[time-nuts] Using digital broadcast TV for timing?
jerryfi_99 at yahoo.com
Thu Feb 9 00:38:08 UTC 2012
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.....
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?
> <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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