Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!apple!oliveb!sun!xor!rom
From: rom@xor.Sun.COM (Achyutram Bhamidipaty)
Newsgroups: sci.electronics
Subject: More need advice on descrambler
Keywords: cable descrambler
Message-ID: <111777@sun.Eng.Sun.COM>
Date: 22 Jun 89 17:01:22 GMT
Sender: news@sun.Eng.Sun.COM
Lines: 62


Follow up to request for help with building a descrambler.

Just to clarify I do have access to an oscilloscope, but its just an old
tektronix that can withstand a direct ICBM hit.

Some notes on what I have observed about the scrambling method.

The sound is fine, when I tune to a scrambled station I can hear all the audio.

If the cable company does anything to the vertical sync it does not affect my
TV, because the picture does not roll.  My assumption that the vertical sync
is normal my not but right but it makes some sense.

The horizontal sync it messed up. I have noticed some interesting things 
though, one is that when the picture is totally out of sync (horizontally)
the color seems normal. Any bits of the picture I can see look ok. However
once in a while the TV will actually lock in the entire picture, when this
happens the picture has really strange colors, it looks like the negative of
the picture, but the only thing I can say for sure is that when the picture is
locked in the color is wrong.

I have hooked my scope up to the monitor output of my TV and this is what the
signal looks like:

###########                  ##########
###########    |--|  -X-|    ##########
###########    |  |  |  |    ##########
###########    |  |  |  |    ##########
###########    |  ---|  |    ##########
###########____|        |____##########____ etc...

The '#' sections are where the picture information is stored. The X represents
a small section where a low amplitude sine wave has been put in, I think. I dont
get a steady trace for the X or the # areas, so the X may have something to
do with the picture. For the sake of having a reference I will show what I get
when I look at the signal for an unscrambled signal.

###########                  ##########
###########                  ##########
###########                  ##########
###########                  ##########
###########                  ##########
###########_____  ___X_______##########____ etc...
               |  |
	       |  |
	       ----

I am doing this from memory I cant remember exactly where the X goes in the
unscrambled version. But I do remember that it was placed in a location 
similar to the scrambled version.

Some other notes on the situation. I plan on using the monitor output of my TV,
this way I dont have to deal with demodulating the signal from the cable 
company. So the final set up, if it works will look like this:

--------|       |-----------|       |--------|
  TV1	|-------|descrambler|-------| TV2    |
--------|       |-----------|       |--------|

-Rom
rom@xor.sun.com