lite board.
> I believe you can order low-noise divide-by-2 blue-top boxes from Wenzel
> already packaged-up and connectorized as well.
> Hope that helps,
> Said
> Hi Said
> I was one of those looking for 10Mhz but I just thought again now that it
> might be just as well to divide the standard 20Mhz output by 2 using a FF.
> I think that would preserve all the desirable characteristics of the 20Mhz
> signal which I understand to just be square wave at CMOS 3.3v levels
> anyway. Is that correct?
> Thanks
> Jim
> _______________________________________________
> time-nuts mailing list -- _time-nuts-***@public.gmane.org_ (mailto:time-nuts-***@public.gmane.org)
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
>
>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>


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Neil Schroeder
2014-10-17 20:19:07 UTC
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Raw Message
How much would we guess that Wenzel blue-top would run you?

Relative to the low cost GPSDO, my understanding is the Wenzel parts are
priced appropriately to their quality.



On Fri, Oct 17, 2014 at 11:32 AM, S. Jackson via time-nuts <
time-nuts-***@public.gmane.org> wrote:

>
> Hello Jim,
> let me answer through Time Nuts as this may interest other parties as
> well.
> Yes, using a fast flip flop to generate 10MHz out of the 20MHz TCXO 3.0V
> CMOS output from the LTE-Lite module will preserve the phase noise
> (actually
> improve it by up to 6dB due to the 20log(n/m) noise improvement) and will
> not add any spurs if you use the clean 3.0V output from the LTE-Lite
> module
> or an external clean power supply (please note the LTE-Lite TCXO RF output
> is 3.0V due to the internal 3.3V to 3.0V Low Noise regulator feeding the
> TCXO and buffer).
> Use fast logic such as 74AC74, 74FCT74, or the like. We do exactly that on
> our ULN-2550 boards to generate 50MHz and 25MHz out of the 100MHz, and
> using a fast CMOS divider will result in additive phase noise that will be
> below the crystal oscillator phase noise floor.
> That will result in significantly better phase noise and much lower spurs
> than using the synthesized 10MHz output from the board, and one 74' chip
> can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite output. This is
> exactly what we would do here if we needed a clean 10MHz from the 20MHz
> LTE-Lite board.
> I believe you can order low-noise divide-by-2 blue-top boxes from Wenzel
> already packaged-up and connectorized as well.
> Hope that helps,
> Said
> Hi Said
> I was one of those looking for 10Mhz but I just thought again now that it
> might be just as well to divide the standard 20Mhz output by 2 using a FF.
> I think that would preserve all the desirable characteristics of the 20Mhz
> signal which I understand to just be square wave at CMOS 3.3v levels
> anyway. Is that correct?
> Thanks
> Jim
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
S. Jackson via time-nuts
2014-10-18 01:12:25 UTC
Permalink
Raw Message
And lastly the entire setup as tested:


In a message dated 10/17/2014 11:32:49 Pacific Daylight Time,
SAIDJACK-***@public.gmane.org writes:


Hello Jim,
let me answer through Time Nuts as this may interest other parties as
well.
Yes, using a fast flip flop to generate 10MHz out of the 20MHz TCXO 3.0V
CMOS output from the LTE-Lite module will preserve the phase noise (actually
improve it by up to 6dB due to the 20log(n/m) noise improvement) and will
not add any spurs if you use the clean 3.0V output from the LTE-Lite module
or an external clean power supply (please note the LTE-Lite TCXO RF output
is 3.0V due to the internal 3.3V to 3.0V Low Noise regulator feeding the
TCXO and buffer).
Use fast logic such as 74AC74, 74FCT74, or the like. We do exactly that on
our ULN-2550 boards to generate 50MHz and 25MHz out of the 100MHz, and
using a fast CMOS divider will result in additive phase noise that will be
below the crystal oscillator phase noise floor.
That will result in significantly better phase noise and much lower spurs
than using the synthesized 10MHz output from the board, and one 74' chip
can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite output. This is
exactly what we would do here if we needed a clean 10MHz from the 20MHz
LTE-Lite board.
I believe you can order low-noise divide-by-2 blue-top boxes from Wenzel
already packaged-up and connectorized as well.
Hope that helps,
Said
Hi Said
I was one of those looking for 10Mhz but I just thought again now that it
might be just as well to divide the standard 20Mhz output by 2 using a FF.
I think that would preserve all the desirable characteristics of the 20Mhz
signal which I understand to just be square wave at CMOS 3.3v levels
anyway. Is that correct?
Thanks
Jim
S. Jackson via time-nuts
2014-10-18 01:10:01 UTC
Permalink
Raw Message
Jim, et. al.,

I spent some time today and put together a Divide-by-2 circuit. Attached
are the schematics, I will send some photos in additional mails so we don't
overload the mail system.

Some comments:

* I grab the 3.0V from capacitor C6 on the eval board. That is the
low-noise filtered analog supply. By loading it with the FF, that voltage goes
down to 2.86V.. Using the digital 3.3V supply resulted in excessive spurs.

* I used only two additional components: a cap and a series resistor

* The IC I used was an old Fairchild 74LVX74 SO-14 chip I had laying around

* Notice the nice improvement in phase noise, and the absence of any
measurable spurs

* Notice the nice 6dB phase noise improvement compared to using the direct
outptut, even the floor improved to close to my reference noise floor, so
theory meets practice

* I spent less than 45 minutes building this on a small copper-clad board,
using the ground of the board as much as possible

* The output power of the 74LVC74 driving the 50 Ohms input impedance of
the analyzer is pretty low, less than 7dBm, so a nice buffer would help

* Notice how I set the Q output of the unused FF to 0V, and then connect
that pin to ground to use it as an additional ground pin

* While I wired up the 3.0V power to the eval board, I did not even bother
wiring up the ground. I simply used the coax cables as DC ground return

* The LTE-Lite board was powered from a Thinkpad PC via USB cable, and
disciplining to GPS so I did not even use an external low-noise isolated 5V lab
supply or anything like that, just the noise PC's USB port.

Bye,
Said



In a message dated 10/17/2014 11:32:49 Pacific Daylight Time,
SAIDJACK-***@public.gmane.org writes:


Hello Jim,
let me answer through Time Nuts as this may interest other parties as
well.
Yes, using a fast flip flop to generate 10MHz out of the 20MHz TCXO 3.0V
CMOS output from the LTE-Lite module will preserve the phase noise (actually
improve it by up to 6dB due to the 20log(n/m) noise improvement) and will
not add any spurs if you use the clean 3.0V output from the LTE-Lite module
or an external clean power supply (please note the LTE-Lite TCXO RF output
is 3.0V due to the internal 3.3V to 3.0V Low Noise regulator feeding the
TCXO and buffer).
Use fast logic such as 74AC74, 74FCT74, or the like. We do exactly that on
our ULN-2550 boards to generate 50MHz and 25MHz out of the 100MHz, and
using a fast CMOS divider will result in additive phase noise that will be
below the crystal oscillator phase noise floor.
That will result in significantly better phase noise and much lower spurs
than using the synthesized 10MHz output from the board, and one 74' chip
can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite output. This is
exactly what we would do here if we needed a clean 10MHz from the 20MHz
LTE-Lite board.
I believe you can order low-noise divide-by-2 blue-top boxes from Wenzel
already packaged-up and connectorized as well.
Hope that helps,
Said
Hi Said
I was one of those looking for 10Mhz but I just thought again now that it
might be just as well to divide the standard 20Mhz output by 2 using a FF.
I think that would preserve all the desirable characteristics of the 20Mhz
signal which I understand to just be square wave at CMOS 3.3v levels
anyway. Is that correct?
Thanks
Jim
S. Jackson via time-nuts
2014-10-18 01:10:52 UTC
Permalink
Raw Message
Jim,

Here is the resulting 10MHz phase noise plot from the 20MHz TCXO output:


In a message dated 10/17/2014 11:32:49 Pacific Daylight Time,
SAIDJACK-***@public.gmane.org writes:


Hello Jim,
let me answer through Time Nuts as this may interest other parties as
well.
Yes, using a fast flip flop to generate 10MHz out of the 20MHz TCXO 3.0V
CMOS output from the LTE-Lite module will preserve the phase noise (actually
improve it by up to 6dB due to the 20log(n/m) noise improvement) and will
not add any spurs if you use the clean 3.0V output from the LTE-Lite module
or an external clean power supply (please note the LTE-Lite TCXO RF output
is 3.0V due to the internal 3.3V to 3.0V Low Noise regulator feeding the
TCXO and buffer).
Use fast logic such as 74AC74, 74FCT74, or the like. We do exactly that on
our ULN-2550 boards to generate 50MHz and 25MHz out of the 100MHz, and
using a fast CMOS divider will result in additive phase noise that will be
below the crystal oscillator phase noise floor.
That will result in significantly better phase noise and much lower spurs
than using the synthesized 10MHz output from the board, and one 74' chip
can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite output. This is
exactly what we would do here if we needed a clean 10MHz from the 20MHz
LTE-Lite board.
I believe you can order low-noise divide-by-2 blue-top boxes from Wenzel
already packaged-up and connectorized as well.
Hope that helps,
Said
Hi Said
I was one of those looking for 10Mhz but I just thought again now that it
might be just as well to divide the standard 20Mhz output by 2 using a FF.
I think that would preserve all the desirable characteristics of the 20Mhz
signal which I understand to just be square wave at CMOS 3.3v levels
anyway. Is that correct?
Thanks
Jim
John C. Westmoreland, P.E.
2014-10-18 01:37:14 UTC
Permalink
Raw Message
Said,

What tool(s) did you use to generate that data and output the graph?

Thanks,
John


On Fri, Oct 17, 2014 at 6:10 PM, S. Jackson via time-nuts <
time-nuts-***@public.gmane.org> wrote:

> Jim,
>
> Here is the resulting 10MHz phase noise plot from the 20MHz TCXO output:
>
>
> In a message dated 10/17/2014 11:32:49 Pacific Daylight Time,
> SAIDJACK-***@public.gmane.org writes:
>
>
> Hello Jim,
> let me answer through Time Nuts as this may interest other parties as
> well.
> Yes, using a fast flip flop to generate 10MHz out of the 20MHz TCXO 3.0V
> CMOS output from the LTE-Lite module will preserve the phase noise
> (actually
> improve it by up to 6dB due to the 20log(n/m) noise improvement) and will
> not add any spurs if you use the clean 3.0V output from the LTE-Lite
> module
> or an external clean power supply (please note the LTE-Lite TCXO RF output
> is 3.0V due to the internal 3.3V to 3.0V Low Noise regulator feeding the
> TCXO and buffer).
> Use fast logic such as 74AC74, 74FCT74, or the like. We do exactly that on
> our ULN-2550 boards to generate 50MHz and 25MHz out of the 100MHz, and
> using a fast CMOS divider will result in additive phase noise that will be
> below the crystal oscillator phase noise floor.
> That will result in significantly better phase noise and much lower spurs
> than using the synthesized 10MHz output from the board, and one 74' chip
> can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite output. This is
> exactly what we would do here if we needed a clean 10MHz from the 20MHz
> LTE-Lite board.
> I believe you can order low-noise divide-by-2 blue-top boxes from Wenzel
> already packaged-up and connectorized as well.
> Hope that helps,
> Said
> Hi Said
> I was one of those looking for 10Mhz but I just thought again now that it
> might be just as well to divide the standard 20Mhz output by 2 using a FF.
> I think that would preserve all the desirable characteristics of the 20Mhz
> signal which I understand to just be square wave at CMOS 3.3v levels
> anyway. Is that correct?
> Thanks
> Jim
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
S. Jackson via time-nuts
2014-10-18 01:11:56 UTC
Permalink
Raw Message
Some photos of the divider module I built:


In a message dated 10/17/2014 11:32:49 Pacific Daylight Time,
SAIDJACK-***@public.gmane.org writes:


Hello Jim,
let me answer through Time Nuts as this may interest other parties as
well.
Yes, using a fast flip flop to generate 10MHz out of the 20MHz TCXO 3.0V
CMOS output from the LTE-Lite module will preserve the phase noise (actually
improve it by up to 6dB due to the 20log(n/m) noise improvement) and will
not add any spurs if you use the clean 3.0V output from the LTE-Lite module
or an external clean power supply (please note the LTE-Lite TCXO RF output
is 3.0V due to the internal 3.3V to 3.0V Low Noise regulator feeding the
TCXO and buffer).
Use fast logic such as 74AC74, 74FCT74, or the like. We do exactly that on
our ULN-2550 boards to generate 50MHz and 25MHz out of the 100MHz, and
using a fast CMOS divider will result in additive phase noise that will be
below the crystal oscillator phase noise floor.
That will result in significantly better phase noise and much lower spurs
than using the synthesized 10MHz output from the board, and one 74' chip
can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite output. This is
exactly what we would do here if we needed a clean 10MHz from the 20MHz
LTE-Lite board.
I believe you can order low-noise divide-by-2 blue-top boxes from Wenzel
already packaged-up and connectorized as well.
Hope that helps,
Said
Hi Said
I was one of those looking for 10Mhz but I just thought again now that it
might be just as well to divide the standard 20Mhz output by 2 using a FF.
I think that would preserve all the desirable characteristics of the 20Mhz
signal which I understand to just be square wave at CMOS 3.3v levels
anyway. Is that correct?
Thanks
Jim
S. Jackson via time-nuts
2014-10-18 01:54:37 UTC
Permalink
Raw Message
John,

I used John Miles Timepod and associated application software, now
available from Microsemi, and highly recommended. I fed the output of the DFF
directly into the timepod (via a DC-block and 33 Ohms series resistor).

The reference was an HP 58503A GPSDO which limits the noise floor of the
measurement a bit.

bye,
Said


In a message dated 10/17/2014 18:45:11 Pacific Daylight Time,
john-***@public.gmane.org writes:

Said,

What tool(s) did you use to generate that data and output the graph?

Thanks,
John


On Fri, Oct 17, 2014 at 6:10 PM, S. Jackson via time-nuts <
time-nuts-***@public.gmane.org> wrote:

> Jim,
>
> Here is the resulting 10MHz phase noise plot from the 20MHz TCXO output:
>
>
> In a message dated 10/17/2014 11:32:49 Pacific Daylight Time,
> SAIDJACK-***@public.gmane.org writes:
>
>
> Hello Jim,
> let me answer through Time Nuts as this may interest other parties as
> well.
> Yes, using a fast flip flop to generate 10MHz out of the 20MHz TCXO 3.0V
> CMOS output from the LTE-Lite module will preserve the phase noise
> (actually
> improve it by up to 6dB due to the 20log(n/m) noise improvement) and
will
> not add any spurs if you use the clean 3.0V output from the LTE-Lite
> module
> or an external clean power supply (please note the LTE-Lite TCXO RF
output
> is 3.0V due to the internal 3.3V to 3.0V Low Noise regulator feeding the
> TCXO and buffer).
> Use fast logic such as 74AC74, 74FCT74, or the like. We do exactly that
on
> our ULN-2550 boards to generate 50MHz and 25MHz out of the 100MHz, and
> using a fast CMOS divider will result in additive phase noise that will
be
> below the crystal oscillator phase noise floor.
> That will result in significantly better phase noise and much lower
spurs
> than using the synthesized 10MHz output from the board, and one 74' chip
> can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite output. This
is
> exactly what we would do here if we needed a clean 10MHz from the 20MHz
> LTE-Lite board.
> I believe you can order low-noise divide-by-2 blue-top boxes from
Wenzel
> already packaged-up and connectorized as well.
> Hope that helps,
> Said
> Hi Said
> I was one of those looking for 10Mhz but I just thought again now that
it
> might be just as well to divide the standard 20Mhz output by 2 using a
FF.
> I think that would preserve all the desirable characteristics of the
20Mhz
> signal which I understand to just be square wave at CMOS 3.3v levels
> anyway. Is that correct?
> Thanks
> Jim
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
_______________________________________________
time-nuts mailing list -- time-nuts-***@public.gmane.org
To unsubscribe, go to
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and follow the instructions there.
Dr. David Kirkby (Kirkby Microwave Ltd)
2014-10-18 13:34:48 UTC
Permalink
Raw Message
On 17 Oct 2014 19:33, "S. Jackson via time-nuts" <time-nuts-***@public.gmane.org> wrote:
>
>
> Hello Jim,
> let me answer through Time Nuts as this may interest other parties as
> well.
> Yes, using a fast flip flop to generate 10MHz out of the 20MHz TCXO 3.0V
> CMOS output from the LTE-Lite module will preserve the phase noise
(actually
> improve it by up to 6dB due to the 20log(n/m) noise improvement)

Hi Said,

I am only looking for a good clean 10 MHz reference for my lab to feed into
instruments like my SA, VNA, signal generator etc. Would I be right in
concluding the best way to achieve this is to use the 20 MHz version and
the simple divide by 2 that you showed?

I was going to place an order for the 10 MHz version, despite the long lead
time, but if I understand you correctly I would get better performance in
less time by going for the 20 MHz version and a ÷2.

The other thing I am not so sure about is what the specification of the
external TCXO/OCXO needs to be. I gather it is 3.3 V, but does it need to
generate a sine or square wave? What amolitude? I was wondering if there
would be some advantage in using a 10 MHz OCXO, such as an HP 10811A rather
than the inbuilt TCXO. Without knowing what your board expects to see, it
is impossible to know what to type to add.

Dave



and will
> not add any spurs if you use the clean 3.0V output from the LTE-Lite
module
> or an external clean power supply (please note the LTE-Lite TCXO RF
output
> is 3.0V due to the internal 3.3V to 3.0V Low Noise regulator feeding the
> TCXO and buffer).
> Use fast logic such as 74AC74, 74FCT74, or the like.

We do exactly that on
> our ULN-2550 boards to generate 50MHz and 25MHz out of the 100MHz, and
> using a fast CMOS divider will result in additive phase noise that will
be
> below the crystal oscillator phase noise floor.
> That will result in significantly better phase noise and much lower spurs
> than using the synthesized 10MHz output from the board, and one 74' chip
> can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite output. This
is
> exactly what we would do here if we needed a clean 10MHz from the 20MHz
> LTE-Lite board.
> I believe you can order low-noise divide-by-2 blue-top boxes from Wenzel
> already packaged-up and connectorized as well.
> Hope that helps,
> Said
> Hi Said
> I was one of those looking for 10Mhz but I just thought again now that it
> might be just as well to divide the standard 20Mhz output by 2 using a
FF.
> I think that would preserve all the desirable characteristics of the
20Mhz
> signal which I understand to just be square wave at CMOS 3.3v levels
> anyway. Is that correct?
> Thanks
> Jim
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
Bob Camp
2014-10-18 17:43:15 UTC
Permalink
Raw Message
Hi

For a lab reference, “clean” is a relative term. Most (as in every one I’ve ever seen) instruments expect a dirty signal on the reference input. They phase lock an internal oscillator to clean it up. Past some (unfortunately variable) offset, the reference signal has no impact on the instrument at all. In most cases, that offset is below 50 Hz in order to reject power line induced spurs on the reference signal. Yes, phase noise inside 10 or 20 Hz may matter. ADEV at 1 sec and longer is probably a better thing to look at.

How good does it need to be? Most counters are quite happy with an ADEV at the 1x10^-11 level at 1 second. VNA’s and spectrum analyzers will be happy with something even less stable. Synthesizers will (ultimately) pass along what ever is on the reference to the output. Your specific test application will dictate if a 1x10^-12 wander at 100,000 seconds on your synthesizer is important or not.

Bob

> On Oct 18, 2014, at 9:34 AM, Dr. David Kirkby (Kirkby Microwave Ltd) <drkirkby-***@public.gmane.org> wrote:
>
> On 17 Oct 2014 19:33, "S. Jackson via time-nuts" <time-nuts-***@public.gmane.org> wrote:
>>
>>
>> Hello Jim,
>> let me answer through Time Nuts as this may interest other parties as
>> well.
>> Yes, using a fast flip flop to generate 10MHz out of the 20MHz TCXO 3.0V
>> CMOS output from the LTE-Lite module will preserve the phase noise
> (actually
>> improve it by up to 6dB due to the 20log(n/m) noise improvement)
>
> Hi Said,
>
> I am only looking for a good clean 10 MHz reference for my lab to feed into
> instruments like my SA, VNA, signal generator etc. Would I be right in
> concluding the best way to achieve this is to use the 20 MHz version and
> the simple divide by 2 that you showed?
>
> I was going to place an order for the 10 MHz version, despite the long lead
> time, but if I understand you correctly I would get better performance in
> less time by going for the 20 MHz version and a ÷2.
>
> The other thing I am not so sure about is what the specification of the
> external TCXO/OCXO needs to be. I gather it is 3.3 V, but does it need to
> generate a sine or square wave? What amolitude? I was wondering if there
> would be some advantage in using a 10 MHz OCXO, such as an HP 10811A rather
> than the inbuilt TCXO. Without knowing what your board expects to see, it
> is impossible to know what to type to add.
>
> Dave
>
>
>
> and will
>> not add any spurs if you use the clean 3.0V output from the LTE-Lite
> module
>> or an external clean power supply (please note the LTE-Lite TCXO RF
> output
>> is 3.0V due to the internal 3.3V to 3.0V Low Noise regulator feeding the
>> TCXO and buffer).
>> Use fast logic such as 74AC74, 74FCT74, or the like.
>
> We do exactly that on
>> our ULN-2550 boards to generate 50MHz and 25MHz out of the 100MHz, and
>> using a fast CMOS divider will result in additive phase noise that will
> be
>> below the crystal oscillator phase noise floor.
>> That will result in significantly better phase noise and much lower spurs
>> than using the synthesized 10MHz output from the board, and one 74' chip
>> can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite output. This
> is
>> exactly what we would do here if we needed a clean 10MHz from the 20MHz
>> LTE-Lite board.
>> I believe you can order low-noise divide-by-2 blue-top boxes from Wenzel
>> already packaged-up and connectorized as well.
>> Hope that helps,
>> Said
>> Hi Said
>> I was one of those looking for 10Mhz but I just thought again now that it
>> might be just as well to divide the standard 20Mhz output by 2 using a
> FF.
>> I think that would preserve all the desirable characteristics of the
> 20Mhz
>> signal which I understand to just be square wave at CMOS 3.3v levels
>> anyway. Is that correct?
>> Thanks
>> Jim
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
S. Jackson via time-nuts
2014-10-18 18:19:24 UTC
Permalink
Raw Message
Hi guys,

lots of questions, let me try to answer some of these. Bob, David, et. al,
thanks for answering some of these already!

Dave, as Bob said "it depends on your application" -- and your time frame.
Also, please check the FAQ for an answer on the external TCXO requirement,
specifically item 35. in the FAQ on the Ebay website for the product.

Jim, I ended up doing the "appnote" in email format, and sending out a
description, schematics, PN plot, and photos yesterday, please check your
emails. I won't do a formal appnote, sorry no time.. I hope the description of
what I wired-up yesterday is good enough for folks to try the same.

Ernie, as mentioned here the price is $185 plus shipping on Ebay for the
entire kit. Shipping is calculated by Ebay, and should be a flat-rate of $10
in the continental US

Hal, MY BAD!! I should have known better and super-imposed both the
original 20MHz and 10MHz plots on the same plot. I will do so shortly. On the
table in the plot: the TimePod tries to determine spurs, and display them on
the upper right hand of the plot in a table, and with the phase noise being
as clean as it is I guess the TimePod software could only find two spurs,
one at 0.8 and one at 0.9Hz offset from carrier, which was not even shown in
that plot since it starts at 1Hz.

Thanks so much for your feedback, lively discussion, and good questions
guys.

I hope that answers all questions,
bye,
Said


In a message dated 10/18/2014 10:43:40 Pacific Daylight Time, ***@n1k.org
writes:

Hi

For a lab reference, “clean” is a relative term. Most (as in every one I’
ve ever seen) instruments expect a dirty signal on the reference input.
They phase lock an internal oscillator to clean it up. Past some
(unfortunately variable) offset, the reference signal has no impact on the instrument at
all. In most cases, that offset is below 50 Hz in order to reject power
line induced spurs on the reference signal. Yes, phase noise inside 10 or 20
Hz may matter. ADEV at 1 sec and longer is probably a better thing to look
at.

How good does it need to be? Most counters are quite happy with an ADEV at
the 1x10^-11 level at 1 second. VNA’s and spectrum analyzers will be happy
with something even less stable. Synthesizers will (ultimately) pass along
what ever is on the reference to the output. Your specific test
application will dictate if a 1x10^-12 wander at 100,000 seconds on your synthesizer
is important or not.

