Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!tut.cis.ohio-state.edu!att!icus!limbic!gil
From: gil@limbic.UUCP (Gil Kloepfer Jr.)
Newsgroups: sci.electronics
Subject: Television VBI Data transmissions
Message-ID: <599@limbic.UUCP>
Date: 8 Jan 90 06:49:19 GMT
Organization: ICUS Software Systems, Islip, NY
Lines: 43

As some folks may know, there is an space in the TV video signal called
the vertical blank interval.  There has been recent technology (close
captioning, "Silent Radio" system, etc) which is taking advantage of
some "dead space" in this interval and transmitting signals on it.
Those curious about it can turn the vertical hold control on their TV
set while watching a station transmitting such information, and will
see a little dashed line skipping along in that wide bar which will
roll up or down the screen.

My questions about this, for those in-the-know are:

	1.  Are there any FCC regulations or industry standards
	    which govern the VBI, and how signals are to be
	    superimposed here?

	2.  Specifically, how is closed captioning transmitted?  Is
	    it data, or a slow-scan representation of pixels to be
	    overlayed on the TV picture?

	3.  What is the best way to get at the information on the VBI?
	    Specifically, what is the best way to detect the start
	    and end of the "dead" portion where information would be
	    transmitted?

It seems that the information being stored here is a well-kept secret
much like the SCA subcarrier transmitted with FM broadcasts.  For those
who don't know, SCA, or subsidiary communications authorization, is a
subcarrier transmitted by many FM broadcast stations, and contains
programming such as Muzak, foreign-language broadcasts, medical news,
reading for the blind, etc.  I believe that one is supposed to subscribe
(ie. pay) to use these services for a business, but one can receive the
broadcasts using a box designed to receive the subcarrier (projects
for such boxes have been published in electronics hobby magazines) and
a standard FM radio.  I am looking to do the same kind of thing with VBI
information.

If you e-mail a response, please post it to the net also because I'm
sure that others will be interested in this subject.

------
| Gil Kloepfer, Jr.
| ICUS Software Systems/Bowne Management Systems (depending on where I am)
| ...ames!limbic!gil