[time-nuts] OCXO inside the FEI AN/URQ-23

Tom Van Baak tvb at LeapSecond.com
Tue Jul 25 12:50:09 EDT 2017

> In my opinion ADEV does hide changes in Frequency and we see it when
> we compare ADEV plots with at the same time frequency measurements.

On purpose ADEV reduces hundreds, even hundreds of thousands of measurements to a single number. If this is what you mean by "hide" then ok. In my opinion, ADEV does not hide changes in frequency; it statistically summarizes them in a standard way.

In general one should always look at phase residual or relative frequency strip charts before using ADEV. Another trick is using Stable32's DAVAR or TimeLab's multi-trace feature, both of which will expose variations in ADEV across a large data set. Or use histograms, etc.

However, as you seem to imply, if you are seeing unexpected differences between frequency measurements and time (phase) measurements or between freq / time and ADEV statistics, then your measurement system(s) are broken. With only a single DUT, if different "at the same time" measurement systems report different results, then that's a smoking gun to find which measurement system(s) is failing you.

> The URQ shows frequency specs 2E-12 most likely ADEV.

See Table II on Page 9 of the manual [1].


[1] http://mil-spec.tpub.com/MIL-T/MIL-T-28816/MIL-T-2881600009.htm

-------- Original message --------
From: Tom Van Baak <tvb at LeapSecond.com> 
Date: 7/25/17 11:37 AM (GMT-05:00) 
To: Discussion of precise time and frequency measurement <time-nuts at febo.com> 
Subject: Re: [time-nuts] OCXO inside the FEI AN/URQ-23 


In the early days of time-nuts the URQ-10, and especially the URQ-23, were highly sought after because of their reported stability. By now they are quite rare. Do you have one?

If it's important I can dig one out from the closet and run tests for you.

> "Question if it is frequency or ADEV".

I'm not sure what you mean. There is no such thing as "frequency" vs. "ADEV".


----- Original Message ----- 
From: "Bert Kehren via time-nuts" <time-nuts at febo.com>
To: <time-nuts at febo.com>
Sent: Tuesday, July 25, 2017 7:48 AM
Subject: [time-nuts] OCXO inside the FEI AN/URQ-23

> Has any one run tests of the OCXO inside the AN/URQ-23. Data in the manual  
> looks promising. Question if it is frequency or ADEV
> Bert Kehren

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