[time-nuts] Using digital broadcast TV for timing?

Bob Camp lists at rtty.us
Thu Feb 9 00:43:49 UTC 2012


Hi

The whole cesium lock approach died back in the 90's. These days your local station buffers / retimes / reframes everything. If you are lucky they use a Rb for the timing.

Bob



On Feb 8, 2012, at 7:38 PM, jerryfi <jerryfi_99 at yahoo.com> wrote:

> A bit off topic, but historically related....  back in the 70's, I tapped off the color burst 
> 
> oscillator in my TV (a Heathkit) to get a 3.579545.... MHz  (315/88 MHz) source to 
> 
> calibrate my homebrew frequency counter. The TV's color burst oscillator was phase 
> 
> locked to the color burst signal on the broadcast signal  (which was on the "back 
> 
> porch" of the hori sync signals).  Supposedly, the networks were locked to Cesium 
> 
> standards traceable to NBS for LIVE broadcasts, such as news and sports.  Taped 
> 
> programs, of course, were not usable as an accurate source.  In any case, that signal
> served my purposes at the time (providing a reference for calibrating my counter that
> was more accurate than anything else available to me).
> 
> I'm not sure if, what, or where analog TV is still broadcast, but I think there are still a 
> 
> few stations (low power) around.  You might still be able to use that signal, IF you can 
> 
> dig it out of your old analog TV.  ;-)  I do have analog tv's hooked up to my cable 
> 
> box - I suspect that live broadcasts would still have an accurate color burst, so maybe.... 
> 
> I think the other methods discussed here (ie, GPS) would provide easier and more 
> 
> reliable timing sources. ;-)  
> 
> 
> Trying to locate the appropriate signal(s) in a digital TV today would be interesting.  
> 
> Just as a historical aside.....
> 
> 
> 
> Jerry Finn
> Santa Maria, CA  
> 
> 
> 
>> Date: Tue, 7 Feb 2012 18:01:26 -0800
>> From: Chris Albertson <albertson.chris at gmail.com>
>> To: Discussion of precise time and frequency measurement
>>     <time-nuts at febo.com>
>> Subject: [time-nuts] Using digital broadcast TV for timing?
>> Message-ID:
>>     <CABbxVHvb3SKzuMx+bDyKTtesGzuf2k5HSJWYpdKK+RQOArxRgA at mail.gmail.com>
>> Content-Type: text/plain; charset=ISO-8859-1
>> 
>> GPS requires a good view of the sky,  Hard to do in say the 7th floor
>> of a 40 story building if you have no windows.   I'm wondering about
>> using the new digital TV signals for timing.
>> 
>> I'm pretty sure there is time code in the signal and I'm pretty sure
>> the bits are clocked at a very accurate rate.   Also TV receivers are
>> very easy to find and put "hooks" into.      I'd bet the broadcast TV
>> signal could be almost as good as GPS.
>> 
>> The plan is to try and phase lock a local oscillator and use a very
>> long time constant on the loop filter.   I bet the TV transmitters are
>> locked to GPS and over a long enough time are as good as GPS.  Also in
>> many cities there are many TV transmitters, should be able to take
>> advantage of that.
>> 
>> Before I try some experiments anyone want to tell me why I'm wrong?
>> -- 
>> 
>> Chris Albertson
>> Redondo Beach, California
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