My GPSDO project: OCXO Thermal Oscillation?

[Bob Stewart]

I'm converting the code for the VE2ZAZ FLL to a PLL.  I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies).  The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value.  I feel pretty confident with my code at this point.  I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information.  Could this oscillating phase correction be some sort of thermal oscillation?  I've tried two separate 34310s and both act more or less the same.  My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect.  Is this good, bad, or indifferent for a GPSDO?  I started this project not knowing what to expect, and I still don't.  Experienced help, speculation, or even just kind words at this point would be appreciated!  =)  I don't have a known good/stable reference to compare this
to.

Bob - AE6RV

[Bob Camp]

Hi

Ok, let's try some math and see if I can do it without blinking this time….

+/-4 Hz for 6 volts is 0.66 Hz / V
output is 10 MHz so 1 Hz is 0.1 ppm
your OCXO is running at 0.066 ppm / V
That's also 66 ppb / V

0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt

The UT+ has a sawtooth output that's about 45 ns
That's 45 ppb at one second

5 minutes is 300 seconds

so 45 / 300 = 0.15 ppb or 150 ppt

If it's the later clone version it might be about 1/2 of that.

Are you doing sawtooth correction?

Bob

I'm converting the code for the VE2ZAZ FLL to a PLL. I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies). The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value. I feel pretty confident with my code at this point. I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information. Could this oscillating phase correction be some sort of thermal oscillation? I've tried two separate 34310s and both act more or less the same. My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect. Is this good, bad, or indifferent for a GPSDO? I started this project not knowing what to expect, and I still don't. Experienced help, speculation, or even just kind words at this point would be appreciated! =) I don't have a known good/stable reference to compare this
to.
Bob - AE6RV
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[Bob Stewart]

Hi Bob,

So, assuming your math is right at .15 ppb, that seems to be within the figures you gave for the 34310-T.

I'm not attempting sawtooth correction for a number of reasons, the biggest of which is the uncertainty factor in the PIC.  I think I read in the datasheet that the CCP1 input where I'm getting the 1PPS pulse has a delay of 3-4 oscillator ticks, but I can't find that at the moment.  Assuming that's correct, with an 8MHz oscillator, that works out to an uncertainty of 125ns.  I don't know what the uncertainty is on the T1CKI input (10MHz) but let's say that it's the same 125ns.  That's 250ns, to which we have to add an uncertainty of +/- 52ns for the UT+ sawtooth.  Those figures seem to be borne out by the second to second variance I'm seeing in the clock count.  It can go as high as 5 ticks when the oscillator starts moving. 

So, I've set the hysteresis for the PLL at +/- 2 ticks of the 10MHz oscillator.  Anything above that and I count it as a phase error and move the DAC by ~0.0003V  (not a typo).  If I see a phase error above 8 ticks, I count it as a error, move the DAC by ~0.0048V, and zero the cumulative phase error so it doesn't go into a tailspin.  Generally this doesn't happen except during the power up/oven warming period, though I have seen it once.

So, bottom line:  is .15 ppb over 5 minutes a reasonable accuracy for what I have to work with? 

Bob

________________________________
Sent: Friday, August 16, 2013 10:47 AM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Ok, let's try some math and see if I can do it without blinking this time….
+/-4 Hz for 6 volts is 0.66 Hz / V
output is 10 MHz so 1 Hz is 0.1 ppm
your OCXO is running at 0.066 ppm / V
That's also 66 ppb / V
0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt
The UT+ has a sawtooth output that's about 45 ns
That's 45 ppb at one second
5 minutes is 300 seconds
so 45 / 300 = 0.15 ppb or 150 ppt
If it's the later clone version it might be  about 1/2 of that.
Are you doing sawtooth correction?
Bob

Post by Bob Stewart
I'm converting the code for the VE2ZAZ FLL to a PLL.  I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies).  The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value.  I feel pretty confident with my code at this point.  I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information.  Could this oscillating phase correction be some sort of thermal oscillation?  I've tried two separate 34310s and both act more or less the same.  My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect.  Is this good, bad, or indifferent for a GPSDO?  I started this project not knowing what to expect, and I still don't.  Experienced help, speculation, or even just kind words at this point would be appreciated!  =)  I don't have a known good/stable reference to compare

this

Post by Bob Stewart
to.
Bob - AE6RV
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[Bob Camp]

Hi

If your resolution plus sawtooth is ~ 250 ns, then you have 250 ppb at 1 second. At 300 seconds you would have just under 1 ppb. To get close to the full range temp stability of the OCXO you would have to run at least 10X that long. Put another way, the GPS can only stop hurting things past about 60 minutes. The OCXO is likely stable at a constant ambient to < 10 ppt for moderate amounts of time. The GPS could only start helping the OCXO past about 600 minutes.

That all assumes the loop settles instantly with no error. If you have a more normal loop, multiply all those times by some number between 3 and 20. If you use 10 then the GPS would start helping at about 6,000 minutes ( 100 hours or 4 days). That's not a "moderate amount of time" so the real cross over should be a bit sooner than that.

Bob

Post by Volker Esper
Hi Bob,
So, assuming your math is right at .15 ppb, that seems to be within the figures you gave for the 34310-T.
I'm not attempting sawtooth correction for a number of reasons, the biggest of which is the uncertainty factor in the PIC. I think I read in the datasheet that the CCP1 input where I'm getting the 1PPS pulse has a delay of 3-4 oscillator ticks, but I can't find that at the moment. Assuming that's correct, with an 8MHz oscillator, that works out to an uncertainty of 125ns. I don't know what the uncertainty is on the T1CKI input (10MHz) but let's say that it's the same 125ns. That's 250ns, to which we have to add an uncertainty of +/- 52ns for the UT+ sawtooth. Those figures seem to be borne out by the second to second variance I'm seeing in the clock count. It can go as high as 5 ticks when the oscillator starts moving.
So, I've set the hysteresis for the PLL at +/- 2 ticks of the 10MHz oscillator. Anything above that and I count it as a phase error and move the DAC by ~0.0003V (not a typo). If I see a phase error above 8 ticks, I count it as a error, move the DAC by ~0.0048V, and zero the cumulative phase error so it doesn't go into a tailspin. Generally this doesn't happen except during the power up/oven warming period, though I have seen it once.
So, bottom line: is .15 ppb over 5 minutes a reasonable accuracy for what I have to work with?
Bob

