bg7tbl gpsdo master reference

[mojoe]

Thanks for the reply. I understand that the PPS is better after the survey, as that was the reason for doing it. I also know that it takes a while for an oscillator to settle. I'm hoping that someone who knows the intricacies of LH will respond, and enlighten us all.

[FPSychotic]

Hi, I'm trying to update the GPSDO version 2017 , without LCD, with a neo-m8t, I think it is soldered properly,I did 3 times ,it is recognised in the port com and u-center will connect, but it is mot showing any data or loading any config.
Had anyone this issue?
Does anyone knows other place to ask?

[Electro Fan]

Hi, I have an older (2018-06-05) BG7TBL GPSDO and it has been an excellent performer.  I use the GPSDO and a BG7TBL distribution amplifier to provide a 10 MHz ref input to various test equipment such as the freq generator and freq counter shown below along with an oscilloscope and a spectrum analyzer and a few other pieces of test equipment.

I'm interested in adding a new BG7TBL GPSDO that will handle 2 or more GNSSs concurrently (probably GPS and Galileo but others and more - up to 3 or 4 would be of interest).

If possible I'd like to have the multi GNSS unit with the LCD display.

Just checking to see what the latest date code anyone has for a BG7TBL GPDSO that supports multiple systems, and also what the latest u-blox concurrent GNSS timing module anyone has found inside (M8, M9, M10 or some variants of these)?

Also, if anyone has determined how much if any 10 MHz accuracy might be gained by configuring the GPSDO for one vs 2 vs 3 or possibly 4 systems that would be interesting to hear.

Thanks for any help with any of this.  EF

[Ringmodulator]

Hi Electro Fan,

it looks like the wafeform generator and the counter are synced to the same source, probably the gpsdo (and this is just a guess and might be wrong).

In this case the displayed results on the counter do not say anything about the quality/accuracy of the gpsdo.

I own two gpsdos, of which one is a bg7tbl which can use up to three gnss (M8T) and FA-2 /FA-3.

Tony Albus has a video on YT on accuracy vs multiple GNSS.
https://www.youtube.com/@TonyAlbus

He has multiple ones on gpsdos and I dont remember which one it was. You may find it with the search function.

Regards
Chris

[Electro Fan]

Hi Ringmodulator,

Thanks for your comments, I appreciate it.  I read a number of your earlier posts and they have always been helpful - Thx!

Your comments motivated me to run a few quick tests as shown in the attachments.

If you or anyone else would like to see some other tests let me know.

Part 1: with attachments

Edit Notes:

Image 1 - is with 30MHz signal from generator with GPSDO Ref input to Generator and Counter

Image 2 - is same thing but over longer time

Image 4 - shows 30 MHz signal from generator without Ext Lock (which can be seen in post 1002 above)

[Electro Fan]

Hi Ringmodulator,

Thanks for your comments, I appreciate it.  I read a number of your earlier posts and they have always been helpful - Thx!

Your comments motivated me to run a few quick tests as shown in the attachments.

If you or anyone else would like to see some other tests let me know.

Part 2: with attachments

[Electro Fan]

Ok Ringmodulator, you have made me move around from what was a comfy spot in the rabbit hole and now I am rethinking and retesting lots of stuff.

I happened to have in inventory a second BG7TBL GPSDO with the same date:  2018-06-05.

So I connected both with almost exactly the same cabling (except the BNC to SMA adapter for one channel) to the BG7TBL counter inputs - using just the counter's internal ref.

I ran GPSDO 2 over night so it accumulated more reads than GPSDO 1 (but GPSDO 1 was on over night and warmed up).

Results show pretty similar average readings to within ~0.17 Hz of 10 MHz (and to within ~0.003 Hz of each other on 10 MHz).

So, given the new rigor that your post prompted, I think all we can say is that these two BG7TBL GPSDO's are performing pretty similarly.  They both use the same model antenna with the same antenna cabling.  The antennas are next to each other (about 3cm apart) facing the sky (somewhat obscured by tree branches).  The signal strengths are not real strong - both GPSDO LCD indicators generally show only 1-2 bars due to the tree branches.  I attached the Sky View and SNR table below.

I also dug up an Oscilloquartz Star 4+ GPSDO that I will test as soon as I get a cable that will duplicate the cabling of the BG7TBL antennas but some preliminary testing shows the Star 4+ ref output is not so similar to the two BGTBL GPSDOs - but it might not have been fully warmed up.