Bob

> On Oct 18, 2014, at 9:34 AM, Dr. David Kirkby (Kirkby Microwave Ltd)
<drkirkby-***@public.gmane.org> wrote:
>
> On 17 Oct 2014 19:33, "S. Jackson via time-nuts" <time-nuts-***@public.gmane.org>
wrote:
>>
>>
>> Hello Jim,
>> let me answer through Time Nuts as this may interest other parties as
>> well.
>> Yes, using a fast flip flop to generate 10MHz out of the 20MHz TCXO
3.0V
>> CMOS output from the LTE-Lite module will preserve the phase noise
> (actually
>> improve it by up to 6dB due to the 20log(n/m) noise improvement)
>
> Hi Said,
>
> I am only looking for a good clean 10 MHz reference for my lab to feed
into
> instruments like my SA, VNA, signal generator etc. Would I be right in
> concluding the best way to achieve this is to use the 20 MHz version and
> the simple divide by 2 that you showed?
>
> I was going to place an order for the 10 MHz version, despite the long
lead
> time, but if I understand you correctly I would get better performance in
> less time by going for the 20 MHz version and a ÷2.
>
> The other thing I am not so sure about is what the specification of the
> external TCXO/OCXO needs to be. I gather it is 3.3 V, but does it need to
> generate a sine or square wave? What amolitude? I was wondering if there
> would be some advantage in using a 10 MHz OCXO, such as an HP 10811A
rather
> than the inbuilt TCXO. Without knowing what your board expects to see, it
> is impossible to know what to type to add.
>
> Dave
>
>
>
> and will
>> not add any spurs if you use the clean 3.0V output from the LTE-Lite
> module
>> or an external clean power supply (please note the LTE-Lite TCXO RF
> output
>> is 3.0V due to the internal 3.3V to 3.0V Low Noise regulator feeding the
>> TCXO and buffer).
>> Use fast logic such as 74AC74, 74FCT74, or the like.
>
> We do exactly that on
>> our ULN-2550 boards to generate 50MHz and 25MHz out of the 100MHz, and
>> using a fast CMOS divider will result in additive phase noise that will
> be
>> below the crystal oscillator phase noise floor.
>> That will result in significantly better phase noise and much lower
spurs
>> than using the synthesized 10MHz output from the board, and one 74'
chip
>> can generate both 10MHz and 5MHz out of the 20MHz LTE-Lite output. This
> is
>> exactly what we would do here if we needed a clean 10MHz from the 20MHz
>> LTE-Lite board.
>> I believe you can order low-noise divide-by-2 blue-top boxes from
Wenzel
>> already packaged-up and connectorized as well.
>> Hope that helps,
>> Said
>> Hi Said
>> I was one of those looking for 10Mhz but I just thought again now that
it
>> might be just as well to divide the standard 20Mhz output by 2 using a
> FF.
>> I think that would preserve all the desirable characteristics of the
> 20Mhz
>> signal which I understand to just be square wave at CMOS 3.3v levels
>> anyway. Is that correct?
>> Thanks
>> Jim
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

_______________________________________________
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Jim Sanford
2014-10-18 22:26:08 UTC
Permalink
Raw Message
Said:
Your email "app note" was VERY clear, thanks.

You also mentioned somewhere that the synthesizer output of 10 MHz is
cleaner than most freq counters, etc., need, so I will probably just use
that for the test equipment. I will use the 20 MHz as reference for
microwave LOs, and will do the divide by two board so I have a good 10
MHz reference as well.

I've already ordered, holding my breath for arrival!

Thanks,
Jim

On 10/18/2014 2:19 PM, S. Jackson via time-nuts wrote:
> Hi guys,
>
> Jim, I ended up doing the "appnote" in email format, and sending out a
> description, schematics, PN plot, and photos yesterday, please check your
> emails. I won't do a formal appnote, sorry no time.. I hope the description of
> what I wired-up yesterday is good enough for folks to try the same.
>
>


---
This email is free from viruses and malware because avast! Antivirus protection is active.
http://www.avast.com
S. Jackson via time-nuts
2014-10-18 19:55:37 UTC
Permalink
Raw Message
Guys,
we have been getting a good number of emails with questions that have
already been addressed in the user manual or the FAQ, see the below link. We
spent a lot of time putting the collateral together, may I please ask that
you first look into these two documents to see if your question might already
be addressed there?
Paul,
please search the LTE Lite user manual for "Hammond" and you will find it
there:
http://www.jackson-labs.com/index.php/products/lte_lite
Thanks,
Said
_____________________
Do you have a recommended Hammond chassis part number?
--
Paul
S. Jackson via time-nuts
2014-10-18 20:10:29 UTC
Permalink
Raw Message
Hal,

attached is the superimposed plot of the standard 20MHz TCXO Phase Noise
and the 10MHz output of my bare-bones divide by 2 flip-flop. The green trace
is the new 20MHz plot, the blue the one I had sent out yesterday at 10MHz,
both sourced from the same TCXO.


You can nicely see that the noise improves by almost exactly 6dB at 100Hz
just as theory would have it. One problem is that my reference has "only" a
noise floor of about -160dBc/Hz at 10MHz, so when I measure 20MHz signals
that actually degrades to the equivalent of -154dBc/Hz due to the reference
noise floor.


Are these plots going to be the same on all the boards? No, these are
typical plots for the particular random unit I tested here, and my particular
test setup. Some of the units will have better noise, some worse. The
variations in performance from crystal to crystal have been discussed here on this
email list many times in the past.


BTW: we recently noticed a very peculiar caveat:


When plugging in the external TCXO (and by the way we decided to mount a
TCXO socket on every one of the eval kits to make life easier for everyone)
and running from the external TCXO there could be a beat frequency from the
internal TCXO, because while the output of the internal TCXO is disabled,
the crystal itself is still powered up and running and thus causing a slight
interference with the external TCXO.

What happens when an external 10MHz TCXO is plugged in with the internal
20MHz TCXO is that there is harmonic mixing at 20MHz, 30MHz etc, and due to
the fact that only the external TCXO is disciplined (the internal TCXO gets
the same exact EFC voltage but will run at a harmonic offset of typically
many hertz) there is a beat frequency that results.

On our particular unit with 20MHz internal TCXO and 10MHz external TCXO
that beat frequency happens to be about 10Hz between the two crystals. So this
results in a number of fairly strong spurs at 10Hz, 20Hz, 30Hz, etc etc
offsets from the carrier.

To fix that issue there are two solutions:

1) Use an external TCXO that is not harmonically related to the internal
TCXO. Such as 10MHz on a 19.2MHz board, or 15.36MHz on a 20MHz board. I
realize that this may not be practical

2) remove the internal TCXO carefully with a heat-gun when using the
external TCXO

Unfortunately we have no way to power-off the internal TCXO completely, and
we cannot avoid physics..

The 10MHz boards with external TCXO won't have this problem as there will
not be a small SMT TCXO mounted on the LTE-Lite module itself, so no
harmonic mixing will happen.

Bye,
Said


In a message dated 10/18/2014 00:36:27 Pacific Daylight Time,
hmurray-8cQiHa/C+6Go9G/***@public.gmane.org writes:

> Here is the resulting 10MHz phase noise plot from the 20MHz TCXO
output:

There is a box in the upper right that says -76.8 dBc at 0.8 Hz and -85
dBc
at 0.9 Hz. I can't make sense out of that. It's off scale to the left of
the plot, but looks like it would be higher than those values.

It would be neat to see the phase noise of the un-divided 20 Mhz OSC and
also
the 10 MHz OSC.



--
These are my opinions. I hate spam.
S. Jackson via time-nuts
2014-10-18 22:13:04 UTC
Permalink
Raw Message
Guys,

one last email. The board will not fit into the Hammond enclosure without
reworking the enclosure or removing the TCXO socket. We initially planned to
ship the board without the socket, now all of them will have it. The
board was designed to be used without the TCXO/Socket to fit into that
enclosure.

Caveat: please expect some rework to be necessary when using the suggested
Hammond enclosure.

bye,
Said


In a message dated 10/18/2014 12:56:06 Pacific Daylight Time,
time-nuts-***@public.gmane.org writes:


Guys,
we have been getting a good number of emails with questions that have
already been addressed in the user manual or the FAQ, see the below link.
We
spent a lot of time putting the collateral together, may I please ask
that
you first look into these two documents to see if your question might
already
be addressed there?
Paul,
please search the LTE Lite user manual for "Hammond" and you will find it
there:
http://www.jackson-labs.com/index.php/products/lte_lite
Thanks,
Said
_____________________
Do you have a recommended Hammond chassis part number?
--
Paul
_______________________________________________
time-nuts mailing list -- time-nuts-***@public.gmane.org
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Said Jackson via time-nuts
2014-10-18 22:52:31 UTC
Permalink
Raw Message
Hi Bill,

I think it makes perfect sense. But I have no idea how the units' loop stability would be with the 10811. That kind of testing is on the plate.

You would preferably set the OCXO to a nominal tuning voltage of 1.5V using the mechanical adjustment, then let the LTE Lite do the rest.

Please note that the LTE board will auto-sense the external ocxo frequency, so any of the boards would work.

Please also note that due to the harmonic mixing issues I described earlier the best board to use for that setup would be the 19.2MHz version(!) or to remove the on-board tcxo altogether.

Bye,
Said

Sent From iPhone

> On Oct 18, 2014, at 15:24, Bill Dailey <docdailey-***@public.gmane.org> wrote:
>
> Said,
>
> How tough would it be to mate the 10Mhz version up to a really good 10811? I have one that I acquired from Corby some time ago. I was going to spin my own but I wont realistically get to that with everything else I have going on. I was thinking of throwing the LTE-Lite and the 10811 in a box. I woudl then have a stock fury, An enhanced OEM fury (datum-1111c) and then this gadget with a 10-13 10811. Let me know if this doesnt make sense. I am an amateur.
>
> Bill
>
>> On Sat, Oct 18, 2014 at 5:13 PM, S. Jackson via time-nuts <time-***@febo.com> wrote:
>> Guys,
>>
>> one last email. The board will not fit into the Hammond enclosure without
>> reworking the enclosure or removing the TCXO socket. We initially planned to
>> ship the board without the socket, now all of them will have it. The
>> board was designed to be used without the TCXO/Socket to fit into that
>> enclosure.
>>
>> Caveat: please expect some rework to be necessary when using the suggested
>> Hammond enclosure.
>>
>> bye,
>> Said
>>
>>
>> In a message dated 10/18/2014 12:56:06 Pacific Daylight Time,
>> time-nuts-***@public.gmane.org writes:
>>
>>
>> Guys,
>> we have been getting a good number of emails with questions that have
>> already been addressed in the user manual or the FAQ, see the below link.
>> We
>> spent a lot of time putting the collateral together, may I please ask
>> that
>> you first look into these two documents to see if your question might
>> already
>> be addressed there?
>> Paul,
>> please search the LTE Lite user manual for "Hammond" and you will find it
>> there:
>> http://www.jackson-labs.com/index.php/products/lte_lite
>> Thanks,
>> Said
>> _____________________
>> Do you have a recommended Hammond chassis part number?
>> --
>> Paul
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
>
>
> --
> Doc
>
> Bill Dailey
> KXØO
>
>
>
>
Bill Riches
2014-10-19 12:00:27 UTC
Permalink
Raw Message
Hi Said,

Thank you for taking the time to answer questions and provide info on the LTE unit to our group. I know we will not add much to your bottom line as we are a small group. We have come a long way with Thunderbolt without any help whatsoever with that company. Will be an interesting ride with your products!

73,

Bill, WA2DVU
Cape May, NJ

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces-***@public.gmane.org] On Behalf Of Said Jackson via time-nuts
Sent: Saturday, October 18, 2014 6:53 PM
To: Bill Dailey
Cc: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] LTE-Lite module

Hi Bill,

I think it makes perfect sense. But I have no idea how the units' loop stability would be with the 10811. That kind of testing is on the plate.

You would preferably set the OCXO to a nominal tuning voltage of 1.5V using the mechanical adjustment, then let the LTE Lite do the rest.

Please note that the LTE board will auto-sense the external ocxo frequency, so any of the boards would work.

Please also note that due to the harmonic mixing issues I described earlier the best board to use for that setup would be the 19.2MHz version(!) or to remove the on-board tcxo altogether.

Bye,
Said

Sent From iPhone

> On Oct 18, 2014, at 15:24, Bill Dailey <docdailey-***@public.gmane.org> wrote:
>
> Said,
>
> How tough would it be to mate the 10Mhz version up to a really good 10811? I have one that I acquired from Corby some time ago. I was going to spin my own but I wont realistically get to that with everything else I have going on. I was thinking of throwing the LTE-Lite and the 10811 in a box. I woudl then have a stock fury, An enhanced OEM fury (datum-1111c) and then this gadget with a 10-13 10811. Let me know if this doesnt make sense. I am an amateur.
>
> Bill
>
>> On Sat, Oct 18, 2014 at 5:13 PM, S. Jackson via time-nuts <time-***@febo.com> wrote:
>> Guys,
>>
>> one last email. The board will not fit into the Hammond enclosure
>> without reworking the enclosure or removing the TCXO socket. We
>> initially planned to ship the board without the socket, now all of
>> them will have it. The board was designed to be used without the
>> TCXO/Socket to fit into that enclosure.
>>
>> Caveat: please expect some rework to be necessary when using the
>> suggested Hammond enclosure.
>>
>> bye,
>> Said
>>
>>
>> In a message dated 10/18/2014 12:56:06 Pacific Daylight Time,
>> time-nuts-***@public.gmane.org writes:
>>
>>
>> Guys,
>> we have been getting a good number of emails with questions that
>> have already been addressed in the user manual or the FAQ, see the below link.
>> We
>> spent a lot of time putting the collateral together, may I please
>> ask that you first look into these two documents to see if your
>> question might already be addressed there?
>> Paul,
>> please search the LTE Lite user manual for "Hammond" and you will
>> find it
>> there:
>> http://www.jackson-labs.com/index.php/products/lte_lite
>> Thanks,
>> Said
>> _____________________
>> Do you have a recommended Hammond chassis part number?
>> --
>> Paul
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
>
>
> --
> Doc
>
> Bill Dailey
> KXØO
>
>
>
>
_______________________________________________
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Bill Riches
2014-10-19 12:00:27 UTC
Permalink
Raw Message
Hi Said,

Thank you for taking the time to answer questions and provide info on the LTE unit to our group. I know we will not add much to your bottom line as we are a small group. We have come a long way with Thunderbolt without any help whatsoever with that company. Will be an interesting ride with your products!

73,

Bill, WA2DVU
Cape May, NJ

-----Original Message-----
From: time-nuts [mailto:time-nuts-***@febo.com] On Behalf Of Said Jackson via time-nuts
Sent: Saturday, October 18, 2014 6:53 PM
To: Bill Dailey
Cc: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] LTE-Lite module

Hi Bill,

I think it makes perfect sense. But I have no idea how the units' loop stability would be with the 10811. That kind of testing is on the plate.

You would preferably set the OCXO to a nominal tuning voltage of 1.5V using the mechanical adjustment, then let the LTE Lite do the rest.

Please note that the LTE board will auto-sense the external ocxo frequency, so any of the boards would work.

Please also note that due to the harmonic mixing issues I described earlier the best board to use for that setup would be the 19.2MHz version(!) or to remove the on-board tcxo altogether.

Bye,
Said

Sent From iPhone

> On Oct 18, 2014, at 15:24, Bill Dailey <***@gmail.com> wrote:
>
> Said,
>
> How tough would it be to mate the 10Mhz version up to a really good 10811? I have one that I acquired from Corby some time ago. I was going to spin my own but I wont realistically get to that with everything else I have going on. I was thinking of throwing the LTE-Lite and the 10811 in a box. I woudl then have a stock fury, An enhanced OEM fury (datum-1111c) and then this gadget with a 10-13 10811. Let me know if this doesnt make sense. I am an amateur.
>
> Bill
>
>> On Sat, Oct 18, 2014 at 5:13 PM, S. Jackson via time-nuts <time-***@febo.com> wrote:
>> Guys,
>>
>> one last email. The board will not fit into the Hammond enclosure
>> without reworking the enclosure or removing the TCXO socket. We
>> initially planned to ship the board without the socket, now all of
>> them will have it. The board was designed to be used without the
>> TCXO/Socket to fit into that enclosure.
>>
>> Caveat: please expect some rework to be necessary when using the
>> suggested Hammond enclosure.
>>
>> bye,
>> Said
>>
>>
>> In a message dated 10/18/2014 12:56:06 Pacific Daylight Time,
>> time-***@febo.com writes:
>>
>>
>> Guys,
>> we have been getting a good number of emails with questions that
>> have already been addressed in the user manual or the FAQ, see the below link.
>> We
>> spent a lot of time putting the collateral together, may I please
>> ask that you first look into these two documents to see if your
>> question might already be addressed there?
>> Paul,
>> please search the LTE Lite user manual for "Hammond" and you will
>> find it
>> there:
>> http://www.jackson-labs.com/index.php/products/lte_lite
>> Thanks,
>> Said
>> _____________________
>> Do you have a recommended Hammond chassis part number?
>> --
>> Paul
>> _______________________________________________
>> time-nuts mailing list -- time-***@febo.com To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>> _______________________________________________
>> time-nuts mailing list -- time-***@febo.com To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
>
>
> --
> Doc
>
> Bill Dailey
> KXØO
>
>
>
>
_______________________________________________
time-nuts mailing list -- time-***@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Bill Dailey
2014-10-18 22:24:55 UTC
Permalink
Raw Message
Said,

How tough would it be to mate the 10Mhz version up to a really good 10811?
I have one that I acquired from Corby some time ago. I was going to spin
my own but I wont realistically get to that with everything else I have
going on. I was thinking of throwing the LTE-Lite and the 10811 in a
box. I woudl then have a stock fury, An enhanced OEM fury (datum-1111c)
and then this gadget with a 10-13 10811. Let me know if this doesnt make
sense. I am an amateur.

Bill

On Sat, Oct 18, 2014 at 5:13 PM, S. Jackson via time-nuts <
time-nuts-***@public.gmane.org> wrote:

> Guys,
>
> one last email. The board will not fit into the Hammond enclosure without
> reworking the enclosure or removing the TCXO socket. We initially planned
> to
> ship the board without the socket, now all of them will have it. The
> board was designed to be used without the TCXO/Socket to fit into that
> enclosure.
>
> Caveat: please expect some rework to be necessary when using the suggested
> Hammond enclosure.
>
> bye,
> Said
>
>
> In a message dated 10/18/2014 12:56:06 Pacific Daylight Time,
> time-nuts-***@public.gmane.org writes:
>
>
> Guys,
> we have been getting a good number of emails with questions that have
> already been addressed in the user manual or the FAQ, see the below link.
> We
> spent a lot of time putting the collateral together, may I please ask
> that
> you first look into these two documents to see if your question might
> already
> be addressed there?
> Paul,
> please search the LTE Lite user manual for "Hammond" and you will find it
> there:
> http://www.jackson-labs.com/index.php/products/lte_lite
> Thanks,
> Said
> _____________________
> Do you have a recommended Hammond chassis part number?
> --
> Paul
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>



--
Doc

Bill Dailey
KXØO
Charles Steinmetz
2014-10-19 11:48:43 UTC
Permalink
Raw Message
Bill wrote:

>How tough would it be to mate the 10Mhz version up to a really good 10811?
>* * * I was thinking of throwing the LTE-Lite and the 10811 in a box.

Unfortunately, to get the best out of the local oscillator, the
control PLL must be carefully adjusted so that the oscillator itself
controls the stability at averaging times (tau) where it is better
than the GPS (generally, up to tau of several hundred to maybe
several thousand seconds), and the GPS controls the stability at
longer tau. The LTE-Lite has fixed (non-adjustable) loop parameters
that cross over to the GPS at much lower tau than is appropriate for
a good OCXO (but well suited to the installed TXCO).

The other day Said (I think) mentioned some hacks that may sort-of
improve the ability of an LTE-Lite to discipline an OCXO, but that's
all they are -- very approximate hacks. There is really no way to
properly mate an OCXO to the LTE-Lite control loop, which would
require adjusting the PLL loop gain and the location of the loop's
poles and zeroes (and possibly even adding new poles and
zeroes). That would need to be done by changing the PLL parameters
internal to the LTE-Lite, which are inaccessible. Without such
reprogramming, the LTE-Light can never get the best out of an OCXO.

Best regards,

Charles
Poul-Henning Kamp
2014-10-19 12:56:36 UTC
Permalink
Raw Message
--------
In message <20141019155055.osMiKB63-***@public.gmane.org>, Charles Steinmetz
writes:

>zeroes). That would need to be done by changing the PLL parameters
>internal to the LTE-Lite, which are inaccessible. Without such
>reprogramming, the LTE-Light can never get the best out of an OCXO.

It certainly can and it's not even hard:

Configure the LTE to emit a suitable frequency relative to the
OCXO and use an analog PLL to steer the OCXO's EFC.

--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk-***@public.gmane.org | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Charles Steinmetz
2014-10-19 14:39:50 UTC
Permalink
Raw Message
Poul-Henning wrote:

> >zeroes). That would need to be done by changing the PLL parameters
> >internal to the LTE-Lite, which are inaccessible. Without such
> >reprogramming, the LTE-Light can never get the best out of an OCXO.
>
>It certainly can and it's not even hard:
>
>Configure the LTE to emit a suitable frequency relative to the
>OCXO and use an analog PLL to steer the OCXO's EFC.

Any worthwhile OCXO will need a loop with a time constant on the
order of hundreds of seconds (a corner frequency on the order of uHz)
to get the most out of it as a GPSDO. As has been discussed on the
list many times, there is simply no practicable way to design an
analog loop with such a long time constant. So the person designing
the PLL must be able to design and build an all-digital PLL, or
settle for a loop that crosses over to the GPS several decades too
early (which is certainly not getting the most out of the OCXO).

Best regards,

Charles
Poul-Henning Kamp
2014-10-19 15:49:25 UTC
Permalink
Raw Message
--------
In message <20141019183956.dt4Ss5gj-ZlSS+***@public.gmane.org>, Charles Steinmetz
writes:

>>Configure the LTE to emit a suitable frequency relative to the
>>OCXO and use an analog PLL to steer the OCXO's EFC.
>

Then do it digital, it's not like it's rocket science...

Take the analog phase detector output, read it with ADC pin,
do loop in software, drive efc with DAC.

--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk-***@public.gmane.org | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Bob Camp
2014-10-19 15:59:25 UTC
Permalink
Raw Message
Hi

The phase comparison part of the PLL is pretty straightforward if you are looking at two RF frequencies. An XOR gate is one solution, there are many others. Getting something like 100 to 200 ns full scale on the phase comparator makes the rest of the gizmo much easier. A 12 bit ADC on a MCU will get you to 100’s of ps per bit., That is more resolution (it’s < 1 ns) than you need for this. Controlling the OCXO is either an outboard ADC ($2 or so) or a PWM (free with the MCU). There will be a few regulators, resistors, caps, and maybe a pot or two involved as well.

Total parts cost on the digital loop done with an appropriate MCU is probably less than $10. Custom code wise, it’s a few hundred lines of C on a 32 bit ARM. Pre built (wizard driven) device init stuff will be way more than that, but you don’t write any of that. Since it’s just a PLL and not a full GPSDO, there’s not a whole lot to it. If building up the MCU board is the issue, there are *many* eval boards out there for < $15 that will do the trick.

Debug, optimization and tweaking are where the major effort is (like 80 to 90%). That will take at least few months of work and require some test gear. Any time you plug in a significantly different oscillator, you will have to put in this part of the effort. Getting the long run ADEV data, making sure it’s right, and then analyzing the result is something there is no magic shortcut around. If you are set up for it (you are a TIme Nut right?) , there’s no cost other than your time. If it’s a hobby - your time is free (or is it …).

No it’s not a “plug in a pre-made gizmo and forget about it” sort of thing. There is real work, lots of time, mental effort, working gear, and patience involved. You *will* get it wrong more often than you get it right as you go through the process. Stuff happens, runs crash, gear fails, it’s the real world. That’s the learning part of the project. If its a hobby that’s what you are doing this for.

Bob

> On Oct 19, 2014, at 10:39 AM, Charles Steinmetz <csteinmetz-zJpx2rpV7r/QT0dZR+***@public.gmane.org> wrote:
>
> Poul-Henning wrote:
>
>> >zeroes). That would need to be done by changing the PLL parameters
>> >internal to the LTE-Lite, which are inaccessible. Without such
>> >reprogramming, the LTE-Light can never get the best out of an OCXO.
>>
>> It certainly can and it's not even hard:
>>
>> Configure the LTE to emit a suitable frequency relative to the
>> OCXO and use an analog PLL to steer the OCXO's EFC.
>
> Any worthwhile OCXO will need a loop with a time constant on the order of hundreds of seconds (a corner frequency on the order of uHz) to get the most out of it as a GPSDO. As has been discussed on the list many times, there is simply no practicable way to design an analog loop with such a long time constant. So the person designing the PLL must be able to design and build an all-digital PLL, or settle for a loop that crosses over to the GPS several decades too early (which is certainly not getting the most out of the OCXO).
>
> Best regards,
>
> Charles
>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
Charles Steinmetz
2014-10-19 19:35:18 UTC
Permalink
Raw Message
Bob wrote (alluding also to something Poul-Henning wrote):

>The phase comparison part of the PLL is pretty
>straightforward if you are looking at two RF
>frequencies. An XOR gate is one solution, there
>are many others. Getting something like 100 to
>200 ns full scale on the phase comparator makes
>the rest of the gizmo much easier.