________________________________
Sent: Friday, August 16, 2013 10:47 AM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Ok, let's try some math and see if I can do it without blinking this time….
+/-4 Hz for 6 volts is 0.66 Hz / V
output is 10 MHz so 1 Hz is 0.1 ppm
your OCXO is running at 0.066 ppm / V
That's also 66 ppb / V
0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt
The UT+ has a sawtooth output that's about 45 ns
That's 45 ppb at one second
5 minutes is 300 seconds
so 45 / 300 = 0.15 ppb or 150 ppt
If it's the later clone version it might be about 1/2 of that.
Are you doing sawtooth correction?
Bob

I'm converting the code for the VE2ZAZ FLL to a PLL. I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies). The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value. I feel pretty confident with my code at this point. I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information. Could this oscillating phase correction be some sort of thermal oscillation? I've tried two separate 34310s and both act more or less the same. My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect. Is this good, bad, or indifferent for a GPSDO? I started this project not knowing what to expect, and I still don't. Experienced help, speculation, or even just kind words at this point would be appreciated! =) I don't have a known good/stable reference to compare

this

to.
Bob - AE6RV
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[Bob Stewart]

Hi again Bob,

D'oh, I think I totally misunderstood your figures in my first response.  The .16ppb is not the frequency accuracy of my GPSDO.  It's the amount that I'm moving the OCXO during a 5 minute timeframe, which is something else entirely.  Like I said I do not have a known good oscillator to compare to.  However, I have a DDS oscillator I made some time ago, and it seems to be pretty stable if I let it be.  So, what I've done is to hook the GPSDO to the clock input of my 5335A.  I've then adjusted the DDS so that it reads near 10.000000 MHz, and watched it over a round-trip 5 minute period several times with a large enough gate that I get 8 decimal points on the counter.  I don't see any relationship between the few milli-Hz movement the counter shows and the changes to the DAC.  During several runs last night, I saw less than 30 mHz of movement, which, if true, would be 3E-9, or 3ppb, right?  Or would that be +/- 1.5ppb?

Bob

________________________________
Sent: Friday, August 16, 2013 10:47 AM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Ok, let's try some math and see if I can do it without blinking this time….
+/-4 Hz for 6 volts is 0.66 Hz / V
output is 10 MHz so 1 Hz is 0.1 ppm
your OCXO is running at 0.066 ppm / V
That's also 66 ppb / V
0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt
The UT+ has a sawtooth output that's about 45 ns
That's 45 ppb at one second
5 minutes is 300 seconds
so 45 / 300 = 0.15 ppb or 150 ppt
If it's the later clone version it might be  about 1/2 of that.
Are you doing sawtooth correction?
Bob

Post by Bob Stewart
I'm converting the code for the VE2ZAZ FLL to a PLL.  I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies).  The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value.  I feel pretty confident with my code at this point.  I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information.  Could this oscillating phase correction be some sort of thermal oscillation?  I've tried two separate 34310s and both act more or less the same.  My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect.  Is this good, bad, or indifferent for a GPSDO?  I started this project not knowing what to expect, and I still don't.  Experienced help, speculation, or even just kind words at this point would be appreciated!  =)  I don't have a known good/stable reference to compare

this

Post by Bob Stewart
to.
Bob - AE6RV
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[Bob Camp]

Hi

With the 5335 you have a measurement with dead time. That makes things a bit hard to figure out. A much better way to go is to feed a pair of 1 pps signals into the 5335 and measure their time difference. Unless they are quite close, you can go for a while with no ambiguity to the reading. The effective resolution increases linearly with the time length of the observation. There also are a number of very nice programs that will let you collect the data from the 5335 via GPIB.

Assuming your 5335 works like mine does it's got about a 1 ns resolution at 1 second. It'll give you 1 ppb at a 1 second gate and 1 ppt at a 1,000 second gate. By the time it gets to 1,000 seconds the internal counters have overflowed and the reading is a bit messed up.

Without some sort of accurate reference, there's really no way to know for sure what's going on with a GPSDO. One solution is to build two or three of them and watch them fight with each other. Another solution is to pick up a Hydrogen Maser. It's always a "what's in your wallet" sort of decision.

Bob

Post by Bob Stewart
Hi again Bob,
D'oh, I think I totally misunderstood your figures in my first response. The .16ppb is not the frequency accuracy of my GPSDO. It's the amount that I'm moving the OCXO during a 5 minute timeframe, which is something else entirely. Like I said I do not have a known good oscillator to compare to. However, I have a DDS oscillator I made some time ago, and it seems to be pretty stable if I let it be. So, what I've done is to hook the GPSDO to the clock input of my 5335A. I've then adjusted the DDS so that it reads near 10.000000 MHz, and watched it over a round-trip 5 minute period several times with a large enough gate that I get 8 decimal points on the counter. I don't see any relationship between the few milli-Hz movement the counter shows and the changes to the DAC. During several runs last night, I saw less than 30 mHz of movement, which, if true, would be 3E-9, or 3ppb, right? Or would that be +/- 1.5ppb?
Bob

________________________________
Sent: Friday, August 16, 2013 10:47 AM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Ok, let's try some math and see if I can do it without blinking this time….
+/-4 Hz for 6 volts is 0.66 Hz / V
output is 10 MHz so 1 Hz is 0.1 ppm
your OCXO is running at 0.066 ppm / V
That's also 66 ppb / V
0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt
The UT+ has a sawtooth output that's about 45 ns
That's 45 ppb at one second
5 minutes is 300 seconds
so 45 / 300 = 0.15 ppb or 150 ppt
If it's the later clone version it might be about 1/2 of that.
Are you doing sawtooth correction?
Bob

I'm converting the code for the VE2ZAZ FLL to a PLL. I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies). The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value. I feel pretty confident with my code at this point. I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information. Could this oscillating phase correction be some sort of thermal oscillation? I've tried two separate 34310s and both act more or less the same. My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect. Is this good, bad, or indifferent for a GPSDO? I started this project not knowing what to expect, and I still don't. Experienced help, speculation, or even just kind words at this point would be appreciated! =) I don't have a known good/stable reference to compare

this

to.
Bob - AE6RV
_______________________________________________
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

_______________________________________________
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[Angus]

Hi,

To be able to test GPSDO's (and GPS in general) was one of the main reasons that I made a temp controlled chassis for an LPRO and gave it air pressure compensation. That was good for tau's of hundreds to tens of thousands of seconds, and even longer with drift compensation. Add in a clean-up oscillator if desired, and you have a pretty good reference.