I'd like to figure out what is the most accurate clock source but I'm not sure yet how to determine that - I'm open to any test configs you or others might suggest.

My current thinking is that while it's hard to know exactly how long a Hz should be, I might have to accept that close enough will have to be good enough; but even more so, I think I'd like that whatever the best Hz is, I'd like it to be the same across all my devices.  Kind of like maybe my ruler isn't perfect but at least I'll have a consistent unit of measurement when measuring, building, and testing things.

[Electro Fan]

https://www.livescience.com/space/the-sun/the-2024-summer-solstice-will-be-the-earliest-for-228-years-heres-why

wouldn’t want to be late for anything

[Electro Fan]

fwiw, I have the Oscilloquartz Star 4+ GPSDO running - providing both the input signal and the Ref in to the counter.

When compared to the BG7TBL doing the same thing, the Star 4+ holds it's own with pretty similar results. 

I've tried various combinations of tests (some posted here and above, and others not posted) and I can't quite figure out how to isolate what's what.  Seems like it should be simple but so far it hasn't become clear to me.   

I'm now of the opinion (just guess) that the Agilent generator by itself might possibly be accurate to within about 1-2 Hz on 10 MHz (even though the spec says approx +/- 1 ppm).

I think the BG7TBL counter is more accurate than the Agilent generator but that's also a guess.

I'm pretty sure that the 3 GPSDO's are the most reliable reference clocks, but again it's just a guess.

Comments, questions, and especially suggestions welcome.  Thx

---

https://en.wikipedia.org/wiki/Segal%27s_law

"From Wikipedia, the free encyclopedia

Segal's law is an adage that states:
A man with a watch knows what time it is. A man with two watches is never sure.[1]

At surface level, the adage emphasizes the consistency that arises when information comes from a single source and points out the potential pitfalls of having too much conflicting information. However, the underlying message is to question the apparent certainty of anyone who only has one source of information. The man with one watch has no way to identify error or uncertainty."

History
The saying was coined by the San Diego Union on September 20, 1930: "Confusion.—Retail jewelers assert that every man should carry two watches. But a man with one watch knows what time it is, and a man with two watches could never be sure." Later this was — mistakenly — attributed to Lee Segall of KIXL, then to be misquoted again by Arthur Bloch as "Segal's Law".[2]"

[Electro Fan]

Next...

Here is the Agilent generator using it's internal oscillator providing a 10 MHz signal to the counter with the counter taking Ref from the Star 4+ GPSDO. 

[MIS42N]

I don't know the design of the bg7tbl GPSDO, but most designs are phase locked to the GPS - i.e. on average the frequency will be exact within the limits of the GPS system. The GPSDO tries to minimise the phase difference between the local oscillator and what it thinks the GPS is telling it. However, what it thinks the GPS is telling it and the actual GPS time can differ slightly due to conditions between the satellites and the receiver.

What this means is the actual frequency of the GPSDO will wander between slightly high to slightly low due to changing conditions.

Comparing two GPSDOs of the same nominal frequency should yield nothing more than a phase difference between the two. If the phase difference is changing, then the instantaneous frequency of the two is different by the rate of change of the phase difference. It doesn't say if either is better than the other.

Two similar GPSDOs running in the same location from similar or (as some people do) the same antenna are going to react similarly to changes in conditions between the satellites and the receiver. Their frequency variations will track together so the phase difference won't show much.

One way of finding out which GPSDO is better is phase comparison with a local oscillator known to be stable. It doesn't need to be accurate. If the phase change over time (e.g per second) is constant, then the GPSDO is also stable. And knowing it is accurate in the long term confirms that it is also accurate in the short term (which is the desired outcome). This may be beyond the capability of a hobbyist as the phase change variation second to second can be small and not detected by many instruments.

Maybe the best the hobbyist can do is try to minimise external variability. A good quality OCXO in a stable environment (temperature, supply voltage, loading) controlled by a stable control voltage derived from a timing GPS receiver with a well placed antenna. Just how far one is prepared to refine the accuracy of a GPSDO is determined by what it is used for. If it is used for nothing more than the joy of getting ever better accuracy then the rabbit hole goes very deep. If the use is more practical, most GPSDOs are far more accurate than most hobbyists need.

[Electro Fan]

Here is the Agilent generator using it's internal oscillator providing a 10 MHz signal to the counter with the counter taking Ref from the BG7BL GPSDO 1.

