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[time-freq] Analog TVRO & color burst

John Ackermann N8UR jra at febo.com
Fri Mar 17 16:22:59 UTC 2006


Please ignore my message below... I completely missed that you were 
talking about TVRO, and gave you information you already have.

I do suspect, though, that the network feeds aren't paying any 
particular attention to long-term stability.

John
----

John Ackermann N8UR wrote:
> Owen, Michael wrote:
> 
>> Friends,
>>  
>> Does anyone on the list know about stability of the color burst
>> frequency in analog TVRO signals?  A local TV station's engineer tells
>> me that it is good to a few nanoseconds per day.  I'm looking for
>> corroboration before heading out on a goose chase.
>>  
>> I already know that terrestrial signals aren't reliable because local TV
>> stations generate their own color burst signal from who-knows-what time
>> base.  I'm wondering about the quality of network feeds through
>> geostationary satellites.
>>  
>> I'm asking on this forum because REFLOCK II might be a good way to lock
>> an OCXO to the color burst.
> 
> 
> There was a time (70s and 80s) when the colorburst and horizontal sync 
> was reliable as a time source; the networks had Rb standards at their 
> distribution centers.  The NBS monitored network affiliates and 
> published offsets from USFS.
> 
> The problem is that when digital video started to be used, the local 
> stations ended up resyncing everything and traceability back to the 
> networks was lost.  So, today you can't use the TV signal for frequency 
> calibration.
> 
> You could still lock to the signal, but you're at the mercy of whatever 
> master sync source they're using (and if the stations I've visited are 
> any indication, it ain't atomic).  There may also be discontinuities in 
> the digital switching; I'm not sure about that.
> 
> John
> 
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