[time-nuts] ADEV

[Mike Feher]

I agree with all of the comments. My problem now is attempting to fight an
internal Gov't battle, where there is too much emphasis on ADEV, as an
indicator to overall system performance. Thanks for all the replies. Regards
- Mike

Mike B. Feher, EOZ Inc.
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960 office
908-901-9193 cell


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Bob Camp
Sent: Saturday, November 13, 2010 9:06 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] ADEV

Hi

I see ADEV not as a solution to a system design problem, but an oscillator
measurement issue. If you look at the measures being used in the 60's, most
of them had serious statistical flaws. You could measure them several ways
and get multiple results. What ADEV gave us is a measure that could be done
repeatably. You still have to do it right, but if you do it repeats.  If
there is a systems rationale in the development of the measurement it's
awfully well hidden in the early papers.

Bob


On Nov 13, 2010, at 8:53 AM, Magnus Danielson wrote:

> On 11/13/2010 02:20 PM, Mike Feher wrote:
>> I sure do agree, that with very low data rate systems it is significant.
In
>> fact, when David Allan&  Fred Walls came up with the proposal of using
this
>> measurement as an FOM for oscillators over 30 years ago, digital
>> communication rates were slow, and, the measurement was a good one.
> 
> ADEV can be trace back to 1966, but even prior to that similar estimates
was being used in the scientific research, but the Allan article of 1966
provides part of the critical analysis which makes the M-sample analysis
into the Allan-variance as we know it.
> 
> Their concerns where with oscillators and not data-communication which has
its own set of problems and measures.
> 
>> Due to the filtering process within ADEV by collecting and integrating a
large
>> number of samples, has a filtering effect of its own. Therefore, it can,
and
>> will, miss the fact that there may be instantaneous phase transitions
that
>> could cause havoc with high data rates and higher order PSK modulation
>> schemes.  So, again, I apologize, as I should have mentioned higher data
>> rates.
> 
> Data-rates is actually not particularly interesting, it is the dynamic
properties regardless of rate, which is only a scale-factor. The property of
phase-jumps is well covered in the MTIE measurement which is used along-side
the TDEV measurement for telecommunication systems.
> MTIE provides the Maximum Time Interval Error... so for a window of length
tau, what is the maximum difference between high and low? This is measured
by taking the difference between max and min in a window, slide it over the
data and take the maximum difference. This relates very well to buffer-size
action and if converted over to a sine-tolerance curve (using f=1/(pi*tau) )
also can be made to match up with PLL responses.
> 
> Come to think of it, I have not seen any good Wikipedia article on it.
> 
> Anyway, one really has to understand what kind of measurement is adequate
for the technical problem one is trying to address.
> 
> Cheers,
> Magnus
> 
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