Xref: utzoo sci.electronics:3742 rec.video:4153
Path: utzoo!utgpu!water!watmath!clyde!att!osu-cis!tut.cis.ohio-state.edu!rutgers!mcnc!unccvax!dya
From: dya@unccvax.UUCP (York David Anthony @ W06BF-TV, Concord, NC)
Newsgroups: sci.electronics,rec.video
Subject: Re: VCR comercial eliminator
Message-ID: <1087@unccvax.UUCP>
Date: 2 Sep 88 14:28:07 GMT
References: <257@ivucsb.UUCP> <16314@apple.Apple.COM> <17659@glacier.STANFORD.EDU> <1039@mtund.ATT.COM>
Organization: Univ. of NC at Charlotte, Charlotte, NC
Lines: 38

In article <1039@mtund.ATT.COM>, smc@mtund.ATT.COM (Steven Casagrande) writes:

> A few years back there was a device that would detect the Color SubCarrier
> transmitted by the TV Station.  Apparently, if you were trying to tape
> a B&W movie (i.e., late at night), it would detect the switch from
> the B&W movie to the COLOR commercial, and would then stop the tape

	Not no more, however.  The FCC has (or is imminently about to)
repeal the "turn off the burst during monochrome programs" rule, 
because it is a pain in the ass.  The reason that killing the burst
is such a pain is that distribution channels for programs, even
monochrome programs, distribute via videotape, etc...synchronising
the stuff through a TBC (so it can be routed through the TV station
plant and thence to the transmitter, synchronised with all the other
TV station plant) requires the presence of color burst to derive
the sampling clock, etc.

	The usual burst-killing method involved switching in 
(electronically) an appropriate trap during the burst flag interval,
or otherwise obliterating it at the transmitter.

	WTBS's burst is present during monochrome programs (on
satellite distribution) and I'm pretty sure that WJZY (local Belmont
station) leaves it on all the time as well.

	There was also a "turn off the 19 kc pilot tone" rule for
FM stations which is repealed.  I actually did this during my 
God Squad shift days at a local FM.  Technically, you'd have to
turn it off for commercials at this (and many) stations with 
mono cart machines....

	Since cross-chroma is no longer a problem with encoders and
decoders, it looks like the color burst is "defacto" part of the
commercial TV RS-170A sync signal. (Ever try to build a purely
monochrome TBC??? Yecch!)

York David Anthony
DataSpan, Inc