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

Wed Feb 22 22:59:39 UTC 2012

For a history on the color subcarrier you can try:
http://www.videointerchange.com/pal_secam_conversions.htm#3.579545 Color
Subcarrier Explained

Here in Italy, before the digital switchover, our national broadcast
company used to sync the PAL color subcarrier to a Cs reference and my
company sold 5MHz disciplined oscillators locked to the PAL (or NTSC) color
subcarrier using the Philips TDA9181 (or something like that, I can't
remember the exact part-number right now). The OCXO was an expensive double
oven Oscilloquartz 8666A driven by a 16bit Analog Devices DAC.

On Tue, Feb 21, 2012 at 2:33 AM, paul swed <paulswedb at gmail.com> wrote:

> Stan
> By gosh that really is an old one. ABC very well could have been driven by
> a Rb ref. Though as I mentioned CBS was CS. So a bit hard to believe ABC
> and NBC were not. But I really simply do not remember. There had been a
> time when the networks were used for freq dissemination and thats why at
> least CBS had the CS.
> An alternate thought could be that it came from a local owned an operated
> station. And it was adjusted to the network.
> Some inside pixs would be pretty neat top see. Like you I chose to leave
> the USNO sticker on my sad but semi operational CS reference.
> Regards
> Paul
> WB8TSL
>
> On Mon, Feb 20, 2012 at 7:48 PM, Stan Searing <timenutstan at gmail.com>
> wrote:
>
> > 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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