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

Stan Searing timenutstan at gmail.com
Tue Feb 21 00:48:37 UTC 2012


Does anyone know if ABC used Cesium or just Rubidium standards?
I have the Tracor 304SC shown in this URL:
http://www.bdairfield.com/stan/time-nuts/Tracor-304SC/IMG_4216.JPG
I assume the SC in the model number stands for the color subcarrier
frequency for NTSC: 3.579545 MHz.
The boards seem to be mostly hand wired on turret pins, so I don't think
they made very many.  I usually try and clean up front panels and remove
non-manufacturer
stickers, but I thought the "ABC New York", "Rubidium 1" and "ADJ May 21 84"
were cool, so the stickers stayed.  Under the top cover is a tag that says:
Model 304-SC
S/N 127
Frequency relative to USFS -300 X 10 ** -10
DATE 10-11-68

The front panel has a "5 MHz" output, while the back has a "3.58 MC" output.

I'm told this unit no longer works.  KO4BB does not have the manual on his
site, if you know where one is, send me a link off list.

If some folks know more about the history of network broadcast color
subcarrier frequency
standards, I think it's an interesting subject that would be worth hearing
more about.

Stan



On Wed, Feb 8, 2012 at 7:07 PM, paul swed <paulswedb at gmail.com> wrote:

> All gone these days in the US.
> Indeed I can speak to the CBS network it was driven by CS references in the
> 80s and 90s.
> I used CBS for aligning my references Xtal oven oscillators that were never
> ever turned off in a large facility that uplinked all 8 CBS regions and 22
> other cable networks.
>
> Unfortunately few could get to that color burst signal as devices called
> frame synchronizers came into play from the 80s to the 90s. They would
> strip off that burst and insert the local reference of generally much lower
> quality.
>
> As far as todays digital TV signals they can contain significant jitter.
> But its actually trickier then that and I honestly have to say I am not
> sure that you might not be able to get something useful.
> Several interesting points. Many of the television transmitters do use GPS
> referenced sources. Its an interesting exploration. I simply don't have the
> time though.
> Regards
> Paul
> WB8TSL
>
> On Wed, 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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