Incidentally, I tested 2 FEI5680A's, a Temex LPFRS and 3 LPRO's in this type of setup, but only the LPRO's allowed the air pressure effects to be almost completely cancelled out. For some reason the others did not react to fluctuating air pressure as predictably.

Angus.

From: "Bob Camp"
To: "Discussion of precise time and frequency measurement"
Sent: August 16, 2013 7:45 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?

Hi

With the 5335 you have a measurement with dead time. That makes things a bit hard to figure out. A much better way to go is to feed a pair of 1 pps signals into the 5335 and measure their time difference. Unless they are quite close, you can go for a while with no ambiguity to the reading. The effective resolution increases linearly with the time length of the observation. There also are a number of very nice programs that will let you collect the data from the 5335 via GPIB.

Assuming your 5335 works like mine does it's got about a 1 ns resolution at 1 second. It'll give you 1 ppb at a 1 second gate and 1 ppt at a 1,000 second gate. By the time it gets to 1,000 seconds the internal counters have overflowed and the reading is a bit messed up.

Without some sort of accurate reference, there's really no way to know for sure what's going on with a GPSDO. One solution is to build two or three of them and watch them fight with each other. Another solution is to pick up a Hydrogen Maser. It's always a "what's in your wallet" sort of decision.

Bob

Post by Bob Stewart
Hi again Bob,
D'oh, I think I totally misunderstood your figures in my first response. The .16ppb is not the frequency accuracy of my GPSDO. It's the amount that I'm moving the OCXO during a 5 minute timeframe, which is something else entirely. Like I said I do not have a known good oscillator to compare to. However, I have a DDS oscillator I made some time ago, and it seems to be pretty stable if I let it be. So, what I've done is to hook the GPSDO to the clock input of my 5335A. I've then adjusted the DDS so that it reads near 10.000000 MHz, and watched it over a round-trip 5 minute period several times with a large enough gate that I get 8 decimal points on the counter. I don't see any relationship between the few milli-Hz movement the counter shows and the changes to the DAC. During several runs last night, I saw less than 30 mHz of movement, which, if true, would be 3E-9, or 3ppb, right? Or would that be +/- 1.5ppb?
Bob

________________________________
From: Bob Camp
To: Discussion of precise time and frequency measurement
Sent: Friday, August 16, 2013 10:47 AM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Ok, let's try some math and see if I can do it without blinking this time….
+/-4 Hz for 6 volts is 0.66 Hz / V
output is 10 MHz so 1 Hz is 0.1 ppm
your OCXO is running at 0.066 ppm / V
That's also 66 ppb / V
0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt
The UT+ has a sawtooth output that's about 45 ns
That's 45 ppb at one second
5 minutes is 300 seconds
so 45 / 300 = 0.15 ppb or 150 ppt
If it's the later clone version it might be about 1/2 of that.
Are you doing sawtooth correction?
Bob

I'm converting the code for the VE2ZAZ FLL to a PLL. I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies). The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value. I feel pretty confident with my code at this point. I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information. Could this oscillating phase correction be some sort of thermal oscillation? I've tried two separate 34310s and both act more or less the same. My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect. Is this good, bad, or indifferent for a GPSDO? I started this project not knowing what to expect, and I still don't. Experienced help, speculation, or even just kind words at this point would be appreciated! =) I don't have a known good/stable reference to compare

this

to.
Bob - AE6RV
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and follow the instructions there.

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[Bob Camp]

Hi

THe FE's have an "interesting" approach to temperature compensation. It creates a broad ADEV hump from about 30 seconds out to several thousand seconds. If you get lucky your local ambient does not "excite" the process. It the rest of the world, you get a goofy hump.

Bob

Post by Angus
Hi,
To be able to test GPSDO's (and GPS in general) was one of the main reasons that I made a temp controlled chassis for an LPRO and gave it air pressure compensation. That was good for tau's of hundreds to tens of thousands of seconds, and even longer with drift compensation. Add in a clean-up oscillator if desired, and you have a pretty good reference.
Incidentally, I tested 2 FEI5680A's, a Temex LPFRS and 3 LPRO's in this type of setup, but only the LPRO's allowed the air pressure effects to be almost completely cancelled out. For some reason the others did not react to fluctuating air pressure as predictably.
Angus.
From: "Bob Camp"
To: "Discussion of precise time and frequency measurement"
Sent: August 16, 2013 7:45 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
With the 5335 you have a measurement with dead time. That makes things a bit hard to figure out. A much better way to go is to feed a pair of 1 pps signals into the 5335 and measure their time difference. Unless they are quite close, you can go for a while with no ambiguity to the reading. The effective resolution increases linearly with the time length of the observation. There also are a number of very nice programs that will let you collect the data from the 5335 via GPIB.
Assuming your 5335 works like mine does it's got about a 1 ns resolution at 1 second. It'll give you 1 ppb at a 1 second gate and 1 ppt at a 1,000 second gate. By the time it gets to 1,000 seconds the internal counters have overflowed and the reading is a bit messed up.
Without some sort of accurate reference, there's really no way to know for sure what's going on with a GPSDO. One solution is to build two or three of them and watch them fight with each other. Another solution is to pick up a Hydrogen Maser. It's always a "what's in your wallet" sort of decision.
Bob

Post by Bob Stewart
Hi again Bob,
D'oh, I think I totally misunderstood your figures in my first response. The .16ppb is not the frequency accuracy of my GPSDO. It's the amount that I'm moving the OCXO during a 5 minute timeframe, which is something else entirely. Like I said I do not have a known good oscillator to compare to. However, I have a DDS oscillator I made some time ago, and it seems to be pretty stable if I let it be. So, what I've done is to hook the GPSDO to the clock input of my 5335A. I've then adjusted the DDS so that it reads near 10.000000 MHz, and watched it over a round-trip 5 minute period several times with a large enough gate that I get 8 decimal points on the counter. I don't see any relationship between the few milli-Hz movement the counter shows and the changes to the DAC. During several runs last night, I saw less than 30 mHz of movement, which, if true, would be 3E-9, or 3ppb, right? Or would that be +/- 1.5ppb?
Bob

