Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!ames!uakari.primate.wisc.edu!nic.MR.NET!ns!logajan
From: logajan@ns.network.com (John Logajan)
Newsgroups: sci.electronics
Subject: Re: Cable TV descramblers / Rental movie stabilizers
Message-ID: <1990Jan13.005314.5145@ns.network.com>
Date: 13 Jan 90 00:53:14 GMT
References: <235@mojo.UUCP>
Sender: news@ns.network.com
Organization: Network Systems Corporation, Mpls., MN
Lines: 56

In article <235@mojo.UUCP> finn@mojo.UUCP (Finn Markmanrud) writes:
>Does anyone have any experience with these things, or know if
>they work or not? I am most of all wondering what the "Descramblers" are 
>capable of descrambling. HBO, Cinemax etc. (i.e. "pay channels"), or just 
>ESPN, FOX, etc. ("basic service channels")? 

There are two functions needed in cable -converting- and -descrabling-.
Some cable ready tv sets come with built in converters, this is due to
the fact that cable uses all the radio frequencey space on the cable for
TV signals, whereas airwave broadcast TV has large gaps devoted to other
services.  There is a small gap between ch4 and ch5 and a large gap between
ch6 and ch7 and a huge gap between ch13 and ch14 (or is it 12 and 13?).
The other tv channles 2-3, 7-13, and 14-83 are next to each other.

So the converter usually converts the cable channels down to one broadcast
channel (3 or 4) and you tune the converter rather than the tv.

Pay services are usually scrambled, so in addition to a converter you need
a descrambler.  The typical descrambler is built inside of the converter
but for some units you can get external descrablers.  The type sold by
the various "pirate" outfits usually use reconditioned converter/descrambler
units salvaged from who knows where.  I've often suspected that the
cable equipment manufacturors secretly funnel these reconditioned units
to the pirate outfits -- how else to explain the huge volume of units in
the pirate inventory.

Anyhow, the descrabler units DO WORK if you have the right type for your
system (there are several systems around and they are not necessarily
compatible so you have to make sure you get the right equipment.) Once
you get the correct manufacturor type you should be able to view
ALL channels.

Several past Radio-Electronics magazine issues have discussed how
descrambling is done, and they have give construction projects with
complete plans.

>that the device is mostly used for copying rental movies

I am not very familiar with the latest rental movie protection techniques,
but it used to be more popular.  They would play around with the vertical
sync timing such that a VCR trying to record with get wacked out.  It
takes longer for a VCR scanning head to adjust speed than the TV CRT.
Unfortunately, it also takes longer for the VCR player heads to adjust
so that method can cause problems in normal viewing -- and fell into
disfavor -- I thought.

There are moves afoot to do the same kind of vertical sync monkeying on
cable channels that don't want you to be able to record. But the main force
behind this is a company trying to sell its technology.  The cable
channels are pretty competitive, and few want to be the first to disallow
VCR taping -- for fear of losing their customer base.  So I don't see this
happening anytime soon.

-- 
- John Logajan @ Network Systems; 7600 Boone Ave; Brooklyn Park, MN 55428
- logajan@ns.network.com, john@logajan.mn.org, 612-424-4888, Fax 424-2853