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C

CubeCentral

Wed, Nov 15, 2017 4:12 PM

Greetings, time-nuts!

After reading [ http://www.leapsecond.com/pages/adev/adev-why.htm ] I felt
that I better understood how an Allan Deviation is calculated and endeavored
to try an experiment. It should be noted that I have a hobbyist-level
understanding of the concepts described and tools used below. If my
thinking or test methodology is incorrect, please let me know so that I
might learn something.

A GPSDO with a 10MHz output was run into the EXT TIME BASE input on the back
of an HP5335A.
Then, the TIME BASE OUT on the back was run to the A input on the front of
the HP5335A.
My intention was to characterize the performance of the HP5335A counter
itself so that I might understand better future plots involving other GPSDO
and the counter's internal clock (which was bypassed for this test).

The settings of the HP5335A were as follows:
Gate Mode: Normal
Cycle: Normal

A Input ------------------------------
Trigger Adjust: Full left to 'Preset' detent
Z select = in = 50ohm
x10 ATTN = in = x10 ATTN (should have been out/off?)
Slope = out = up
AC = in = AC coupled
COMA = out = Not ComA
AutoTrig = out = Not Auto Tiggered (should have been in/on?)

(Tangentially, if someone has a good 'primer' or how-to resource detailing
Universal Counter operation, showing when/why/how to set the knobs in
certain situations it would be welcome!)

I then set the Time Lab V1.29 software to repeatedly acquire data for 12
hours, starting the next test as soon as I could. This means that,
normally, a test was run during the day for 12 hours, and then overnight for
12 hours.

The results are shown here: [ https://i.imgur.com/0sMVMfk.png ] The
associated .TIM files are available upon request.

So, now we get to the heart of the matter and the questions this test and
results have raised.
I am trying to understand what the data is telling me about the test, and
therefore the character of the counter.

Why are the plots a straight line from ~0.25s until ~100s?
Why, after falling at the start, do the plots all seem to go back up
from ~100s to ~1000s?
What do the "peaks" mean, after the plot has fallen and begin to rise
again?
Why is the period from ~1000s to ~10000s so chaotic?
The pattern "Fall to a minimum point, then rise to a peak, then fall
again" seems to be prevalent. What does that indicate?
Why does that pattern in question (5) seem to repeat sometimes? What is
that showing me?

And finally, some general questions about looking at these plots.
a) Would a "perfect" plot be a straight line falling from left to right?
(Meaning a hypothetical "ideal" source with perfect timing?)
b) Is there some example showing plots from two different sources that then
describes why one source is better than the other (based upon the ADEV
plot)?
c) I believe that if I understood the math better, these types of plots
would be more telling. Without having to dive back into my college Calculus
or Statistics books, is there a good resource for me to be able to
understand this better?

Lastly, thank you for your patience and for keeping this brain-trust alive.
I am quite grateful for all the time and energy members pour into this list.
The archives have been a good source of learning material.

-Randal (at CubeCentral Labs...)

Greetings, time-nuts! After reading [ http://www.leapsecond.com/pages/adev/adev-why.htm ] I felt that I better understood how an Allan Deviation is calculated and endeavored to try an experiment. It should be noted that I have a hobbyist-level understanding of the concepts described and tools used below. If my thinking or test methodology is incorrect, please let me know so that I might learn something. A GPSDO with a 10MHz output was run into the EXT TIME BASE input on the back of an HP5335A. Then, the TIME BASE OUT on the back was run to the A input on the front of the HP5335A. My intention was to characterize the performance of the HP5335A counter itself so that I might understand better future plots involving other GPSDO and the counter's internal clock (which was bypassed for this test). The settings of the HP5335A were as follows: Gate Mode: Normal Cycle: Normal A Input ------------------------------ Trigger Adjust: Full left to 'Preset' detent Z select = in = 50ohm x10 ATTN = in = x10 ATTN (should have been out/off?) Slope = out = up AC = in = AC coupled COMA = out = Not ComA AutoTrig = out = Not Auto Tiggered (should have been in/on?) (Tangentially, if someone has a good 'primer' or how-to resource detailing Universal Counter operation, showing when/why/how to set the knobs in certain situations it would be welcome!) I then set the Time Lab V1.29 software to repeatedly acquire data for 12 hours, starting the next test as soon as I could. This means that, normally, a test was run during the day for 12 hours, and then overnight for 12 hours. The results are shown here: [ https://i.imgur.com/0sMVMfk.png ] The associated .TIM files are available upon request. So, now we get to the heart of the matter and the questions this test and results have raised. I am trying to understand what the data is telling me about the test, and therefore the character of the counter. 1) Why are the plots a straight line from ~0.25s until ~100s? 2) Why, after falling at the start, do the plots all seem to go back up from ~100s to ~1000s? 3) What do the "peaks" mean, after the plot has fallen and begin to rise again? 4) Why is the period from ~1000s to ~10000s so chaotic? 5) The pattern "Fall to a minimum point, then rise to a peak, then fall again" seems to be prevalent. What does that indicate? 6) Why does that pattern in question (5) seem to repeat sometimes? What is that showing me? And finally, some general questions about looking at these plots. a) Would a "perfect" plot be a straight line falling from left to right? (Meaning a hypothetical "ideal" source with perfect timing?) b) Is there some example showing plots from two different sources that then describes why one source is better than the other (based upon the ADEV plot)? c) I believe that if I understood the math better, these types of plots would be more telling. Without having to dive back into my college Calculus or Statistics books, is there a good resource for me to be able to understand this better? Lastly, thank you for your patience and for keeping this brain-trust alive. I am quite grateful for all the time and energy members pour into this list. The archives have been a good source of learning material. -Randal (at CubeCentral Labs...)