All true. However...

>A 12 bit ADC on a MCU will get you to 100's of
>ps per bit. That is more resolution (it's < 1 ns) than you need for this.

Getting an ADC to sample fast and accurately
enough to provide that honest resolution is not
trivial. And if you have that, you'll almost
certainly have the resources to do the phase
comparator digitally, too, which brings many
advantages -- so I see no reason to use an analog PC.

>Custom code wise, it's a few hundred lines of C
>on a 32 bit ARM. Pre built (wizard driven)
>device init stuff will be way more than that, but you don't write any of that.

A proper digital filter that computes a new
running value at least every second will be more
complex than that, but you're right, it's not an unfathomable task.

Then comes the real work, well summarized by Bob:

>Debug, optimization and tweaking are where the
>major effort is (like 80 to 90%). That will take
>at least few months of work and require some
>test gear. Any time you plug in a significantly
>different oscillator, you will have to put in
>this part of the effort. Getting the long run
>ADEV data, making sure it's right, and then
>analyzing the result is something there is no magic shortcut around. * * *
>
>No it's not a "plug in a pre-made gizmo and
>forget about it" sort of thing. There is real
>work, lots of time, mental effort, working
>gear, and patience involved. You *will* get it
>wrong more often than you get it right as you go through the process.

All of this explains why the woods are not full
of state-of-the-art GPSDO controllers just
waiting for people to couple them with whatever OCXO they bought on ebay.

BTW, I mean no slight to the LTE-Light. Judging
from the JL products I've used, I expect that it
is a fine product well-designed for its
task. But that task is controlling a TCXO, not
controlling an OCXO that is stable to 10e-12 or
better at tau from 1 to 100 seconds (unless one
goes to the trouble described above).

For a general look at the magnitude of the
stability difference between a TCXO and a number
of OCXOs and other frequency standards, see
attached (if the pic doesn't make it through the
listserv, see <http://leapsecond.com/museum/manyadev.gif>).

Best regards,

Charles
Bob Camp
2014-10-19 20:08:09 UTC
Permalink
Raw Message
Hi

> On Oct 19, 2014, at 3:35 PM, Charles Steinmetz <csteinmetz-zJpx2rpV7r/QT0dZR+***@public.gmane.org> wrote:
>
> Bob wrote (alluding also to something Poul-Henning wrote):
>
>> The phase comparison part of the PLL is pretty straightforward if you are looking at two RF frequencies. An XOR gate is one solution, there are many others. Getting something like 100 to 200 ns full scale on the phase comparator makes the rest of the gizmo much easier.
>
> All true. However...
>
>> A 12 bit ADC on a MCU will get you to 100's of ps per bit. That is more resolution (it's < 1 ns) than you need for this.
>
> Getting an ADC to sample fast and accurately enough to provide that honest resolution is not trivial. And if you have that, you'll almost certainly have the resources to do the phase comparator digitally, too, which brings many advantages -- so I see no reason to use an analog PC.

If you take a look at some of the newer ARM MCU’s they are getting 13+ solid bits out of their ADC’s at a > 10 KHz rate. That’s more than good enough for anything you are trying to do with this design. There’s no need to make it any more complex.

A single gate XOR plus the eval board is just a about all you need. One dead bug part on the eval board and the assembly process is pretty much done. Maybe 45 minutes of work if you need to go find all the bits and pieces around your bench. Since almost nothing in the design is running at high speed, layout issues should not be a big deal. You could also do it on a fragment of board like the divider from earlier in this thread.

>
>> Custom code wise, it's a few hundred lines of C on a 32 bit ARM. Pre built (wizard driven) device init stuff will be way more than that, but you don't write any of that.
>
> A proper digital filter that computes a new running value at least every second will be more complex than that, but you're right, it's not an unfathomable task.
>
> Then comes the real work, well summarized by Bob:
>
>> Debug, optimization and tweaking are where the major effort is (like 80 to 90%). That will take at least few months of work and require some test gear. Any time you plug in a significantly different oscillator, you will have to put in this part of the effort. Getting the long run ADEV data, making sure it's right, and then analyzing the result is something there is no magic shortcut around. * * *
>>
>> No it's not a "plug in a pre-made gizmo and forget about it" sort of thing. There is real work, lots of time, mental effort, working gear, and patience involved. You *will* get it wrong more often than you get it right as you go through the process.
>
> All of this explains why the woods are not full of state-of-the-art GPSDO controllers just waiting for people to couple them with whatever OCXO they bought on ebay.

The optimization process is at least 90% perspiration and preparation. Neither of those are outside the range of what an average Joe can handle. The other (at most) 10% is very much a “that depends” sort of thing. You can head down all sorts of rabbit holes as you dig into this or that. For that, the list archives have tons of information to work from.

There is *way* more in a GPSDO than what we are talking about here. TimeNuts may or may not care much about that extra stuff, but it’s in there.

>
> BTW, I mean no slight to the LTE-Light. Judging from the JL products I've used, I expect that it is a fine product well-designed for its task. But that task is controlling a TCXO, not controlling an OCXO that is stable to 10e-12 or better at tau from 1 to 100 seconds (unless one goes to the trouble described above).
>
> For a general look at the magnitude of the stability difference between a TCXO and a number of OCXOs and other frequency standards, see attached (if the pic doesn't make it through the listserv, see <http://leapsecond.com/museum/manyadev.gif>).
>
> Best regards,
>
> Charles
>
>
> <Oscillator_comparison_tvb.jpg>_______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

The idea is not to make it as complex as you possibly could, but to make it as simple as possible and still have it work fine. There are a lot of shortcuts you can take with a one off unit that a commercial design would never use.

Bob
Jim Lux
2014-10-19 21:00:56 UTC
Permalink
Raw Message
On 10/19/14, 1:08 PM, Bob Camp wrote:
> Hi
>
>> On Oct 19, 2014, at 3:35 PM, Charles Steinmetz
>> <csteinmetz-zJpx2rpV7r/QT0dZR+***@public.gmane.org> wrote:
>>
>> Bob wrote (alluding also to something Poul-Henning wrote):
>>
>>> The phase comparison part of the PLL is pretty straightforward if
>>> you are looking at two RF frequencies. An XOR gate is one
>>> solution, there are many others. Getting something like 100 to
>>> 200 ns full scale on the phase comparator makes the rest of the
>>> gizmo much easier.
>>
>> All true. However...
>>
>>> A 12 bit ADC on a MCU will get you to 100's of ps per bit. That
>>> is more resolution (it's < 1 ns) than you need for this.
>>
>> Getting an ADC to sample fast and accurately enough to provide that
>> honest resolution is not trivial. And if you have that, you'll
>> almost certainly have the resources to do the phase comparator
>> digitally, too, which brings many advantages -- so I see no reason
>> to use an analog PC.
>
> If you take a look at some of the newer ARM MCU’s they are getting
> 13+ solid bits out of their ADC’s at a > 10 KHz rate. That’s more
> than good enough for anything you are trying to do with this design.
> There’s no need to make it any more complex.

I'm using the Freescale Kinetix K20 parts, which have 16 bit
differential input ADCs, and built in averaging. The raw ADC can sample
at about 400kHz.

You can easily get 14 bit performance from these at tens of kHz rates.
I need I/Q, so I sample two inputs at 50 kHz (read one, then the other)
without averaging (so they're about 2.5 microseconds apart), and then
decimate them through a 2 stage CIC and a 13 tap FIR filter down to 200
Hz. This takes about 60% of the processor running at 48MHz.
Bob Camp
2014-10-19 21:13:24 UTC
Permalink
Raw Message
Hi

> On Oct 19, 2014, at 5:00 PM, Jim Lux <jimlux-***@public.gmane.org> wrote:
>
> On 10/19/14, 1:08 PM, Bob Camp wrote:
>> Hi
>>
>>> On Oct 19, 2014, at 3:35 PM, Charles Steinmetz
>>> <csteinmetz-zJpx2rpV7r/QT0dZR+***@public.gmane.org> wrote:
>>>
>>> Bob wrote (alluding also to something Poul-Henning wrote):
>>>
>>>> The phase comparison part of the PLL is pretty straightforward if
>>>> you are looking at two RF frequencies. An XOR gate is one
>>>> solution, there are many others. Getting something like 100 to
>>>> 200 ns full scale on the phase comparator makes the rest of the
>>>> gizmo much easier.
>>>
>>> All true. However...
>>>
>>>> A 12 bit ADC on a MCU will get you to 100's of ps per bit. That
>>>> is more resolution (it's < 1 ns) than you need for this.
>>>
>>> Getting an ADC to sample fast and accurately enough to provide that
>>> honest resolution is not trivial. And if you have that, you'll
>>> almost certainly have the resources to do the phase comparator
>>> digitally, too, which brings many advantages -- so I see no reason
>>> to use an analog PC.
>>
>> If you take a look at some of the newer ARM MCU’s they are getting
>> 13+ solid bits out of their ADC’s at a > 10 KHz rate. That’s more
>> than good enough for anything you are trying to do with this design.
>> There’s no need to make it any more complex.
>
> I'm using the Freescale Kinetix K20 parts, which have 16 bit differential input ADCs, and built in averaging. The raw ADC can sample at about 400kHz.
>
> You can easily get 14 bit performance from these at tens of kHz rates.
> I need I/Q, so I sample two inputs at 50 kHz (read one, then the other) without averaging (so they're about 2.5 microseconds apart), and then decimate them through a 2 stage CIC and a 13 tap FIR filter down to 200 Hz. This takes about 60% of the processor running at 48MHz.

I’m using parts from the same family, but not doing the whole DDS thing. Single input and control loop - the part sleeps about 98% of the time. The demo boards (Freedom boards) are all below $15 and free if you go to one of their (often free) classes.

Bob

> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
Chris Albertson
2014-10-19 22:14:29 UTC
Permalink
Raw Message
At the low end of the spectrum, I tried to make the simplest possible
GPSDO what would still work. Assuming you have a GPS with 1PPS
output, an OCXO and a small DC power supply I was able to get the
entire parts for the controller, board, hookup wire and all for under
$5. I purposely took the lowest cost solution at each decision point
just to see what you'd end up with. Part were from eBay.

The result is not bad. but I don't have a really good way to test it.
I'm using a Thunderbolt for the 1PPS and a pretty decent OXCO part.
Why build a low-end GPSDO when yo have a Thunderbolt? It's and
experiment. The way I test is to place the sine output from the TB
and from my GPSDO both on a dual channel scope and adjust it so the
two sine waves are superimposed. Then I wait for them not to be
superimposed. What I see is that over 1/2 hour or so they get
slightly out of phase but then drift back in phase, This happens
cyclically. It is because of the VERY simply controller. I tried to
minimize lines of C++ code. It's running about 16 lines of code, more
or less. Using my counter I think the GPSDO is good to 1E-10.

Rather than using a $15 ARM MCU board I used a $3 AVR board and used
100% 16-bit integer math in a very simple control loop. There is one
external chip because the little AVR could not deal with the 10MHz
signal from the OCXO so I used a divider chip. I use two 8-bit DACs
to control the EFC on the OCXO. One is curse adjustment, one fine.
Added with a resister network and an RC filter with almost a 1 second
time constant.

If you can spend $35 you can build a very sophisticated controller
that logs internal diagnostic data to a computer over USB and displays
it's internal status on a graphic LCD panel. Well, actually my
controller has an LCD status display and logs data to a PC. But with
those parts plugged in the cost is closer to $10.

On Sun, Oct 19, 2014 at 2:13 PM, Bob Camp <kb8tq-***@public.gmane.org> wrote:
> Hi
>
>> On Oct 19, 2014, at 5:00 PM, Jim Lux <jimlux-***@public.gmane.org> wrote:
>>
>> On 10/19/14, 1:08 PM, Bob Camp wrote:
>>> Hi
>>>
>>>> On Oct 19, 2014, at 3:35 PM, Charles Steinmetz
>>>> <csteinmetz-zJpx2rpV7r/QT0dZR+***@public.gmane.org> wrote:
>>>>
>>>> Bob wrote (alluding also to something Poul-Henning wrote):
>>>>
>>>>> The phase comparison part of the PLL is pretty straightforward if
>>>>> you are looking at two RF frequencies. An XOR gate is one
>>>>> solution, there are many others. Getting something like 100 to
>>>>> 200 ns full scale on the phase comparator makes the rest of the
>>>>> gizmo much easier.
>>>>
>>>> All true. However...
>>>>
>>>>> A 12 bit ADC on a MCU will get you to 100's of ps per bit. That
>>>>> is more resolution (it's < 1 ns) than you need for this.
>>>>
>>>> Getting an ADC to sample fast and accurately enough to provide that
>>>> honest resolution is not trivial. And if you have that, you'll
>>>> almost certainly have the resources to do the phase comparator
>>>> digitally, too, which brings many advantages -- so I see no reason
>>>> to use an analog PC.
>>>
>>> If you take a look at some of the newer ARM MCU’s they are getting
>>> 13+ solid bits out of their ADC’s at a > 10 KHz rate. That’s more
>>> than good enough for anything you are trying to do with this design.
>>> There’s no need to make it any more complex.
>>
>> I'm using the Freescale Kinetix K20 parts, which have 16 bit differential input ADCs, and built in averaging. The raw ADC can sample at about 400kHz.
>>
>> You can easily get 14 bit performance from these at tens of kHz rates.
>> I need I/Q, so I sample two inputs at 50 kHz (read one, then the other) without averaging (so they're about 2.5 microseconds apart), and then decimate them through a 2 stage CIC and a 13 tap FIR filter down to 200 Hz. This takes about 60% of the processor running at 48MHz.
>
> I’m using parts from the same family, but not doing the whole DDS thing. Single input and control loop - the part sleeps about 98% of the time. The demo boards (Freedom boards) are all below $15 and free if you go to one of their (often free) classes.
>
> Bob
>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
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--

Chris Albertson
Redondo Beach, California
Bob Camp
2014-10-20 00:40:27 UTC
Permalink
Raw Message
Hi

We seem to have swung from “it’s impossible, don’t even try” to “it’s trivial, you should have it done in a few minutes” :) (Yes I know that’s *not* at all what was said in either case. We have swung a ways though)

Yes, I can do it for less than $1 in parts. That’s not to say it’s the *right* way to do it. Yes, I can have it “done" (locked up) in a few hours (from scratch, including the parts). That’s not to say you *should* do it that way. My way most certainly should not be your way. The stuff I have sitting around is not the stuff you have lying around. What I paid may not be what you pay.

We spend a lot of time playing “I can do it cheaper”. Unless a few months of your time *really* is worth $10, the “cheaper” part simply does not count past some point. The cost of even one meal out over several months will wipe out that advantage. Doing it with a part that is running a 10 bit ADC that really gives you 8 bit performance will indeed impact the result. It’s cheaper, but how much struggle will there be to make it work well? Will it add a month or three to the project? Will you start over from scratch? Who knows. Are we comparing a board anybody can get for < $15 to just the cpu on another board .. maybe we are. If what counts is a price that somebody got once, I have boards that I got for free. Do they count as $0 in a project? There’s really no value even going down that road.

Each time this comes up on the list, we typically spend a month with everybody tossing up their favorite board. We each post several messages talking about the great deal we got. We never seem to get around to actually doing much with those cheap boards compared to the time everybody spends extolling their virtues (and ignoring their drawbacks). A $50 board is no different than a $1 board in this case. They both have near zero impact on the total investment in the project. If they did / do - buy a $135 OCXO based GPSDO rather than the $185 LTE board. That puts you $50 and months of your time ahead.

If you want to start from scratch and get a result that is “OCXO” caliber, it will take a while. 1x10^-10 is not your target. The LTE part pretty much does that. Your target is at least 1x10^-11 short term and much better a you go to a few hundred seconds. In order to say you have hit it, you need to test it and verify that you have hit it. No I can’t do a run that takes a month to verify a part I build in a short time.Nobody can do that, it takes time. No I don’t have a gizmo that’ stable to 1x10^-13 over a month sitting in the basement. If I already had that, why would I need to put an OCXO on a LTE board? I have to do some work simply to do the test (like build several and cross check them).

How much time does the testing take? You want something around 100 samples for a good ADEV number. You need data out to 1,000 seconds (and more likely 10,000 seconds) to check the loop out. Each run will be in the 1 to 10 days range. Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. If you have a really good setup, you will get good data 4 runs out of 5. With a basement setup, that may drop to 2 in 5.

The job is not done once the first one is locked. That’s the quick and easy part. The full job is only done once you have it optimized and know you have done so from measured data. That’s true if you are making one, or making a few hundred thousand of them.

Bob



> On Oct 19, 2014, at 6:14 PM, Chris Albertson <albertson.chris-***@public.gmane.org> wrote:
>
> At the low end of the spectrum, I tried to make the simplest possible
> GPSDO what would still work. Assuming you have a GPS with 1PPS
> output, an OCXO and a small DC power supply I was able to get the
> entire parts for the controller, board, hookup wire and all for under
> $5. I purposely took the lowest cost solution at each decision point
> just to see what you'd end up with. Part were from eBay.
>
> The result is not bad. but I don't have a really good way to test it.
> I'm using a Thunderbolt for the 1PPS and a pretty decent OXCO part.
> Why build a low-end GPSDO when yo have a Thunderbolt? It's and
> experiment. The way I test is to place the sine output from the TB
> and from my GPSDO both on a dual channel scope and adjust it so the
> two sine waves are superimposed. Then I wait for them not to be
> superimposed. What I see is that over 1/2 hour or so they get
> slightly out of phase but then drift back in phase, This happens
> cyclically. It is because of the VERY simply controller. I tried to
> minimize lines of C++ code. It's running about 16 lines of code, more
> or less. Using my counter I think the GPSDO is good to 1E-10.
>
> Rather than using a $15 ARM MCU board I used a $3 AVR board and used
> 100% 16-bit integer math in a very simple control loop. There is one
> external chip because the little AVR could not deal with the 10MHz
> signal from the OCXO so I used a divider chip. I use two 8-bit DACs
> to control the EFC on the OCXO. One is curse adjustment, one fine.
> Added with a resister network and an RC filter with almost a 1 second
> time constant.
>
> If you can spend $35 you can build a very sophisticated controller
> that logs internal diagnostic data to a computer over USB and displays
> it's internal status on a graphic LCD panel. Well, actually my
> controller has an LCD status display and logs data to a PC. But with
> those parts plugged in the cost is closer to $10.
>
> On Sun, Oct 19, 2014 at 2:13 PM, Bob Camp <kb8tq-***@public.gmane.org> wrote:
>> Hi
>>
>>> On Oct 19, 2014, at 5:00 PM, Jim Lux <jimlux-***@public.gmane.org> wrote:
>>>
>>> On 10/19/14, 1:08 PM, Bob Camp wrote:
>>>> Hi
>>>>
>>>>> On Oct 19, 2014, at 3:35 PM, Charles Steinmetz
>>>>> <csteinmetz-zJpx2rpV7r/QT0dZR+***@public.gmane.org> wrote:
>>>>>
>>>>> Bob wrote (alluding also to something Poul-Henning wrote):
>>>>>
>>>>>> The phase comparison part of the PLL is pretty straightforward if
>>>>>> you are looking at two RF frequencies. An XOR gate is one
>>>>>> solution, there are many others. Getting something like 100 to
>>>>>> 200 ns full scale on the phase comparator makes the rest of the
>>>>>> gizmo much easier.
>>>>>
>>>>> All true. However...
>>>>>
>>>>>> A 12 bit ADC on a MCU will get you to 100's of ps per bit. That
>>>>>> is more resolution (it's < 1 ns) than you need for this.
>>>>>
>>>>> Getting an ADC to sample fast and accurately enough to provide that
>>>>> honest resolution is not trivial. And if you have that, you'll
>>>>> almost certainly have the resources to do the phase comparator
>>>>> digitally, too, which brings many advantages -- so I see no reason
>>>>> to use an analog PC.
>>>>
>>>> If you take a look at some of the newer ARM MCU’s they are getting
>>>> 13+ solid bits out of their ADC’s at a > 10 KHz rate. That’s more
>>>> than good enough for anything you are trying to do with this design.
>>>> There’s no need to make it any more complex.
>>>
>>> I'm using the Freescale Kinetix K20 parts, which have 16 bit differential input ADCs, and built in averaging. The raw ADC can sample at about 400kHz.
>>>
>>> You can easily get 14 bit performance from these at tens of kHz rates.
>>> I need I/Q, so I sample two inputs at 50 kHz (read one, then the other) without averaging (so they're about 2.5 microseconds apart), and then decimate them through a 2 stage CIC and a 13 tap FIR filter down to 200 Hz. This takes about 60% of the processor running at 48MHz.
>>
>> I’m using parts from the same family, but not doing the whole DDS thing. Single input and control loop - the part sleeps about 98% of the time. The demo boards (Freedom boards) are all below $15 and free if you go to one of their (often free) classes.
>>
>> Bob
>>
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
>
>
> --
>
> Chris Albertson
> Redondo Beach, California
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
Bob Stewart
2014-10-20 01:26:35 UTC
Permalink
Raw Message
Hi Bob Camp,


In your response to Chris, you said: "Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. "

Could I ask you what you meant by these "once a day issues"? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know.


Bob - AE6RV


________________________________
Bob Camp
2014-10-20 01:50:42 UTC
Permalink
Raw Message
Hi

The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing.

Bob

> On Oct 19, 2014, at 9:26 PM, Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org> wrote:
>
> Hi Bob Camp,
>
>
> In your response to Chris, you said: "Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. "
>
> Could I ask you what you meant by these "once a day issues"? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know.
>
>
> Bob - AE6RV
>
>
> ________________________________
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
Bob Stewart
2014-10-20 02:01:12 UTC
Permalink
Raw Message
Hi Bob, (Yahoo let me down again and I responded only to you. Here is my reply again.)


OK, it sounds like something that would not be clearly noticeable with the
equipment I have. I haven't run many multi-day tests, so that's another handicap on this end. Still developing and testing, but things are
looking better than the last time I spoke about my unit.


thanks,


Bob


________________________________
From: Bob Camp <kb8tq-***@public.gmane.org>
To: Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org>; Discussion of precise time and frequency measurement <time-nuts-***@public.gmane.org>
Sent: Sunday, October 19, 2014 8:50 PM
Subject: Re: [time-nuts] "GPS once a day issues" ?


Hi

The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing.

Bob


> On Oct 19, 2014, at 9:26 PM, Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org> wrote:
>
> Hi Bob Camp,
>
>
> In your response to Chris, you said: "Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. "
>
> Could I ask you what you meant by these "once a day issues"? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know.
>
>
> Bob - AE6RV
>
>
> ________________________________
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
Bob Stewart
2014-10-20 02:18:30 UTC
Permalink
Raw Message
Hi Bob,

This multiple antenna issue is one I've been wanting to ask about, as well. I've got a GPS Source MS14 splitter (right place at the right time) so I don't specifically use multiple antennas. But, I've got the one still in the attic (disconnected) and the current one I put on the eave on the south side of the house. Those are both $5 powered pucks from ebay. I've also got a couple of Adafruits with the built-in antenna laying around. Do I really need to worry about the interaction of those antennas? I didn't get a feel for the spacing of interaction from previous posts on the subject. They're all at least 10 ft away from each other.

FWIW, I only have one receiver hooked up to the splitter at the moment, and I do not have any terminators on the SMA ports as I don't think they're needed. The splitter has its own power supply. I'm only using the ports that are DC isolated from the antenna.


Bob



________________________________
From: Bob Camp <kb8tq-***@public.gmane.org>
To: Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org>
Sent: Sunday, October 19, 2014 9:01 PM
Subject: Re: [time-nuts] "GPS once a day issues" ?


Hi

One of the reasons you want to wide space antennas if you are putting up more than one it a *hope* that worst case on one will not be identical to worst case on the other.

The other way you can catch the problem is to simply look at what you loop is doing. If it does exactly the same “bump” every night at about 3AM…..

