Hi Bob,
On 12/15/2014 02:22 AM, Bob Camp wrote:
Hi
(yes, this is a bit confusing … it’s my replies to a forward from Magnus who
got a bounce on submittal)
Whe're confusing Bob, I think they got that part now.
Begin forwarded message:
Date: December 14, 2014 at 7:57:39 PM EST
From: Magnus Danielson <mag...@rubidium.se>
To: Bob Camp <kb...@n1k.org>
Cc: mag...@rubidium.se
Subject: Re: [time-nuts] Homebrew frequency counter, need help
Hi Bob,
Repost my email as I accidentally posted it with wrong from address.
On 12/14/2014 08:26 PM, Bob Camp wrote:
… and this is where it gets complicated. I would toss in the Hadamard deviation
into that mix as well.
The Hadamard deviation is a great tool as it is not sensitive to linear
frequency drift as Allan deviation is. This would help to remove the systematic
effect, just as a quadratic curve-fitting of the raw-data and ADEV of the
residual.
I like the Hadamard because it’s a bit better for mapping to the frequency
domain. It’s what HP used to get phase noise from phase error data. I find that
it gives a bit better detail on some types of problems.
I use if regularly, but TimeLab unfortunatly does not have the MHDEV.
The whole process of getting *correct* versions of things into a program is
(unfortunately) much harder than simply tossing it in there. I’m glad that the
stuff in TimeLab works correctly.
I do know that, and it's not the only culprit, John naturally wants one
that works correctly in update form, and not batch form. He also does
not want too many of these running in parallel.
Modified Hadamard deviation (MHDEV) is a good replacement for MDEV, with the
same properties for drift. Similarly will Time Hadarmard Deviation (THDEV)
replace TDEV. However, for longer taus you want better processing, so therefore
you want to consider the TOTAL set of deviations, such that confidence
intervals is better.
If I had to only use three, I would include it with modified ADEV (MDEV) and
TDEV. All three are available in TimeLab with the click of a button. If you
start getting lots of data (9,000 points per second) I would toss in a
frequency domain (FFT) analysis as well. FFT on phase data is not (as far as I
know) a feature of TimeLab.
FFT on phase-data is only available in TimeLab when doing phase-noise
measurements. FFT is the way to analyse systematic noise rather than random
noise where ADEV and friends is being used. You need to separate them, and the
ADEV plot is not good for both.
There is a set of FFT based ADEV-style measures, which uses FFT, filtering of
the various ADEV styles. There is a nice set of articles covering that
approach, and actually the only style of ADEV processing that I haven't yet
implemented, even if I have done most others.
Stable-32 will take phase data and convert it to the frequency domain.
Depending on what processing you are going to do, phase or frequency may be
optimum.
Phase is better for normal deviations.
Frequency is better for modified deviations.
Stable 32 is nice in that it will convert one to the other with the click of a
button.
I'm sure it is fine, but it does not fit my needs in one way, it doesn't
run on Linux. My milage with Wine on different applications vary.
TimeLab works, but is free. For an application I pay for and not knowing
it works would be strange. Besides, I try to minimize my dependence on
Windows apps, as they tend to bite me. Stable 32 thus does not fit my
needs very well, even if I'm sure it is a fine application.
To start with, on all of these measures, you are looking for bumps and spikes.
They are telling you that something is wrong. If you flip over to the phase
plot in TimeLab, spikes and abrupt steps in it also are telling you the same
sort of thing. Exactly what this or that bump is telling you may not be obvious
at first. Posting plots to the list is a great way to get things sorted out.
Bumps, spikes and slopes... ADEV isn't the only tool one should be using, FFT
might be much better for systematic noises.
Right, so when you see them, alarm bells should go off. Something is indeed
wrong and further investigation is required.
Maybe, ADEV is good at smoothing out things, so spikes in spectrum-analysis
might not be as easy to spot in the ADEV form.
A good reason to look at multiple data sets and analysis approaches
Which is what I am say, do not rely on ADEV alone, and move your
analysis of systematics out of the ADEV plot and remove those effects
fro the ADEV plot so it becomes better at modeling the random noises.
In the end of the day, there is an overbeleife in ADEV both as a scale as well
as a processing tool, to analyze deviations, without considering the separation
of various systmeatic effect and systematic noises, while ADEV and friends is
there to analyze random noise types, it does not handle systematics good. Seems
like we have to kill ADEV as the universal measure. Ah well.
It’s been around much longer than some of the others. It also has some nice
convergence properties. That’s made it the spec of choice when describing the
performance of a wide range of products. You could buy a box that had a
“measure ADEV” button on it a very long time ago …. like back when I started
doing this … Having a piece of gear to point at for a spec measurement is a
real good thing. It eliminates a wide range of discussions. That goes at least
double if it has the logo of a well known test gear outfit on it.
That may be, but ADEV is often misused to be the only plot.
Ok, so what gear with a major label on it would you use in the 1980’s and
1990’s to measure spec performance on a few million OCXO’s …..
You are off in a different track here. I'm discussing processing
techniques and their missuses. I think you have a particular application
in mind and a particular historic context in mind. We are not discussing
the same thing.
Rather than saying "throw it through ADEV and be done with it" I say
"analyse the phase FFT, ADEV and plot the phase, preferably compensate
systematics out of ADEV". This is not saying "box A from vendor V is not
going to do it".
I actually got an old Timing Solutions
At least up to the end of the 1990’s that name would get you a Timing Who?
response from > 90% of the customers of OCXO’s.
test-set that does ADEV at 0.1, 1, 10 and 100 s using an offset rubidium at
5.000055 MHz. I've never been able to get the serial port to do anything
useful. Love to pull the data out of that one and into TimeLab.
They are good boxes. They just are from a very specialized outfit. That also
makes getting them repaired a bit tough.
Being a DMTD setup in a box with a whooping 6502 processor doing
real-time processing, presentation, front panel operation etc it's doing
quite well.
Cheers,
Magnus
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