________________________________
From: Bob Camp
To: Discussion of precise time and frequency measurement
Sent: Friday, August 16, 2013 10:47 AM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Ok, let's try some math and see if I can do it without blinking this time….
+/-4 Hz for 6 volts is 0.66 Hz / V
output is 10 MHz so 1 Hz is 0.1 ppm
your OCXO is running at 0.066 ppm / V
That's also 66 ppb / V
0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt
The UT+ has a sawtooth output that's about 45 ns
That's 45 ppb at one second
5 minutes is 300 seconds
so 45 / 300 = 0.15 ppb or 150 ppt
If it's the later clone version it might be about 1/2 of that.
Are you doing sawtooth correction?
Bob

I'm converting the code for the VE2ZAZ FLL to a PLL. I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies). The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value. I feel pretty confident with my code at this point. I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information. Could this oscillating phase correction be some sort of thermal oscillation? I've tried two separate 34310s and both act more or less the same. My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect. Is this good, bad, or indifferent for a GPSDO? I started this project not knowing what to expect, and I still don't. Experienced help, speculation, or even just kind words at this point would be appreciated! =) I don't have a known good/stable reference to compare

this

to.
Bob - AE6RV
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[Bob Stewart]

I'll figure out something.  I'm thinking of icing down my DDS device to put it at a known temperature so I can do drift comparisons.  If not that, there'll be something else I can try.

On another note: I thought I had destroyed everything when I swapped the UT+ back into the GPSDO.  Fortunately it was just that the UT+ needed to be reset, and I had destroyed a USB-TTL adapter and not my new little Adafruit.  I'm going to have to figure out exactly what command sequence needs to be sent to the UT+ to get the comms working again and write a short program to do it.  For some reason the WinCore12 program wasn't able to bring it up.

Bob

________________________________
Sent: Friday, August 16, 2013 6:14 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi,
To be able to test GPSDO's (and GPS in general) was one of the main reasons that I made a temp controlled chassis for an LPRO and gave it air pressure compensation. That was good for tau's of hundreds to tens of thousands of seconds, and even longer with drift compensation. Add in a clean-up oscillator if desired, and you have a pretty good reference.
Incidentally, I tested 2 FEI5680A's, a Temex LPFRS and 3 LPRO's in this type of setup, but only the LPRO's allowed the air pressure effects to be almost completely cancelled out. For some reason the others did not react to fluctuating air pressure as predictably.
Angus.
From: "Bob Camp"
To: "Discussion of precise time and frequency measurement"
Sent: August 16, 2013 7:45 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
With the 5335 you have a measurement with dead time. That makes things a bit hard to figure out. A much better way to go is to feed a pair of 1 pps signals into the 5335 and measure their time difference. Unless they are quite close, you can go for a while with no ambiguity to the reading. The effective resolution increases linearly with the time length of the observation. There also are a number of very nice programs that will let you collect the data from the 5335 via GPIB.
Assuming your 5335 works like mine does it's got about a 1 ns resolution at 1 second. It'll give you 1 ppb at a 1 second gate and 1 ppt at a 1,000 second gate. By the time it gets to 1,000 seconds the internal counters have overflowed and the reading is a bit messed up.
Without some sort of accurate reference, there's really no way to know for sure what's going on with a GPSDO. One solution is to build two or three of them and watch them fight with each other. Another solution is to pick up a Hydrogen Maser. It's always a "what's in your wallet" sort of decision.
Bob

Post by Bob Stewart
Hi again Bob,
D'oh, I think I totally misunderstood your figures in my first response.  The .16ppb is not the frequency accuracy of my GPSDO.  It's the amount that I'm moving the OCXO during a 5 minute timeframe, which is something else entirely.  Like I said I do not have a known good oscillator to compare to.  However, I have a DDS oscillator I made some time ago, and it seems to be pretty stable if I let it be.  So, what I've done is to hook the GPSDO to the clock input of my 5335A.  I've then adjusted the DDS so that it reads near 10.000000 MHz, and watched it over a round-trip 5 minute period several times with a large enough gate that I get 8 decimal points on the counter.  I don't see any relationship between the few milli-Hz movement the counter shows and the changes to the DAC.  During several runs last night, I saw less than 30 mHz of movement, which, if true, would be 3E-9, or 3ppb, right?  Or would that be +/- 1.5ppb?
Bob

________________________________
From: Bob Camp
To: Discussion of precise time and frequency measurement 
Sent: Friday, August 16, 2013 10:47 AM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Ok, let's try some math and see if I can do it without blinking this time….
+/-4 Hz for 6 volts is 0.66 Hz / V
output is 10 MHz so 1 Hz is 0.1 ppm
your OCXO is running at 0.066 ppm / V
That's also 66 ppb / V
0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt
The UT+ has a sawtooth output that's about 45 ns
That's 45 ppb at one second
5 minutes is 300 seconds
so 45 / 300 = 0.15 ppb or 150 ppt
If it's the later clone version it might be  about 1/2 of that.
Are you doing sawtooth correction?
Bob

Post by Bob Stewart
I'm converting the code for the VE2ZAZ FLL to a PLL.  I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies).  The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value.  I feel pretty confident with my code at this point.  I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information.  Could this oscillating phase correction be some sort of thermal oscillation?  I've tried two separate 34310s and both act more or less the same.  My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect.  Is this good, bad, or indifferent for a GPSDO?  I started this project not knowing what to expect, and I still don't.  Experienced help, speculation, or even just kind words at this point would be appreciated!  =)  I don't have a known good/stable reference to compare

this

Post by Bob Stewart
to.
Bob - AE6RV
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[Bob Camp]

Hi

Also remember - you need to do a survey on the UT+ and put it into position hold / timing mode. If you don't you can add a bit more to your error budget.

