[Test-Equipment] Ch 5 video carrier freq ref

Wed, 6 Nov 2002 01:15:03 -0800

Gary -

I expect we'll have some broadcast folks jump in here and give you the
generic "state of the union" information regarding timing chain generation
in the TV broadcast industry.  However, to get details for this specific
station, your best bet is probably a brief call to the station's engineer.

If you've been around enough years, you may remember the QST or Ham Radio
article discussing the use of TV sweep signals to calibrate their frequency
counters.  One could to do so only when the local station was
re-broadcasting a signal acquired from ABC, NBC or CBS as they were locking
to atomic standards and the local stations were not necessarily doing so.

Years ago, all of the major broadcast stations began using rubidium and/or
cesium standards to drive their timing chains.  Typically due to tube life
and expense, it would not be unusual for operating standards to be Rubidium
based and periodically calibrated to a Cesium standard.  (Rubidium and
Cesium standards have similar short term accuracy but Rubidium standards
exhibit a small frequency drift over time.)

I've not kept up with that environment.  These days, with the availability
of low cost GPS locked standards, they may have migrated that direction.
With appropriate hardware, performance is equivalent to having an in-house
Cesium standard at much lower cost.

- greg

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of Gary Chatters
Sent: Tuesday, November 05, 2002 1:50 PM
To: [email protected]
Subject: [Test-Equipment] Ch 5 video carrier freq ref

A while back someone mentioned that the video carrier of
the channel 5 TV station in the DC area was set by a cesium beam
reference.  Does anyone have a URL of a web page that describes what they
are doing?  My main interest is in confirming that they are still doing it
and what accuracy they maintain.  I've done various web searches and
haven't found anything.

TNX ES 73
Gary

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