[time-nuts] Measuring TV delays

[Glenn Little]

This system of messaging is in place now, at least with ABC.
It is called NAS {Network Alert System}.
It is used to display network time,program scheduling and timings of 
each segment with the time for affiliate commercial insertion.
It is also used to alert the affiliate to special reports and network cutins.
I do not remember what line or PID was used.
The decoder box had an output that had the decoded data superimposed 
on the network video.
This is was displayed only in Master Control.
There was a discrete output from the box to trigger an audio sounder 
to alert the sleepy Master Control operator of the impending cutin.
We used the loudest siren that we could find that ran off of 12 Volts 
in a small form factor.
When it went off, you could hear it anywhere in the building.

The time was always retarded from local time and the offset was never 
constant due to encode/decode delays.

It would be possible to decode this and display the same data at a 
remote receiver, it was not stripped from the broadcast signal.

73
Glenn
WB4UIV




At 12:55 PM 1/2/2014, you wrote:
>On Thu, Jan 2, 2014 at 11:10 AM, Gregory Muir <engineering at mt.net> wrote:
>
> > Reading all of this brings back memories of a project I was involved in
> > back in the early 70's in the Denver area.  NBS-Boulder was experimenting
> > with injecting their time standard into the video of the analog signal
> > before it hit the transmitter.
>
>
>I bet they encoded it into a single line of the vertical interval. I worked
>on a similar project at PBS but there it was used that to implement a
>message broadcast service to send textual messages to selected affiliate
>stations. It was an outgrowth of the closed-captioning system. PBS didn't
>want to pay telephone charges to send the same message to all 200 stations
>in the US when they already had a "pipe" into every station.
>
>And I do remember being intrigued with the creation of the network master
>clock to ensure that all the video sources were synchronized. I also
>remember the early digital frame buffers that were there to deal with
>different frame clock phase from non-PBS-network sources. As I recall, WWVB
>was the preferred frequency reference but I also remember that they had
>either a couple of Rb or Cs local references. (It was 1980 and my mind is
>going. So much to remember.)
>
>--
>Brian Lloyd, WB6RQN/J79BPL
>706 Flightline Drive
>Spring Branch, TX 78070
>brian at lloyd.com
>+1.916.877.5067
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