🚀 go-pugleaf

From article <111377@sun.Eng.Sun.COM>, by rom@xor.Sun.COM (Achyutram Bhamidipaty):
> 
> I have decided to tackle a new project and I would like some advice on some
> points.  What I would like to do is build a descrambler for my cable system.
> I am sure that this is not entirely legal, but the engineer part of me can't
> pass up a challange like this.  

Cable piracy is quite illegal.  Signal theft can (and often WILL) result in
fines and/or imprisonment.  If everyone stole cable premium signals, the
services would cease to exist for economics.

That disclaimer out of the way.....

Many engineers construct descramblers for the challenge of it, or for other
experimental reasons.

There are 525 lines per frame and 59.94 fields per second in the standard
NTSC television image.  This, however does not have much to do with
descrambling, i.e. it is NOT the key (exactly)..

Your first mission is to determine which encription scheme is being used
at YOUR site.  Common systems include:

      Gated Sync 
      Oak
      Orion
      
And several variations.  

A more common method of signal encryption, which is most economical for
the cable company is to insert a pulse modulated signal BETWEEN the
audio and video carriers.  You can determine if this is in use because
the signal pulses and beeps at a fast rate.  A simple resonant frequency
filter is all that is needed to remove this signal.

As for the rest of the scrambling systems, they employ variations on the
theme of "sync confusion"  most often by inserting an out of phase sync
component at the vertical rate, or by stripping off one of the synch
signals (vertical always as far as I know) and "hiding it" in the fm band
or somewhere else.

Without a scope, it is pretty hard to see just which system your company
is using.  A trained eye can hazard a guess though.

As to constructing your own descrambler... I refer you to Radio Electronics
Magazine, available in most grocery stores.  Actually all Electronics
magazines I know of have ads for companies that offer theory books,
construction plans and even kits for the experimenter.

I am posting this because most of the mail I send in reply mode bounces.
Also thought others on the net might be curious.


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