AK

Attila Kinali

Wed, Nov 15, 2017 11:46 PM

Hi,

There are other, more qualified people who should answer your questions,
but until they get around to it, let me give you some pointers to read
up upon.

First of all, you probably want to read [1] and [2]. Especially the
latter does explain the effects of the different noise types and
how they look like in the *DEV plots quite nicely.

On Wed, 15 Nov 2017 09:12:22 -0700
"CubeCentral" cubecentral@gmail.com wrote:

I then set the Time Lab V1.29 software to repeatedly acquire data for 12
hours, starting the next test as soon as I could. This means that,
normally, a test was run during the day for 12 hours, and then overnight for
12 hours.

The results are shown here: [ https://i.imgur.com/0sMVMfk.png ] The
associated .TIM files are available upon request.

For this kind of test, I would rather use TDEV, as it shows more details
especially at longer taus, but if you are specifically looking for
frequency stability measures, ADEV (or MDEV) should be fine.

You should also switch on the error bars. Especially if you are looking
at the longer taus, close to your measurement length.

Why are the plots a straight line from ~0.25s until ~100s?

Because they are dominated by white phase noise and flicker phase
noise which falls with 1/tau. The start point on the left side
is limited by your measurement precision, ie minimum resolution
of the instrument and its (white) noise.

Why, after falling at the start, do the plots all seem to go back up
from ~100s to ~1000s?

Because other noise types (white frequency, flicker frequency,...) become
dominant. What you see there is basically the instability of the measurement
electronics, the change in delays within the instrument due to temperature,
humidity, aging and other effects, trigger point changes, etc

What do the "peaks" mean, after the plot has fallen and begin to rise
again?

They are probably statistically insignificant, but it's impossible
to tell without the error bars. What wavy *DEV usually mean is,
that you have some periodic disturbance (A/C unit cycling, diurnal temperature
change, people walking in at specific times, train passing by on track nearby).

It's also a good idea to look at the phase plot or frequency plot
to see whether there are any deterministic effects that you can see.

Why is the period from ~1000s to ~10000s so chaotic?

Statistical instability. You are measuring for 12h, that's 43200 seconds.
So at a tau of 10k, you only have roughly 4 samples. You cannot do any
valid statistics with that.

The pattern "Fall to a minimum point, then rise to a peak, then fall
again" seems to be prevalent. What does that indicate?

Ideally, it should go down first (WPM, FPM), reach a minimum (WFM)
then go up again (FFM,...). But with such a short run it will not
be that way (statistical uncertainty). But then, very few plots
are really that way, because at the longer tau, the effects that
affect the measurement tend to be less and less gaus distributed
and you start to see patterns.

Why does that pattern in question (5) seem to repeat sometimes? What is
that showing me?

The repetition is a prime characteristic of a periodic disturbance.
But in this case it's more likely that it's just the bad statistics
tricking you into thinking you see a pattern where there is none
(at least none of statistical significance).

And finally, some general questions about looking at these plots.
a) Would a "perfect" plot be a straight line falling from left to right?
(Meaning a hypothetical "ideal" source with perfect timing?)

Yes. If you had only white and flicker phase noise. But this is
quite hard to achieve with frequency counters that have dead time
between measurements.

b) Is there some example showing plots from two different sources that then
describes why one source is better than the other (based upon the ADEV
plot)?