Bob




> On Oct 19, 2014, at 9:58 PM, Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org> wrote:
>
> Hi Bob,
>
> OK, it sounds like something that would not be clearly noticeable with the equipment I have. I haven't run many multi-day tests, so that's another handicap on this end. Still developing and testing, but things are looking better than the last time I spoke about my unit.
>
> thanks,
>
> Bob
>
> From: Bob Camp <kb8tq-***@public.gmane.org>
> To: Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org>; Discussion of precise time and frequency measurement <time-nuts-***@public.gmane.org>
> Sent: Sunday, October 19, 2014 8:50 PM
> Subject: Re: [time-nuts] "GPS once a day issues" ?
>
> Hi
>
> The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing.
>
> Bob
>
>
>
> > On Oct 19, 2014, at 9:26 PM, Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org> wrote:
> >
> > Hi Bob Camp,
> >
> >
> > In your response to Chris, you said: "Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. "
> >
> > Could I ask you what you meant by these "once a day issues"? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know.
> >
> >
> > Bob - AE6RV
> >
> >
> > ________________________________
> > _______________________________________________
> > time-nuts mailing list -- time-nuts-***@public.gmane.org
> > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
>
>
Magnus Danielson
2014-10-20 07:43:05 UTC
Permalink
Raw Message
Bob,

Since the satellite orbit the earth with a period of 11 hours and 58
minutes, it is actually twice a day.

Cheers,
Magnus

On 10/20/2014 03:50 AM, Bob Camp wrote:
> Hi
>
> The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing.
>
> Bob
>
>> On Oct 19, 2014, at 9:26 PM, Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org> wrote:
>>
>> Hi Bob Camp,
>>
>>
>> In your response to Chris, you said: "Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. "
>>
>> Could I ask you what you meant by these "once a day issues"? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know.
>>
>>
>> Bob - AE6RV
>>
>>
>> ________________________________
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
mike cook
2014-10-20 09:03:48 UTC
Permalink
Raw Message
The constellation may repeat at 12hr intervals , but at any static position you will only see one per day , no? , the other being 180 degrees way. I only get one regular bump.


Le 20 oct. 2014 à 09:43, Magnus Danielson a écrit :

> Bob,
>
> Since the satellite orbit the earth with a period of 11 hours and 58 minutes, it is actually twice a day.
>
> Cheers,
> Magnus
>
> On 10/20/2014 03:50 AM, Bob Camp wrote:
>> Hi
>>
>> The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing.
>>
>> Bob
>>
>>> On Oct 19, 2014, at 9:26 PM, Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org> wrote:
>>>
>>> Hi Bob Camp,
>>>
>>>
>>> In your response to Chris, you said: "Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. "
>>>
>>> Could I ask you what you meant by these "once a day issues"? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know.
>>>
>>>
>>> Bob - AE6RV
>>>
>>>
>>> ________________________________
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
David J Taylor
2014-10-20 09:15:32 UTC
Permalink
Raw Message
Bob,

Since the satellite orbit the earth with a period of 11 hours and 58
minutes, it is actually twice a day.

Cheers,
Magnus
================================

I've been reminded of that before, but the fact remains that here the
interruptions when they happen are at 24-hour intervals, not 12-hour
intervals, and precess at a few minutes per day. Perhaps the low signal
coincides with greater background noise/interference at certain times of the
day? Although I've not plotted them, I do get the impression that
07:00-09:00 local is worse than other times....

Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-taylor-***@public.gmane.org
Bob Camp
2014-10-20 11:15:40 UTC
Permalink
Raw Message
Hi

Yes, but there’s this large object in the sky that modifies the ionosphere as it travels in a “about one a day” track. It appears to be coming up just about now, but I do need more coffee to be sure …

The combination of the constellation and the ionosphere are what I believe give you the once a day (rather than once per 12 hours) bump.

Bob

> On Oct 20, 2014, at 3:43 AM, Magnus Danielson <magnus-0aYeopylZ8Qi5CQI31g/***@public.gmane.orgrg> wrote:
>
> Bob,
>
> Since the satellite orbit the earth with a period of 11 hours and 58 minutes, it is actually twice a day.
>
> Cheers,
> Magnus
>
> On 10/20/2014 03:50 AM, Bob Camp wrote:
>> Hi
>>
>> The GPS constellation repeats roughly once a day. It is not at all uncommon to have a “worst case” sattelite geometry for a given antenna location. If you have one, it will repeat once a day and show up as a bump in the timing out of your GPS module. If you track long term data, it will / may / can keep you from getting to the sort of stability you would expect in the 100,000 second range. It’s one of the main reasons that things like GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes having a Cs or something similar helps a lot looking for this sort of thing.
>>
>> Bob
>>
>>> On Oct 19, 2014, at 9:26 PM, Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org> wrote:
>>>
>>> Hi Bob Camp,
>>>
>>>
>>> In your response to Chris, you said: "Once you have it “right” you really need to check it over a month or two to watch for GPS “once a day” issues. "
>>>
>>> Could I ask you what you meant by these "once a day issues"? Was this a general comment, or was it about something specific? As you know I'm working on a GPSDO and am doing a lot of testing, so if there's something else I should be looking for, please let me know.
>>>
>>>
>>> Bob - AE6RV
>>>
>>>
>>> ________________________________
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
John C. Westmoreland, P.E.
2014-10-20 11:31:44 UTC
Permalink
Raw Message
Bob,

You mean the Sun, correct?

Regards,
John
On Oct 20, 2014 4:16 AM, "Bob Camp" <kb8tq-***@public.gmane.org> wrote:

> Hi
>
> Yes, but there’s this large object in the sky that modifies the ionosphere
> as it travels in a “about one a day” track. It appears to be coming up just
> about now, but I do need more coffee to be sure …
>
> The combination of the constellation and the ionosphere are what I believe
> give you the once a day (rather than once per 12 hours) bump.
>
> Bob
>
> > On Oct 20, 2014, at 3:43 AM, Magnus Danielson <
> magnus-0aYeopylZ8Qi5CQI31g/s0B+***@public.gmane.org> wrote:
> >
> > Bob,
> >
> > Since the satellite orbit the earth with a period of 11 hours and 58
> minutes, it is actually twice a day.
> >
> > Cheers,
> > Magnus
> >
> > On 10/20/2014 03:50 AM, Bob Camp wrote:
> >> Hi
> >>
> >> The GPS constellation repeats roughly once a day. It is not at all
> uncommon to have a “worst case” sattelite geometry for a given antenna
> location. If you have one, it will repeat once a day and show up as a bump
> in the timing out of your GPS module. If you track long term data, it will
> / may / can keep you from getting to the sort of stability you would expect
> in the 100,000 second range. It’s one of the main reasons that things like
> GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes
> having a Cs or something similar helps a lot looking for this sort of thing.
> >>
> >> Bob
> >>
> >>> On Oct 19, 2014, at 9:26 PM, Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org> wrote:
> >>>
> >>> Hi Bob Camp,
> >>>
> >>>
> >>> In your response to Chris, you said: "Once you have it “right” you
> really need to check it over a month or two to watch for GPS “once a day”
> issues. "
> >>>
> >>> Could I ask you what you meant by these "once a day issues"? Was this
> a general comment, or was it about something specific? As you know I'm
> working on a GPSDO and am doing a lot of testing, so if there's something
> else I should be looking for, please let me know.
> >>>
> >>>
> >>> Bob - AE6RV
> >>>
> >>>
> >>> ________________________________
> >>> _______________________________________________
> >>> time-nuts mailing list -- time-nuts-***@public.gmane.org
> >>> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> >>> and follow the instructions there.
> >>
> >> _______________________________________________
> >> time-nuts mailing list -- time-nuts-***@public.gmane.org
> >> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> >> and follow the instructions there.
> >>
> > _______________________________________________
> > time-nuts mailing list -- time-nuts-***@public.gmane.org
> > To unsubscribe, go to
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> > and follow the instructions there.
>
> _______________________________________________
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> and follow the instructions there.
>
Bob Camp
2014-10-20 11:43:50 UTC
Permalink
Raw Message
Hi

Gee, now after a few cups of coffee … yes that does appear to be the sun.

————

The GPS system does it’s best to model the ionosphere and transmit that data. Unfortunately the model / model resolution is not as good as it could be. That lets the ionosphere creep into the solution more than it might with a perfect model. My *guess* (as in I have no data) is that constellations with a significant number of low(er) angle sats *and* a sun rise / sun set over one end of the constellation are the worst ones. That could easily be pure bunk.

Bob

> On Oct 20, 2014, at 7:31 AM, John C. Westmoreland, P.E. <***@westmorelandengineering.com> wrote:
>
> Bob,
>
> You mean the Sun, correct?
>
> Regards,
> John
> On Oct 20, 2014 4:16 AM, "Bob Camp" <kb8tq-***@public.gmane.org> wrote:
>
>> Hi
>>
>> Yes, but there’s this large object in the sky that modifies the ionosphere
>> as it travels in a “about one a day” track. It appears to be coming up just
>> about now, but I do need more coffee to be sure …
>>
>> The combination of the constellation and the ionosphere are what I believe
>> give you the once a day (rather than once per 12 hours) bump.
>>
>> Bob
>>
>>> On Oct 20, 2014, at 3:43 AM, Magnus Danielson <
>> magnus-0aYeopylZ8Qi5CQI31g/s0B+***@public.gmane.org> wrote:
>>>
>>> Bob,
>>>
>>> Since the satellite orbit the earth with a period of 11 hours and 58
>> minutes, it is actually twice a day.
>>>
>>> Cheers,
>>> Magnus
>>>
>>> On 10/20/2014 03:50 AM, Bob Camp wrote:
>>>> Hi
>>>>
>>>> The GPS constellation repeats roughly once a day. It is not at all
>> uncommon to have a “worst case” sattelite geometry for a given antenna
>> location. If you have one, it will repeat once a day and show up as a bump
>> in the timing out of your GPS module. If you track long term data, it will
>> / may / can keep you from getting to the sort of stability you would expect
>> in the 100,000 second range. It’s one of the main reasons that things like
>> GPSD-Rb’s lock up with time constants much longer than 100K seconds. Yes
>> having a Cs or something similar helps a lot looking for this sort of thing.
>>>>
>>>> Bob
>>>>
>>>>> On Oct 19, 2014, at 9:26 PM, Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org> wrote:
>>>>>
>>>>> Hi Bob Camp,
>>>>>
>>>>>
>>>>> In your response to Chris, you said: "Once you have it “right” you
>> really need to check it over a month or two to watch for GPS “once a day”
>> issues. "
>>>>>
>>>>> Could I ask you what you meant by these "once a day issues"? Was this
>> a general comment, or was it about something specific? As you know I'm
>> working on a GPSDO and am doing a lot of testing, so if there's something
>> else I should be looking for, please let me know.
>>>>>
>>>>>
>>>>> Bob - AE6RV
>>>>>
>>>>>
>>>>> ________________________________
>>>>> _______________________________________________
>>>>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>>>>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>>> and follow the instructions there.
>>>>
>>>> _______________________________________________
>>>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>>>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>>> and follow the instructions there.
>>>>
>>> _______________________________________________
>>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
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>> and follow the instructions there.
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> _______________________________________________
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Brian Lloyd
2014-10-20 12:43:02 UTC
Permalink
Raw Message
On Mon, Oct 20, 2014 at 2:43 AM, Magnus Danielson <
magnus-0aYeopylZ8Qi5CQI31g/s0B+***@public.gmane.org> wrote:

> Bob,
>
> Since the satellite orbit the earth with a period of 11 hours and 58
> minutes, it is actually twice a day.
>

But then your house has only completed half an orbit.

--
Brian Lloyd
Lloyd Aviation
706 Flightline Drive
Spring Branch, TX 78070
brian-***@public.gmane.org
+1.210.802-8FLY (1.210.802-8359)
Tom Van Baak
2014-10-20 13:49:20 UTC
Permalink
Raw Message
The GPS satellites are at an altitude that gives them an orbit of 12* hours. But during that time the earth has made half a rotation. Thus it takes -two- SV orbits and -one- earth rotation to get back to the same geometry. It is this 24* hour ground-track repeat time that is of interest in high-precision work.

That's why you often see GPS time-transfer data based on days*, rather than just a few thousand seconds or 12 hours. This is not likely to affect any of you working on home GPSDO projects. But it is a concern for the folks that do positioning at mm levels.

* Fun facts:
1) Right, it's not actually 24 hours (solar day); instead it's closer to 23h 56m (sidereal day).
2) However, if you look closely you find it's not precisely a sidereal day (86164 s) either; instead the repeat time is closer to 86155 s, due to gravitational effects (inclined orbits, non-spherical earth).
3) If you look even closer you find each SV has its own repeat time; 86155 is merely the constellation average.
4) Also the per-SV repeat times are not constant; they slowly drift by about 10 seconds a year. As the orbit decays and the repeat time gets out of spec, an orbital maneuver puts the SV back.

For a nice description of this effect, here's a short 2-page summary:
http://www.insidegnss.com/pdf/ig0806_gnss-solutions.pdf

For deeper technical details, start with these papers:
http://spot.colorado.edu/~kristine/gpsrep.pdf
http://www.isprs.org/proceedings/XXXVII/congress/4_pdf/162.pdf
http://web.gps.caltech.edu/classes/ge167/file/Ragheb2007.pdf

And finally, to see the effect on a GPSDO, I have some ADEV plots at:
http://leapsecond.com/pages/sidereal/
http://leapsecond.com/pages/sidereal/14years.htm

/tvb
Tim Shoppa
2014-10-20 11:23:05 UTC
Permalink
Raw Message
having kept watch over oscillators for about half a century now... My first
assumption would be that a once-a-day bump in time offset or tuning word,
is due to earthside changes especially temperature of the earthside
oscillator environment.


Tim N3QE



On Sunday, October 19, 2014, Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org> wrote:

> Hi Bob Camp,
>
>
> In your response to Chris, you said: "Once you have it “right” you really
> need to check it over a month or two to watch for GPS “once a day” issues. "
>
> Could I ask you what you meant by these "once a day issues"? Was this a
> general comment, or was it about something specific? As you know I'm
> working on a GPSDO and am doing a lot of testing, so if there's something
> else I should be looking for, please let me know.
>
>
> Bob - AE6RV
>
>
> ________________________________
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org <javascript:;>
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
Charles Steinmetz
2014-10-25 15:23:57 UTC
Permalink
Raw Message
Bob wrote:

>PHK has a roughly 6 line code snippet that does a basic PLL. Add two
>more lines to check / clamp the integrator if you wish. That's 8
>lines. If you want a D term (to give it an FLL component) add 2 more
>lines. We're up to 10 lines.
>
>It's just a control loop, not a full GPSDO. There's not a lot to it.

There's a bit more to it than that. For any loop slow (narrowband)
enough to be useful disciplining a good OCXO, I consider a dual- or
triple-rate loop filter to be essential. There is also always a fair
amount of error-trapping, and other overhead. These can add lines
fairly quickly.

I'm sure I have lots more to learn about writing efficient
code. (But note that there is a difference between coding one's
chosen algorithm more efficiently and choosing a different algorithm
that is not really what you want, just because it is more efficient.)

Best regards,

Charles



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Bob Camp
2014-10-25 18:53:22 UTC
Permalink
Raw Message
Hi

We are not talking about a system (like GPS) that has junk data coming in. In this case, the phase detector gives you a very good estimate of the delta between input and output in real time. The error trapping / shifting / multi this and that simply isn’t needed in this case. The solution is much easier than the GPSDO.

Let the OCXO warm up for a day or two. Yes it could be a week.

Adjust it with a pot to be close to frequency. (This is a basement project).

Fire up the loop.

Let it settle.

Come back in an hour or two and all is well. Confirm this by watching a (good) DVM on the EFC line.

It’s a low gain / long time constant loop. It will take a bit to settle. Yes, if code is what gets you excited, put in an array for the coefficients. Then add a timer to step the index. The timer will add about 4 lines. The step process will be on auto-pilot, but that makes it easy. You will settle faster, the net result after settling will be about the same.

If a year from now it’s unlocked, re-adjust the pot. Maybe check it with a DVM every so often and adjust it before it unlocks.

Not a lot to it. Simple code to write Easy board to build. Does just what it needs to do. Not a commercial system at all. It does not need to be. It’s going to do everything you need to do and be much easier to get running than something far more complex. The idea is to make the simplest system that will do the trick, not make it so hard that nobody ever tries. The target audience is a basement experimenter not NIST. It’s ok in this case to replace a bunch of code with an inquiring mind.

Bob

> On Oct 25, 2014, at 11:23 AM, Charles Steinmetz <***@yandex.com> wrote:
>
> Bob wrote:
>
>> PHK has a roughly 6 line code snippet that does a basic PLL. Add two more lines to check / clamp the integrator if you wish. That's 8 lines. If you want a D term (to give it an FLL component) add 2 more lines. We're up to 10 lines.
>>
>> It's just a control loop, not a full GPSDO. There's not a lot to it.
>
> There's a bit more to it than that. For any loop slow (narrowband) enough to be useful disciplining a good OCXO, I consider a dual- or triple-rate loop filter to be essential. There is also always a fair amount of error-trapping, and other overhead. These can add lines fairly quickly.
>
> I'm sure I have lots more to learn about writing efficient code. (But note that there is a difference between coding one's chosen algorithm more efficiently and choosing a different algorithm that is not really what you want, just because it is more efficient.)
>
> Best regards,
>
> Charles
>
>
>
> _______________________________________________
> time-nuts mailing list -- time-***@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

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Chris Albertson
2014-10-25 19:52:16 UTC
Permalink
Raw Message
Mostly we don't even write the guts of those algorithms. For example,
you'd use a PID library. One line to create a PID controller object
then one line to call the PID for each phase measurement.

This goes double for, say, drawing a graph of the phase over time to
an LCD display, you'd use a graphic library for that. And for
communicating over USB to a computer. Who would want to take time to
learn the details of USB and LCD graphic controllers? Most code we
write is just "glue" that connects functions.

After a a few decades doing this I'd have to say that reinventing
well-tested wheels is the certain mark of a beginner/amateur. Either
they don't understand how to use these libraries or they don't know
they exist or think they can do it better. They spend 4X longer to
get something working and then it still does not cover all the "corner
cases and exceptions" those libraries might cover.

Ages ago CPU performance or space might mean you HAD to tightly code,
but now even a $1.79 8-bit AVR chip can hold well over the
equivalent of 1,000 lines of C++ code. OK there is the case a
manufactures who wants to be able to use the $1.69 chip and save 10
cents but most projects are not going to be built in high qualities.

Back on-tpic. Now that we have many low cast ($10 and under) uP
development boards building a GPSDO is simple. You don't even need a
custom PCB or many chips. And the simple $10 controller can have a
fancy LCD screen and connect to a computer and log stats and it can
all be up and running in a day or two.

If someone today wanted a harder challenge type project that would
push the state of that art out a little, why not build an "ensemble"
type device? One that accepts PPS timing from several sources,
figures out in realtime which of them to accept then runs several
local oscillators, perhaps an Rb and a couple OCXOs and compares their
outputs. So now you use both Rb and GPS, maybe a few of each to
track timing.

A while back I tried to prove to myself how easy it is now to build a
GPSDO that was good enough to drive typical lab equipment. Something
like a dozen lines of C code and $8 did it. It's no longer "cutting
edge to built these. Time to think about the next generation kind of
low-cost device. So maybe one could combine the best properties of
several different kinds of devices? Has this been done yet?



On Sat, Oct 25, 2014 at 8:23 AM, Charles Steinmetz
<***@yandex.com> wrote:
> Bob wrote:
>
>> PHK has a roughly 6 line code snippet that does a basic PLL. Add two more
>> lines to check / clamp the integrator if you wish. That's 8 lines. If you
>> want a D term (to give it an FLL component) add 2 more lines. We're up to 10
>> lines.
>>
>> It's just a control loop, not a full GPSDO. There's not a lot to it.
>
>
> There's a bit more to it than that. For any loop slow (narrowband) enough
> to be useful disciplining a good OCXO, I consider a dual- or triple-rate
> loop filter to be essential. There is also always a fair amount of
> error-trapping, and other overhead. These can add lines fairly quickly.
>
> I'm sure I have lots more to learn about writing efficient code. (But note
> that there is a difference between coding one's chosen algorithm more
> efficiently and choosing a different algorithm that is not really what you
> want, just because it is more efficient.)
>
> Best regards,
>
> Charles
>
>
>
> _______________________________________________
> time-nuts mailing list -- time-***@febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.



--

Chris Albertson
Redondo Beach, California
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Poul-Henning Kamp
2014-10-20 06:55:59 UTC
Permalink
Raw Message
--------
In message <20141019233526.ZNMKxMfK-***@public.gmane.org>, Charles Steinmetz
writes:

>A proper digital filter that computes a new
>running value at least every second will be more
>complex than that, but you're right, it's not an unfathomable task.

No, it will not, a simple running average will do just fine.

PLLs are really not that hard, and as it happens I wrote this a
couple of days ago about it:

http://phk.freebsd.dk/time/20141018.html

--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk-***@public.gmane.org | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Charles Steinmetz
2014-10-20 09:51:32 UTC
Permalink
Raw Message
Poul-Henning wrote:

>PLLs are really not that hard [context: we have been discussing
>all-digital PLLs ("ADPLLs")]

Yes, I know -- I have designed more than a few. I have also reviewed
more than a dozen hobbyist designs and modeled some of them, and
found that few hobbyists seem to have mastered the art. Judging also
by on-list responses over the years, it does not appear that many
time nuts are interested in designing and building their own
ADPLLs. So, I conclude that disciplining a good OCXO with GPS and
getting the best stability the OCXO can deliver is not practicable
for most hobbyists.

The OP in this sub-thread indicated that he was considering using an
LTE-Lite to discipline a "really good" 10811, and it appeared that
his expectation was to end up with a GPSDO more or less as good as
his 10811. My point was simply to put realistic bounds on the expectation.

Said posted that a quick lash-up with an OCXO produced stability
about 10x better than with the on-board TCXO. That is a useful
improvement, but a good OCXO (certainly, a "really good" 10811) will
have stability about 3 orders of magnitude better than a TCXO
(1000x), so two decades of possible improvement were not realized.

Said's experiment was a proof-of-concept exercise and not a careful
optimization, so it is almost certain one could do better than 10x
with some further work. But I very much doubt that optimization can
gain the entire two decades of potential improvement (short of
designing a full ADPLL, in which case you don't need the LTE-Lite at
all -- all you need is a source of PPS), and I doubt it is possible
to gain even one whole decade.

So, I am inclined to think that there are better (and easier) ways to
discipline a 10811 to reach its ful potential, that's all.

Best regards,

Charles
Bob Camp
2014-10-20 11:48:28 UTC
Permalink
Raw Message
Hi

We tend to focus on this or that enhanced feature in a piece of code. It’s fun to talk about. That’s not what keeps most designs from doing what they should. By focusing on this rather than the testing required, we set people up to fail. If you start off the project believing you mostly need fancy code when you mostly need long term testing instead, you hit a wall pretty fast. Setting up for one is not at all the same as setting up for the other.

Bob

> On Oct 20, 2014, at 5:51 AM, Charles Steinmetz <csteinmetz-zJpx2rpV7r/QT0dZR+***@public.gmane.org> wrote:
>
> Poul-Henning wrote:
>
>> PLLs are really not that hard [context: we have been discussing all-digital PLLs ("ADPLLs")]
>
> Yes, I know -- I have designed more than a few. I have also reviewed more than a dozen hobbyist designs and modeled some of them, and found that few hobbyists seem to have mastered the art. Judging also by on-list responses over the years, it does not appear that many time nuts are interested in designing and building their own ADPLLs. So, I conclude that disciplining a good OCXO with GPS and getting the best stability the OCXO can deliver is not practicable for most hobbyists.
>
> The OP in this sub-thread indicated that he was considering using an LTE-Lite to discipline a "really good" 10811, and it appeared that his expectation was to end up with a GPSDO more or less as good as his 10811. My point was simply to put realistic bounds on the expectation.
>
> Said posted that a quick lash-up with an OCXO produced stability about 10x better than with the on-board TCXO. That is a useful improvement, but a good OCXO (certainly, a "really good" 10811) will have stability about 3 orders of magnitude better than a TCXO (1000x), so two decades of possible improvement were not realized.
>
> Said's experiment was a proof-of-concept exercise and not a careful optimization, so it is almost certain one could do better than 10x with some further work. But I very much doubt that optimization can gain the entire two decades of potential improvement (short of designing a full ADPLL, in which case you don't need the LTE-Lite at all -- all you need is a source of PPS), and I doubt it is possible to gain even one whole decade.
>
> So, I am inclined to think that there are better (and easier) ways to discipline a 10811 to reach its ful potential, that's all.
>
> Best regards,
>
> Charles
>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
Charles Steinmetz
2014-10-20 12:54:40 UTC
Permalink
Raw Message
Bob wrote:

>We tend to focus on this or that enhanced feature in a piece of
>code. It's fun to talk about. That's not what keeps most designs
>from doing what they should. By focusing on this rather than the
>testing required, we set people up to fail. If you start off the
>project believing you mostly need fancy code when you mostly need
>long term testing instead, you hit a wall pretty fast. Setting up
>for one is not at all the same as setting up for the other.

