[GPS_Standard] Interesting paper

[Bob Stewart]

"Make sure that you understand that all frequencies he is referencing are multiplied by 250, so when he says the "ZAZ" GPSDO is off by a constant 2.7 Hz, he means multiplied to 2500 MHz, which corresponds to an error of 0.0108 Hz at 10 MHz."

Thanks for clarifying that.  I missed it as I skimmed through the paper and the 2.7Hz figure made no sense.

As to whether Bert's code is an FLL.  I don't think it is.  My understanding of it is that it is a Frequency Averaging System.  It's been so long since I looked at nothing but Bert's code, but I believe that it loses samples between sampling periods, which is what got me interested in rewriting it.  Of course, I may have been misled by my testing at the time.  I have never tested it for phase accuracy.  Too little time.  But I can say that my current code, which does not throw samples away, does not carry phase corrections forward.  This has to do with the way phase errors are encountered and the extremely long dead zone between phase points.

Bob





>________________________________
> From: Graham <grahamh at austin.rr.com>
>To: gps_standard at mailman.qth.net 
>Sent: Monday, November 18, 2013 12:43 PM
>Subject: Re: [GPS_Standard] Interesting paper
> 
>
>All:
>
>Make sure that you understand that all frequencies he is referencing
>are multiplied by 250, so when he says the "ZAZ" GPSDO is off by
>a constant 2.7 Hz, he means multiplied to 2500 MHz, which corresponds
>to an error of 0.0108 Hz at 10 MHz.
>
>This also brings up a question of whether the "ZAZ" GPSDO is frequency
>locked or phase locked.  If the software does not zero-out the frequency
>counter register, but keeps adding to the "rolled-over" counter, (which is
>what I think it does, at least that is what the version I built does) 
>then the
>behavior is closer to a phase lock loop than a frequency locked loop, but
>not exactly equivalent to a phase lock loop.  Any phase errors will be
>accumulated, and will still drive the correction loop.
>
>--- Graham / KE9H
>
>==
>
>On 11/18/2013 10:01 AM, Zack Widup wrote:
>> I just came across this:
>>
>> http://www.g4jnt.com/10MHz_Reference_Source_Stability.pdf
>>
>> He analyzes the VE2ZAZ standard as the last one in the paper.
>>
>> 73, Zack W9SZ
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