Lower is better... but where it should be lower depends on your
target application.

c) I believe that if I understood the math better, these types of plots
would be more telling. Without having to dive back into my college Calculus
or Statistics books, is there a good resource for me to be able to
understand this better?

The two documents I listed below should get you started.
The problem is, if you really want to understand what's going
on you will need to understand what the different noise types
are, how they behave mathematically and that's where things
get... weird. If you go that road, you will soon learn that
your college calculus will only be a very rough guide, like a
1:25'0000 map while trying to navigate a city. While white
phase noise is relatively easy to understand with Probability 101,
the higher order noises are not.

I am currently trying to put a small document together of what
I've learned about noise, but it's increadibly hard as the math
is quite often beyond me. Not to mention the knowledge is very
fragmented over the fields of mathematics (statistics/probability,
fractals, stochastic calculus, fractional calculus, ...), physics
(solid state physics, fluid dynamics, ....) and engineering...
and each of these (sub-)fields using a different nomenclature
and different notation.

		Attila Kinali

[1] "Characterization of Clocks and Oscillators", NIST Technical Note 1337,
by Sulivan, Allan, Howe, Walls, 1990
http://tf.nist.gov/general/pdf/868.pdf

[2] "Handbook of Frequency Stability Analysis", NIST Special Publication 1065,
by Riley 2008
http://tf.nist.gov/timefreq/general/pdf/2220.pdf

PS: It's Allan Deviation, not Allen.

You know, the very powerful and the very stupid have one thing in common.
They don't alters their views to fit the facts, they alter the facts to
fit the views, which can be uncomfortable if you happen to be one of the
facts that needs altering. -- The Doctor

Hi, There are other, more qualified people who should answer your questions, but until they get around to it, let me give you some pointers to read up upon. First of all, you probably want to read [1] and [2]. Especially the latter does explain the effects of the different noise types and how they look like in the *DEV plots quite nicely. On Wed, 15 Nov 2017 09:12:22 -0700 "CubeCentral" <cubecentral@gmail.com> wrote: > I then set the Time Lab V1.29 software to repeatedly acquire data for 12 > hours, starting the next test as soon as I could. This means that, > normally, a test was run during the day for 12 hours, and then overnight for > 12 hours. > The results are shown here: [ https://i.imgur.com/0sMVMfk.png ] The > associated .TIM files are available upon request. For this kind of test, I would rather use TDEV, as it shows more details especially at longer taus, but if you are specifically looking for frequency stability measures, ADEV (or MDEV) should be fine. You should also switch on the error bars. Especially if you are looking at the longer taus, close to your measurement length. > 1) Why are the plots a straight line from ~0.25s until ~100s? Because they are dominated by white phase noise and flicker phase noise which falls with 1/tau. The start point on the left side is limited by your measurement precision, ie minimum resolution of the instrument and its (white) noise. > 2) Why, after falling at the start, do the plots all seem to go back up > from ~100s to ~1000s? Because other noise types (white frequency, flicker frequency,...) become dominant. What you see there is basically the instability of the measurement electronics, the change in delays within the instrument due to temperature, humidity, aging and other effects, trigger point changes, etc > 3) What do the "peaks" mean, after the plot has fallen and begin to rise > again? They are probably statistically insignificant, but it's impossible to tell without the error bars. What wavy *DEV usually mean is, that you have some periodic disturbance (A/C unit cycling, diurnal temperature change, people walking in at specific times, train passing by on track nearby). It's also a good idea to look at the phase plot or frequency plot to see whether there are any deterministic effects that you can see. > 4) Why is the period from ~1000s to ~10000s so chaotic? Statistical instability. You are measuring for 12h, that's 43200 seconds. So at a tau of 10k, you only have roughly 4 samples. You cannot do any valid statistics with that. > 5) The pattern "Fall to a minimum point, then rise to a peak, then fall > again" seems to be prevalent. What does that indicate? Ideally, it should go down first (WPM, FPM), reach a minimum (WFM) then go up again (FFM,...). But with such a short run it will not be that way (statistical uncertainty). But then, very few plots are really that way, because at the longer tau, the effects that affect the measurement tend to be less and less gaus distributed and you start to see patterns. > 6) Why does that pattern in question (5) seem to repeat sometimes? What is > that showing me? The repetition is a prime characteristic of a periodic disturbance. But in this case it's more likely that it's just the bad statistics tricking you into thinking you see a pattern where there is none (at least none of statistical significance). > And finally, some general questions about looking at these plots. > a) Would a "perfect" plot be a straight line falling from left to right? > (Meaning a hypothetical "ideal" source with perfect timing?) Yes. If you had only white and flicker phase noise. But this is quite hard to achieve with frequency counters that have dead time between measurements. > b) Is there some example showing plots from two different sources that then > describes why one source is better than the other (based upon the ADEV > plot)? Lower is better... but where it should be lower depends on your target application. > c) I believe that if I understood the math better, these types of plots > would be more telling. Without having to dive back into my college Calculus > or Statistics books, is there a good resource for me to be able to > understand this better? The two documents I listed below should get you started. The problem is, if you really want to understand what's going on you will need to understand what the different noise types are, how they behave mathematically and that's where things get... weird. If you go that road, you will soon learn that your college calculus will only be a very rough guide, like a 1:25'0000 map while trying to navigate a city. While white phase noise is relatively easy to understand with Probability 101, the higher order noises are not. I am currently trying to put a small document together of what I've learned about noise, but it's increadibly hard as the math is quite often beyond me. Not to mention the knowledge is very fragmented over the fields of mathematics (statistics/probability, fractals, stochastic calculus, fractional calculus, ...), physics (solid state physics, fluid dynamics, ....) and engineering... and each of these (sub-)fields using a different nomenclature and different notation. Attila Kinali [1] "Characterization of Clocks and Oscillators", NIST Technical Note 1337, by Sulivan, Allan, Howe, Walls, 1990 http://tf.nist.gov/general/pdf/868.pdf [2] "Handbook of Frequency Stability Analysis", NIST Special Publication 1065, by Riley 2008 http://tf.nist.gov/timefreq/general/pdf/2220.pdf PS: It's Allan Deviation, not Allen. -- You know, the very powerful and the very stupid have one thing in common. They don't alters their views to fit the facts, they alter the facts to fit the views, which can be uncomfortable if you happen to be one of the facts that needs altering. -- The Doctor

