[time-nuts] Darn you people....

Bob Bownes bownes at gmail.com
Sat May 7 00:06:05 UTC 2011


Thanks to all for the discussion, but I'm still not sure why I have a
(now) consistent 1.495 hz frequency difference between the thunderbolt
and the VE2ZAZ FLL.

On a similar note, forgive my ignorance, but is there a simple
explanation why there are different frequency readings on my 5370B
when selecting frequency with a 1s gate vs frequency with 100k
samples? Not a few uHz, 1sec gate reading of the VE2ZAZ is
10,000,001.4946 Hz (+/- noise in the last digit) while 100k sample
reading is 9,997,322.2 Hz +/- noise in the last four digits.

Thanks,
Bob the geology major

On Tue, May 3, 2011 at 9:43 PM, Luis Cupido <cupido at mail.ua.pt> wrote:
> Hi Bert,
>
> Well, without the averaging I think I was correct
> (I was obviously not considering the averaging).
> Your implementation with averaging surely smooth this proportionally
> and yes you end up better than 0.0625 as more you integrate.
> Please consider then the numbers you may find relevant and the
> corresponding integration time. (that was not really the
> point in my email).
>
> But since all topologies can average I presume you
> agree that potential differences between systems
> as remarked in my email still apply. Namely an offset
> at a frequency drift that is basic behavior of any FLL
> you wont have on a PLL.
>
> All that may fall below most practical needs(1), I agree...
> But in the timenuts spirit ought to be pointed out... right ?  ;-)
>
> Luis Cupido
> ct1dmk.
>
>
> p.s. (1) folks running several Cesium stds don't
> be offended I'm not saying your needs are not practical  :-)
> ;-) hi....
>
>
>
>
>
>
> Bert, VE2ZAZ wrote:
>>
>> Luis,
>>
>> You said: <<Furthermore the frequency counting resolution is 16 seconds,
>> so the ZAZ gpsdo won't lock better than 0.0625Hz.>>
>>
>>
>> On my GPSDO design, a single 16-second frequency sample does have a
>> resolution of 0.0625Hz. But the FLL firmware does averaging over as many
>> samples as you want before adjusting the OCXO. So I don't agree with your
>> statement that the ZAZ gpsdo won't lock better than 0.0625Hz. In fact, I
>> have never seen my design go worse than 1x10E-9. It usually sit below
>> 5x10E-10. This concurs with the many reports I got from other users.
>>
>>
>> Please elaborate.
>>
>> Thanks,
>>
>> Bert, VE2ZAZ
>
>
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