Allan variance by sine-wave fitting
I've been comparing the ADEV produced by the sine-wave fitter (discussed
last November) with that of a counter-based system. See the enclosed plot.
We ran the test in Leo Hollberg's lab at Stanford, using a 5071a Cesium
standard and my own 5065a Rubidium standard. Leo first measured the ADEV
using a Keysight 53230a counter with a 100 second gate time. We then
substituted the fitter for the counter and took 10,000 points at 20 second
intervals. The two systems produce the same ADEV all the way down to the
5x10(-14) level where (presumably) temperature and pressure variations make
the Rb wobble around a bit.
The revised paper has been published online at Rev. Sci. Instr.
Hi Ralph,
Nice test. Two comments.
-
Your 5065A is working really well; is it one of Corby's "super" ones? What sort of environmental controls did you have during the run, if any. How long had the 5065A been powered up before you ran the test?
-
Is there a reason you didn't or couldn't make simultaneous measurements using both counters? That would have allowed an interesting study of the residuals. Plots of phase, frequency, spectrum, and ADEV of the residuals provides insight into how well the two counters match. This would also probably remove the awkward divergence of your two ADEV plots past tau 1 hour.
/tvb
----- Original Message -----
From: "Ralph Devoe" rgdevoe@gmail.com
To: time-nuts@febo.com
Sent: Monday, February 12, 2018 1:52 PM
Subject: [time-nuts] Allan variance by sine-wave fitting
I've been comparing the ADEV produced by the sine-wave fitter (discussed
last November) with that of a counter-based system. See the enclosed plot.
We ran the test in Leo Hollberg's lab at Stanford, using a 5071a Cesium
standard and my own 5065a Rubidium standard. Leo first measured the ADEV
using a Keysight 53230a counter with a 100 second gate time. We then
substituted the fitter for the counter and took 10,000 points at 20 second
intervals. The two systems produce the same ADEV all the way down to the
5x10(-14) level where (presumably) temperature and pressure variations make
the Rb wobble around a bit.
The revised paper has been published online at Rev. Sci. Instr.
This note is a follow-up to Ralph Devoe's ADEV posting earlier this month.
It's a long story but last week I was in the Bay Area with a car full of batteries, BVA and cesium references, hp counters, and a TimePod. I was able to double check Ralph's Digilent-based ADEV device [1] and also to independently measure various frequency standards, including the actual 5065A and 5071A that he used in his experiment.
For the range of tau where we overlap, his ADEV measurements closely match my ADEV measurements. So that's very good news. His Digilent plot [2] and my TimePod / TimeLab plot are attached.
Note that his Digilent+Python setup isn't currently set up for continuous or short-tau measurement intervals -- plus I didn't have my isolation amplifiers -- so we didn't try a concurrent Digilent and TimePod measurement.
I'm sure more will come of his project over time and I hope to make additional measurements using a wider variety of stable / unstable sources, either down there in CA with another clock trip or up here in WA with a clone of his prototype. It would be nice to further validate this wave fitting technique, perhaps uncover and quantify subtle biases that depend on power law noise (or ADC resolution, or sample rate, or sample size, etc.), and also to explore environmental stability of the instrument.
I can tell Ralph put a lot of work into this project and I'm pleased he chose to share his results with time nuts. I mean, it's not every day that national lab or university level projects embrace our little community.
/tvb
[1] http://aip.scitation.org/doi/pdf/10.1063/1.5010140 (PDF)
[2] https://www.febo.com/pipermail/time-nuts/2018-February/108857.html
----- Original Message -----
From: "Ralph Devoe" rgdevoe@gmail.com
To: time-nuts@febo.com
Sent: Monday, February 12, 2018 1:52 PM
Subject: [time-nuts] Allan variance by sine-wave fitting
I've been comparing the ADEV produced by the sine-wave fitter (discussed
last November) with that of a counter-based system. See the enclosed plot.
We ran the test in Leo Hollberg's lab at Stanford, using a 5071a Cesium
standard and my own 5065a Rubidium standard. Leo first measured the ADEV
using a Keysight 53230a counter with a 100 second gate time. We then
substituted the fitter for the counter and took 10,000 points at 20 second
intervals. The two systems produce the same ADEV all the way down to the
5x10(-14) level where (presumably) temperature and pressure variations make
the Rb wobble around a bit.
The revised paper has been published online at Rev. Sci. Instr.
On Mon, 26 Feb 2018 02:43:04 -0800
"Tom Van Baak" tvb@LeapSecond.com wrote:
This note is a follow-up to Ralph Devoe's ADEV posting earlier this month.
