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From: brown@nic_vax.UUCP
Newsgroups: net.consumers
Subject: Re: Cable TV
Message-ID: <134@nic_vax.UUCP>
Date: Mon, 22-Apr-85 11:14:58 EST
Article-I.D.: nic_vax.134
Posted: Mon Apr 22 11:14:58 1985
Date-Received: Wed, 24-Apr-85 03:19:21 EST
References: <5250@tekecs.UUCP> <847@peora.UUCP>
Organization: Nicolet Instrument Corp. Madison WI
Lines: 43

> >  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.

Sounds like sine-wave-sync-suppress to me, which is too expensive to do
at the juction box.  Even physically impossible as the electronics needed
to do that wouldn't fit in a junction box.  Even more expensive to duplicate
in each and every juction box.  But, I would have to see it to believe it.

> 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.

If the system is a sine-wave-synce-suppress system, as I mentioned above,
the sine-wave signal tends to also destroy the vertical sync.  I know, we
have the 2fh system here in Madison, WI.

> 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.

HBO has been shipping descrambling units to the west coast area first.  The
east coast feed will be next.  There are other companys going that route
as well.  ESPN wants to do it, SHOWTIME and THE MOVIE CHANNEL want to do it,
and of course CINEMAX, because they belong to HBO.

Mr. Video