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From: depolo@eniac.seas.upenn.edu (Jeff DePolo)
Newsgroups: sci.electronics
Subject: Re: Descramble Cable Using Filter?
Message-ID: <27223@netnews.upenn.edu>
Date: 18 Jul 90 20:13:57 GMT
References: <3525@umbc3.UMBC.EDU> <6900012@eola>
Sender: news@netnews.upenn.edu
Reply-To: depolo@eniac.seas.upenn.edu.UUCP (Jeff DePolo)
Organization: University of Pennsylvania
Lines: 26

On some of the older systems, there are filtering methods that will work.
In fact, when you decide to "buy" one of the pay channels, they just
come to your house and put a filter in line.

Probably the most common scrambling system nowadays is SSAVI, which
stands for suppressed-sync audio-video inversion.  It's basically
works just like it says.  The sync signal is supressed below what a 
normal TV is capable of locking on and the audio and video are "swapped"
positions inside the normal TV channel bandwidth.  So, to get a usable
signal, you first have to swap the audio and video back to where
they are supposed to be, and they boost the sync signal back up to
a usable level.  Obviously filtering the signal doesn't get you anywhere.

I'm no expert on the subject, so maybe somebody else can give you more
and better info.

								--- Jeff



+-----------------------+-----------------------------------------------------+
| Jeff DePolo N3HBZ/AA  | Internet: depolo@eniac.seas.upenn.edu               |
| Univ. of Pennsylvania | RF: 146.685- 224.40- 442.70+ 144.455s (Philadelpia) |
| Computer Science Eng. | Twisted pair: (215) 386-7199 home                   |
|     Class of 1991     | Carrier pigeon: 420 South 42nd St. Philly, PA 19104 |
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