Bob

I'll figure out something. I'm thinking of icing down my DDS device to put it at a known temperature so I can do drift comparisons. If not that, there'll be something else I can try.
On another note: I thought I had destroyed everything when I swapped the UT+ back into the GPSDO. Fortunately it was just that the UT+ needed to be reset, and I had destroyed a USB-TTL adapter and not my new little Adafruit. I'm going to have to figure out exactly what command sequence needs to be sent to the UT+ to get the comms working again and write a short program to do it. For some reason the WinCore12 program wasn't able to bring it up.
Bob

________________________________
Sent: Friday, August 16, 2013 6:14 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi,
To be able to test GPSDO's (and GPS in general) was one of the main reasons that I made a temp controlled chassis for an LPRO and gave it air pressure compensation. That was good for tau's of hundreds to tens of thousands of seconds, and even longer with drift compensation. Add in a clean-up oscillator if desired, and you have a pretty good reference.
Incidentally, I tested 2 FEI5680A's, a Temex LPFRS and 3 LPRO's in this type of setup, but only the LPRO's allowed the air pressure effects to be almost completely cancelled out. For some reason the others did not react to fluctuating air pressure as predictably.
Angus.
From: "Bob Camp"
To: "Discussion of precise time and frequency measurement"
Sent: August 16, 2013 7:45 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
With the 5335 you have a measurement with dead time. That makes things a bit hard to figure out. A much better way to go is to feed a pair of 1 pps signals into the 5335 and measure their time difference. Unless they are quite close, you can go for a while with no ambiguity to the reading. The effective resolution increases linearly with the time length of the observation. There also are a number of very nice programs that will let you collect the data from the 5335 via GPIB.
Assuming your 5335 works like mine does it's got about a 1 ns resolution at 1 second. It'll give you 1 ppb at a 1 second gate and 1 ppt at a 1,000 second gate. By the time it gets to 1,000 seconds the internal counters have overflowed and the reading is a bit messed up.
Without some sort of accurate reference, there's really no way to know for sure what's going on with a GPSDO. One solution is to build two or three of them and watch them fight with each other. Another solution is to pick up a Hydrogen Maser. It's always a "what's in your wallet" sort of decision.
Bob

Post by Bob Stewart
Hi again Bob,
D'oh, I think I totally misunderstood your figures in my first response. The .16ppb is not the frequency accuracy of my GPSDO. It's the amount that I'm moving the OCXO during a 5 minute timeframe, which is something else entirely. Like I said I do not have a known good oscillator to compare to. However, I have a DDS oscillator I made some time ago, and it seems to be pretty stable if I let it be. So, what I've done is to hook the GPSDO to the clock input of my 5335A. I've then adjusted the DDS so that it reads near 10.000000 MHz, and watched it over a round-trip 5 minute period several times with a large enough gate that I get 8 decimal points on the counter. I don't see any relationship between the few milli-Hz movement the counter shows and the changes to the DAC. During several runs last night, I saw less than 30 mHz of movement, which, if true, would be 3E-9, or 3ppb, right? Or would that be +/- 1.5ppb?
Bob

________________________________
From: Bob Camp
To: Discussion of precise time and frequency measurement
Sent: Friday, August 16, 2013 10:47 AM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Ok, let's try some math and see if I can do it without blinking this time….
+/-4 Hz for 6 volts is 0.66 Hz / V
output is 10 MHz so 1 Hz is 0.1 ppm
your OCXO is running at 0.066 ppm / V
That's also 66 ppb / V
0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt
The UT+ has a sawtooth output that's about 45 ns
That's 45 ppb at one second
5 minutes is 300 seconds
so 45 / 300 = 0.15 ppb or 150 ppt
If it's the later clone version it might be about 1/2 of that.
Are you doing sawtooth correction?
Bob

I'm converting the code for the VE2ZAZ FLL to a PLL. I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies). The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value. I feel pretty confident with my code at this point. I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information. Could this oscillating phase correction be some sort of thermal oscillation? I've tried two separate 34310s and both act more or less the same. My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect. Is this good, bad, or indifferent for a GPSDO? I started this project not knowing what to expect, and I still don't. Experienced help, speculation, or even just kind words at this point would be appreciated! =) I don't have a known good/stable reference to compare

this

to.
Bob - AE6RV
_______________________________________________
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[Bob Stewart]

I thought I could just re-enter the numbers from the last survey I did.  But either something is wrong or I'm missing something (betting on the latter).  I can't seem to enable TRAIM.  I thought I had it setup just like previously, but under WinCore12 it simply won't turn it on.  So, I'm just letting it do a survey again, I guess.  IOW, I dunno.


And I have a question about MATH functions on the 5335A, if you don't mind.  (I'm an HP newbie.)  Is there away to use Ratio A/B and have it give a greater resolution than a whole number, perhaps by having it average over multiple B ticks?  I think I figured out how to enter an Offset, but I just get the ratio in single digits which doesn't really give me anything.


Bob

________________________________
Sent: Friday, August 16, 2013 7:26 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Also remember - you need to do a survey on the UT+ and put it into position hold / timing mode. If you don't you can add a bit more to your error budget.
Bob

Post by Bob Stewart
I'll figure out something.  I'm thinking of icing down my DDS device to put it at a known temperature so I can do drift comparisons.  If not that, there'll be something else I can try.
On another note: I thought I had destroyed everything when I swapped the UT+ back into the GPSDO.  Fortunately it was just that the UT+ needed to be reset, and I had destroyed a USB-TTL adapter and not my new little Adafruit.  I'm going to have to figure out exactly what command sequence needs to be sent to the UT+ to get the comms working again and write a short program to do it.  For some reason the WinCore12 program wasn't able to bring it up.
Bob

________________________________
Sent: Friday, August 16, 2013 6:14 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi,
To be able to test GPSDO's (and GPS in general) was one of the main reasons that I made a temp controlled chassis for an LPRO and gave it air pressure compensation. That was good for tau's of hundreds to tens of thousands of seconds, and even longer with drift compensation. Add in a clean-up oscillator if desired, and you have a pretty good reference.
Incidentally, I tested 2 FEI5680A's, a Temex LPFRS and 3 LPRO's in this type of setup, but only the LPRO's allowed the air pressure effects to be almost completely cancelled out. For some reason the others did not react to fluctuating air pressure as predictably.
Angus.
From: "Bob Camp"
To: "Discussion of precise time and frequency measurement"
Sent: August 16, 2013 7:45 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
With the 5335 you have a measurement with dead time. That makes things a bit hard to figure out. A much better way to go is to feed a pair of 1 pps signals into the 5335 and measure their time difference. Unless they are quite close, you can go for a while with no ambiguity to the reading. The effective resolution increases linearly with the time length of the observation. There also are a number of very nice programs that will let you collect the data from the 5335 via GPIB.
Assuming your 5335 works like mine does it's got about a 1 ns resolution at 1 second. It'll give you 1 ppb at a 1 second gate and 1 ppt at a 1,000 second gate. By the time it gets to 1,000 seconds the internal counters have overflowed and the reading is a bit messed up.
Without some sort of accurate reference, there's really no way to know for sure what's going on with a GPSDO. One solution is to build two or three of them and watch them fight with each other. Another solution is to pick up a Hydrogen Maser. It's always a "what's in your wallet" sort of decision.
Bob

