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...@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.ch...@gmail.com> >> To: Discussion of precise time and frequency measurement >> <time-nuts@febo.com> >> Subject: [time-nuts] Using digital broadcast TV for timing? >> Message-ID: >> <cabbxvhvb3skzumx+bdykttesgzuf2k5hsjwypdkk+rqoarx...@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 > _______________________________________________ > time-nuts mailing list -- time-nuts@febo.com > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