[Electro Fan]

I don't know the design of the bg7tbl GPSDO, but most designs are phase locked to the GPS - i.e. on average the frequency will be exact within the limits of the GPS system. The GPSDO tries to minimise the phase difference between the local oscillator and what it thinks the GPS is telling it. However, what it thinks the GPS is telling it and the actual GPS time can differ slightly due to conditions between the satellites and the receiver.

What this means is the actual frequency of the GPSDO will wander between slightly high to slightly low due to changing conditions.

Comparing two GPSDOs of the same nominal frequency should yield nothing more than a phase difference between the two. If the phase difference is changing, then the instantaneous frequency of the two is different by the rate of change of the phase difference. It doesn't say if either is better than the other.

Two similar GPSDOs running in the same location from similar or (as some people do) the same antenna are going to react similarly to changes in conditions between the satellites and the receiver. Their frequency variations will track together so the phase difference won't show much.

One way of finding out which GPSDO is better is phase comparison with a local oscillator known to be stable. It doesn't need to be accurate. If the phase change over time (e.g per second) is constant, then the GPSDO is also stable. And knowing it is accurate in the long term confirms that it is also accurate in the short term (which is the desired outcome). This may be beyond the capability of a hobbyist as the phase change variation second to second can be small and not detected by many instruments.

Maybe the best the hobbyist can do is try to minimise external variability. A good quality OCXO in a stable environment (temperature, supply voltage, loading) controlled by a stable control voltage derived from a timing GPS receiver with a well placed antenna. Just how far one is prepared to refine the accuracy of a GPSDO is determined by what it is used for. If it is used for nothing more than the joy of getting ever better accuracy then the rabbit hole goes very deep. If the use is more practical, most GPSDOs are far more accurate than most hobbyists need.

Hi MIS42N,

Thanks for the info and explanations. 

In my case I'm not yet at the point of looking at phase change variation, I'm just trying to figure out how to set up what I have so I can reasonably know frequency, ideally to at least 1 Hz and preferably a couple or a few digits better.  Once I'm pretty sure I have some frequency dialed in I'd like to try to watch for phase drift. 

I'm thinking that any of the 3 GPSDO's I have are likely to be the most accurate clock providers I have - more so than the oscillators in my generators and counters, with the BG7TBL counter being more accurate than my two HP counters. 

So, that brings me full circle to Ringmodulator's post that had/has me thinking I'm maybe misconfiguring my setup by using the GPSDO to provide ref inputs to both my Agilent generator and the BGTBL counter, but after traveling around the rabbit hole I've gone full circle and I'm thinking that's my best setup.  Or maybe not??  Thx

[Electro Fan]

Back to square 1.  (Generator taking ref from BG7TBL GPSDO is providing 10 MHz signal to counter which is also taking ref from BG7TBL GPSDO.)

[Electro Fan]

Here is a ~$14 Amazon 10 MHz OCXO feeding Channel 1 on the BG7TBL counter with the counter taking the ref from the BG7TBL GPSDO 1 unit.  The Amazon OCXO can be very stable around 10,000,000.7 Hz for 10-40 or more 10 second gates and then it will be off on one gate count by about 10 Hz.  I think this might be something related to the power supply as it seems to happen when the air conditioning comes on.  My thought was that if it was stable I could use it for some benchmark testing but it might be mostly a decoration in the rabbit hole. 

Update - as I'm writing this the Amazon OCXO is now remaining stable to 100 1215 7164 10 second gates, so maybe it just needed longer to warm up and/or I need to keep the AC off.

As it warmed up with a 12V power supply the current draw dropped to ~193mA at ~150 gates and since then it's been running steady.  If it keeps going it might be a deal for $14, or maybe with the luck of the draw one of these units could do better?

One of my thoughts in all this is that more test equipment should have a 10 MHz ref input. 

[MIS42N]

Update - as I'm writing this the Amazon OCXO is now remaining stable to 100 150 200 1215 10 second gates, so maybe it just needed longer to warm up and/or I need to keep the AC off.

If you are relying on a local crystal oscillator it needs plenty of time to settle down to the sort of stability needed to compare with a GPSDO. I've watched them improve markedly over a week. I've played with a lot of OSC5A2B02 second hand and they are not really stable for days. The design of my GPSDO (a different thread) is different from all others in that I allow the OCXO to free run for a period then apply a fixed change to the control voltage. It is a way to determine if the oscillator is running OK as it is comparing but not adjusting. The results below are a log of a OSC5A2B02 that has been powered and not moved for months. Adjustments are made at 1024 second intervals (about 17 minutes). The absolute accuracy is unknown, but an upper estimate can be made by the size of the adjustments. The results indicate it is running better than 10MHz ± 1mHz (the largest change is 0.036 parts per billion or 0.36mHz).