It's a long story but last week I was in the Bay Area with a car full of
batteries, BVA and cesium references, hp counters, and a TimePod. I was able
to double check Ralph's Digilent-based ADEV device [1] and also to
independently measure various frequency standards, including the actual 5065A
and 5071A that he used in his experiment.
For the range of tau where we overlap, his ADEV measurements closely match my
ADEV measurements. So that's very good news. His Digilent plot [2] and my
TimePod / TimeLab plot are attached.
Nice. Thank you!
BTW: Do you know the cause of the oscillations in the 5065 vs BVA plot?
I'm sure more will come of his project over time and I hope to make
additional measurements using a wider variety of stable / unstable sources,
either down there in CA with another clock trip or up here in WA with a clone
of his prototype. It would be nice to further validate this wave fitting
technique, perhaps uncover and quantify subtle biases that depend on power
law noise (or ADC resolution, or sample rate, or sample size, etc.), and also
to explore environmental stability of the instrument.
For this, we would need a better understanding of what noise is
mathematically and how it is affected by various components in
the signal path. But our mathematical description is lacking
at best (we only can descirbe white and 1/f^2 noise properly).
Attila Kinali
--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
BTW: Do you know the cause of the oscillations in the 5065 vs BVA plot?
The ADEV wiggles aren't visible with normal tau 1 s measurements. But since the TimePod can go down to tau 1 ms, when I first measure a standard I like to run at that resolution so effects like this show up. Once that's done, 1 ms resolution is overkill.
In this case it appears to be power supply noise. Attached are the ADEV, PN, and TDEV plots.
The spur at 120 Hz is massive; there's also a bit at 240 Hz; almost nothing at 60 Hz. When integrated these cause the bumps you see in the ADEV plot. It's best seen as a bump at ~4 ms in the TDEV plot.
Note the cute little spur at 137 Hz. Not sure what causes the one at ~3630 Hz.
/tvb
Hi
One of the TimePods that I had access to in the past was particularly good
at telling you it was sitting on top of a power transformer. It didn’t matter a lot
which instrument the power transformer was in. For some weird reason it
was a good magnetometer at line frequencies. I never bothered to send it
back for analysis. Simply moving it onto the bench top (rather than stacked
on top of this or that) would take care of the issue.
As far as I could tell, it was just the one unit that had the issue. None of the
others in the fleet of TimePods seemed to behave this way. Given that they
normally are very good at rejecting all sorts of crud and ground loops, it was
somewhat odd to see.
Bob
On Feb 26, 2018, at 7:13 AM, Tom Van Baak tvb@LeapSecond.com wrote:
BTW: Do you know the cause of the oscillations in the 5065 vs BVA plot?
The ADEV wiggles aren't visible with normal tau 1 s measurements. But since the TimePod can go down to tau 1 ms, when I first measure a standard I like to run at that resolution so effects like this show up. Once that's done, 1 ms resolution is overkill.
In this case it appears to be power supply noise. Attached are the ADEV, PN, and TDEV plots.
The spur at 120 Hz is massive; there's also a bit at 240 Hz; almost nothing at 60 Hz. When integrated these cause the bumps you see in the ADEV plot. It's best seen as a bump at ~4 ms in the TDEV plot.
Note the cute little spur at 137 Hz. Not sure what causes the one at ~3630 Hz.
/tvb
<5065a-adev.png><5065a-pn.png><5065a-tdev.png>_______________________________________________
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at telling you it was sitting on top of a power transformer. It didn’t matter a lot
I did ten runs of various standards that were within a couple of meters of the bench; the TimePod did not move the entire time. Each standard had a different looking PN plot, so I'm pretty sure the 120 Hz spur we see is the 5065A itself, not something in the lab.
File http://leapsecond.com/tmp/2018b-Ralph-2-pn.png is attached.
Fun fact -- there's a wide spur at ~2 Hz on the 5065A phase noise plot. What do you think that is? On a hunch I opened the front panel and reset the blinking amber battery alarm lamp, and voila, that noise went away. Makes sense when you think of the power variations associated with a blinking incandescent lamp.
/tvb
----- Original Message -----
From: "Bob kb8tq" kb8tq@n1k.org
To: "Tom Van Baak" tvb@leapsecond.com; "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Monday, February 26, 2018 7:00 AM
Subject: Re: [time-nuts] Allan variance by sine-wave fitting
Hi
One of the TimePods that I had access to in the past was particularly good
at telling you it was sitting on top of a power transformer. It didn’t matter a lot
which instrument the power transformer was in. For some weird reason it
was a good magnetometer at line frequencies. I never bothered to send it
back for analysis. Simply moving it onto the bench top (rather than stacked
on top of this or that) would take care of the issue.
