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From: jer@peora.UUCP (J. Eric Roskos)
Newsgroups: net.consumers
Subject: Re: Cable TV
Message-ID: <847@peora.UUCP>
Date: Fri, 19-Apr-85 08:25:49 EST
Article-I.D.: peora.847
Posted: Fri Apr 19 08:25:49 1985
Date-Received: Sat, 20-Apr-85 03:44:19 EST
References: <5250@tekecs.UUCP>
Organization: Perkin-Elmer SDC, Orlando, Fl.
Lines: 32

>  One other point. I know of no cable systems that "scramble"
>  signals at the junction box. What's at the junction box is
>  a filter. The signal is unscrambled but the carrier is taken
>  out with a notch filter so you are unable to receive it.

CableVision here in Orlando does "scramble" signals at the junction box.
More accurately, they apparently inject some signal into the channels you
don't pay for so that the horizontal sync occurs at the wrong place.  The
picture comes out "shifted" to the right so that the edges of the picture
are in the center; but the picture (and sound) are still there.

Actually, here it's more complicated (and interesting).  One channel
(Cinemax) uses both the above method, and some kind of modification (or
elimination) of the vertical sync.  What is interesting is that for that
channel, there is apparently a "descrambler" built into the cable tuner.
The cable from the tuner to the control box contains wires for a switch
which may be connected such that the switch turns on for particular
channels (only Cinemax in this area); when the switch is on, vertical sync
is restored.

Incidentally, this raises an interesting question.  Recently HBO bought a
new scrambling system for their satellite signal, which uses an encryption
key (so that even if you have a descrambler, you can't descramble it unless
you can keep getting the new encryption keys each time they change them).
The facility for doing this was a new, low-cost one.  Have they started
using it yet?  It would seem to be a strong reason for not buying an "earth
station" satellite receiver.
-- 
Full-Name:  J. Eric Roskos
UUCP:       ..!{decvax,ucbvax,ihnp4}!vax135!petsd!peora!jer
US Mail:    MS 795; Perkin-Elmer SDC;
	    2486 Sand Lake Road, Orlando, FL 32809-7642