Post by Bob Stewart
Hi again Bob,
D'oh, I think I totally misunderstood your figures in my first response.  The .16ppb is not the frequency accuracy of my GPSDO.  It's the amount that I'm moving the OCXO during a 5 minute timeframe, which is something else entirely.  Like I said I do not have a known good oscillator to compare to.  However, I have a DDS oscillator I made some time ago, and it seems to be pretty stable if I let it be.  So, what I've done is to hook the GPSDO to the clock input of my 5335A.  I've then adjusted the DDS so that it reads near 10.000000 MHz, and watched it over a round-trip 5 minute period several times with a large enough gate that I get 8 decimal points on the counter.  I don't see any relationship between the few milli-Hz movement the counter shows and the changes to the DAC.  During several runs last night, I saw less than 30 mHz of movement, which, if true, would be 3E-9, or 3ppb, right?  Or would that be +/- 1.5ppb?
Bob

________________________________
From: Bob Camp
To: Discussion of precise time and frequency measurement 
Sent: Friday, August 16, 2013 10:47 AM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Ok, let's try some math and see if I can do it without blinking this time….
+/-4 Hz for 6 volts is 0.66 Hz / V
output is 10 MHz so 1 Hz is 0.1 ppm
your OCXO is running at 0.066 ppm / V
That's also 66 ppb / V
0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt
The UT+ has a sawtooth output that's about 45 ns
That's 45 ppb at one second
5 minutes is 300 seconds
so 45 / 300 = 0.15 ppb or 150 ppt
If it's the later clone version it might be  about 1/2 of that.
Are you doing sawtooth correction?
Bob

Post by Bob Stewart
I'm converting the code for the VE2ZAZ FLL to a PLL.  I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies).  The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value.  I feel pretty confident with my code at this point.  I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information.  Could this oscillating phase correction be some sort of thermal oscillation?  I've tried two separate 34310s and both act more or less the same.  My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect.  Is this good, bad, or indifferent for a GPSDO?  I started this project not knowing what to expect, and I still don't.  Experienced help, speculation, or even just kind words at this point would be appreciated!  =)  I don't have a known good/stable reference to

compare

Post by Bob Stewart

Post by Bob Stewart
this

Post by Bob Stewart
to.
Bob - AE6RV
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[Bob Camp]

Hi

I thought I could just re-enter the numbers from the last survey I did. But either something is wrong or I'm missing something (betting on the latter). I can't seem to enable TRAIM. I thought I had it setup just like previously, but under WinCore12 it simply won't turn it on. So, I'm just letting it do a survey again, I guess. IOW, I dunno.

If:

1) you have the numbers in the right format
2) they came from a long enough survey
3) they came from the same card
4) you have the right commands

Yes you can push them into the card. For the rest of us, it's off to survey land. For quick testing you can use a short survey. If you are looking at > 24 hour runs, then you need a good survey.

And I have a question about MATH functions on the 5335A, if you don't mind. (I'm an HP newbie.) Is there away to use Ratio A/B and have it give a greater resolution than a whole number, perhaps by having it average over multiple B ticks?

not really. They just take a very standard reading on each channel and do simple math on it. There's no resolution increase. To do a full ratio very near 10 MHz, use one of the signals as the reference to the counter. Still no real resolution increase, but a cool thing to do.

To get more resolution, put it in start / stop gate mode and run really long gate times. The easy way to time it and run it is via the GPIB. You fairly quickly find out that the internal counters overflow and 10 MHz goes to 5 MHz then to 2.5 MHz on the display. It's the top end overflowing so the stuff you are after (the LSB's) are still fine. It does mess up the nifty math function you spent all that time punching in though. Since you are likely running via GPIB at this point correcting things is a couple lines of code.

I think I figured out how to enter an Offset, but I just get the ratio in single digits which doesn't really give me anything.

first do a subtract to remove the 10 MHz likely by entering OFFSET CHS 1 EEX 7 ENTER

next make sure it looks right on the display, likely 0.123 or 1.23E-4

after that put in the scaling factor. For 10 MHz it's just a decimal shift for 16.384 MHz it would be a bit more complex (and even more useful)
likely key strokes are SCALE 1 E CHS 7 ENTER (CHS location could be off)

Bob

Bob

________________________________
Sent: Friday, August 16, 2013 7:26 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Also remember - you need to do a survey on the UT+ and put it into position hold / timing mode. If you don't you can add a bit more to your error budget.
Bob

I'll figure out something. I'm thinking of icing down my DDS device to put it at a known temperature so I can do drift comparisons. If not that, there'll be something else I can try.
On another note: I thought I had destroyed everything when I swapped the UT+ back into the GPSDO. Fortunately it was just that the UT+ needed to be reset, and I had destroyed a USB-TTL adapter and not my new little Adafruit. I'm going to have to figure out exactly what command sequence needs to be sent to the UT+ to get the comms working again and write a short program to do it. For some reason the WinCore12 program wasn't able to bring it up.
Bob

________________________________
Sent: Friday, August 16, 2013 6:14 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi,
To be able to test GPSDO's (and GPS in general) was one of the main reasons that I made a temp controlled chassis for an LPRO and gave it air pressure compensation. That was good for tau's of hundreds to tens of thousands of seconds, and even longer with drift compensation. Add in a clean-up oscillator if desired, and you have a pretty good reference.
Incidentally, I tested 2 FEI5680A's, a Temex LPFRS and 3 LPRO's in this type of setup, but only the LPRO's allowed the air pressure effects to be almost completely cancelled out. For some reason the others did not react to fluctuating air pressure as predictably.
Angus.
From: "Bob Camp"
To: "Discussion of precise time and frequency measurement"
Sent: August 16, 2013 7:45 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
With the 5335 you have a measurement with dead time. That makes things a bit hard to figure out. A much better way to go is to feed a pair of 1 pps signals into the 5335 and measure their time difference. Unless they are quite close, you can go for a while with no ambiguity to the reading. The effective resolution increases linearly with the time length of the observation. There also are a number of very nice programs that will let you collect the data from the 5335 via GPIB.
Assuming your 5335 works like mine does it's got about a 1 ns resolution at 1 second. It'll give you 1 ppb at a 1 second gate and 1 ppt at a 1,000 second gate. By the time it gets to 1,000 seconds the internal counters have overflowed and the reading is a bit messed up.
Without some sort of accurate reference, there's really no way to know for sure what's going on with a GPSDO. One solution is to build two or three of them and watch them fight with each other. Another solution is to pick up a Hydrogen Maser. It's always a "what's in your wallet" sort of decision.
Bob

