[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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