Not really sure what this has to do with my post to which you
replied?? I assure you, I do not find code to be a fun, or even very
interesting, topic of conversation, and I did not mention it at all
in that post. Really, the only thing I've said about code is that
I've found it takes more than 100 lines to do a proper ADPLL. When I
have some time, I have to sit down and study Poul-Henning's code to
see what I can learn from it about parsimony.

Best regards,

Charles
Bob Camp
2014-10-20 21:52:44 UTC
Permalink
Raw Message
Hi

PHK has a roughly 6 line code snippet that does a basic PLL. Add two more lines to check / clamp the integrator if you wish. That’s 8 lines. If you want a D term (to give it an FLL component) add 2 more lines. We’re up to 10 lines.

It’s just a control loop, not a full GPSDO. There’s not a lot to it.

The code and some magic hardware to run it on is not the key to all this. Setting up and spending the time testing and optimizing is.

Bob

> On Oct 20, 2014, at 8:54 AM, Charles Steinmetz <csteinmetz-zJpx2rpV7r/QT0dZR+***@public.gmane.org> wrote:
>
> Bob wrote:
>
>> We tend to focus on this or that enhanced feature in a piece of code. It's fun to talk about. That's not what keeps most designs from doing what they should. By focusing on this rather than the testing required, we set people up to fail. If you start off the project believing you mostly need fancy code when you mostly need long term testing instead, you hit a wall pretty fast. Setting up for one is not at all the same as setting up for the other.
>
> Not really sure what this has to do with my post to which you replied?? I assure you, I do not find code to be a fun, or even very interesting, topic of conversation, and I did not mention it at all in that post. Really, the only thing I've said about code is that I've found it takes more than 100 lines to do a proper ADPLL. When I have some time, I have to sit down and study Poul-Henning's code to see what I can learn from it about parsimony.
>
> Best regards,
>
> Charles
>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Brian Lloyd
2014-10-20 17:20:51 UTC
Permalink
Raw Message
On Mon, Oct 20, 2014 at 6:48 AM, Bob Camp <kb8tq-***@public.gmane.org> wrote:

> Hi
>
> We tend to focus on this or that enhanced feature in a piece of code. It’s
> fun to talk about. That’s not what keeps most designs from doing what they
> should. By focusing on this rather than the testing required, we set people
> up to fail. If you start off the project believing you mostly need fancy
> code when you mostly need long term testing instead, you hit a wall pretty
> fast. Setting up for one is not at all the same as setting up for the other.
>

Sounds to me like the hardware and code are pretty straight-forward. The
difference comes from the terms and coefficients in the PLL loop filter and
those need to be optimized for each OCXO. There appear to be here a handful
of people who have a pretty good idea of what those coefficients should be
for various well-known OCXOs out there.

So why not do the GPSD hardware, software, and then provide the
coefficients that will get a handful of the more popular OCXOs available
out there to within a decade of optimum, certainly closer than what one
would be talking about by just bolting x-random OCXO onto an LTE-lite? I
suspect there would be a market in the time-nut world for such a critter.

--
Brian Lloyd
Lloyd Aviation
706 Flightline Drive
Spring Branch, TX 78070
brian-***@public.gmane.org
+1.210.802-8FLY (1.210.802-8359)
Poul-Henning Kamp
2014-10-20 19:58:12 UTC
Permalink
Raw Message
--------
In message <CAGVVbuGv_-cFDAA=T6hGE1ey32=oMxXcg-cxUb5sCusAo_T5eA-JsoAwUIsXosN+***@public.gmane.org>
, Brian Lloyd writes:

>So why not do the GPSD hardware, software, [...]

It would be a really worthwhile project in general, and it could be
made very general with very little trouble.

I would find a cheap ARM board (Olimex ?) that can support ChibiOS:

http://www.chibios.org/dokuwiki/doku.php?id=news

and add a "cape" PCB with a high resolution DAC for EFC control
and two phase detectors, one for 100kHz-20MHz frequencies and one
for 1-100Hz frequencies. (The latter could have a TVB PIC divider
as an option on the reference input).

Maybe add a couple of isolated distribution amp outputs also ?

That would make for a really experimenter-friendly computer PLL
platform.

People who want to code can do so, people less ambitious could
tweak PLL params in the default firmware using the ChibiOS command
line interface...

Count me in...


--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk-***@public.gmane.org | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Bob Camp
2014-10-20 21:58:22 UTC
Permalink
Raw Message
Hi

The problem is that there are no “magic coefficients”. What you run depends very much on the exact OCXO you have, the environment you run it in, and the result you are after.

For instance, Bert is after frequency stability. Tom is after the right time. Each of them will have very different coefficients for the same oscillator.

My Morion OCXO has a floor of 2x10^-12, Bert has some that are 10X better than that (maybe). His coefficients and mine will be very different.

I had an antenna outdoors. It got many sat’s all the time. Now I have one indoors. It’s not getting lots of sats all the time. My old coefficients are not going to be my new coefficients.

No magic bullet, you have to do the work.

Bob

> On Oct 20, 2014, at 1:20 PM, Brian Lloyd <brian-***@public.gmane.org> wrote:
>
> On Mon, Oct 20, 2014 at 6:48 AM, Bob Camp <kb8tq-***@public.gmane.org> wrote:
>
>> Hi
>>
>> We tend to focus on this or that enhanced feature in a piece of code. It’s
>> fun to talk about. That’s not what keeps most designs from doing what they
>> should. By focusing on this rather than the testing required, we set people
>> up to fail. If you start off the project believing you mostly need fancy
>> code when you mostly need long term testing instead, you hit a wall pretty
>> fast. Setting up for one is not at all the same as setting up for the other.
>>
>
> Sounds to me like the hardware and code are pretty straight-forward. The
> difference comes from the terms and coefficients in the PLL loop filter and
> those need to be optimized for each OCXO. There appear to be here a handful
> of people who have a pretty good idea of what those coefficients should be
> for various well-known OCXOs out there.
>
> So why not do the GPSD hardware, software, and then provide the
> coefficients that will get a handful of the more popular OCXOs available
> out there to within a decade of optimum, certainly closer than what one
> would be talking about by just bolting x-random OCXO onto an LTE-lite? I
> suspect there would be a market in the time-nut world for such a critter.
>
> --
> Brian Lloyd
> Lloyd Aviation
> 706 Flightline Drive
> Spring Branch, TX 78070
> brian-***@public.gmane.org
> +1.210.802-8FLY (1.210.802-8359)
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
Timestep
2014-10-20 08:46:57 UTC
Permalink
Raw Message
From: Dave Cawley
Dartmouth United Kingdom


Femtosecond Systems FSS 600 phase noise detector

Guys

Just won this on eBay. Try as I might, I can't find any details especially a circuit/schematic diagram. Can anyone help please ?

Thanks

Dave
Tom Van Baak
2014-10-20 15:30:17 UTC
Permalink
Raw Message
> http://phk.freebsd.dk/time/20141018.html

PHK,

This is the best news I've heard in a long time; an overhaul of NTP!

One suggestion I'd like to make. You've seen the GPSDO simulator code I started:
http://leapsecond.com/tools/gpsim1.c
And you've seen the growing collection of GPS receiver and OCXO oscillator raw data:
http://leapsecond.com/pages/gpsdo-sim/

Instead of tweaking GPSDO algorithms or tuning parameters and having to wait days to see if it works or not, the idea was to "replay" pre-recorded 1PPS data and pre-recorded oscillator data into the PLL. This means one can test any new design change in a GPSDO in a matter of seconds instead of days.

So the question is -- could you do the same for NTP? On your own, or with world-wide contributions, you could collect long data sets (phase or frequency) of free-running PC clock oscillators, every shape and size and environment. And then also collect high-precision real-life NTP packet timings, warts and all (especially outlier examples).

Then instead of testing iterations of your new code on live NTP servers you merely apply previously collected packet data and previously collected clock data. With a little scripting you'd get performance plots within seconds instead of waiting hours or days. Moreover, the plots you generate would cover tens or hundreds of historical scenarios instead of just the few you could find in real time.

/tvb
Poul-Henning Kamp
2014-10-20 19:41:42 UTC
Permalink
Raw Message
--------
In message <***@pc52>, "Tom Van Baak" writes:
>> http://phk.freebsd.dk/time/20141018.html
>
>PHK,
>
>This is the best news I've heard in a long time; an overhaul of NTP!

Indeed :-)

>Instead of tweaking GPSDO algorithms or tuning parameters and
>having to wait days to see if it works or not, the idea was to
>"replay" pre-recorded 1PPS data and pre-recorded oscillator data
>into the PLL. This means one can test any new design change in a
>GPSDO in a matter of seconds instead of days.
>
>So the question is -- could you do the same for NTP?

Well, first of all it's not days any longer. My proto-PLL wrangles
the clock phase in a matter of seconds and frequency in a few
minutes. Some of the (really) old NTP assumptions and metrics no
longer hold, revisiting them opens up a lot of parameter space.

Second, I'm already doing such simulations, and the ability to
do that is part of the design basis of what I'm doing.

I spent a month of my NTP-time trying to resurrect the "SIM" code in
ntpd, in order to get some kind of reproducible test-bench going and
in the end I concluded that 100k lines of code is not the way forward.

My current plan is to release a brand new client-only NTP daemon
with a decent PLL and high attack resistance before X-mas and then
work from there to one or two other programs: NTP-slave server (ie:
stratum 2..14) and a NTP-master/stratum 1 server.

All along the way, the intent is to try to pull PTP into this also,
since there is no material (ie: only protocol) difference between
a NTP and PTP timekeeping program, and the user shouldn't need to
notice the difference.

More as it happens.

The "mini-blog" entries I've started will happen every so often
when there is some progress to report or interesting data to
present.


--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk-***@public.gmane.org | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Bob Camp
2014-10-20 22:06:17 UTC
Permalink
Raw Message
Hi

The top of my list for “new NTP” would be to bring the 1588 hardware packet time tagging into the NTP code base. There’s a pretty good base of hardware out there that tags. It should help things on a loaded system.

Bob

> On Oct 20, 2014, at 3:41 PM, Poul-Henning Kamp <phk-HF+***@public.gmane.org> wrote:
>
> --------
> In message <***@pc52>, "Tom Van Baak" writes:
>>> http://phk.freebsd.dk/time/20141018.html
>>
>> PHK,
>>
>> This is the best news I've heard in a long time; an overhaul of NTP!
>
> Indeed :-)
>
>> Instead of tweaking GPSDO algorithms or tuning parameters and
>> having to wait days to see if it works or not, the idea was to
>> "replay" pre-recorded 1PPS data and pre-recorded oscillator data
>> into the PLL. This means one can test any new design change in a
>> GPSDO in a matter of seconds instead of days.
>>
>> So the question is -- could you do the same for NTP?
>
> Well, first of all it's not days any longer. My proto-PLL wrangles
> the clock phase in a matter of seconds and frequency in a few
> minutes. Some of the (really) old NTP assumptions and metrics no
> longer hold, revisiting them opens up a lot of parameter space.
>
> Second, I'm already doing such simulations, and the ability to
> do that is part of the design basis of what I'm doing.
>
> I spent a month of my NTP-time trying to resurrect the "SIM" code in
> ntpd, in order to get some kind of reproducible test-bench going and
> in the end I concluded that 100k lines of code is not the way forward.
>
> My current plan is to release a brand new client-only NTP daemon
> with a decent PLL and high attack resistance before X-mas and then
> work from there to one or two other programs: NTP-slave server (ie:
> stratum 2..14) and a NTP-master/stratum 1 server.
>
> All along the way, the intent is to try to pull PTP into this also,
> since there is no material (ie: only protocol) difference between
> a NTP and PTP timekeeping program, and the user shouldn't need to
> notice the difference.
>
> More as it happens.
>
> The "mini-blog" entries I've started will happen every so often
> when there is some progress to report or interesting data to
> present.
>
>
> --
> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
> phk-***@public.gmane.org | TCP/IP since RFC 956
> FreeBSD committer | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
S. Jackson via time-nuts
2014-10-18 21:40:46 UTC
Permalink
Raw Message
Dave, et.al.,

upon popular request I put together a PDF of my email describing how I
generated a low-phase-noise 10MHz output from the CMOS 20MHz output of the
LTE-Lite GPSDO. Here it is.

No guarantees whatsoever guys, and it does take good equipment, a very
steady hand, and a lot of experience to put this together and make it work
properly.

This design can work up to 145MHz according to the 74LVX74 datasheet if
powered at 3.3V.

bye,
Said


In a message dated 10/18/2014 14:09:54 Pacific Daylight Time,
kc0wjn-***@public.gmane.org writes:

Hi, Said.

I would be interested in having a copy of your "app-note", if that is
possible. I'd like to purchase one of the GPSDOs, but will need to wait
for amonth or so.

Thanks.

Cheers,
DaveD

On 10/18/2014 12:19 PM, S. Jackson via time-nuts wrote:
> Hi guys,
>
> lots of questions, let me try to answer some of these. Bob, David, et.
al,
> thanks for answering some of these already!
>
> Dave, as Bob said "it depends on your application" -- and your time
frame.
> Also, please check the FAQ for an answer on the external TCXO
requirement,
> specifically item 35. in the FAQ on the Ebay website for the product.
>
> Jim, I ended up doing the "appnote" in email format, and sending out a
> description, schematics, PN plot, and photos yesterday, please check
your
> emails. I won't do a formal appnote, sorry no time.. I hope the
description of
> what I wired-up yesterday is good enough for folks to try the same.
>
> Ernie, as mentioned here the price is $185 plus shipping on Ebay for the
> entire kit. Shipping is calculated by Ebay, and should be a flat-rate
of $10
> in the continental US
>
> Hal, MY BAD!! I should have known better and super-imposed both the
> original 20MHz and 10MHz plots on the same plot. I will do so shortly.
On the
> table in the plot: the TimePod tries to determine spurs, and display
them on
> the upper right hand of the plot in a table, and with the phase noise
being
> as clean as it is I guess the TimePod software could only find two spurs,
> one at 0.8 and one at 0.9Hz offset from carrier, which was not even
shown in
> that plot since it starts at 1Hz.
>
> Thanks so much for your feedback, lively discussion, and good questions
> guys.
>
> I hope that answers all questions,
> bye,
> Said
>
Dr. David Kirkby (Kirkby Microwave Ltd)
2014-10-19 00:23:57 UTC
Permalink
Raw Message
I am sorry, but I can't follow the circuit diagram. It is not clear to me
what pins are joined, and what are not. Sometimes you have used a filled
circle to indicate lines are joined, and in another case there's a
semicircle to indicate that they are not. But on some of the others, I
don't know what are supposed to be joined and what are not.

Dave
On 19 Oct 2014 01:00, "S. Jackson via time-nuts" <time-nuts-***@public.gmane.org> wrote:

> Dave, et.al.,
>
> upon popular request I put together a PDF of my email describing how I
> generated a low-phase-noise 10MHz output from the CMOS 20MHz output of the
> LTE-Lite GPSDO. Here it is.
>
> No guarantees whatsoever guys, and it does take good equipment, a very
> steady hand, and a lot of experience to put this together and make it work
> properly.
>
> This design can work up to 145MHz according to the 74LVX74 datasheet if
> powered at 3.3V.
>
> bye,
> Said
>
>
> In a message dated 10/18/2014 14:09:54 Pacific Daylight Time,
> kc0wjn-***@public.gmane.org writes:
>
> Hi, Said.
>
> I would be interested in having a copy of your "app-note", if that is
> possible. I'd like to purchase one of the GPSDOs, but will need to wait
> for amonth or so.
>
> Thanks.
>
> Cheers,
> DaveD
>
> On 10/18/2014 12:19 PM, S. Jackson via time-nuts wrote:
> > Hi guys,
> >
> > lots of questions, let me try to answer some of these. Bob, David, et.
> al,
> > thanks for answering some of these already!
> >
> > Dave, as Bob said "it depends on your application" -- and your time
> frame.
> > Also, please check the FAQ for an answer on the external TCXO
> requirement,
> > specifically item 35. in the FAQ on the Ebay website for the product.
> >
> > Jim, I ended up doing the "appnote" in email format, and sending out a
> > description, schematics, PN plot, and photos yesterday, please check
> your
> > emails. I won't do a formal appnote, sorry no time.. I hope the
> description of
> > what I wired-up yesterday is good enough for folks to try the same.
> >
> > Ernie, as mentioned here the price is $185 plus shipping on Ebay for the
> > entire kit. Shipping is calculated by Ebay, and should be a flat-rate
> of $10
> > in the continental US
> >
> > Hal, MY BAD!! I should have known better and super-imposed both the
> > original 20MHz and 10MHz plots on the same plot. I will do so shortly.
> On the
> > table in the plot: the TimePod tries to determine spurs, and display
> them on
> > the upper right hand of the plot in a table, and with the phase noise
> being
> > as clean as it is I guess the TimePod software could only find two
> spurs,
> > one at 0.8 and one at 0.9Hz offset from carrier, which was not even
> shown in
> > that plot since it starts at 1Hz.
> >
> > Thanks so much for your feedback, lively discussion, and good questions
> > guys.
> >
> > I hope that answers all questions,
> > bye,
> > Said
> >
>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
Bob Camp
2014-10-19 00:48:50 UTC
Permalink
Raw Message
Hi

The 20 MHz connects only to pin 3.

+3V connects to pin 4 , but not pins 2 or 3.

Pin 6 hooks only to pin 2 and nothing else.

Bob


> On Oct 18, 2014, at 8:23 PM, Dr. David Kirkby (Kirkby Microwave Ltd) <drkirkby-***@public.gmane.org> wrote:
>
> I am sorry, but I can't follow the circuit diagram. It is not clear to me
> what pins are joined, and what are not. Sometimes you have used a filled
> circle to indicate lines are joined, and in another case there's a
> semicircle to indicate that they are not. But on some of the others, I
> don't know what are supposed to be joined and what are not.
>
> Dave
> On 19 Oct 2014 01:00, "S. Jackson via time-nuts" <time-nuts-***@public.gmane.org> wrote:
>
>> Dave, et.al.,
>>
>> upon popular request I put together a PDF of my email describing how I
>> generated a low-phase-noise 10MHz output from the CMOS 20MHz output of the
>> LTE-Lite GPSDO. Here it is.
>>
>> No guarantees whatsoever guys, and it does take good equipment, a very
>> steady hand, and a lot of experience to put this together and make it work
>> properly.
>>
>> This design can work up to 145MHz according to the 74LVX74 datasheet if
>> powered at 3.3V.
>>
>> bye,
>> Said
>>
>>
>> In a message dated 10/18/2014 14:09:54 Pacific Daylight Time,
>> kc0wjn-***@public.gmane.org writes:
>>
>> Hi, Said.
>>
>> I would be interested in having a copy of your "app-note", if that is
>> possible. I'd like to purchase one of the GPSDOs, but will need to wait
>> for amonth or so.
>>
>> Thanks.
>>
>> Cheers,
>> DaveD
>>
>> On 10/18/2014 12:19 PM, S. Jackson via time-nuts wrote:
>>> Hi guys,
>>>
>>> lots of questions, let me try to answer some of these. Bob, David, et.
>> al,
>>> thanks for answering some of these already!
>>>
>>> Dave, as Bob said "it depends on your application" -- and your time
>> frame.
>>> Also, please check the FAQ for an answer on the external TCXO
>> requirement,
>>> specifically item 35. in the FAQ on the Ebay website for the product.
>>>
>>> Jim, I ended up doing the "appnote" in email format, and sending out a
>>> description, schematics, PN plot, and photos yesterday, please check
>> your
>>> emails. I won't do a formal appnote, sorry no time.. I hope the
>> description of
>>> what I wired-up yesterday is good enough for folks to try the same.
>>>
>>> Ernie, as mentioned here the price is $185 plus shipping on Ebay for the
>>> entire kit. Shipping is calculated by Ebay, and should be a flat-rate
>> of $10
>>> in the continental US
>>>
>>> Hal, MY BAD!! I should have known better and super-imposed both the
>>> original 20MHz and 10MHz plots on the same plot. I will do so shortly.
>> On the
>>> table in the plot: the TimePod tries to determine spurs, and display
>> them on
>>> the upper right hand of the plot in a table, and with the phase noise
>> being
>>> as clean as it is I guess the TimePod software could only find two
>> spurs,
>>> one at 0.8 and one at 0.9Hz offset from carrier, which was not even
>> shown in
>>> that plot since it starts at 1Hz.
>>>
>>> Thanks so much for your feedback, lively discussion, and good questions
>>> guys.
>>>
>>> I hope that answers all questions,
>>> bye,
>>> Said
>>>
>>
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
Tom Miller
2014-10-19 00:48:05 UTC
Permalink
Raw Message
This looks pretty interesting:
74G series PO74G74

http://www.ebay.com/itm/330551715157?_trksid=p2060778.m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT#ht_411wt_664

600+ MHz cmos 3.5 volt

Tom


----- Original Message -----
From: "S. Jackson via time-nuts" <time-nuts-***@public.gmane.org>
To: <kc0wjn-***@public.gmane.org>; <time-nuts-***@public.gmane.org>
Sent: Saturday, October 18, 2014 5:40 PM
Subject: Re: [time-nuts] LTE-Lite module


> Dave, et.al.,
>
> upon popular request I put together a PDF of my email describing how I
> generated a low-phase-noise 10MHz output from the CMOS 20MHz output of the
> LTE-Lite GPSDO. Here it is.
>
> No guarantees whatsoever guys, and it does take good equipment, a very
> steady hand, and a lot of experience to put this together and make it work
> properly.
>
> This design can work up to 145MHz according to the 74LVX74 datasheet if
> powered at 3.3V.
>
> bye,
> Said
>
>
> In a message dated 10/18/2014 14:09:54 Pacific Daylight Time,
> kc0wjn-***@public.gmane.org writes:
>
> Hi, Said.
>
> I would be interested in having a copy of your "app-note", if that is
> possible. I'd like to purchase one of the GPSDOs, but will need to wait
> for amonth or so.
>
> Thanks.
>
> Cheers,
> DaveD
>
> On 10/18/2014 12:19 PM, S. Jackson via time-nuts wrote:
>> Hi guys,
>>
>> lots of questions, let me try to answer some of these. Bob, David, et.
> al,
>> thanks for answering some of these already!
>>
>> Dave, as Bob said "it depends on your application" -- and your time
> frame.
>> Also, please check the FAQ for an answer on the external TCXO
> requirement,
>> specifically item 35. in the FAQ on the Ebay website for the product.
>>
>> Jim, I ended up doing the "appnote" in email format, and sending out a
>> description, schematics, PN plot, and photos yesterday, please check
> your
>> emails. I won't do a formal appnote, sorry no time.. I hope the
> description of
>> what I wired-up yesterday is good enough for folks to try the same.
>>
>> Ernie, as mentioned here the price is $185 plus shipping on Ebay for the
>> entire kit. Shipping is calculated by Ebay, and should be a flat-rate
> of $10
>> in the continental US
>>
>> Hal, MY BAD!! I should have known better and super-imposed both the
>> original 20MHz and 10MHz plots on the same plot. I will do so shortly.
> On the
>> table in the plot: the TimePod tries to determine spurs, and display
> them on
>> the upper right hand of the plot in a table, and with the phase noise
> being
>> as clean as it is I guess the TimePod software could only find two
>> spurs,
>> one at 0.8 and one at 0.9Hz offset from carrier, which was not even
> shown in
>> that plot since it starts at 1Hz.
>>
>> Thanks so much for your feedback, lively discussion, and good questions
>> guys.
>>
>> I hope that answers all questions,
>> bye,
>> Said
>>
>
>
>


--------------------------------------------------------------------------------


> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>
Thomas S. Knutsen
2014-10-19 01:51:03 UTC
Permalink
Raw Message
The potatochips are quite excelent high speed devices, and by selling them
on e-bay, they make it avaible to us who are not able to go through the
normal supplier chains.

Br.
Thomas.