Post by Bob Stewart
Hi again Bob,
D'oh, I think I totally misunderstood your figures in my first response. The .16ppb is not the frequency accuracy of my GPSDO. It's the amount that I'm moving the OCXO during a 5 minute timeframe, which is something else entirely. Like I said I do not have a known good oscillator to compare to. However, I have a DDS oscillator I made some time ago, and it seems to be pretty stable if I let it be. So, what I've done is to hook the GPSDO to the clock input of my 5335A. I've then adjusted the DDS so that it reads near 10.000000 MHz, and watched it over a round-trip 5 minute period several times with a large enough gate that I get 8 decimal points on the counter. I don't see any relationship between the few milli-Hz movement the counter shows and the changes to the DAC. During several runs last night, I saw less than 30 mHz of movement, which, if true, would be 3E-9, or 3ppb, right? Or would that be +/- 1.5ppb?
Bob

________________________________
From: Bob Camp
To: Discussion of precise time and frequency measurement
Sent: Friday, August 16, 2013 10:47 AM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Ok, let's try some math and see if I can do it without blinking this time….
+/-4 Hz for 6 volts is 0.66 Hz / V
output is 10 MHz so 1 Hz is 0.1 ppm
your OCXO is running at 0.066 ppm / V
That's also 66 ppb / V
0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt
The UT+ has a sawtooth output that's about 45 ns
That's 45 ppb at one second
5 minutes is 300 seconds
so 45 / 300 = 0.15 ppb or 150 ppt
If it's the later clone version it might be about 1/2 of that.
Are you doing sawtooth correction?
Bob

I'm converting the code for the VE2ZAZ FLL to a PLL. I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies). The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value. I feel pretty confident with my code at this point. I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information. Could this oscillating phase correction be some sort of thermal oscillation? I've tried two separate 34310s and both act more or less the same. My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect. Is this good, bad, or indifferent for a GPSDO? I started this project not knowing what to expect, and I still don't. Experienced help, speculation, or even just kind words at this point would be appreciated! =) I don't have a known good/stable reference to

compare

Post by Bob Stewart
this

to.
Bob - AE6RV
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[Bob Camp]

Hi

If one of your sources can be offset (it's a DDS) then mixing the two is a good way to increase the resolution. Separate the two by a couple Hz and feed them into a double balanced mixer. Run the beat note into an amp and limiter. Output of the limiter drives the 5335. Resolution goes up by 10^7 if you are at 1 Hz. The gotcha is that you can't use all the resolution you gain due to noise.

The old style approach was to use a pair of OP-37 op amps, the first as a ~ 10X gain amp. The second as an inverting limiter. Simple R/C filters were used both as high pass and low pass on the signal ahead of the limiter. There is a simple / non-critical L/C filter between the mixer and the first amp. There are a number of other ways to do it.

A Mini-Circuits RPD-1 makes a pretty good mixer for a simple setup. The whole thing can be done on perf board including the +/- 18V three terminal regulators. If you have a bit of this and that in your junk box, cost should be < $50. That of course assumes you already have a lab supply to drive the regulators...

Bob

I thought I could just re-enter the numbers from the last survey I did. But either something is wrong or I'm missing something (betting on the latter). I can't seem to enable TRAIM. I thought I had it setup just like previously, but under WinCore12 it simply won't turn it on. So, I'm just letting it do a survey again, I guess. IOW, I dunno.
And I have a question about MATH functions on the 5335A, if you don't mind. (I'm an HP newbie.) Is there away to use Ratio A/B and have it give a greater resolution than a whole number, perhaps by having it average over multiple B ticks? I think I figured out how to enter an Offset, but I just get the ratio in single digits which doesn't really give me anything.
Bob

________________________________
Sent: Friday, August 16, 2013 7:26 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Also remember - you need to do a survey on the UT+ and put it into position hold / timing mode. If you don't you can add a bit more to your error budget.
Bob

I'll figure out something. I'm thinking of icing down my DDS device to put it at a known temperature so I can do drift comparisons. If not that, there'll be something else I can try.
On another note: I thought I had destroyed everything when I swapped the UT+ back into the GPSDO. Fortunately it was just that the UT+ needed to be reset, and I had destroyed a USB-TTL adapter and not my new little Adafruit. I'm going to have to figure out exactly what command sequence needs to be sent to the UT+ to get the comms working again and write a short program to do it. For some reason the WinCore12 program wasn't able to bring it up.
Bob

________________________________
Sent: Friday, August 16, 2013 6:14 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi,
To be able to test GPSDO's (and GPS in general) was one of the main reasons that I made a temp controlled chassis for an LPRO and gave it air pressure compensation. That was good for tau's of hundreds to tens of thousands of seconds, and even longer with drift compensation. Add in a clean-up oscillator if desired, and you have a pretty good reference.
Incidentally, I tested 2 FEI5680A's, a Temex LPFRS and 3 LPRO's in this type of setup, but only the LPRO's allowed the air pressure effects to be almost completely cancelled out. For some reason the others did not react to fluctuating air pressure as predictably.
Angus.
From: "Bob Camp"
To: "Discussion of precise time and frequency measurement"
Sent: August 16, 2013 7:45 PM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
With the 5335 you have a measurement with dead time. That makes things a bit hard to figure out. A much better way to go is to feed a pair of 1 pps signals into the 5335 and measure their time difference. Unless they are quite close, you can go for a while with no ambiguity to the reading. The effective resolution increases linearly with the time length of the observation. There also are a number of very nice programs that will let you collect the data from the 5335 via GPIB.
Assuming your 5335 works like mine does it's got about a 1 ns resolution at 1 second. It'll give you 1 ppb at a 1 second gate and 1 ppt at a 1,000 second gate. By the time it gets to 1,000 seconds the internal counters have overflowed and the reading is a bit messed up.
Without some sort of accurate reference, there's really no way to know for sure what's going on with a GPSDO. One solution is to build two or three of them and watch them fight with each other. Another solution is to pick up a Hydrogen Maser. It's always a "what's in your wallet" sort of decision.
Bob