 Time 012123 UTC. Ctrl 1.641806 0.026 ppb
 Time 013827 UTC. Ctrl 1.641828 0.017 ppb
 Time 015531 UTC. Ctrl 1.641834 0.005 ppb
 Time 021235 UTC. Ctrl 1.641847 0.010 ppb
 Time 022939 UTC. Ctrl 1.641836 -0.008 ppb
 Time 024643 UTC. Ctrl 1.641812 -0.020 ppb
 Time 030347 UTC. Ctrl 1.641800 -0.009 ppb
 Time 032051 UTC. Ctrl 1.641785 -0.012 ppb
 Time 033755 UTC. Ctrl 1.641804 0.015 ppb
 Time 035459 UTC. Ctrl 1.641805 0.001 ppb
 Time 041203 UTC. Ctrl 1.641804 0.001 ppb
 Time 042907 UTC. Ctrl 1.641833 0.023 ppb
 Time 044611 UTC. Ctrl 1.641826 -0.006 ppb
 Time 050315 UTC. Ctrl 1.641805 -0.017 ppb
 Time 052019 UTC. Ctrl 1.641792 -0.010 ppb
 Time 053723 UTC. Ctrl 1.641765 -0.021 ppb
 Time 055427 UTC. Ctrl 1.641760 -0.004 ppb
 Time 061131 UTC. Ctrl 1.641785 0.020 ppb
 Time 062835 UTC. Ctrl 1.641790 0.005 ppb
 Time 064539 UTC. Ctrl 1.641779 -0.009 ppb
 Time 070243 UTC. Ctrl 1.641762 -0.013 ppb
 Time 071947 UTC. Ctrl 1.641752 -0.008 ppb
 Time 073651 UTC. Ctrl 1.641797 0.036 ppb
 Time 075355 UTC. Ctrl 1.641769 -0.022 ppb

[Ringmodulator]

Hi  Electro Fan,

the topic of timing, accuracy and stability is a much wider and deeper field, as it looks from the ouside (the rabbithole of time nuttery).
And I am in no means an expert in this.

If you feed the couter input with its 10 MHz outut, you see the "hard limit" of the counter. Your results can never be better and it does not mean, that your results can be as good.
If you feed the counter with a signal form a generator and both are synced to the same soure, imho there is not much to gain from that.

If you want to evaluate an oscillater, you need another one which is at least a magnitude better.

The BG7TBL GPSDOs are rumored to have an inherent error in the range of about 2 mHz. It is not clear to me which models are affected.
I have a BG7TBL and a Samsung gpsdo and I have found this to be the case for my unit, but I have not done extended tests.

I suggest to check out the tinyPFA Phase Frequency Analyzer:
https://www.tinydevices.org/wiki/pmwiki.php?n=TinyPFA.Homepage

I got a used NanoVNA-H4, which can be flashed with the TinyPFA firmware.
I found this to be a very interesting low cost device to experiment with GPSDO, OCXO and counters.

The FA-2/FA-3 and the TinyPFA do work with the Timelab software.
This can keep you busy for quite some time

Regards
Chris

[Electro Fan]

Hi  Electro Fan,

the topic of timing, accuracy and stability is a much wider and deeper field, as it looks from the ouside (the rabbithole of time nuttery).
And I am in no means an expert in this.

If you feed the couter input with its 10 MHz outut, you see the "hard limit" of the counter. Your results can never be better and it does not mean, that your results can be as good.
If you feed the counter with a signal form a generator and both are synced to the same soure, imho there is not much to gain from that.

If you want to evaluate an oscillater, you need another one which is at least a magnitude better.

The BG7TBL GPSDOs are rumored to have an inherent error in the range of about 2 mHz. It is not clear to me which models are affected.
I have a BG7TBL and a Samsung gpsdo and I have found this to be the case for my unit, but I have not done extended tests.

I suggest to check out the tinyPFA Phase Frequency Analyzer:
https://www.tinydevices.org/wiki/pmwiki.php?n=TinyPFA.Homepage

I got a used NanoVNA-H4, which can be flashed with the TinyPFA firmware.
I found this to be a very interesting low cost device to experiment with GPSDO, OCXO and counters.

The FA-2/FA-3 and the TinyPFA do work with the Timelab software.
This can keep you busy for quite some time

Regards
Chris

Hi Ringmodulator, 

So, if a person had one of these:

https://www2.randl.com/index.php?main_page=product_info&cPath=16_16990&products_id=75961

Theoretically it would enable such a person to determine which of his devices (GPSDOs, generators, counters, etc.) was the most accurate with respect to frequency measurement?  (In other words, you think the TinyPFA is more accurate than a BG7TBL GPSDO and the FA-2?)  Or the TinyPFA would just provide more data (regarding phase relationships, etc.) for the rabbit hole?    Thx

Edit:  It looks like the answer is the TinyPFA isn't going to do much to discern frequency accuracy....
"ATTENTION: The tinyPFA does not contain an internal high stability reference. It will only perform a high accuracy phase difference measurement between two input clocks."

PS, Also, just to confirm, you think a BG7TBL GPSDO might be accurate to ~2 mHz? 

PSS, "If you feed the couter input with its 10 MHz outut, you see the "hard limit" of the counter. Your results can never be better and it does not mean, that your results can be as good."
- These are fascinating ideas.  
Thx again!

[Electro Fan]

Ringmodulator,

Here is the BG7TBL FA-2 Counter with the internal Ref output feeding the Channel 1 input.

"If you feed the couter input with its 10 MHz outut, you see the "hard limit" of the counter. Your results can never be better and it does not mean, that your results can be as good."

- if I understood this^ correctly, it means that the hard limit of this particular FA-2 is ~0.000,015,6 Hz (or given the Min and Max shown for the Pk-Pk variation, the unit could be approximately +/- 8 or 9 micro Hz (on the hard limit).  To your full point, it can never be better, and it does not mean that it as good as this - but it is a datapoint.  Yes?  If so, it seems plausible that the FA-2 can do better than 1 mHz, and likewise I'm pretty sure the BG7TBL GPSDO does better than 1 mHz (just my guess).  If this happened to be correct, we'd just be down to whether they are truly in sync including not only frequency but also phase.  Assuming they might be close but not identical on frequency, why would we potentially care about some amount of phase offset?  It seems like we would only care about phase offset if we were within some specified amount of frequency, ie to some Hz or some fraction of a Hz.... yes/no?  Thanks

[MIS42N]

If this happened to be correct, we'd just be down to whether they are truly in sync including not only frequency but also phase.  Assuming they might be close but not identical on frequency, why would we potentially care about some amount of phase offset?  It seems like we would only care about phase offset if we were within some specified amount of frequency, ie to some Hz or some fraction of a Hz.... yes/no?  Thanks

When two sources identical in frequency are compared, there is a constant phase offset (which may be zero, in which case they are in sync). If they are not identical in frequency, then the phase offset changes at the rate of the difference in frequency. If the two frequencies are wide apart, say a difference of 100Hz, then general terminology sees the difference as a beat frequency of 100Hz or a heterodyne. If the two frequencies are within a few Hz then the terminology talks about change of phase differences (in radians or degrees). For instance, comparing 10MHz with 10,000,000.1Hz the phase changes 1/10th of a circle or by 36 degrees a second. There's no difference between the fundamentals of the two examples, just the terminology changes.

So when comparing two close frequencies, it is more practical to measure the change in phase offset over some period than by counting cycles. For example if the difference is 10µHz then it will take 100,000 seconds for one signal to have one more cycle than the other. The period of a 10MHz signal is 100ns (nanoseconds) and a 9,999,999.99999Hz signal is 100.0000000001ns. So the difference between say the zero crossing of each signal is changing by 0.0000000001ns per cycle (a ridiculously small amount of time). But over a 1 second period the difference is .001ns - 1ps (one picosecond). This is measurable with a nanoVNA configured as a Phase Frequency Analyzer.

So phase offset changes are of importance when comparing two close frequencies. From the specification of the BG7TBL FA-2 Counter it would appear it uses phase change to measure frequency as it claims a resolution of 0.0001Hz@10MHz with a 1s gate. However, this says nothing about its accuracy. That is determined by whatever reference signal it is using.

Does that make sense?

