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[time-freq] Analog TVRO & color burst

John Ackermann N8UR jra at febo.com
Fri Mar 17 16:20:58 UTC 2006


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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