Post by Bob Stewart
Hi again Bob,
D'oh, I think I totally misunderstood your figures in my first response. The .16ppb is not the frequency accuracy of my GPSDO. It's the amount that I'm moving the OCXO during a 5 minute timeframe, which is something else entirely. Like I said I do not have a known good oscillator to compare to. However, I have a DDS oscillator I made some time ago, and it seems to be pretty stable if I let it be. So, what I've done is to hook the GPSDO to the clock input of my 5335A. I've then adjusted the DDS so that it reads near 10.000000 MHz, and watched it over a round-trip 5 minute period several times with a large enough gate that I get 8 decimal points on the counter. I don't see any relationship between the few milli-Hz movement the counter shows and the changes to the DAC. During several runs last night, I saw less than 30 mHz of movement, which, if true, would be 3E-9, or 3ppb, right? Or would that be +/- 1.5ppb?
Bob

________________________________
From: Bob Camp
To: Discussion of precise time and frequency measurement
Sent: Friday, August 16, 2013 10:47 AM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Ok, let's try some math and see if I can do it without blinking this time….
+/-4 Hz for 6 volts is 0.66 Hz / V
output is 10 MHz so 1 Hz is 0.1 ppm
your OCXO is running at 0.066 ppm / V
That's also 66 ppb / V
0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt
The UT+ has a sawtooth output that's about 45 ns
That's 45 ppb at one second
5 minutes is 300 seconds
so 45 / 300 = 0.15 ppb or 150 ppt
If it's the later clone version it might be about 1/2 of that.
Are you doing sawtooth correction?
Bob

I'm converting the code for the VE2ZAZ FLL to a PLL. I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies). The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value. I feel pretty confident with my code at this point. I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information. Could this oscillating phase correction be some sort of thermal oscillation? I've tried two separate 34310s and both act more or less the same. My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect. Is this good, bad, or indifferent for a GPSDO? I started this project not knowing what to expect, and I still don't. Experienced help, speculation, or even just kind words at this point would be appreciated! =) I don't have a known good/stable reference to

compare

Post by Bob Stewart
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[Bob Camp]

Hi

If my numbers are correct, your DAC is moving the OCXO 0.016 ppb or 16 ppt. Your 5335 would read that as a last digit flip with a 100 second gate.

For really large numbers on the 5335 it's *much* more convenient to use the built in math functions. In this case subtract 10 MHz from the reading before it's displayed. Far easier on the eyes. For even more fun use the multiply function to make it come up in ppb. That makes it a lot easier on the brain….

If the OCXO is at 0.5 ppb stability p-p over 50 degrees C that would be 10 ppt per degree. (It could easily be 5X better than that - who knows…) If your room is moving one or two degrees then the OCXO could easily wander by 10 or 20 ppt.

Bob

Post by Bob Stewart
Hi again Bob,
D'oh, I think I totally misunderstood your figures in my first response. The .16ppb is not the frequency accuracy of my GPSDO. It's the amount that I'm moving the OCXO during a 5 minute timeframe, which is something else entirely. Like I said I do not have a known good oscillator to compare to. However, I have a DDS oscillator I made some time ago, and it seems to be pretty stable if I let it be. So, what I've done is to hook the GPSDO to the clock input of my 5335A. I've then adjusted the DDS so that it reads near 10.000000 MHz, and watched it over a round-trip 5 minute period several times with a large enough gate that I get 8 decimal points on the counter. I don't see any relationship between the few milli-Hz movement the counter shows and the changes to the DAC. During several runs last night, I saw less than 30 mHz of movement, which, if true, would be 3E-9, or 3ppb, right? Or would that be +/- 1.5ppb?
Bob

________________________________
Sent: Friday, August 16, 2013 10:47 AM
Subject: Re: [time-nuts] My GPSDO project: OCXO Thermal Oscillation?
Hi
Ok, let's try some math and see if I can do it without blinking this time….
+/-4 Hz for 6 volts is 0.66 Hz / V
output is 10 MHz so 1 Hz is 0.1 ppm
your OCXO is running at 0.066 ppm / V
That's also 66 ppb / V
0.02 V at 66 ppb / V is 0.0132 ppb or 13.2 ppt
The UT+ has a sawtooth output that's about 45 ns
That's 45 ppb at one second
5 minutes is 300 seconds
so 45 / 300 = 0.15 ppb or 150 ppt
If it's the later clone version it might be about 1/2 of that.
Are you doing sawtooth correction?
Bob

I'm converting the code for the VE2ZAZ FLL to a PLL. I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies). The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value. I feel pretty confident with my code at this point. I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information. Could this oscillating phase correction be some sort of thermal oscillation? I've tried two separate 34310s and both act more or less the same. My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect. Is this good, bad, or indifferent for a GPSDO? I started this project not knowing what to expect, and I still don't. Experienced help, speculation, or even just kind words at this point would be appreciated! =) I don't have a known good/stable reference to compare

this

to.
Bob - AE6RV
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[Volker Esper]

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[Bob Camp]

Hi

To answer your OCXO question:

The so called 34310-T is a double oven. It should be stable over some range (say 0 to 70 or -20 to 70) to about 0.1 to 0.5 ppb p-p. Trimble seems to like +12 on it so one would guess that +12 +/- 5% stable to +/- 0.5% should be fine. They seem to use it in open air / moving air.

Assuming you are inside that sort of temperature and voltage range, then no, it should not oscillate thermally. Anything can be broken and if it is you should see the oven current going nuts.

Bob

I'm converting the code for the VE2ZAZ FLL to a PLL. I'm seeing the phase correction change the EFC up and down about .02V to .03V over a period of 5 minutes or so (it varies). The full range on the OCXO is about +/- 4Hz varied by 0 to +6V, so at least this is a tiny value. I feel pretty confident with my code at this point. I'm using a Trimble 34310-T OCXO for which I've been able to find almost no information. Could this oscillating phase correction be some sort of thermal oscillation? I've tried two separate 34310s and both act more or less the same. My GPS device is normally a UT+, but I just now swapped in an "Adafruit Ultimate GPS Breakout" to the same effect. Is this good, bad, or indifferent for a GPSDO? I started this project not knowing what to expect, and I still don'

t. Experienced help, speculation, or even just kind words at this point would be appreciated! =) I don't have a known good/stable reference to compare this

to.
Bob - AE6RV
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