Discussion:
suggestions on getting 24 Mhz ?
(too old to reply)
Pete Lancashire
2018-04-11 10:00:23 UTC
Permalink
Needed for SDR project as external clock source.

-pete
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j***@att.net
2018-04-11 11:49:37 UTC
Permalink
Leo Bodnar GPSDO - adjustable Low-jitter GPS-locked precision frequency reference 400 Hz to 810 MHz . He has a new one, single output for 99 british pounds.

Jerry NY2KW

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From: time-nuts <time-nuts-***@febo.com> On Behalf Of Pete Lancashire
Sent: Wednesday, April 11, 2018 6:00 AM
To: Discussion of precise time and frequency measurement <time-***@febo.com>
Subject: [time-nuts] suggestions on getting 24 Mhz ?

Needed for SDR project as external clock source.

-pete
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Jerry Hancock
2018-04-11 16:00:25 UTC
Permalink
For and RSP? I used an HP 3325 locked to my Cs beam and took the signal from the back. I think I paid no more than $100 for the 3325a and one I got for free.

Regards,

Jerry
Post by j***@att.net
Leo Bodnar GPSDO - adjustable Low-jitter GPS-locked precision frequency reference 400 Hz to 810 MHz . He has a new one, single output for 99 british pounds.
Jerry NY2KW
-----Original Message-----
Sent: Wednesday, April 11, 2018 6:00 AM
Subject: [time-nuts] suggestions on getting 24 Mhz ?
Needed for SDR project as external clock source.
-pete
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Pete Lancashire
2018-04-11 16:04:44 UTC
Permalink
Yea, was also thinking of grabbing one of my 3325B's and hiding it under
the desk :-)

Going to see on Ebay if there are any 24 MHz VXCO's

-pete
Post by Jerry Hancock
For and RSP? I used an HP 3325 locked to my Cs beam and took the signal
from the back. I think I paid no more than $100 for the 3325a and one I
got for free.
Regards,
Jerry
Post by j***@att.net
Leo Bodnar GPSDO - adjustable Low-jitter GPS-locked precision frequency
reference 400 Hz to 810 MHz . He has a new one, single output for 99
british pounds.
Post by j***@att.net
Jerry NY2KW
-----Original Message-----
Lancashire
Post by j***@att.net
Sent: Wednesday, April 11, 2018 6:00 AM
To: Discussion of precise time and frequency measurement <
Subject: [time-nuts] suggestions on getting 24 Mhz ?
Needed for SDR project as external clock source.
-pete
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Graham / KE9H
2018-04-11 16:11:37 UTC
Permalink
Phase noise is (usually) more important than absolute frequency accuracy.

I suggest some kind of low phase noise master oscillator (OCXO) feeding a
DDS without an internal multiplier.

If internal multiplier in DDS, that, rather than the frequency reference
source will set the phase noise floor of the sampling.

--- Graham

==
Post by Jerry Hancock
For and RSP? I used an HP 3325 locked to my Cs beam and took the signal
from the back. I think I paid no more than $100 for the 3325a and one I
got for free.
Regards,
Jerry
Post by j***@att.net
Leo Bodnar GPSDO - adjustable Low-jitter GPS-locked precision frequency
reference 400 Hz to 810 MHz . He has a new one, single output for 99
british pounds.
Post by j***@att.net
Jerry NY2KW
-----Original Message-----
Lancashire
Post by j***@att.net
Sent: Wednesday, April 11, 2018 6:00 AM
To: Discussion of precise time and frequency measurement <
Subject: [time-nuts] suggestions on getting 24 Mhz ?
Needed for SDR project as external clock source.
-pete
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Bob kb8tq
2018-04-11 18:15:45 UTC
Permalink
Hi
Post by Graham / KE9H
Phase noise is (usually) more important than absolute frequency accuracy.
It’s probably well worth looking into exactly what you are after in terms of phase noise,
spurs, and stability *before* deciding on a solution. In some cases things like DDS spurs
are a non-issue. In other cases phase noise at certain offsets is a really big deal, but at
other offsets … it’s a non-issue.

