Path: utzoo!attcan!uunet!samsung!zaphod.mps.ohio-state.edu!sdd.hp.com!decwrl!ucbvax!hplabs!hpfcso!hpldola!paul
From: paul@hpldola.HP.COM (Paul Bame)
Newsgroups: sci.electronics
Subject: Re: Descramble Cable Using Filter?
Message-ID: <10960029@hpldola.HP.COM>
Date: 29 Jun 90 22:23:34 GMT
References: <3525@umbc3.UMBC.EDU>
Organization: HP Elec. Design Div. -ColoSpgs
Lines: 29

Go to your friendly SAMS book outlet and find their book on TV scrambling.
It's also been in magazines for several years - with a not too bad series in
Radio-Electronics - check the periodical guide at your local library.

In short:

	There are many scrambling methods in use today but they 
	fall into about 4 (could be more) categories
	for cable TV - and another for pay satellite.

	One scrambling method does involve narrow-band jamming
	and it is old and easy to defeat with the notch filter
	as mentioned.  You can purchase probably-suitable notch 
	filters as "interference filters" from companies 
	advertising in the back of popular elecronics magazines.  

	Most recent methods mess with the video sync in one or
	more ways - sometimes (varisync) to the detriment of
	your properly unscrambled picture.  The earliest of these
	was probably gated sync supression.  Moving the sound to
	another frequency is also done.

	You can buy your own descrambling boxes of any kind from these
	magazine advertisers too - ostensibly to save the monthly box 
	rental fee - not to dodge the cable services fee.


			-Paul "Spice is the Variety of Life"
			paul@hpldola.hp.com	N0KCL