[time-nuts] Method for comparing oscillators

WarrenS warrensjmail-one at yahoo.com
Mon Aug 3 17:45:56 UTC 2009


Ulrich

You are of course correct about Accuracy and Stability, BUT I think it is you that is confused.
I may be wrong here but  it would seem to me that  ALL John really cares to know for now,  like most NON-Nuts, is what the freq (difference) is of several of his good oscillators.
This is all that is important to us non Allen Deviation nuts, because first that is something easy to deal with and correct with a simple adjustment and 2nd the stability and Allen numbers, while interesting, there is little that the average user can do to improve them except to get yet another unneeded oscillator,  and MORE ironically,  usually the numbers do not tell anything about the one thing that most want to know (because freq offset is first removed), and that is what frequency is it running at right now, not what it may change by  in another  sec, min or hour. All the nice Allen numbers also show nothing about how close (due to the limited freq adj resolution) that the Osc can really be set to.

ws
****************
----- Original Message ----- 
From: "Ulrich Bangert" <df6jb at ulrich-bangert.de>
To: "'Discussion of precise time and frequency measurement'" <time-nuts at febo.com>
Sent: Monday, August 03, 2009 8:31 AM
Subject: Re: [time-nuts] Method for comparing oscillators


>John,
>I see you in the danger to confuse accuracy and stabilility. "Accuracy" of
>an oscillator and "stability" of an oscillator are (albeit the fact that our
>wishful thinking usually expects both from a good oscillator) two completely
>different things that you should not mix against each other. 
>
>Your oscilloscope method (without proper handling of phase ambiguities)
>measures a compound of both properties and is not well suited for stability
>measurements. You have to realize that one of the oscillators that you are
>going to compare may be totally inaccurate so that you will see lots of
>phase changes in time occuring. Nevertheless this inaccurate oscillator may
>be perfectly stable running on its wrong frequency. Do you see the
>difference?
>
>Best regards
>Ulrich Bangert
>****************
>> -----Ursprungliche Nachricht-----
>> Von: time-nuts-bounces at febo.com 
>> [mailto:time-nuts-bounces at febo.com] Im Auftrag von John Green
>> Gesendet: Montag, 3. August 2009 16:59
>> An: time-nuts at febo.com
>> Betreff: Re: [time-nuts] Method for comparing oscillators
>>  
>> I have studied the dual mixer approach and the consensus is 
>> that it is the most accurate method. However, it seems pretty 
>> difficult to obtain that accuracy. 
>> ...
>>  I can't produce graphs showing frequency 
>> stability but that isn't a big deal for me. I just want to be 
>> able to compare a Rb source to a GPSDO and look at several 
>> OCXOs either stand alone or in equipment we have here. 

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