From: brown@vidiot.UUCP (Vidiot)
Newsgroups: rec.video.cable-tv
Subject: Re: Sharing FM and TV Cable
Date: 21 Dec 92 18:30:18 GMT
Reply-To: brown@vidiot.UUCP (Vidiot)
Organization: Vidiot's Hangout

In article <1992Dec21.072624.11763@ultb.isc.rit.edu> rxv9839@ritvax.isc.rit.edu writes:
<In article <1992Dec21.000237.6699@welchgate.welch.jhu.edu>, peterli@welchgate.
<welch.jhu.edu (Peter Li) writes:
<>In article <4614@vidiot.UUCP> brown@vidiot.UUCP (Vidiot) writes:
<>>
<>>The cable-FM frequencies are NEVER the same as the over-the-air frequencies.
<
<never say never, so the saying goes.  Many cable companies have all or part of
<their FM channels (stations) on exactly the same frequency as they are off-air. 
<The primary determinant is the strength of the particular signal throughout the
<area served by the headend (cableese for central transmission facility, the
<phone equivalent would be the central office).  If the signal is low enough,
<frequency offset is not needed.  In short the cable signal is so strong that it
<will overpower the off-air signal.  The reason that any interference occurs in
<the first place is because of the time delay introduced by the cable amplifying
<equipment and line transmission time.  Most cable FM services include some
<stereo re-broadcast of cable stations like HBO, a leftover from the days when
<TV's were not stereo.  Stereo simulcasts of HBO concert specials used to be a
<big thing.  They sent the FM over a local radio station which cable carried on
<the FM or the sub just got the sound offair.

Very weak, long distant, FM simulcasts could be used at the same frequency.
But, any local towered station should not be on the same frequency, ever.
Since isolation is so poor, the cable-FM version of the station would not
be stronger than the over-the-air signal.

I am in my basement and can pick up local stations with no problem what-so-ever.
About a year ago, a new 6kw ERP FM station went on the air at 105.5, the
frequency used by MTV on cable.  Needless to say there were problems and the
cable company had to move MTV to 107.7.  Yes, we still have FM service for
things like HBO, MTV, Showtime.  I prefer those, since they are better than MTS.

<>>Think about it for a moment...yep, that's right, interference.  If you put on
<>>cable the same frequency as the over-the-air frequency you can end up with
<>>crap.  They will interfere with each other.  So, cable-FM always uses a
<
<The original poster wanted to run in his FM on  the same cable as an antenna (or
<cable TV)  While interference is possible in the TV antenna/FM antenna
<combination, if the lead lengths between the two antennas are kept the same and
<they are co-located they will probably add signal strength.  In the
<FMantenna/cable TV combination there is a high probability of interference, on
<every channel that is the same on cable as off the air.  If there is nothing in
<the FM band, then there would be no problem.  It may well be illegal for one to
<hookup anything to the cable line and if no isolation is provided you could
<easily wind up broadcasting all the cable channels out over the FM antenna
<which well interfer with other airwave users.

The subject had changed a little bit, but it is illegal to connect an antenna
to cable, PERIOD.  The thing would radiate onto aircraft frequencies.
-- 
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Newsgroups: rec.video.cable-tv