2014-10-19 2:48 GMT+02:00 Tom Miller <tmiller11147-H+***@public.gmane.org>:

> This looks pretty interesting:
> 74G series PO74G74
>
> http://www.ebay.com/itm/330551715157?_trksid=p2060778.
> m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT#ht_411wt_664
>
> 600+ MHz cmos 3.5 volt
>
> Tom
>
>
> ----- Original Message ----- From: "S. Jackson via time-nuts" <
> time-nuts-***@public.gmane.org>
> To: <kc0wjn-***@public.gmane.org>; <time-nuts-***@public.gmane.org>
> Sent: Saturday, October 18, 2014 5:40 PM
> Subject: Re: [time-nuts] LTE-Lite module
>
>
>
> Dave, et.al.,
>>
>> upon popular request I put together a PDF of my email describing how I
>> generated a low-phase-noise 10MHz output from the CMOS 20MHz output of the
>> LTE-Lite GPSDO. Here it is.
>>
>> No guarantees whatsoever guys, and it does take good equipment, a very
>> steady hand, and a lot of experience to put this together and make it work
>> properly.
>>
>> This design can work up to 145MHz according to the 74LVX74 datasheet if
>> powered at 3.3V.
>>
>> bye,
>> Said
>>
>>
>> In a message dated 10/18/2014 14:09:54 Pacific Daylight Time,
>> kc0wjn-***@public.gmane.org writes:
>>
>> Hi, Said.
>>
>> I would be interested in having a copy of your "app-note", if that is
>> possible. I'd like to purchase one of the GPSDOs, but will need to wait
>> for amonth or so.
>>
>> Thanks.
>>
>> Cheers,
>> DaveD
>>
>> On 10/18/2014 12:19 PM, S. Jackson via time-nuts wrote:
>>
>>> Hi guys,
>>>
>>> lots of questions, let me try to answer some of these. Bob, David, et.
>>>
>> al,
>>
>>> thanks for answering some of these already!
>>>
>>> Dave, as Bob said "it depends on your application" -- and your time
>>>
>> frame.
>>
>>> Also, please check the FAQ for an answer on the external TCXO
>>>
>> requirement,
>>
>>> specifically item 35. in the FAQ on the Ebay website for the product.
>>>
>>> Jim, I ended up doing the "appnote" in email format, and sending out a
>>> description, schematics, PN plot, and photos yesterday, please check
>>>
>> your
>>
>>> emails. I won't do a formal appnote, sorry no time.. I hope the
>>>
>> description of
>>
>>> what I wired-up yesterday is good enough for folks to try the same.
>>>
>>> Ernie, as mentioned here the price is $185 plus shipping on Ebay for the
>>> entire kit. Shipping is calculated by Ebay, and should be a flat-rate
>>>
>> of $10
>>
>>> in the continental US
>>>
>>> Hal, MY BAD!! I should have known better and super-imposed both the
>>> original 20MHz and 10MHz plots on the same plot. I will do so shortly.
>>>
>> On the
>>
>>> table in the plot: the TimePod tries to determine spurs, and display
>>>
>> them on
>>
>>> the upper right hand of the plot in a table, and with the phase noise
>>>
>> being
>>
>>> as clean as it is I guess the TimePod software could only find two
>>> spurs,
>>> one at 0.8 and one at 0.9Hz offset from carrier, which was not even
>>>
>> shown in
>>
>>> that plot since it starts at 1Hz.
>>>
>>> Thanks so much for your feedback, lively discussion, and good questions
>>> guys.
>>>
>>> I hope that answers all questions,
>>> bye,
>>> Said
>>>
>>>
>>
>>
>>
>
> ------------------------------------------------------------
> --------------------
>
>
>
> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to https://www.febo.com/cgi-bin/
>> mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/
> mailman/listinfo/time-nuts
> and follow the instructions there.
>



--

Please avoid sending me Word or PowerPoint attachments.
See <http://www.gnu.org/philosophy/no-word-attachments.html>
PDF is an better alternative and there are always LaTeX!
Bob Camp
2014-10-19 02:23:52 UTC
Permalink
Raw Message
Hi

Didn’t we just hash through all the Potato Chip stuff earlier this week when Bert brought them up?

Bob

> On Oct 18, 2014, at 9:51 PM, Thomas S. Knutsen <la3pna-***@public.gmane.org> wrote:
>
> The potatochips are quite excelent high speed devices, and by selling them
> on e-bay, they make it avaible to us who are not able to go through the
> normal supplier chains.
>
> Br.
> Thomas.
>
> 2014-10-19 2:48 GMT+02:00 Tom Miller <tmiller11147-H+***@public.gmane.org>:
>
>> This looks pretty interesting:
>> 74G series PO74G74
>>
>> http://www.ebay.com/itm/330551715157?_trksid=p2060778.
>> m1438.l2649&ssPageName=STRK%3AMEBIDX%3AIT#ht_411wt_664
>>
>> 600+ MHz cmos 3.5 volt
>>
>> Tom
>>
>>
>> ----- Original Message ----- From: "S. Jackson via time-nuts" <
>> time-nuts-***@public.gmane.org>
>> To: <kc0wjn-***@public.gmane.org>; <time-nuts-***@public.gmane.org>
>> Sent: Saturday, October 18, 2014 5:40 PM
>> Subject: Re: [time-nuts] LTE-Lite module
>>
>>
>>
>> Dave, et.al.,
>>>
>>> upon popular request I put together a PDF of my email describing how I
>>> generated a low-phase-noise 10MHz output from the CMOS 20MHz output of the
>>> LTE-Lite GPSDO. Here it is.
>>>
>>> No guarantees whatsoever guys, and it does take good equipment, a very
>>> steady hand, and a lot of experience to put this together and make it work
>>> properly.
>>>
>>> This design can work up to 145MHz according to the 74LVX74 datasheet if
>>> powered at 3.3V.
>>>
>>> bye,
>>> Said
>>>
>>>
>>> In a message dated 10/18/2014 14:09:54 Pacific Daylight Time,
>>> kc0wjn-***@public.gmane.org writes:
>>>
>>> Hi, Said.
>>>
>>> I would be interested in having a copy of your "app-note", if that is
>>> possible. I'd like to purchase one of the GPSDOs, but will need to wait
>>> for amonth or so.
>>>
>>> Thanks.
>>>
>>> Cheers,
>>> DaveD
>>>
>>> On 10/18/2014 12:19 PM, S. Jackson via time-nuts wrote:
>>>
>>>> Hi guys,
>>>>
>>>> lots of questions, let me try to answer some of these. Bob, David, et.
>>>>
>>> al,
>>>
>>>> thanks for answering some of these already!
>>>>
>>>> Dave, as Bob said "it depends on your application" -- and your time
>>>>
>>> frame.
>>>
>>>> Also, please check the FAQ for an answer on the external TCXO
>>>>
>>> requirement,
>>>
>>>> specifically item 35. in the FAQ on the Ebay website for the product.
>>>>
>>>> Jim, I ended up doing the "appnote" in email format, and sending out a
>>>> description, schematics, PN plot, and photos yesterday, please check
>>>>
>>> your
>>>
>>>> emails. I won't do a formal appnote, sorry no time.. I hope the
>>>>
>>> description of
>>>
>>>> what I wired-up yesterday is good enough for folks to try the same.
>>>>
>>>> Ernie, as mentioned here the price is $185 plus shipping on Ebay for the
>>>> entire kit. Shipping is calculated by Ebay, and should be a flat-rate
>>>>
>>> of $10
>>>
>>>> in the continental US
>>>>
>>>> Hal, MY BAD!! I should have known better and super-imposed both the
>>>> original 20MHz and 10MHz plots on the same plot. I will do so shortly.
>>>>
>>> On the
>>>
>>>> table in the plot: the TimePod tries to determine spurs, and display
>>>>
>>> them on
>>>
>>>> the upper right hand of the plot in a table, and with the phase noise
>>>>
>>> being
>>>
>>>> as clean as it is I guess the TimePod software could only find two
>>>> spurs,
>>>> one at 0.8 and one at 0.9Hz offset from carrier, which was not even
>>>>
>>> shown in
>>>
>>>> that plot since it starts at 1Hz.
>>>>
>>>> Thanks so much for your feedback, lively discussion, and good questions
>>>> guys.
>>>>
>>>> I hope that answers all questions,
>>>> bye,
>>>> Said
>>>>
>>>>
>>>
>>>
>>>
>>
>> ------------------------------------------------------------
>> --------------------
>>
>>
>>
>> _______________________________________________
>>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>>> To unsubscribe, go to https://www.febo.com/cgi-bin/
>>> mailman/listinfo/time-nuts
>>> and follow the instructions there.
>>>
>>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to https://www.febo.com/cgi-bin/
>> mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
>
>
>
> --
>
> Please avoid sending me Word or PowerPoint attachments.
> See <http://www.gnu.org/philosophy/no-word-attachments.html>
> PDF is an better alternative and there are always LaTeX!
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
S. Jackson via time-nuts
2014-10-19 01:44:45 UTC
Permalink
Raw Message
Thanks for helping out Bob,

sometimes I get ahead of myself.

Dave, you can also trace the wiring on the photo I had sent of the actual
module, its more or less clearly visible under the lupe. Please note that
on that module I mounted the IC upside down, with the pins sticking up, and
bending the grounded pins down toward the PCB.

bye,
Said




In a message dated 10/18/2014 17:55:36 Pacific Daylight Time, kb8tq-***@public.gmane.org
writes:

Hi


The 20 MHz connects only to pin 3.

+3V connects to pin 4 , but not pins 2 or 3.

Pin 6 hooks only to pin 2 and nothing else.

Bob


> On Oct 18, 2014, at 8:23 PM, Dr. David Kirkby (Kirkby Microwave Ltd)
<drkirkby-***@public.gmane.org> wrote:
>
> I am sorry, but I can't follow the circuit diagram. It is not clear to
me
> what pins are joined, and what are not. Sometimes you have used a filled
> circle to indicate lines are joined, and in another case there's a
> semicircle to indicate that they are not. But on some of the others, I
> don't know what are supposed to be joined and what are not.
>
> Dave
> On 19 Oct 2014 01:00, "S. Jackson via time-nuts" <time-nuts-***@public.gmane.org>
wrote:
>
>> Dave, et.al.,
>>
>> upon popular request I put together a PDF of my email describing how I
>> generated a low-phase-noise 10MHz output from the CMOS 20MHz output of
the
>> LTE-Lite GPSDO. Here it is.
>>
>> No guarantees whatsoever guys, and it does take good equipment, a very
>> steady hand, and a lot of experience to put this together and make it
work
>> properly.
>>
>> This design can work up to 145MHz according to the 74LVX74 datasheet if
>> powered at 3.3V.
>>
>> bye,
>> Said
>>
>>
>> In a message dated 10/18/2014 14:09:54 Pacific Daylight Time,
>> kc0wjn-***@public.gmane.org writes:
>>
>> Hi, Said.
>>
>> I would be interested in having a copy of your "app-note", if that is
>> possible. I'd like to purchase one of the GPSDOs, but will need to wait
>> for amonth or so.
>>
>> Thanks.
>>
>> Cheers,
>> DaveD
>>
>> On 10/18/2014 12:19 PM, S. Jackson via time-nuts wrote:
>>> Hi guys,
>>>
>>> lots of questions, let me try to answer some of these. Bob, David,
et.
>> al,
>>> thanks for answering some of these already!
>>>
>>> Dave, as Bob said "it depends on your application" -- and your time
>> frame.
>>> Also, please check the FAQ for an answer on the external TCXO
>> requirement,
>>> specifically item 35. in the FAQ on the Ebay website for the product.
>>>
>>> Jim, I ended up doing the "appnote" in email format, and sending out a
>>> description, schematics, PN plot, and photos yesterday, please check
>> your
>>> emails. I won't do a formal appnote, sorry no time.. I hope the
>> description of
>>> what I wired-up yesterday is good enough for folks to try the same.
>>>
>>> Ernie, as mentioned here the price is $185 plus shipping on Ebay for
the
>>> entire kit. Shipping is calculated by Ebay, and should be a flat-rate
>> of $10
>>> in the continental US
>>>
>>> Hal, MY BAD!! I should have known better and super-imposed both the
>>> original 20MHz and 10MHz plots on the same plot. I will do so shortly.
>> On the
>>> table in the plot: the TimePod tries to determine spurs, and display
>> them on
>>> the upper right hand of the plot in a table, and with the phase noise
>> being
>>> as clean as it is I guess the TimePod software could only find two
>> spurs,
>>> one at 0.8 and one at 0.9Hz offset from carrier, which was not even
>> shown in
>>> that plot since it starts at 1Hz.
>>>
>>> Thanks so much for your feedback, lively discussion, and good
questions
>>> guys.
>>>
>>> I hope that answers all questions,
>>> bye,
>>> Said
>>>
>>
>>
>>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to
>> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

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Bert Kehren via time-nuts
2014-10-19 20:23:50 UTC
Permalink
Raw Message
With all the work around if you want very good performance use a Shera. We
have super results with a Morion, Shera and ublox M7
Bert Kehren


In a message dated 10/19/2014 4:08:32 P.M. Eastern Daylight Time,
kb8tq-***@public.gmane.org writes:

Hi

> On Oct 19, 2014, at 3:35 PM, Charles Steinmetz <csteinmetz-zJpx2rpV7r/QT0dZR+***@public.gmane.org>
wrote:
>
> Bob wrote (alluding also to something Poul-Henning wrote):
>
>> The phase comparison part of the PLL is pretty straightforward if you
are looking at two RF frequencies. An XOR gate is one solution, there are
many others. Getting something like 100 to 200 ns full scale on the phase
comparator makes the rest of the gizmo much easier.
>
> All true. However...
>
>> A 12 bit ADC on a MCU will get you to 100's of ps per bit. That is
more resolution (it's < 1 ns) than you need for this.
>
> Getting an ADC to sample fast and accurately enough to provide that
honest resolution is not trivial. And if you have that, you'll almost
certainly have the resources to do the phase comparator digitally, too, which
brings many advantages -- so I see no reason to use an analog PC.

If you take a look at some of the newer ARM MCU’s they are getting 13+
solid bits out of their ADC’s at a > 10 KHz rate. That’s more than good
enough for anything you are trying to do with this design. There’s no need to
make it any more complex.

A single gate XOR plus the eval board is just a about all you need. One
dead bug part on the eval board and the assembly process is pretty much done.
Maybe 45 minutes of work if you need to go find all the bits and pieces
around your bench. Since almost nothing in the design is running at high
speed, layout issues should not be a big deal. You could also do it on a
fragment of board like the divider from earlier in this thread.

>
>> Custom code wise, it's a few hundred lines of C on a 32 bit ARM. Pre
built (wizard driven) device init stuff will be way more than that, but you
don't write any of that.
>
> A proper digital filter that computes a new running value at least every
second will be more complex than that, but you're right, it's not an
unfathomable task.
>
> Then comes the real work, well summarized by Bob:
>
>> Debug, optimization and tweaking are where the major effort is (like 80
to 90%). That will take at least few months of work and require some test
gear. Any time you plug in a significantly different oscillator, you will
have to put in this part of the effort. Getting the long run ADEV data,
making sure it's right, and then analyzing the result is something there is no
magic shortcut around. * * *
>>
>> No it's not a "plug in a pre-made gizmo and forget about it" sort of
thing. There is real work, lots of time, mental effort, working gear, and
patience involved. You *will* get it wrong more often than you get it right
as you go through the process.
>
> All of this explains why the woods are not full of state-of-the-art
GPSDO controllers just waiting for people to couple them with whatever OCXO
they bought on ebay.

The optimization process is at least 90% perspiration and preparation.
Neither of those are outside the range of what an average Joe can handle. The
other (at most) 10% is very much a “that depends” sort of thing. You can
head down all sorts of rabbit holes as you dig into this or that. For that,
the list archives have tons of information to work from.

There is *way* more in a GPSDO than what we are talking about here.
TimeNuts may or may not care much about that extra stuff, but it’s in there.

>
> BTW, I mean no slight to the LTE-Light. Judging from the JL products
I've used, I expect that it is a fine product well-designed for its task.
But that task is controlling a TCXO, not controlling an OCXO that is stable
to 10e-12 or better at tau from 1 to 100 seconds (unless one goes to the
trouble described above).
>
> For a general look at the magnitude of the stability difference between
a TCXO and a number of OCXOs and other frequency standards, see attached
(if the pic doesn't make it through the listserv, see
<http://leapsecond.com/museum/manyadev.gif>).
>
> Best regards,
>
> Charles
>
>
>
<Oscillator_comparison_tvb.jpg>_______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

The idea is not to make it as complex as you possibly could, but to make
it as simple as possible and still have it work fine. There are a lot of
shortcuts you can take with a one off unit that a commercial design would
never use.

Bob

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Bert Kehren via time-nuts
2014-10-19 22:36:45 UTC
Permalink
Raw Message
We did the same using a 1 KHz out of the $ 14 ubolx M7 and a Morion .
Results better than 1 E-10. Some time nuts are now assembling and testing the
same. Total cost less than $ 10 not counting OCXO or GPS. Most expensive item
is the filter capacitor.
Bert Kehren


In a message dated 10/19/2014 6:15:06 P.M. Eastern Daylight Time,
albertson.chris-***@public.gmane.org writes:

At the low end of the spectrum, I tried to make the simplest possible
GPSDO what would still work. Assuming you have a GPS with 1PPS
output, an OCXO and a small DC power supply I was able to get the
entire parts for the controller, board, hookup wire and all for under
$5. I purposely took the lowest cost solution at each decision point
just to see what you'd end up with. Part were from eBay.

The result is not bad. but I don't have a really good way to test it.
I'm using a Thunderbolt for the 1PPS and a pretty decent OXCO part.
Why build a low-end GPSDO when yo have a Thunderbolt? It's and
experiment. The way I test is to place the sine output from the TB
and from my GPSDO both on a dual channel scope and adjust it so the
two sine waves are superimposed. Then I wait for them not to be
superimposed. What I see is that over 1/2 hour or so they get
slightly out of phase but then drift back in phase, This happens
cyclically. It is because of the VERY simply controller. I tried to
minimize lines of C++ code. It's running about 16 lines of code, more
or less. Using my counter I think the GPSDO is good to 1E-10.

Rather than using a $15 ARM MCU board I used a $3 AVR board and used
100% 16-bit integer math in a very simple control loop. There is one
external chip because the little AVR could not deal with the 10MHz
signal from the OCXO so I used a divider chip. I use two 8-bit DACs
to control the EFC on the OCXO. One is curse adjustment, one fine.
Added with a resister network and an RC filter with almost a 1 second
time constant.

If you can spend $35 you can build a very sophisticated controller
that logs internal diagnostic data to a computer over USB and displays
it's internal status on a graphic LCD panel. Well, actually my
controller has an LCD status display and logs data to a PC. But with
those parts plugged in the cost is closer to $10.

On Sun, Oct 19, 2014 at 2:13 PM, Bob Camp <kb8tq-***@public.gmane.org> wrote:
> Hi
>
>> On Oct 19, 2014, at 5:00 PM, Jim Lux <jimlux-***@public.gmane.org> wrote:
>>
>> On 10/19/14, 1:08 PM, Bob Camp wrote:
>>> Hi
>>>
>>>> On Oct 19, 2014, at 3:35 PM, Charles Steinmetz
>>>> <csteinmetz-zJpx2rpV7r/QT0dZR+***@public.gmane.org> wrote:
>>>>
>>>> Bob wrote (alluding also to something Poul-Henning wrote):
>>>>
>>>>> The phase comparison part of the PLL is pretty straightforward if
>>>>> you are looking at two RF frequencies. An XOR gate is one
>>>>> solution, there are many others. Getting something like 100 to
>>>>> 200 ns full scale on the phase comparator makes the rest of the
>>>>> gizmo much easier.
>>>>
>>>> All true. However...
>>>>
>>>>> A 12 bit ADC on a MCU will get you to 100's of ps per bit. That
>>>>> is more resolution (it's < 1 ns) than you need for this.
>>>>
>>>> Getting an ADC to sample fast and accurately enough to provide that
>>>> honest resolution is not trivial. And if you have that, you'll
>>>> almost certainly have the resources to do the phase comparator
>>>> digitally, too, which brings many advantages -- so I see no reason
>>>> to use an analog PC.
>>>
>>> If you take a look at some of the newer ARM MCU’s they are getting
>>> 13+ solid bits out of their ADC’s at a > 10 KHz rate. That’s more
>>> than good enough for anything you are trying to do with this design.
>>> There’s no need to make it any more complex.
>>
>> I'm using the Freescale Kinetix K20 parts, which have 16 bit
differential input ADCs, and built in averaging. The raw ADC can sample at about
400kHz.
>>
>> You can easily get 14 bit performance from these at tens of kHz rates.
>> I need I/Q, so I sample two inputs at 50 kHz (read one, then the other)
without averaging (so they're about 2.5 microseconds apart), and then
decimate them through a 2 stage CIC and a 13 tap FIR filter down to 200 Hz.
This takes about 60% of the processor running at 48MHz.
>
> I’m using parts from the same family, but not doing the whole DDS thing.
Single input and control loop - the part sleeps about 98% of the time. The
demo boards (Freedom boards) are all below $15 and free if you go to one
of their (often free) classes.
>
> Bob
>
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to
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> and follow the instructions there.



--

Chris Albertson
Redondo Beach, California
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S. Jackson via time-nuts
2014-10-19 23:57:38 UTC
Permalink
Raw Message
Guys,

I spent some hours at the lab today and connected an external DOCXO to the
unit (with 10MHz CMOS output) and did some experiments. See attached
photos.

My setup was so simple, it was almost trivial: I used a BNC T-splitter to
split the 10MHz CMOS output and feed that both into the LTE-Lite and into
the TimePod. Then I used a coax to clip adaptor cable to grab the EFC of pin
1 of the DIP-14 socket. I added one resistor, and ran the units.


THIS IS IMPORTANT: MAKE SURE TO TURN OFF THE POWER OF THE LTE-LITE BEFORE
SELECTING THE "EXTERNAL TCXO" SWITCH SETTING, OTHERWISE THE FLASH OF THE
PROCESSOR MAY BE FRIED DUE TO THE INSTANTANEOUS FREQUENCY CHANGE ON THE
PROCESSOR!


The results are encouraging. First, this OCXO has a control range of -22Hz
to +22Hz (0V to 5V), and a mean EFC voltage of about 2.7V. That means that
the EFC control is both ~10x less sensitive than the standard TCXO, and
that the EFC voltage is very close to the max upper control voltage of the DAC.

To reduce the required DAC voltage I simply soldered a 27K Ohms resistor
from the EFC pin to the 4.7V Reference output pin of the OCXO, that pulls up
the DAC output a bit due to the internal DAC impedance. On an 10811 that
would be solved by simply setting the mechanical adjustment so the nominal
EFC voltage is around 1.5V (50% DAC setting).

Then it took about one hour for the unit to settle down (the loop has no
prediction or speed-up, so it takes a long time to add ~1V to the DAC
output).

The good news is that the Phase Noise of the OCXO is preserved, and the
ADEV is also preserved, but the bad news is that the internal TCXO is now
running about 100Hz too high, and that is causing a spur at about 100Hz offset
etc (see attached plot). I think that spur is either coming through the
EFC line, or through the 10MHz coax, so it might be as simple as adding a
choke to the EFC line to remove the RF noise originating from the 20MHz TCXO,
and using an isolating splitter on the 10MHz line to prevent any noise
coming from the board to get into the OCXO output.

Here is the beauty of the setup: because the OCXO is more than 10x less
sensitive to the EFC voltage changes than the TCXO, the time constant is
automatically increased by about the same length which is exactly what you
want. It makes sense if you think about it, if you have a 1Hz error, it would
take the loop ~10x as long to generate the EFC voltage required to correct
for the 1Hz error if the EFC sensitivity is 9Hz per volt instead of 100Hz per
volt. I also tried an OCXO with only a +/-2Hz tuning range, and that one
did not lock at all, the loop was way too slow to follow the frequency
changes that the OCXO made due to retrace and aging.

One caveat: the loop is now so slow that it initially had difficulty
following the aging curve of the DOCXO (the DOCXO had not been powered on in
many months), so this will only work really well once the OCXO settles down
into slow aging after a couple of days, and if it is not exposed to large
thermal or airflow changes.

I will send the ADEV plots after some hours of testing, they will likely
end up peaking at the low xE-011's which is 10x better than the TCXO and
about the performance of the particular OCXO I used.

CAVEAT EMPTOR: Your mileage may vary considerably depending on your OCXO,
this is not trying to imply that any type of performance for the LTE-Lite
module is possible, I simply hooked up an OCXO I had, and I am presenting the
raw data I am seeing on my particular setup. Your results may vary
considerably.

So in summary:

1) No loop time constant adjustment seems to be required as the 10x lower
EFC sensitivity results in about the same increase in time constant which
puts it at a sweet spot for typical OCXOs.(to be proven once I get a number
of hours of ADEV)

2) The nominal EFC of the oscillator should be set to be around 50% DAC
voltage, or 1.5V. I cheated by adding a 27K Ohms resistor to pull up the DAC
voltage externally, and that probably is also adding some phase noise and
instability

3) You need to insulate the 20MHz RF coming out of the LTE-Lite as best as
you can to reduce the spurs caused by harmonic mixing of both oscillators,
It may be as easy as adding a good RF low-pass filter to the DAC EFC, and
an isolating splitter or buffered splitter with good isolation between the
two 10MHz output ports of the external OCXO.

Bye,
Said



In a message dated 10/19/2014 04:53:22 Pacific Daylight Time,
csteinmetz-zJpx2rpV7r/QT0dZR+***@public.gmane.org writes:

Bill wrote:

>How tough would it be to mate the 10Mhz version up to a really good 10811?
>* * * I was thinking of throwing the LTE-Lite and the 10811 in a
box.