Bob
Post by Graham / KE9H
I suggest some kind of low phase noise master oscillator (OCXO) feeding a
DDS without an internal multiplier.
If internal multiplier in DDS, that, rather than the frequency reference
source will set the phase noise floor of the sampling.
--- Graham
==
Post by Jerry Hancock
For and RSP? I used an HP 3325 locked to my Cs beam and took the signal
from the back. I think I paid no more than $100 for the 3325a and one I
got for free.
Regards,
Jerry
Post by j***@att.net
Leo Bodnar GPSDO - adjustable Low-jitter GPS-locked precision frequency
reference 400 Hz to 810 MHz . He has a new one, single output for 99
british pounds.
Post by j***@att.net
Jerry NY2KW
-----Original Message-----
Lancashire
Post by j***@att.net
Sent: Wednesday, April 11, 2018 6:00 AM
To: Discussion of precise time and frequency measurement <
Subject: [time-nuts] suggestions on getting 24 Mhz ?
Needed for SDR project as external clock source.
-pete
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Mark Goldberg
2018-04-11 20:21:26 UTC
Permalink
Post by Bob kb8tq
Hi
Post by Graham / KE9H
Phase noise is (usually) more important than absolute frequency accuracy.
It’s probably well worth looking into exactly what you are after in terms of phase noise,
spurs, and stability *before* deciding on a solution. In some cases things like DDS spurs
are a non-issue. In other cases phase noise at certain offsets is a really big deal, but at
other offsets … it’s a non-issue.
I am using the single output Bodnar GPSDO driving a frequency locked Wenzel
low phase noise oscillator and using that for my SDR ADC clock. I am using
it to take phase noise measurements and it certainly is as good as the
references I have available, and matches pretty well with measurements on a
$90k phase noise meter.

The Wenzel eliminates far out spurs from the GPSDO. Note that different
register values may result in the same frequency output of the GPSDO, but
spurs can be very different. For some frequencies and with the right
register values, I expect the GPSDO alone may be good enough for an SDR
clock, but I have not tried.

This is the best I can measure with this setup. I think the ADC noise
limits the far out phase noise.

Offset Phase Noise
(Hz) (dBc/Hz)
10 -96.9
20 -103.0
50 -106.9
100 -109.7
200 -117.7
500 -128.4
1,000 -136.4
2,000 -140.1
5,000 -143.1
10,000 -144.9
20,000 -145.6
50,000 -145.7
100,000 -146.2
1,000,000 -146.6

Regards,

Mark
W7MLG
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jimlux
2018-04-11 12:55:25 UTC
Permalink
Post by Pete Lancashire
Needed for SDR project as external clock source.
-pete
I assume you mean derived from a high quality 10 MHz.

some sort of discrete divide multiply? divide by 5 multiply by 12?
A PLL with VCXO with good far out noise? (sort of like "clean up loops"
used for distributing 10 or 100 MHz )
A DDS (with internal multiplier)


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Jimmy D. Burrell
2018-04-11 13:11:57 UTC
Permalink
Hi Pete,

Speaking from limited experience, I wonder if a garden variety OCXO at say 10 MHz + some CMOS logic to act as a frequency multiplier might not fit the build? Then again, perhaps 24MHz is a little fast for the logic chips.. not sure.

Hope this helps spark some discussion.

Jim…
N5SPE
Post by Pete Lancashire
Needed for SDR project as external clock source.
-pete
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Tom Van Baak
2018-04-11 20:35:07 UTC
Permalink
Pete,

Is your goal to make SDR frequency measurements? One solution: grab any 24 MHz oscillator you find but use a counter with known accurate timebase (Rb,Cs,GPSDO) to continuously record its actual frequency. Don't adjust the frequency; just record it. Then, apply those readings as corrections to your SDR measurements. This software (or pencil & paper) correction method should give equivalent results as an atomic- or GPS-disciplined 24 MHz timebase.

/tvb

----- Original Message -----
From: "Pete Lancashire" <***@petelancashire.com>
To: "Discussion of precise time and frequency measurement" <time-***@febo.com>
Sent: Wednesday, April 11, 2018 3:00 AM
Subject: [time-nuts] suggestions on getting 24 Mhz ?
Post by Pete Lancashire
Needed for SDR project as external clock source.
-pete
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Attila Kinali
2018-04-15 10:36:04 UTC
Permalink
On Wed, 11 Apr 2018 03:00:23 -0700
Post by Pete Lancashire
Needed for SDR project as external clock source.
If your goal is, as Jim guessed, to get 24MHz from 10MHz and
you are using something like an RTL-SDR, then how about just
passing the 10MHz through a CMOS gate to square it up and
get nice harmonics, then pass a wire close to the crystal.
This should injection lock the crystal to right frequency.
It wont be a strong lock due to the 5:12 ratio, but for something
like a crystal that is already quite close, that should do the trick.

Alternatively, using an ADF4002 with a small uC to configure it
and a VCXO/VCO should also work.

Attila Kinali
--
<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.
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Pete Lancashire
2018-04-16 10:45:38 UTC
Permalink
Access to " the xtal" is not an option the SDR is enclosed in a metal box.

