From: utzoo!decvax!duke!harpo!eagle!karn
Newsgroups: net.video
Title: Re: taping from VCR to VCR
Article-I.D.: eagle.735
Posted: Thu Jan 20 18:46:18 1983
Received: Sun Jan 23 07:39:34 1983
References: bunker.200 rocheste.458

The methods used for on-air and cable channel scrambling are quite
different from "copyguard" (TM?), and none that I know of distort vertical
sync - they all work by screwing up horizontal sync.  Oak's ON-TV system
uses a sine wave turned off during the vertical interval (to prevent
transmitter overmodulation), while WHT in Newark and most cable systems
use a simple square wave ("posthole") sync suppression scheme.  The sound
is usually on an FM subcarrier (like SCA on FM broadcast stations) or a
suppressed-carrier DSB subcarrier (like the stereo difference info in FM
broadcasting).

On a related topic, does anyone have info on HBO's satellite scrambling
scheme?  I suspect strongly that they will be going to digital audio
(notice their newly proclaimed stereo ability). I also think that going
digital, even without high speed encryption, will be enough to deter
most "pirates", so there may be some hope for those of you with
knowledge of digital modulation techniques.

Phil