[time-nuts] Time Signals on TV signals
W4wj at aol.com
W4wj at aol.com
Wed May 27 02:39:17 UTC 2009
Unfortunately "cesium passthru" went away with the advent of the
use of frame synchronizers to receive the network signal and then
re-clock it to match the local sync generator phase and frequency.
The FCC requirement for the color burst signal (3.579545 MHz)
is plus/minus 1 Hz... and you can certainly do better than that with
most rudimentary oscillators.
So, the phase stability of your local network affiliate is only as good
as their local sync generator...
Some stations do have sync generators with 10MHz EXT REF
capability, allowing use of GPS or stabilized oscillators for that
input...
73,
Don, W4WJ
In a message dated 5/25/2009 1:14:45 P.M. Central Daylight Time,
hmurray at megapathdsl.net writes:
> Why did TV stations stop broadcasting time signals? HDTV requirements?
One thing that may be relevant....
Many years ago, all the TV sources were kept in sync so there wasn't any
glitch when they switched feeds. The sync timing was distributed from at
atomic clock at network headquarters. The time of day probably
piggybacked
on that.
I remember an old NBS booklet describing it. That was back in the late
70s.
(It's probably a valuable collectors item now.) I think HP and NBS used
to
publish a table of delays for several major TV stations. Somebody on
this
list will probably recognize that description.
The breakthrough that got around the timing requirement was frame buffers.
(Thank Moore's law.)
> Could a cable company interfere with the time signals?
Thanks for the laugh. :)
Cable companies do all sorts of strange things.
--
These are my opinions, not necessarily my employer's. I hate spam.
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