MG

Mike Garvey

Thu, Nov 16, 2017 2:59 AM

Could you post some phase plots? The data you show is not 1/tau and very likely not white phase noise.
Mike

-----Original Message-----
From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of CubeCentral
Sent: Wednesday, November 15, 2017 11:12
To: time-nuts@febo.com
Subject: [time-nuts] Interpreting and Understanding Allen Deviation Results

Greetings, time-nuts!

After reading [ http://www.leapsecond.com/pages/adev/adev-why.htm ] I felt that I better understood how an Allan Deviation is calculated and endeavored to try an experiment. It should be noted that I have a hobbyist-level understanding of the concepts described and tools used below. If my thinking or test methodology is incorrect, please let me know so that I might learn something.

A GPSDO with a 10MHz output was run into the EXT TIME BASE input on the back of an HP5335A.
Then, the TIME BASE OUT on the back was run to the A input on the front of the HP5335A.
My intention was to characterize the performance of the HP5335A counter itself so that I might understand better future plots involving other GPSDO and the counter's internal clock (which was bypassed for this test).

The settings of the HP5335A were as follows:
Gate Mode: Normal
Cycle: Normal

A Input ------------------------------
Trigger Adjust: Full left to 'Preset' detent
Z select = in = 50ohm
x10 ATTN = in = x10 ATTN (should have been out/off?)
Slope = out = up
AC = in = AC coupled
COMA = out = Not ComA
AutoTrig = out = Not Auto Tiggered (should have been in/on?)

(Tangentially, if someone has a good 'primer' or how-to resource detailing Universal Counter operation, showing when/why/how to set the knobs in certain situations it would be welcome!)

I then set the Time Lab V1.29 software to repeatedly acquire data for 12 hours, starting the next test as soon as I could. This means that, normally, a test was run during the day for 12 hours, and then overnight for
12 hours.

The results are shown here: [ https://i.imgur.com/0sMVMfk.png ] The associated .TIM files are available upon request.

So, now we get to the heart of the matter and the questions this test and results have raised.
I am trying to understand what the data is telling me about the test, and therefore the character of the counter.

Why are the plots a straight line from ~0.25s until ~100s?
Why, after falling at the start, do the plots all seem to go back up from ~100s to ~1000s?
What do the "peaks" mean, after the plot has fallen and begin to rise again?
Why is the period from ~1000s to ~10000s so chaotic?
The pattern "Fall to a minimum point, then rise to a peak, then fall again" seems to be prevalent. What does that indicate?
Why does that pattern in question (5) seem to repeat sometimes? What is that showing me?