As far as I could tell, it was just the one unit that had the issue. None of the
others in the fleet of TimePods seemed to behave this way. Given that they
normally are very good at rejecting all sorts of crud and ground loops, it was
somewhat odd to see.
Bob
On Feb 26, 2018, at 7:13 AM, Tom Van Baak tvb@LeapSecond.com wrote:
BTW: Do you know the cause of the oscillations in the 5065 vs BVA plot?
The ADEV wiggles aren't visible with normal tau 1 s measurements. But since the TimePod can go down to tau 1 ms, when I first measure a standard I like to run at that resolution so effects like this show up. Once that's done, 1 ms resolution is overkill.
In this case it appears to be power supply noise. Attached are the ADEV, PN, and TDEV plots.
The spur at 120 Hz is massive; there's also a bit at 240 Hz; almost nothing at 60 Hz. When integrated these cause the bumps you see in the ADEV plot. It's best seen as a bump at ~4 ms in the TDEV plot.
Note the cute little spur at 137 Hz. Not sure what causes the one at ~3630 Hz.
/tvb
<5065a-adev.png><5065a-pn.png><5065a-tdev.png>
Am 26.02.2018 um 20:20 schrieb Tom Van Baak:
Fun fact -- there's a wide spur at ~2 Hz on the 5065A phase noise plot. What do you think that is? On a hunch I opened the front panel and reset the blinking amber battery alarm lamp, and voila, that noise went away. Makes sense when you think of the power variations associated with a blinking incandescent lamp.
There was a Tektronix sampler that had a few ps sampling jitter to the tune
of a blinking LED on the mainframe :-)
Cheers, Gerhard
Hi
Yet another reason to nuke the battery and the A2 board.
It is amazing just how small a signal can mess things up at the levels involved in
a good frequency standard. The old “when in doubt, throw it out” mantra may be
a good one to keep in mind relative to a lot of add on features…. how much does
a PIC-DIV pull compared to the 1 pps section of one of these old beasts (Cs or Rb)?
Lots to think about.
Bob
On Feb 26, 2018, at 2:20 PM, Tom Van Baak tvb@LeapSecond.com wrote:
at telling you it was sitting on top of a power transformer. It didn’t matter a lot
I did ten runs of various standards that were within a couple of meters of the bench; the TimePod did not move the entire time. Each standard had a different looking PN plot, so I'm pretty sure the 120 Hz spur we see is the 5065A itself, not something in the lab.
File http://leapsecond.com/tmp/2018b-Ralph-2-pn.png is attached.
Fun fact -- there's a wide spur at ~2 Hz on the 5065A phase noise plot. What do you think that is? On a hunch I opened the front panel and reset the blinking amber battery alarm lamp, and voila, that noise went away. Makes sense when you think of the power variations associated with a blinking incandescent lamp.
/tvb
----- Original Message -----
From: "Bob kb8tq" kb8tq@n1k.org
To: "Tom Van Baak" tvb@leapsecond.com; "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Monday, February 26, 2018 7:00 AM
Subject: Re: [time-nuts] Allan variance by sine-wave fitting
Hi
One of the TimePods that I had access to in the past was particularly good
at telling you it was sitting on top of a power transformer. It didn’t matter a lot
which instrument the power transformer was in. For some weird reason it
was a good magnetometer at line frequencies. I never bothered to send it
back for analysis. Simply moving it onto the bench top (rather than stacked
on top of this or that) would take care of the issue.
As far as I could tell, it was just the one unit that had the issue. None of the
others in the fleet of TimePods seemed to behave this way. Given that they
normally are very good at rejecting all sorts of crud and ground loops, it was
somewhat odd to see.
Bob
On Feb 26, 2018, at 7:13 AM, Tom Van Baak tvb@LeapSecond.com wrote:
BTW: Do you know the cause of the oscillations in the 5065 vs BVA plot?
The ADEV wiggles aren't visible with normal tau 1 s measurements. But since the TimePod can go down to tau 1 ms, when I first measure a standard I like to run at that resolution so effects like this show up. Once that's done, 1 ms resolution is overkill.
In this case it appears to be power supply noise. Attached are the ADEV, PN, and TDEV plots.
The spur at 120 Hz is massive; there's also a bit at 240 Hz; almost nothing at 60 Hz. When integrated these cause the bumps you see in the ADEV plot. It's best seen as a bump at ~4 ms in the TDEV plot.