Unfortunately, to get the best out of the local oscillator, the
control PLL must be carefully adjusted so that the oscillator itself
controls the stability at averaging times (tau) where it is better
than the GPS (generally, up to tau of several hundred to maybe
several thousand seconds), and the GPS controls the stability at
longer tau. The LTE-Lite has fixed (non-adjustable) loop parameters
that cross over to the GPS at much lower tau than is appropriate for
a good OCXO (but well suited to the installed TXCO).

The other day Said (I think) mentioned some hacks that may sort-of
improve the ability of an LTE-Lite to discipline an OCXO, but that's
all they are -- very approximate hacks. There is really no way to
properly mate an OCXO to the LTE-Lite control loop, which would
require adjusting the PLL loop gain and the location of the loop's
poles and zeroes (and possibly even adding new poles and
zeroes). That would need to be done by changing the PLL parameters
internal to the LTE-Lite, which are inaccessible. Without such
reprogramming, the LTE-Light can never get the best out of an OCXO.

Best regards,

Charles



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S. Jackson via time-nuts
2014-10-20 18:52:03 UTC
Permalink
Raw Message
Hi Brian, Bob, Charles, et. al.

Bob has a great point about the difference between a one-off in a basement
lab, and a commercial product that has to work under any circumstances,
wether flying at 50,000 feet at -56C, or in an urban canyon, or under whatever
other stress could be thrown at it. In fact the testing and fine tuning
does take 90% of a product design cycle.

That said here is the ADEV plot from my overnight test with the DOCXO. No
comments.

This was done without any loop adjustment whatsoever, same board and
software that drives the on-board TCXO. I will let the result speak for itself,
save to say the loop, the DAC, the DAC reference, and the GPS with a proper
OCXO can achieve performance at a level approaching two orders of
magnitude better than our spec which is 1ppb for this particular product.

PLEASE(!) do not send me emails once you get your board and plug in your
own OCXO and don't see similar performance for whatever reasons. There is not
much we can do about that, other than say our product meets
specifications. On the other hand if you connect a really good OCXO you may even get
better performance than I got, but who knows.

Thanks,
Said




In a message dated 10/20/2014 10:21:15 Pacific Daylight Time,
brian-***@public.gmane.org writes:

On Mon, Oct 20, 2014 at 6:48 AM, Bob Camp <kb8tq-***@public.gmane.org> wrote:

> Hi
>
> We tend to focus on this or that enhanced feature in a piece of code. It’
s
> fun to talk about. That’s not what keeps most designs from doing what
they
> should. By focusing on this rather than the testing required, we set
people
> up to fail. If you start off the project believing you mostly need fancy
> code when you mostly need long term testing instead, you hit a wall
pretty
> fast. Setting up for one is not at all the same as setting up for the
other.
>

Sounds to me like the hardware and code are pretty straight-forward. The
difference comes from the terms and coefficients in the PLL loop filter and
those need to be optimized for each OCXO. There appear to be here a handful
of people who have a pretty good idea of what those coefficients should be
for various well-known OCXOs out there.

So why not do the GPSD hardware, software, and then provide the
coefficients that will get a handful of the more popular OCXOs available
out there to within a decade of optimum, certainly closer than what one
would be talking about by just bolting x-random OCXO onto an LTE-lite? I
suspect there would be a market in the time-nut world for such a critter.

--
Brian Lloyd
Lloyd Aviation
706 Flightline Drive
Spring Branch, TX 78070
brian-***@public.gmane.org
+1.210.802-8FLY (1.210.802-8359)
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Charles Steinmetz
2014-10-20 22:53:22 UTC
Permalink
Raw Message
>here is the ADEV plot from my overnight test with the DOCXO. * * *
>
>This was done without any loop adjustment whatsoever, same board and
>software that drives the on-board TCXO. I will let the result speak
>for itself,
>save to say the loop, the DAC, the DAC reference, and the GPS with a proper
>OCXO can achieve performance at a level approaching two orders of
>magnitude better than our spec which is 1ppb for this particular product.

Thanks for the ADEV plot, Said -- more pertinent for most time nuts
purposes than PN. Of course, the typical performance of the LTE-Lite
with the TCXO is significantly better than the spec (according to the
user manual, about 5e-11 at 1 second and 1e-10 at 10 seconds, already
1 to 1.5 OOM better than spec), so the typical improvement with the
OCXO wouldn't be a full two orders of magnitude. Still, very
noteworthy performance that *surely* justifies time nuts in buying
one of the good, cheap OCXOs flooding the surplus market to go along
with their LTE-Lite. Good show.

Best regards,

Charles
Bert Kehren via time-nuts
2014-10-20 23:01:54 UTC
Permalink
Raw Message
Allow me to clarify.
I started out with 7 MV 89 one of it a total loss. The remaining 6 after 3
month + burn in show better than 1 E-11 aging per day, 2 closer to 5 E-12.
Only two have been tested for ADEV and are close to 1 E-12, 2X not 10 X.
Bert Kehren


In a message dated 10/20/2014 5:58:37 P.M. Eastern Daylight Time,
kb8tq-***@public.gmane.org writes:

Hi

The problem is that there are no “magic coefficients”. What you run
depends very much on the exact OCXO you have, the environment you run it in, and
the result you are after.

For instance, Bert is after frequency stability. Tom is after the right
time. Each of them will have very different coefficients for the same
oscillator.

My Morion OCXO has a floor of 2x10^-12, Bert has some that are 10X better
than that (maybe). His coefficients and mine will be very different.

I had an antenna outdoors. It got many sat’s all the time. Now I have one
indoors. It’s not getting lots of sats all the time. My old coefficients
are not going to be my new coefficients.

No magic bullet, you have to do the work.

Bob

> On Oct 20, 2014, at 1:20 PM, Brian Lloyd <brian-***@public.gmane.org> wrote:
>
> On Mon, Oct 20, 2014 at 6:48 AM, Bob Camp <kb8tq-***@public.gmane.org> wrote:
>
>> Hi
>>
>> We tend to focus on this or that enhanced feature in a piece of code. It
’s
>> fun to talk about. That’s not what keeps most designs from doing what
they
>> should. By focusing on this rather than the testing required, we set
people
>> up to fail. If you start off the project believing you mostly need
fancy
>> code when you mostly need long term testing instead, you hit a wall
pretty
>> fast. Setting up for one is not at all the same as setting up for the
other.
>>
>
> Sounds to me like the hardware and code are pretty straight-forward. The
> difference comes from the terms and coefficients in the PLL loop filter
and
> those need to be optimized for each OCXO. There appear to be here a
handful
> of people who have a pretty good idea of what those coefficients should
be
> for various well-known OCXOs out there.
>
> So why not do the GPSD hardware, software, and then provide the
> coefficients that will get a handful of the more popular OCXOs available
> out there to within a decade of optimum, certainly closer than what one
> would be talking about by just bolting x-random OCXO onto an LTE-lite? I
> suspect there would be a market in the time-nut world for such a
critter.
>
> --
> Brian Lloyd
> Lloyd Aviation
> 706 Flightline Drive
> Spring Branch, TX 78070
> brian-***@public.gmane.org
> +1.210.802-8FLY (1.210.802-8359)
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

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Bob Camp
2014-10-20 23:10:33 UTC
Permalink
Raw Message
Hi

Ok, so Bob took a little literary license to make a point :)

_________________

If you spread out past just MV 89’s you can indeed span a range from about 4x10^-13 out to 2 or 3x10^-11 for various parts you see for sale on the auction sites. Yes you will buy a *lot* of OCXO’s and sort through them before you find the one that is at the low end of that range. Even if you stick with one model, some of them seem to have a pretty wide spread ….

Bob

> On Oct 20, 2014, at 7:01 PM, Bert Kehren via time-nuts <time-***@febo.com> wrote:
>
> Allow me to clarify.
> I started out with 7 MV 89 one of it a total loss. The remaining 6 after 3
> month + burn in show better than 1 E-11 aging per day, 2 closer to 5 E-12.
> Only two have been tested for ADEV and are close to 1 E-12, 2X not 10 X.
> Bert Kehren
>
>
> In a message dated 10/20/2014 5:58:37 P.M. Eastern Daylight Time,
> kb8tq-***@public.gmane.org writes:
>
> Hi
>
> The problem is that there are no “magic coefficients”. What you run
> depends very much on the exact OCXO you have, the environment you run it in, and
> the result you are after.
>
> For instance, Bert is after frequency stability. Tom is after the right
> time. Each of them will have very different coefficients for the same
> oscillator.
>
> My Morion OCXO has a floor of 2x10^-12, Bert has some that are 10X better
> than that (maybe). His coefficients and mine will be very different.
>
> I had an antenna outdoors. It got many sat’s all the time. Now I have one
> indoors. It’s not getting lots of sats all the time. My old coefficients
> are not going to be my new coefficients.
>
> No magic bullet, you have to do the work.
>
> Bob
>
>> On Oct 20, 2014, at 1:20 PM, Brian Lloyd <brian-***@public.gmane.org> wrote:
>>
>> On Mon, Oct 20, 2014 at 6:48 AM, Bob Camp <kb8tq-***@public.gmane.org> wrote:
>>
>>> Hi
>>>
>>> We tend to focus on this or that enhanced feature in a piece of code. It
> ’s
>>> fun to talk about. That’s not what keeps most designs from doing what
> they
>>> should. By focusing on this rather than the testing required, we set
> people
>>> up to fail. If you start off the project believing you mostly need
> fancy
>>> code when you mostly need long term testing instead, you hit a wall
> pretty
>>> fast. Setting up for one is not at all the same as setting up for the
> other.
>>>
>>
>> Sounds to me like the hardware and code are pretty straight-forward. The
>> difference comes from the terms and coefficients in the PLL loop filter
> and
>> those need to be optimized for each OCXO. There appear to be here a
> handful
>> of people who have a pretty good idea of what those coefficients should
> be
>> for various well-known OCXOs out there.
>>
>> So why not do the GPSD hardware, software, and then provide the
>> coefficients that will get a handful of the more popular OCXOs available
>> out there to within a decade of optimum, certainly closer than what one
>> would be talking about by just bolting x-random OCXO onto an LTE-lite? I
>> suspect there would be a market in the time-nut world for such a
> critter.
>>
>> --
>> Brian Lloyd
>> Lloyd Aviation
>> 706 Flightline Drive
>> Spring Branch, TX 78070
>> brian-***@public.gmane.org
>> +1.210.802-8FLY (1.210.802-8359)
>> _______________________________________________
>> time-nuts mailing list -- time-nuts-***@public.gmane.org
>> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
>> and follow the instructions there.
>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
Tom Van Baak
2014-10-20 23:42:01 UTC
Permalink
Raw Message
To add to Bert's note...

Realize that for a GPSDO, (linear frequency) aging-per-day is irreverent, almost by definition. What matters is phase noise and short-term stability, neither of which you can possibly fix with disciplining against GPS. GPS takes care of the rest.

Long-term stability can be critical for non-GPS applications, which is why oscillators with daily aging rates in the -11's and -12's are so amazing.

Consider this: if you want to run your bench with a clean 10 MHz source, stable to 11 or 12 digits and accurate to 9 digits -- you may be much better off with a free-running, stand-alone OCXO with an aging rate down at 1e-11/day than using a GPSDO/TCXO. To maintain accuracy of your OCXO just re-tune your OCXO *once a year*. Aside from ADEV plots, this is another way to appreciate how amazing some OCXO are, any why many of us still troll eBay for high-stability, low-noise, low-drift quartz oscillators.

/tvb

----- Original Message -----
From: "Bert Kehren via time-nuts" <time-nuts-***@public.gmane.org>
To: <time-nuts-***@public.gmane.org>
Sent: Monday, October 20, 2014 4:01 PM
Subject: Re: [time-nuts] LTE-Lite module


Allow me to clarify.
I started out with 7 MV 89 one of it a total loss. The remaining 6 after 3
month + burn in show better than 1 E-11 aging per day, 2 closer to 5 E-12.
Only two have been tested for ADEV and are close to 1 E-12, 2X not 10 X.
Bert Kehren
Bob Stewart
2014-10-21 00:01:34 UTC
Permalink
Raw Message
Hi Tom,

One of the biggest problems I've unwittingly faces is that of retrace. I had seen the term used several times, but hadn't looked it up until last night. As you can imagine, with a GPSDO under development I've had to remove power more than a few times to make hardware changes. I think the next time power is down I'm going to try to rearrange things so that the OCXO is permanently powered and just the board gets switched. But then again would big jumps in the EFC cause other problems that are almost as bad?


There is just so much to learn to get this going; especially without either an engineering degree or experience in this field. Bob Camp is definitely right that you have to put your time in - lots of it.


Bob - AE6RV


________________________________
From: Tom Van Baak <tvb-AeR/***@public.gmane.org>
To: Discussion of precise time and frequency measurement <time-nuts-***@public.gmane.org>
Sent: Monday, October 20, 2014 6:42 PM
Subject: Re: [time-nuts] LTE-Lite module


To add to Bert's note...

Realize that for a GPSDO, (linear frequency) aging-per-day is irreverent, almost by definition. What matters is phase noise and short-term stability, neither of which you can possibly fix with disciplining against GPS. GPS takes care of the rest.

Long-term stability can be critical for non-GPS applications, which is why oscillators with daily aging rates in the -11's and -12's are so amazing.

Consider this: if you want to run your bench with a clean 10 MHz source, stable to 11 or 12 digits and accurate to 9 digits -- you may be much better off with a free-running, stand-alone OCXO with an aging rate down at 1e-11/day than using a GPSDO/TCXO. To maintain accuracy of your OCXO just re-tune your OCXO *once a year*. Aside from ADEV plots, this is another way to appreciate how amazing some OCXO are, any why many of us still troll eBay for high-stability, low-noise, low-drift quartz oscillators.

/tvb

----- Original Message -----
From: "Bert Kehren via time-nuts" <time-nuts-***@public.gmane.org>
To: <time-nuts-***@public.gmane.org>
Sent: Monday, October 20, 2014 4:01 PM
Subject: Re: [time-nuts] LTE-Lite module


Allow me to clarify.
I started out with 7 MV 89 one of it a total loss. The remaining 6 after 3
month + burn in show better than 1 E-11 aging per day, 2 closer to 5 E-12.
Only two have been tested for ADEV and are close to 1 E-12, 2X not 10 X.
Bert Kehren


_______________________________________________
time-nuts mailing list -- time-nuts-***@public.gmane.org
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Bob Stewart
2014-10-21 00:03:41 UTC
Permalink
Raw Message
OK, Yahoo has done it to me again. Sent to Tom direct and not to the list. So, repeated here:

Hi Tom,

One of the biggest problems I've unwittingly faces is that of retrace. I
had seen the term used several times, but hadn't looked it up until last night. As you can imagine, with a GPSDO under development I've had to
remove power more than a few times to make hardware changes. I think
the next time power is down I'm going to try to rearrange things so that the OCXO is permanently powered and just the board gets switched. But
then again would big jumps in the EFC cause other problems that are
almost as bad?


There is just so much to learn to get this going; especially without either
an engineering degree or experience in this field. Bob Camp is
definitely right that you have to put your time in - lots of it.

Bob - AE6RV


________________________________
From: Tom Van Baak <tvb-AeR/***@public.gmane.org>
To: Discussion of precise time and frequency measurement <time-nuts-***@public.gmane.org>
Sent: Monday, October 20, 2014 6:42 PM
Subject: Re: [time-nuts] LTE-Lite module


To add to Bert's note...

Realize that for a GPSDO, (linear frequency) aging-per-day is irreverent, almost by definition. What matters is phase noise and short-term stability, neither of which you can possibly fix with disciplining against GPS. GPS takes care of the rest.

Long-term stability can be critical for non-GPS applications, which is why oscillators with daily aging rates in the -11's and -12's are so amazing.

Consider this: if you want to run your bench with a clean 10 MHz source, stable to 11 or 12 digits and accurate to 9 digits -- you may be much better off with a free-running, stand-alone OCXO with an aging rate down at 1e-11/day than using a GPSDO/TCXO. To maintain accuracy of your OCXO just re-tune your OCXO *once a year*. Aside from ADEV plots, this is another way to appreciate how amazing some OCXO are, any why many of us still troll eBay for high-stability, low-noise, low-drift quartz oscillators.

/tvb

----- Original Message -----
From: "Bert Kehren via time-nuts" <time-nuts-***@public.gmane.org>
To: <time-nuts-***@public.gmane.org>
Sent: Monday, October 20, 2014 4:01 PM
Subject: Re: [time-nuts] LTE-Lite module


Allow me to clarify.
I started out with 7 MV 89 one of it a total loss. The remaining 6 after 3
month + burn in show better than 1 E-11 aging per day, 2 closer to 5 E-12.
Only two have been tested for ADEV and are close to 1 E-12, 2X not 10 X.
Bert Kehren


_______________________________________________
time-nuts mailing list -- time-nuts-***@public.gmane.org
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Said Jackson via time-nuts
2014-10-21 00:21:22 UTC
Permalink
Raw Message
Bob,

You are on the right track!

Large changes in EFC can cause hysteresis, meaning you go back to an initial voltage but the crystal does not return to the exact initial frequency. It can also create dead bands in the efc vs frequency curve.

Hysteresis can cause integrator wind up as the loop is chasing an ever changing OCXO..

Retrace and hysteresis are two major issues for any disciplined oscillator.

Bye,
Said

Sent From iPhone

> On Oct 20, 2014, at 17:03, Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org> wrote:
>
> OK, Yahoo has done it to me again. Sent to Tom direct and not to the list. So, repeated here:
>
> Hi Tom,
>
> One of the biggest problems I've unwittingly faces is that of retrace. I
> had seen the term used several times, but hadn't looked it up until last night. As you can imagine, with a GPSDO under development I've had to
> remove power more than a few times to make hardware changes. I think
> the next time power is down I'm going to try to rearrange things so that the OCXO is permanently powered and just the board gets switched. But
> then again would big jumps in the EFC cause other problems that are
> almost as bad?
>
>
> There is just so much to learn to get this going; especially without either
> an engineering degree or experience in this field. Bob Camp is
> definitely right that you have to put your time in - lots of it.
>
> Bob - AE6RV
>
>
> ________________________________
> From: Tom Van Baak <tvb-AeR/***@public.gmane.org>
> To: Discussion of precise time and frequency measurement <time-nuts-***@public.gmane.org>
> Sent: Monday, October 20, 2014 6:42 PM
> Subject: Re: [time-nuts] LTE-Lite module
>
>
> To add to Bert's note...
>
> Realize that for a GPSDO, (linear frequency) aging-per-day is irreverent, almost by definition. What matters is phase noise and short-term stability, neither of which you can possibly fix with disciplining against GPS. GPS takes care of the rest.
>
> Long-term stability can be critical for non-GPS applications, which is why oscillators with daily aging rates in the -11's and -12's are so amazing.
>
> Consider this: if you want to run your bench with a clean 10 MHz source, stable to 11 or 12 digits and accurate to 9 digits -- you may be much better off with a free-running, stand-alone OCXO with an aging rate down at 1e-11/day than using a GPSDO/TCXO. To maintain accuracy of your OCXO just re-tune your OCXO *once a year*. Aside from ADEV plots, this is another way to appreciate how amazing some OCXO are, any why many of us still troll eBay for high-stability, low-noise, low-drift quartz oscillators.
>
> /tvb
>
> ----- Original Message -----
> From: "Bert Kehren via time-nuts" <time-nuts-***@public.gmane.org>
> To: <time-nuts-***@public.gmane.org>
> Sent: Monday, October 20, 2014 4:01 PM
> Subject: Re: [time-nuts] LTE-Lite module
>
>
> Allow me to clarify.
> I started out with 7 MV 89 one of it a total loss. The remaining 6 after 3
> month + burn in show better than 1 E-11 aging per day, 2 closer to 5 E-12.
> Only two have been tested for ADEV and are close to 1 E-12, 2X not 10 X.
> Bert Kehren
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
Bob Stewart
2014-10-21 00:30:02 UTC
Permalink
Raw Message
Hi Said,

OK, I hadn't understood the full consequences of hysteresis, but yes, I've seen it. For an hour the DAC ratchets up a step every few minutes and the phase stubbornly stays put. And then, the bottom falls out and it suddenly pushes way past where you want it. Well, at least I have a better understanding of it now. I'll try to avoid any hardware changes for the next few weeks. I may even make changes that will keep the DAC stable when loading new code.

Thanks!


Bob



________________________________
From: Said Jackson <saidjack-***@public.gmane.org>
To: Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org>; Discussion of precise time and frequency measurement <time-nuts-***@public.gmane.org>
Sent: Monday, October 20, 2014 7:21 PM
Subject: Re: [time-nuts] LTE-Lite module


Bob,

You are on the right track!

Large changes in EFC can cause hysteresis, meaning you go back to an initial voltage but the crystal does not return to the exact initial frequency. It can also create dead bands in the efc vs frequency curve.

Hysteresis can cause integrator wind up as the loop is chasing an ever changing OCXO..

Retrace and hysteresis are two major issues for any disciplined oscillator.

Bye,
Said

Sent From iPhone




> On Oct 20, 2014, at 17:03, Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org> wrote:
>
> OK, Yahoo has done it to me again. Sent to Tom direct and not to the list. So, repeated here:
>
> Hi Tom,
>
> One of the biggest problems I've unwittingly faces is that of retrace. I
> had seen the term used several times, but hadn't looked it up until last night. As you can imagine, with a GPSDO under development I've had to
> remove power more than a few times to make hardware changes. I think
> the next time power is down I'm going to try to rearrange things so that the OCXO is permanently powered and just the board gets switched. But
> then again would big jumps in the EFC cause other problems that are
> almost as bad?
>
>
> There is just so much to learn to get this going; especially without either
> an engineering degree or experience in this field. Bob Camp is
> definitely right that you have to put your time in - lots of it.
>
> Bob - AE6RV
>
>
> ________________________________
> From: Tom Van Baak <tvb-AeR/***@public.gmane.org>
> To: Discussion of precise time and frequency measurement <time-nuts-***@public.gmane.org>
> Sent: Monday, October 20, 2014 6:42 PM
> Subject: Re: [time-nuts] LTE-Lite module
>
>
> To add to Bert's note...
>
> Realize that for a GPSDO, (linear frequency) aging-per-day is irreverent, almost by definition. What matters is phase noise and short-term stability, neither of which you can possibly fix with disciplining against GPS. GPS takes care of the rest.
>
> Long-term stability can be critical for non-GPS applications, which is why oscillators with daily aging rates in the -11's and -12's are so amazing.
>
> Consider this: if you want to run your bench with a clean 10 MHz source, stable to 11 or 12 digits and accurate to 9 digits -- you may be much better off with a free-running, stand-alone OCXO with an aging rate down at 1e-11/day than using a GPSDO/TCXO. To maintain accuracy of your OCXO just re-tune your OCXO *once a year*. Aside from ADEV plots, this is another way to appreciate how amazing some OCXO are, any why many of us still troll eBay for high-stability, low-noise, low-drift quartz oscillators.
>
> /tvb
>
> ----- Original Message -----
> From: "Bert Kehren via time-nuts" <time-nuts-***@public.gmane.org>
> To: <time-nuts-***@public.gmane.org>
> Sent: Monday, October 20, 2014 4:01 PM
> Subject: Re: [time-nuts] LTE-Lite module
>
>
> Allow me to clarify.
> I started out with 7 MV 89 one of it a total loss. The remaining 6 after 3
> month + burn in show better than 1 E-11 aging per day, 2 closer to 5 E-12.
> Only two have been tested for ADEV and are close to 1 E-12, 2X not 10 X.
> Bert Kehren
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Said Jackson via time-nuts
2014-10-21 00:50:09 UTC
Permalink
Raw Message
Thats exactly right Bob.

By the time your ocxo jumps to catch up to the efc voltage, you have oversteered, then the process starts in reverse and the ocxo jumps in the opposite direction.

The result is a phase jumping up and down.

You want a crystal that reacts to xE-012 changes in EFC voltage or even better.. We may be talking only 100s of nanovolts per LSB.