[Electro Fan]

If this happened to be correct, we'd just be down to whether they are truly in sync including not only frequency but also phase.  Assuming they might be close but not identical on frequency, why would we potentially care about some amount of phase offset?  It seems like we would only care about phase offset if we were within some specified amount of frequency, ie to some Hz or some fraction of a Hz.... yes/no?  Thanks

When two sources identical in frequency are compared, there is a constant phase offset (which may be zero, in which case they are in sync). If they are not identical in frequency, then the phase offset changes at the rate of the difference in frequency. If the two frequencies are wide apart, say a difference of 100Hz, then general terminology sees the difference as a beat frequency of 100Hz or a heterodyne. If the two frequencies are within a few Hz then the terminology talks about change of phase differences (in radians or degrees). For instance, comparing 10MHz with 10,000,000.1Hz the phase changes 1/10th of a circle or by 36 degrees a second. There's no difference between the fundamentals of the two examples, just the terminology changes.

So when comparing two close frequencies, it is more practical to measure the change in phase offset over some period than by counting cycles. For example if the difference is 10µHz then it will take 100,000 seconds for one signal to have one more cycle than the other. The period of a 10MHz signal is 100ns (nanoseconds) and a 9,999,999.99999Hz signal is 100.0000000001ns. So the difference between say the zero crossing of each signal is changing by 0.0000000001ns per cycle (a ridiculously small amount of time). But over a 1 second period the difference is .001ns - 1ps (one picosecond). This is measurable with a nanoVNA configured as a Phase Frequency Analyzer.

So phase offset changes are of importance when comparing two close frequencies. From the specification of the BG7TBL FA-2 Counter it would appear it uses phase change to measure frequency as it claims a resolution of 0.0001Hz@10MHz with a 1s gate. However, this says nothing about its accuracy. That is determined by whatever reference signal it is using.

Does that make sense?

Thanks for all the info, it makes sense, mostly.  The only thing I'm wrestling with is why we would care much about phase offset if two signals are more than 1 Hz apart (other than possibly to observe drift such as jitter)?  I can see the value in examining phase offset if two signals are less than 1 Hz apart.  Thx again.

[Electro Fan]

If this happened to be correct, we'd just be down to whether they are truly in sync including not only frequency but also phase.  Assuming they might be close but not identical on frequency, why would we potentially care about some amount of phase offset?  It seems like we would only care about phase offset if we were within some specified amount of frequency, ie to some Hz or some fraction of a Hz.... yes/no?  Thanks

When two sources identical in frequency are compared, there is a constant phase offset (which may be zero, in which case they are in sync). If they are not identical in frequency, then the phase offset changes at the rate of the difference in frequency. If the two frequencies are wide apart, say a difference of 100Hz, then general terminology sees the difference as a beat frequency of 100Hz or a heterodyne. If the two frequencies are within a few Hz then the terminology talks about change of phase differences (in radians or degrees). For instance, comparing 10MHz with 10,000,000.1Hz the phase changes 1/10th of a circle or by 36 degrees a second. There's no difference between the fundamentals of the two examples, just the terminology changes.

So when comparing two close frequencies, it is more practical to measure the change in phase offset over some period than by counting cycles. For example if the difference is 10µHz then it will take 100,000 seconds for one signal to have one more cycle than the other. The period of a 10MHz signal is 100ns (nanoseconds) and a 9,999,999.99999Hz signal is 100.0000000001ns. So the difference between say the zero crossing of each signal is changing by 0.0000000001ns per cycle (a ridiculously small amount of time). But over a 1 second period the difference is .001ns - 1ps (one picosecond). This is measurable with a nanoVNA configured as a Phase Frequency Analyzer.

So phase offset changes are of importance when comparing two close frequencies. From the specification of the BG7TBL FA-2 Counter it would appear it uses phase change to measure frequency as it claims a resolution of 0.0001Hz@10MHz with a 1s gate. However, this says nothing about its accuracy. That is determined by whatever reference signal it is using.

Does that make sense?

Thanks for all the info, it makes sense, mostly.  The only thing I'm wrestling with is why we would care much about phase offset if two signals are more than 1 Hz apart (other than possibly to observe drift such as jitter)?  I can see the value in examining phase offset if two signals are less than 1 Hz apart.  Thx again.

Hi MIS42N and Ringmodulator,

I found the info below.  It's all helpful but the first link* especially answers my question(s) about how phase can be used to tune more than just within one Hz.  This is a very cool technique using a very cool device.  Looks like next step is to use a tinyPFA and TimeLab to try to do some ADEV measurements.

Thanks again for the guidance.

---

For anyone wanting to find a door deeper into the rabbit hole, here are some breadcrumbs

*









https://www.tinydevices.org/wiki/pmwiki.php?n=TinyPFA.Homepage

https://www.miles.io/timelab/beta.htm