Xref: utzoo sci.electronics:14542 rec.video:14911
Path: utzoo!attcan!uunet!wuarchive!zaphod.mps.ohio-state.edu!uakari.primate.wisc.edu!uflorida!mlb.semi.harris.com!thumper.mlb.semi.harris.com!jws
From: jws@thumper.mlb.semi.harris.com (James W. Swonger)
Newsgroups: sci.electronics,rec.video
Subject: Re: TV Descrambler
Message-ID: <1990Sep21.125256.16206@mlb.semi.harris.com>
Date: 21 Sep 90 12:52:56 GMT
References: <477@wybbs.mi.org>
Sender: news@mlb.semi.harris.com
Organization: Harris Semiconductor, Melbourne FL
Lines: 34
Nntp-Posting-Host: thumper.mlb.semi.harris.com


 This looks like the type for descrambling the most primitive type of
pay-TV - you know, like the HBO channel that sits by itself on channel 5.
This lonesome channel is made unviewable by overlaying another signal very
close to it. The cable company puts a trap in the line when you pay. Then
you can get that one channel without a new box.

 The other channels, which get grouped together in a pay-channel block,
are doctored in other ways which require more sophistication to restore. 

 I suspect that a simple 1-stage filter might leave something to be desired.
A multi-stage one would probably give better results.

 
 You should NOTE:

 Our local cable monopoly, and probably most of the others, is having a big
push to catch people who are (Gasp!) "stealing" cable services. It is easy for
the cable dudes to find a trap such as the one described by sending the signal
up the line and seeing if there's any funny characteristics at that frequency.

 Question: Does anybody know whether the cable box makers put any sort of
ID marker (e.g. a notch or resonance at some frequency) at the box input to
tell if one of their boxes is on the line? I have had this suspicion for some
time but have not seen anything one way or the other.

 If you are going to be a naughty boy and/or girl, you should be sure to 
isolate whatever you are doing from the cable. Buy a distribution amplifier
(not just a splitter, something which doesn't pass signal backwards) and 
put it in line where the cable enters your house. The idea is to only let the
cable see a straight 75-ohm load, like you have one TV hooked up. Anything
on the other side should be made invisible to prying eyes/ears/test equipment.

 Not that I would advocate illegal acts.