Note the cute little spur at 137 Hz. Not sure what causes the one at ~3630 Hz.
/tvb
<5065a-adev.png><5065a-pn.png><5065a-tdev.png>
<2018b-Ralph-2-pn.png>_______________________________________________
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Yet another reason to nuke the battery and the A2 board.
Yes. Then again, the effect is very minor when you look at the PN and ADEV plots. It falls into the category of "look how sensitive a TimePod is" more than "look how bad a 5065A is". And remember it's just a warning lamp, with a toggle switch to reset the blink.
a PIC-DIV pull compared to the 1 pps section of one of these old beasts (Cs or Rb)?
Right, a PIC divider is much lower power, but if you're driving a 50R load that's still a lot of current. I suspect this is one reason why high-end standards use 10 or 20 us wide pulses and not 50% duty cycle square waves for their 1PPS outputs. Same power but 10 us is 50,000x less energy than 0.5 s. I've stopped using squares waves for 1PPS around here.
BTW, a trick for blinking LED's -- use two of them out of phase: one that the user sees on the front panel and one that is blacked out or hidden inside. A flip-flop (Q and /Q) or even a set of inverters is all you need. The current draw thus remains constant in spite of the blinking.
/tvb
----- Original Message -----
From: "Bob kb8tq" kb8tq@n1k.org
To: "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Monday, February 26, 2018 11:51 AM
Subject: Re: [time-nuts] Allan variance by sine-wave fitting
Hi
Yet another reason to nuke the battery and the A2 board.
It is amazing just how small a signal can mess things up at the levels involved in
a good frequency standard. The old “when in doubt, throw it out” mantra may be
a good one to keep in mind relative to a lot of add on features…. how much does
a PIC-DIV pull compared to the 1 pps section of one of these old beasts (Cs or Rb)?
Lots to think about.
Bob
On Feb 26, 2018, at 2:20 PM, Tom Van Baak tvb@LeapSecond.com wrote:
at telling you it was sitting on top of a power transformer. It didn’t matter a lot
I did ten runs of various standards that were within a couple of meters of the bench; the TimePod did not move the entire time. Each standard had a different looking PN plot, so I'm pretty sure the 120 Hz spur we see is the 5065A itself, not something in the lab.
File http://leapsecond.com/tmp/2018b-Ralph-2-pn.png is attached.
Fun fact -- there's a wide spur at ~2 Hz on the 5065A phase noise plot. What do you think that is? On a hunch I opened the front panel and reset the blinking amber battery alarm lamp, and voila, that noise went away. Makes sense when you think of the power variations associated with a blinking incandescent lamp.
/tvb
----- Original Message -----
From: "Bob kb8tq" kb8tq@n1k.org
To: "Tom Van Baak" tvb@leapsecond.com; "Discussion of precise time and frequency measurement" time-nuts@febo.com
Sent: Monday, February 26, 2018 7:00 AM
Subject: Re: [time-nuts] Allan variance by sine-wave fitting
Hi
One of the TimePods that I had access to in the past was particularly good
at telling you it was sitting on top of a power transformer. It didn’t matter a lot
which instrument the power transformer was in. For some weird reason it
was a good magnetometer at line frequencies. I never bothered to send it
back for analysis. Simply moving it onto the bench top (rather than stacked
on top of this or that) would take care of the issue.
As far as I could tell, it was just the one unit that had the issue. None of the
others in the fleet of TimePods seemed to behave this way. Given that they
normally are very good at rejecting all sorts of crud and ground loops, it was
somewhat odd to see.
Bob
On Feb 26, 2018, at 7:13 AM, Tom Van Baak tvb@LeapSecond.com wrote:
BTW: Do you know the cause of the oscillations in the 5065 vs BVA plot?
The ADEV wiggles aren't visible with normal tau 1 s measurements. But since the TimePod can go down to tau 1 ms, when I first measure a standard I like to run at that resolution so effects like this show up. Once that's done, 1 ms resolution is overkill.
In this case it appears to be power supply noise. Attached are the ADEV, PN, and TDEV plots.
The spur at 120 Hz is massive; there's also a bit at 240 Hz; almost nothing at 60 Hz. When integrated these cause the bumps you see in the ADEV plot. It's best seen as a bump at ~4 ms in the TDEV plot.
Note the cute little spur at 137 Hz. Not sure what causes the one at ~3630 Hz.
/tvb
<5065a-adev.png><5065a-pn.png><5065a-tdev.png>
<2018b-Ralph-2-pn.png>_______________________________________________
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