Bye,
Said

Sent From iPhone

> On Oct 20, 2014, at 17:30, Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org> wrote:
>
> Hi Said,
>
> OK, I hadn't understood the full consequences of hysteresis, but yes, I've seen it. For an hour the DAC ratchets up a step every few minutes and the phase stubbornly stays put. And then, the bottom falls out and it suddenly pushes way past where you want it. Well, at least I have a better understanding of it now. I'll try to avoid any hardware changes for the next few weeks. I may even make changes that will keep the DAC stable when loading new code.
>
> Thanks!
>
> Bob
>
> From: Said Jackson <saidjack-***@public.gmane.org>
> To: Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org>; Discussion of precise time and frequency measurement <time-nuts-***@public.gmane.org>
> Sent: Monday, October 20, 2014 7:21 PM
> Subject: Re: [time-nuts] LTE-Lite module
>
> Bob,
>
> You are on the right track!
>
> Large changes in EFC can cause hysteresis, meaning you go back to an initial voltage but the crystal does not return to the exact initial frequency. It can also create dead bands in the efc vs frequency curve.
>
> Hysteresis can cause integrator wind up as the loop is chasing an ever changing OCXO..
>
> Retrace and hysteresis are two major issues for any disciplined oscillator.
>
> Bye,
> Said
>
> Sent From iPhone
>
>
>
> > On Oct 20, 2014, at 17:03, Bob Stewart <bob-Xpp+C7EF5i2sTnJN9+***@public.gmane.org> wrote:
> >
> > OK, Yahoo has done it to me again. Sent to Tom direct and not to the list. So, repeated here:
> >
> > Hi Tom,
> >
> > One of the biggest problems I've unwittingly faces is that of retrace. I
> > had seen the term used several times, but hadn't looked it up until last night. As you can imagine, with a GPSDO under development I've had to
> > remove power more than a few times to make hardware changes. I think
> > the next time power is down I'm going to try to rearrange things so that the OCXO is permanently powered and just the board gets switched. But
> > then again would big jumps in the EFC cause other problems that are
> > almost as bad?
> >
> >
> > There is just so much to learn to get this going; especially without either
> > an engineering degree or experience in this field. Bob Camp is
> > definitely right that you have to put your time in - lots of it.
> >
> > Bob - AE6RV
> >
> >
> > ________________________________
> > From: Tom Van Baak <tvb-AeR/***@public.gmane.org>
> > To: Discussion of precise time and frequency measurement <time-nuts-***@public.gmane.org>
> > Sent: Monday, October 20, 2014 6:42 PM
> > Subject: Re: [time-nuts] LTE-Lite module
> >
> >
> > To add to Bert's note...
> >
> > Realize that for a GPSDO, (linear frequency) aging-per-day is irreverent, almost by definition. What matters is phase noise and short-term stability, neither of which you can possibly fix with disciplining against GPS. GPS takes care of the rest.
> >
> > Long-term stability can be critical for non-GPS applications, which is why oscillators with daily aging rates in the -11's and -12's are so amazing.
> >
> > Consider this: if you want to run your bench with a clean 10 MHz source, stable to 11 or 12 digits and accurate to 9 digits -- you may be much better off with a free-running, stand-alone OCXO with an aging rate down at 1e-11/day than using a GPSDO/TCXO. To maintain accuracy of your OCXO just re-tune your OCXO *once a year*. Aside from ADEV plots, this is another way to appreciate how amazing some OCXO are, any why many of us still troll eBay for high-stability, low-noise, low-drift quartz oscillators.
> >
> > /tvb
> >
> > ----- Original Message -----
> > From: "Bert Kehren via time-nuts" <time-nuts-***@public.gmane.org>
> > To: <time-nuts-***@public.gmane.org>
> > Sent: Monday, October 20, 2014 4:01 PM
> > Subject: Re: [time-nuts] LTE-Lite module
> >
> >
> > Allow me to clarify.
> > I started out with 7 MV 89 one of it a total loss. The remaining 6 after 3
> > month + burn in show better than 1 E-11 aging per day, 2 closer to 5 E-12.
> > Only two have been tested for ADEV and are close to 1 E-12, 2X not 10 X.
> > Bert Kehren
> >
> >
> > _______________________________________________
> > time-nuts mailing list -- time-nuts-***@public.gmane.org
> > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
> > _______________________________________________
> > time-nuts mailing list -- time-nuts-***@public.gmane.org
> > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
>
>
Poul-Henning Kamp
2014-10-21 06:41:07 UTC
Permalink
Raw Message
--------
In message <766D6811-F733-4AB2-8574-24E4606E45FA-***@public.gmane.org>, Said Jackson via tim
e-nuts writes:
>Thats exactly right Bob.
>
>By the time your ocxo jumps to catch up to the efc voltage, you
>have oversteered, then the process starts in reverse and the ocxo
>jumps in the opposite direction.

This is a well known PI effect called "windup".

The cause is a phase offset of opposite sign of the frequency offset.

The fix is simple:

Start running with only the P term, and engage the I term only after

1. The input phase offset changes sign

or

2a. The input phase offset levels off

or

2b. Some calibrated amount of time has passed.


--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk-***@public.gmane.org | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
Said Jackson via time-nuts
2014-10-21 07:02:58 UTC
Permalink
Raw Message
Poul-Henning,

I mentioned yesterday about integrator windup, this problem is similar but happens even without any I term present:

The problem is that the ocxo maintains its frequency even though the EFC control voltage is changing. Thus phase error is accruing making the efc larger and larger due to the P term.

Then at some point the crystal 'snaps' and jumps in frequency, overshooting the desired frequency and causing the P term to start pushing in the opposite direction repeating the cycle.

Very similar to integrator windup, but not quite the same.

Main problem is the crystal is not following the steering input.

Most TCXOs and cheap ocxos have this problem, and there is no way to do anything about it since in the worst case the crystal simply refuses to run at proper frequency and thus the frequency will be approximated by cycling below and above the target frequency. Mind you we are talking about effects on the tens of parts per trillion levels. Enough to jump 10s' of ns back and forth over many minutes.

Bye,
Said

Sent From iPhone

> On Oct 20, 2014, at 23:41, "Poul-Henning Kamp" <phk-HF+***@public.gmane.org> wrote:
>
> --------
> In message <766D6811-F733-4AB2-8574-24E4606E45FA-***@public.gmane.org>, Said Jackson via tim
> e-nuts writes:
>> Thats exactly right Bob.
>>
>> By the time your ocxo jumps to catch up to the efc voltage, you
>> have oversteered, then the process starts in reverse and the ocxo
>> jumps in the opposite direction.
>
> This is a well known PI effect called "windup".
>
> The cause is a phase offset of opposite sign of the frequency offset.
>
> The fix is simple:
>
> Start running with only the P term, and engage the I term only after
>
> 1. The input phase offset changes sign
>
> or
>
> 2a. The input phase offset levels off
>
> or
>
> 2b. Some calibrated amount of time has passed.
>
>
> --
> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
> phk-***@public.gmane.org | TCP/IP since RFC 956
> FreeBSD committer | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
Poul-Henning Kamp
2014-10-21 07:49:49 UTC
Permalink
Raw Message
--------
In message <9BC23A13-646F-49C6-9FF9-D42FA5EC835D-***@public.gmane.org>, Said Jackson writes:

>Then at some point the crystal 'snaps' and jumps in frequency, overshooting
>the desired frequency and causing the P term to start pushing in the opposite
>direction repeating the cycle.

If your hardware does not respond to the output, any PI(D) loop will go
bezerk, and there's nothing you can do about it.

--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
phk-***@public.gmane.org | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by incompetence.
S. Jackson via time-nuts
2014-10-20 23:07:07 UTC
Permalink
Raw Message
Thanks much Charles,

just to remind everyone that the main idea of making the boards available
was to get folks a good disciplined TCXO, not to work as a development
platform to discipline external OCXOs.. Also as mentioned in the FAQ, the
typical performance plots I have been sending and are also in the user-manual
are gathered under optimal conditions of course: a roof-top antenna, units
shielded from airflow, and units running for a couple of days before testing.

Please also note that I tried an OCXO with only +/-2Hz EFC range and it
did not lock due to the ~10Ks resulting time-constant and the loop being way
to slow to capture the OCXO..

External oscillators should have between 9Hz per Volt to 100Hz+ per Volt
EFC sensitivity from what I can tell, otherwise an OPAMP circuit would be
needed to bring the EFC into that range. Sorry, I cannot propose such a
circuit, but such a circuit had been sent as a schematic to the time nuts some
years ago by someone if I remember correctly.

Bye,
Said


In a message dated 10/20/2014 15:55:45 Pacific Daylight Time,
csteinmetz-zJpx2rpV7r/QT0dZR+***@public.gmane.org writes:


>here is the ADEV plot from my overnight test with the DOCXO. * * *
>
>This was done without any loop adjustment whatsoever, same board and
>software that drives the on-board TCXO. I will let the result speak
>for itself,
>save to say the loop, the DAC, the DAC reference, and the GPS with a
proper
>OCXO can achieve performance at a level approaching two orders of
>magnitude better than our spec which is 1ppb for this particular product.

Thanks for the ADEV plot, Said -- more pertinent for most time nuts
purposes than PN. Of course, the typical performance of the LTE-Lite
with the TCXO is significantly better than the spec (according to the
user manual, about 5e-11 at 1 second and 1e-10 at 10 seconds, already
1 to 1.5 OOM better than spec), so the typical improvement with the
OCXO wouldn't be a full two orders of magnitude. Still, very
noteworthy performance that *surely* justifies time nuts in buying
one of the good, cheap OCXOs flooding the surplus market to go along
with their LTE-Lite. Good show.

Best regards,

Charles



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Hal Murray
2014-10-21 07:12:36 UTC
Permalink
Raw Message
time-nuts-***@public.gmane.org said:
> The problem is that the ocxo maintains its frequency even though the EFC
> control voltage is changing. Thus phase error is accruing making the efc
> larger and larger due to the P term.

> Then at some point the crystal 'snaps' and jumps in frequency, overshooting
> the desired frequency and causing the P term to start pushing in the
> opposite direction repeating the cycle.

Does anybody understand the mechanism behind that behavior?


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Bob Camp
2014-10-21 11:42:35 UTC
Permalink
Raw Message
Hi

The proper term for this is a frequency perturbation. It’s a low amplitude coupled resonance in the crystal. Essentially you are sweeping through another resonance as you tune the EFC. The result is a “blip” in the tuning curve. No they aren’t supposed to be there. Yes they do happen.

Bob

> On Oct 21, 2014, at 3:12 AM, Hal Murray <hmurray-8cQiHa/C+6Go9G/***@public.gmane.org> wrote:
>
>
> time-nuts-***@public.gmane.org said:
>> The problem is that the ocxo maintains its frequency even though the EFC
>> control voltage is changing. Thus phase error is accruing making the efc
>> larger and larger due to the P term.
>
>> Then at some point the crystal 'snaps' and jumps in frequency, overshooting
>> the desired frequency and causing the P term to start pushing in the
>> opposite direction repeating the cycle.
>
> Does anybody understand the mechanism behind that behavior?
>
>
> --
> These are my opinions. I hate spam.
>
>
>
> _______________________________________________
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Said Jackson via time-nuts
2014-10-21 16:04:17 UTC
Permalink
Raw Message
Hi Hal,

This behavior is called hysteresis and it is related to vendors, and related to the chips used (or varactor diode) inside the tcxo/ocxo. It is so subtle that most vendors are not even aware that their oscillator is doing it. Some vendors have product lines that do it and others that don't. We have spent a lot of energy and time locating vendors and products that don't do it, but we still test for it. You can only see it when you discipline the crystal and can measure phase drift over 10's of minutes as the frequency shifts will typically be below the noise floor and masked by thermal stability of the tcxo.

For example if a crystal has 50 parts per trillion hysteresis (5E-011) this means the phase will drift back and forth at up to 0.05ns per second which means the equivalent of less than 50ns every 16 minutes or so. Depending on how fast the loop goes back and forth around this 50ppb dead zone the crystal could phase drift back and forth some 10's of nanoseconds. That makes a big difference in ADEV and standard deviation. The solution: identify vendors and products that don't do it.. This is part of the art.

Bye,
Said





Sent From iPhone

> On Oct 21, 2014, at 0:12, Hal Murray <hmurray-8cQiHa/C+6Go9G/***@public.gmane.org> wrote:
>
>
> time-nuts-***@public.gmane.org said:
>> The problem is that the ocxo maintains its frequency even though the EFC
>> control voltage is changing. Thus phase error is accruing making the efc
>> larger and larger due to the P term.
>
>> Then at some point the crystal 'snaps' and jumps in frequency, overshooting
>> the desired frequency and causing the P term to start pushing in the
>> opposite direction repeating the cycle.
>
> Does anybody understand the mechanism behind that behavior?
>
>
> --
> These are my opinions. I hate spam.
>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts-***@public.gmane.org
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
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Hal Murray
2014-09-15 18:31:26 UTC
Permalink
Raw Message
> Also, another issue with the end termination happens when driving very long
> coax cables: RG-142 for example has about 60 Ohms center conductor
> resistance and 7.5 Ohms shield resistance at 1km length.

RG-142 is far from low-loss. Does anybody use it at that length?

What's the rise time at the end of 1 km with a 1 ns rise time at the input?



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Hal Murray
2014-11-03 17:56:55 UTC
Permalink
Raw Message
> It turns out this is what happens if you switch the "Output Level" from 17
> to 23, obviously an advisory indication to draw attention to the higher
> output. Switching it back reduces the level, as expected, and returns the
> LED function to normal. Phew:-)

> I can't remember switching it but don't suppose it arrived like that so
> guess I must have done.

My pair came with Ref-0 set at 17 and Ref-1 at 23.


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Hal Murray
2014-11-08 09:34:19 UTC
Permalink
Raw Message
> The 74F161 is only rated at 90MHz over temp (TI) and 120MHz or 100MHz
> (unclear) at 25C and then only as "typical" without any max freq being
> indicated at all in the datasheet (Fairchild).

That's just the count frequency. If you want to divide by 5, you have to do
something like use the terminal count output to load it with 15-5.
Unfortunately, the PE (Parallel load Enable) is active low while the TC
(Terminal Count) signal is active high so you have to add an inverter.

Even without the inverter, the clock-out and setup times are way too long.
Clock to out for TC is 10 ns. (typical from Fairchild data sheet)
Setup for PE is 11 ns. (Min at 25C, 5V)


The PAL suggestion was an interesting one. Does anybody have software and/or
a programming setup that still works?

Modern CPLDs or FPGAs would probably work. You can probably get one on a
small board. Not quite a DIP, but might fit. Ahhh. A big DIP. :)
http://www.digilentinc.com/Products/Detail.cfm?NavPath=2,400,798&Prod=CMOD



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Hal Murray
2014-11-08 18:39:40 UTC
Permalink
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> You can program it in my beloved ABEL instead if the dreaded CUPL..

> Lattice sells a cheap USB programmer for these.

Are they usable in a non-Windows environment?


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Hal Murray
2014-11-25 05:23:57 UTC
Permalink
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Said Jackson said:
> Correct, and thats why its all a bad trade off if you have to use 50 Ohms
> termination. Either more heat or more PN, and more circuitry.

> So driving 50 Ohms inputs is not optimal here, 1M inputs are much better for
> this purpose.

That only works if you have a (very) short connection to the next stage.

Things get interesting if you have, say, 10 feet of unterminated coax.

10 MHz is 100 ns, or 50 ns between transitions. Coax is ballpark of 5/8 c so
that's 16 ns one way or 32 ns round drip. That's 60% of the heat as well as
lots of nasty reflections.

(Somebody please check my numbers.)


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Charles Steinmetz
2014-11-25 12:12:23 UTC
Permalink
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Hal wrote:

> > So driving 50 Ohms inputs is not optimal here, 1M inputs are much
> better for
> > this purpose.
>
>That only works if you have a (very) short connection to the next stage.
>Things get interesting if you have, say, 10 feet of unterminated coax.

Thinking that the output was a sine wave, I previously suggested
testing to determine what its actual impedance is and to proceed
accordingly. Said pointed out that it is not a sine output, but
rather 3v CMOS. Still, I think it is worthwhile to test to see what
the actual output capability is. For example, most HC and AC CMOS
outputs will source and sink 20-25mA. The Fairchild "advanced CMOS
family characteristics" document says:

>All SSI and MSI devices (AC, ACT, ACQ or ACTQ) are
>guaranteed to source and sink 24 mA. 74AC/ACTxxx
>devices are capable of driving 50 [ohm] transmission lines.

Some of the newer CMOS logic is similar, including Fairchild
TinyLogic UHS (NC7xZ series), LCX, and LVC devices. Now AFAIK, we do
not know what CMOS device is used for the TCXO output -- and it may
well not be any of these. Testing will provide a definitive answer,
and it may show that there are better options than a 1M termination.

Of course, the TCXO output is used internally to the LTE Lite (and
may be used internally to the TCXO itself), so one cannot count on
having all of the rated device output current available to drive an
external load. Avoid anything that pulls the output logic levels
very far down (logic high) or up (logic low), say by more than 200mV
(such as a termination resistance that is too low), or materially
distorts the output wave shape (such as a Tee or Pi filter, which one
might consider to convert the output to a sine wave and match it to coax).

To test, one would use a voltage divider from the logic supply
voltage to ground, with the TCXO output feeding the center point of
the divider. (See attached diagram.) I will be very surprised if it
will not drive 10k + 10k with ease (already MUCH better than 1M), and
1k + 1k is a distinct possibility [NOTE: in some cases, this scheme
works best if the resistor to the positive supply is about 50% higher
than the one to ground, for example 1.5k + 1k]. You may even find
that it will drive 100 + 100 (or 150 + 100) without problems, in
which case it should directly drive 50 ohm coax. With any of these,
best performance in the final installation will be achieved with the
termination resistors at the far end of any wire, PC trace, or
transmission line longer than a few inches. [Note that the divider
scheme is the right way to terminate CMOS logic for analog uses at
any impedance -- to terminate in 1M ohm, one would use 2M + 2M,
although at that level it matters less.]

Because the CMOS device is a saturated switch, the TCXO and LTE Light
power dissipation will not increase by a significant amount with the
increased load current. The logic supply will need to source some
extra power, but only 45mW even for the 100 + 100 ohm output network.

If the gods are truly with us, we may even find that the TCXO output
will source and sink sufficient current to drive a Tee network if the
circuit is designed properly -- say, a divider with 150 + 150 ohm
resistors (or 220 + 150) feeding a series 10nF capacitor and 200 ohm
resistor to a Tee network using 10uH/50.5pF/10uH -- which would drive
a 0dBm sine wave into terminated 50 ohm coax with harmonics below
-40dBc. (See attached diagram.) This requires peak currents from
the CMOS output of +/- 5mA. But don't count on this until you test
and verify, and don't be surprised if the TCXO output will not
support it. [If one can live with a sine output of < 0dBm, the
divider resistors and the series resistor can all be increased in
value until it does work.]

Best regards,

Charles
"All electronics is analog."
Charles Steinmetz
2014-11-25 17:31:55 UTC
Permalink
Raw Message
Said wrote:

>The increased current for the driver will cause heating near the
>crystal in both the CMOS driver and the 3.0V LDO as the LDO has to
>convert the excess voltage into heat. This may or may not affect the crystal.

There would be next to no additional heating in the CMOS driver,
because there is very little voltage across it in either logic
state. And the additional power supply current is so small that the
increase in LDO dissipation will also be very low. At the extreme
worst, any such effects would be somewhere between imperceptible and
negligible. But on the other hand, if there is a possibility that a
passive filter can create a clean, 50 ohm sine wave output for free,
the potential up side is huge.

>Adding an external buffer is so simple that I just did not think it
>would be worth it..

An external buffer is a fine way to go, but it would need to be very
close to the driver chip -- which is why I suggested on Sunday
building it onto a breakout card that plugs directly onto the LTE
Lite's MMCX output connector. You really don't want to run a naked
CMOS output at 10MHz much farther than that, both for the corruption
it may suffer and also for the mischief that radiation and capacitive
coupling can cause to other nearby circuitry (the LTE Lite) as the
loop gets larger than that.

I'm not sure I see why a small additional source of heat is such a
dramatic concern with the 10MHz TCXO, but apparently not for the
20MHz TCXO, which by accounts has an actual buffer amp that must
create comparatively massive heating. A temperature difference isn't
a problem in and of itself -- only a changing temperature creates a
problem. Whatever the dissipation situation is, it should settle
into stasis if one takes the slightest care with the thermal design.

Best regards,

Charles



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Dave Martindale
2014-11-25 15:34:47 UTC
Permalink
Raw Message
The 20 MHz output should be OK, since it is series-terminated with 50 ohms
at the source and the buffer can source enough current. The driver sees a
100 ohm load (50 ohm resistor in series with 50 ohm coax impedance) for
that 32 ns round trip time, so it will increase power dissipation (as you
note). But the load at the far end of the coax should see a clean edge,
and the reflection should be absorbed when it returns to the source (due to
the source terminator). Just don't look at the signal half way along the
coax.

The other outputs apparently don't have either the current drive or the
source terminator, so a long piece of coax is likely to do unpleasant
things to the edge.

In either case, if you want to run any of the signals 10 feet it's likely
better to run a very short connection from the LTE-Lite to a proper 50 ohm
line driver. That gets the power dissipation off the board, and then you
can use drivers that give you whatever output swing you want, and which can
drive a 100 ohm load continuously so you can use parallel termination at
the far end.

- Dave

On Tue, Nov 25, 2014 at 12:23 AM, Hal Murray <***@megapathdsl.net>
wrote:

>
> Said Jackson said:
> > Correct, and thats why its all a bad trade off if you have to use 50 Ohms
> > termination. Either more heat or more PN, and more circuitry.
>
> > So driving 50 Ohms inputs is not optimal here, 1M inputs are much better
> for
> > this purpose.
>
> That only works if you have a (very) short connection to the next stage.
>
> Things get interesting if you have, say, 10 feet of unterminated coax.
>
> 10 MHz is 100 ns, or 50 ns between transitions. Coax is ballpark of 5/8 c
> so
> that's 16 ns one way or 32 ns round drip. That's 60% of the heat as well
> as
> lots of nasty reflections.
>
> (Somebody please check my numbers.)
>
>
> --
> These are my opinions. I hate spam.
>
>
>
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Hal Murray
2015-04-07 20:58:00 UTC
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> Looking for a platform not needing a fan. While the ATOM and SSD seem to be
> OK w/o direct airflow, the Mini ITX Power Supply fan is needed.

If you are happy with Raspberry Pi or BeagleBone Black, they are the low cost
low power way to go. They run Linux. They don't have a real disk. If you
do a lot of "disk" activity, you might wear out the SD card frequently enough
to be annoying. That hasn't been a problem for me but I don't have a lot of
years on them yet. You could use a USB disk.

The Raspberry Pi has a HDMI connector so you can run a real display. The BBB
has a mini/micro HDMI connector. I ignore those and ssh in from my main PC.
(Some people refer to that mode of operation as headless.)


You can get no-fan style power for Mini-ITX size systems. The ones I'm
familiar with have a tiny DC-DC converter that mounts on the big power
connector and runs off a laptop size external supply.
http://www.mini-box.com/DC-DC


You could just change the fan or whole power supply whenever the fan dies.
Maybe you will get lucky and find one with a fan that lasts a long time.


You could try an old laptop. The battery will decay over the years, but it
will probably work well enough to cover short dropouts and/or let you wander
around for a few minutes. Some laptops have fans. (I have a Dell Latitude
D430. It has been running 24x7 for several years. The fan still works. The
battery is only good for 10 or 15 minutes.)


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Daniel Mendes
2015-04-08 02:09:55 UTC
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Raw Message
On 07/04/2015 17:58, Hal Murray wrote:
> If you are happy with Raspberry Pi or BeagleBone Black, they are the
> low cost low power way to go. They run Linux. They don't have a real
> disk. If you do a lot of "disk" activity, you might wear out the SD
> card frequently enough to be annoying. That hasn't been a problem for
> me but I don't have a lot of years on them yet. You could use a USB disk.

You can configure the main partition to run read only. This improves
lots of things in this regard.

Daniel
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cfo
2015-04-09 14:42:54 UTC
Permalink
Raw Message
On Tue, 07 Apr 2015 13:58:00 -0700, Hal Murray wrote:


> You can get no-fan style power for Mini-ITX size systems. The ones I'm
> familiar with have a tiny DC-DC converter that mounts on the big power
> connector and runs off a laptop size external supply.
> http://www.mini-box.com/DC-DC
>

I use some of the "Wide-Input" ATX (Red-ATX plug) supplies from them ,
they run excellent. Takes up no space , and are totally silent.

I'd recommend the WI model , as you can use a spare laptop-psu or
whatever you have lying around.

CFO

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Hal Murray
2015-07-01 07:18:00 UTC
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time-***@febo.com said:
> As expected, on the leap second the display on the 8183 showed 6:59:60 (the
> 8183-A showed 23:59:60), but the TV400 displayed 7:00:00 at that moment. The
> TV400 remained one second ahead until it displayed 7:00:03 for a two-second
> period, then from 7:00:04 forward it was properly synced.

My guess is that there is a CPU in the TV400 that is smart enough to filter
out noise but not smart enough to know about leap seconds. It considers
23:59:60 to be noise and rejects it. The following data gets rejected
because it doesn't match the predicted time. After a few seconds of data
that is self-consistent, it switches to the new time.


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