Do a web search for RSP2Pro
Post by Attila Kinali
On Wed, 11 Apr 2018 03:00:23 -0700
Post by Pete Lancashire
Needed for SDR project as external clock source.
If your goal is, as Jim guessed, to get 24MHz from 10MHz and
you are using something like an RTL-SDR, then how about just
passing the 10MHz through a CMOS gate to square it up and
get nice harmonics, then pass a wire close to the crystal.
This should injection lock the crystal to right frequency.
It wont be a strong lock due to the 5:12 ratio, but for something
like a crystal that is already quite close, that should do the trick.
Alternatively, using an ADF4002 with a small uC to configure it
and a VCXO/VCO should also work.
Attila Kinali
--
<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.
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jimlux
2018-04-16 14:18:15 UTC
Permalink
Post by Pete Lancashire
Access to " the xtal" is not an option the SDR is enclosed in a metal box.
Do a web search for RSP2Pro
It does have an external reference input..
There's not a lot of info on the Mirics data sheets (or on the sdrplay
website)

It sort of looks like this is a somewhat enhanced version of the parts
used in the RTL-SDR dongles.
(10 bit ADC, instead of 8 bits in the RTL2832)

And of course it needs 24MHz because it has to run the USB interface.

10 bit ADC means that you probably don't need *outstanding* clock
performance - the sample and hold and all the other timing logic is
probably designed to that sort of performance level - getting
femtosecond jitter probably isn't worth it.


If you're just looking for a 24 MHz driver that doesn't need to be
locked to anything, one of the SiTime modules would work, or you could
probably order a TCXO for 24 MHz - it's a standard frequency (viz. USB),
so it's almost certainly available from stock
Post by Pete Lancashire
Post by Attila Kinali
On Wed, 11 Apr 2018 03:00:23 -0700
Post by Pete Lancashire
Needed for SDR project as external clock source.
If your goal is, as Jim guessed, to get 24MHz from 10MHz and
you are using something like an RTL-SDR, then how about just
passing the 10MHz through a CMOS gate to square it up and
get nice harmonics, then pass a wire close to the crystal.
This should injection lock the crystal to right frequency.
It wont be a strong lock due to the 5:12 ratio, but for something
like a crystal that is already quite close, that should do the trick.
Alternatively, using an ADF4002 with a small uC to configure it
and a VCXO/VCO should also work.
Attila Kinali
--
<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.
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Pete Lancashire
2018-04-16 15:02:51 UTC
Permalink
14 bit
Post by jimlux
Post by Pete Lancashire
Access to " the xtal" is not an option the SDR is enclosed in a metal
box.
Post by Pete Lancashire
Do a web search for RSP2Pro
It does have an external reference input..
There's not a lot of info on the Mirics data sheets (or on the sdrplay
website)
It sort of looks like this is a somewhat enhanced version of the parts
used in the RTL-SDR dongles.
(10 bit ADC, instead of 8 bits in the RTL2832)
And of course it needs 24MHz because it has to run the USB interface.
10 bit ADC means that you probably don't need *outstanding* clock
performance - the sample and hold and all the other timing logic is
probably designed to that sort of performance level - getting
femtosecond jitter probably isn't worth it.
If you're just looking for a 24 MHz driver that doesn't need to be
locked to anything, one of the SiTime modules would work, or you could
probably order a TCXO for 24 MHz - it's a standard frequency (viz. USB),
so it's almost certainly available from stock
Post by Pete Lancashire
Post by Attila Kinali
On Wed, 11 Apr 2018 03:00:23 -0700
Post by Pete Lancashire
Needed for SDR project as external clock source.
If your goal is, as Jim guessed, to get 24MHz from 10MHz and
you are using something like an RTL-SDR, then how about just
passing the 10MHz through a CMOS gate to square it up and
get nice harmonics, then pass a wire close to the crystal.
This should injection lock the crystal to right frequency.
It wont be a strong lock due to the 5:12 ratio, but for something
like a crystal that is already quite close, that should do the trick.
Alternatively, using an ADF4002 with a small uC to configure it
and a VCXO/VCO should also work.
Attila Kinali
--
<JaberWorky> The bad part of Zurich is where the degenerates
throw DARK chocolate at you.
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Mark Spencer
2018-05-10 03:00:23 UTC
Permalink
Thanks Tim.

All the best

Mark Spencer

***@alignedsolutions.com
604 762 4099
Hi Mark,
this is a product of Glen VK1XX.
he will have a website with eCommerce up soon and when that happens I will
announce it to the list
Regards
Tim
Hi would anyone be able to point me (off list) in the direction of a bit
more information re this device ?
Many thanks
Mark S
604 762 4099
Post by Jimmy D. Burrell
Hi Pete,
You probably want this...
https://github.com/glenenglishgithub/anylockerFS
Lots of VK's are lining up for the first run of boards to lock their
radios.
Post by Jimmy D. Burrell
regards
Tim
Post by Pete Lancashire
Needed for SDR project as external clock source.
-pete
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