And finally, some general questions about looking at these plots.
a) Would a "perfect" plot be a straight line falling from left to right?
(Meaning a hypothetical "ideal" source with perfect timing?)
b) Is there some example showing plots from two different sources that then describes why one source is better than the other (based upon the ADEV plot)?
c) I believe that if I understood the math better, these types of plots would be more telling. Without having to dive back into my college Calculus or Statistics books, is there a good resource for me to be able to understand this better?

Lastly, thank you for your patience and for keeping this brain-trust alive.
I am quite grateful for all the time and energy members pour into this list.
The archives have been a good source of learning material.

-Randal (at CubeCentral Labs...)

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

Could you post some phase plots? The data you show is not 1/tau and very likely not white phase noise. Mike -----Original Message----- From: time-nuts [mailto:time-nuts-bounces@febo.com] On Behalf Of CubeCentral Sent: Wednesday, November 15, 2017 11:12 To: time-nuts@febo.com Subject: [time-nuts] Interpreting and Understanding Allen Deviation Results Greetings, time-nuts! After reading [ http://www.leapsecond.com/pages/adev/adev-why.htm ] I felt that I better understood how an Allan Deviation is calculated and endeavored to try an experiment. It should be noted that I have a hobbyist-level understanding of the concepts described and tools used below. If my thinking or test methodology is incorrect, please let me know so that I might learn something. A GPSDO with a 10MHz output was run into the EXT TIME BASE input on the back of an HP5335A. Then, the TIME BASE OUT on the back was run to the A input on the front of the HP5335A. My intention was to characterize the performance of the HP5335A counter itself so that I might understand better future plots involving other GPSDO and the counter's internal clock (which was bypassed for this test). The settings of the HP5335A were as follows: Gate Mode: Normal Cycle: Normal A Input ------------------------------ Trigger Adjust: Full left to 'Preset' detent Z select = in = 50ohm x10 ATTN = in = x10 ATTN (should have been out/off?) Slope = out = up AC = in = AC coupled COMA = out = Not ComA AutoTrig = out = Not Auto Tiggered (should have been in/on?) (Tangentially, if someone has a good 'primer' or how-to resource detailing Universal Counter operation, showing when/why/how to set the knobs in certain situations it would be welcome!) I then set the Time Lab V1.29 software to repeatedly acquire data for 12 hours, starting the next test as soon as I could. This means that, normally, a test was run during the day for 12 hours, and then overnight for 12 hours. The results are shown here: [ https://i.imgur.com/0sMVMfk.png ] The associated .TIM files are available upon request. So, now we get to the heart of the matter and the questions this test and results have raised. I am trying to understand what the data is telling me about the test, and therefore the character of the counter. 1) Why are the plots a straight line from ~0.25s until ~100s? 2) Why, after falling at the start, do the plots all seem to go back up from ~100s to ~1000s? 3) What do the "peaks" mean, after the plot has fallen and begin to rise again? 4) Why is the period from ~1000s to ~10000s so chaotic? 5) The pattern "Fall to a minimum point, then rise to a peak, then fall again" seems to be prevalent. What does that indicate? 6) Why does that pattern in question (5) seem to repeat sometimes? What is that showing me? And finally, some general questions about looking at these plots. a) Would a "perfect" plot be a straight line falling from left to right? (Meaning a hypothetical "ideal" source with perfect timing?) b) Is there some example showing plots from two different sources that then describes why one source is better than the other (based upon the ADEV plot)? c) I believe that if I understood the math better, these types of plots would be more telling. Without having to dive back into my college Calculus or Statistics books, is there a good resource for me to be able to understand this better? Lastly, thank you for your patience and for keeping this brain-trust alive. I am quite grateful for all the time and energy members pour into this list. The archives have been a good source of learning material. -Randal (at CubeCentral Labs...) _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.

AB

Azelio Boriani

Thu, Nov 16, 2017 9:10 AM

As already stated here, the best measurement mode is the time-interval
mode. The 5335A is a 2ns single-shot resolution counter. Use the PPS
output from the GPSDO, route it to the A (start) input and to a
coaxial cable used as a delay line (10m, 50ns, should be enough). The
other end of the cable into the B input (stop), select the time
interval mode TIME A -> B. Let the internal reference clock the
counter. Set trigger levels and the various parameter to get stable
readings and collect your data.

On Thu, Nov 16, 2017 at 3:59 AM, Mike Garvey r3m1g4@verizon.net wrote: