[time-nuts] Timing Distribution in Mountainous Terrain

Magnus Danielson magnus at rubidium.dyndns.org
Sat Sep 11 09:02:56 UTC 2010


On 09/10/2010 11:50 PM, jimlux wrote:
> Ralph Smith wrote:
>> OK, stop me if this is really stupid. The initial site is in Colorado.
>> Would it be possible to use WWV? In particular:
>>
>> 1) Lock a reference to the carrier of one of the WWV signals
>> 2) Generate PPS off of WWV-locked reference
>> 3) Periodically send difference of GPSDO PPS and WWV-locked PPS home,
>> along with GPS lock indication
>> 4) When GPS goes away do the math at home and correct for the timing
>> drift
>> of the GPSDO compared to WWV-locked reference
>>
>
> I don't think a received WWV (or WWVB) signal is stable to 30ns...

The critical aspect here is stable to 30 ns _relative_. I.e. common mode 
changes mostly cancels.

I think it is problematic... the frequency of the carrier is too low. 
The vector sum of reflections may shift the group delay, and in this 
case the time error of such sums can be expected to be proportional to 
the wavelength. I would use one wavelength as the rule of thumb as long 
as it is not better quantified, and I would assume that individual 
changes can range that full range...

Cheers,
Magnus




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