From: sch@unx.sas.com (Steve Holzworth)
Subject: Re: Cable TV and you (technical details)
Date: Mon, 9 Nov 1992 22:27:40 GMT
Distribution: nc
Organization: SAS Institute Inc.

sasdst@earl.unx.sas.com (David S. Tyree) writes:


This is going to get technical:

stuff deleted

I wrote:
>|> Cary customers: CVI is currently proposing to do what Raleigh does, and
>|> scramble everything. This WILL RENDER YOUR VCR PROGRAMMING FEATURES USELESS.
>|> It is easier and CHEAPER for the cable companies to make you have a box.

>   Where did you hear this? It is written into the franchise agreement with
>   the Town of Cary that any company providing Cable TV must make its
>   signals "Cable ready". And I beleive that if you only get HBO, they
>   can descramble this at the pole, so you still would not need a box.

I read it in a newspaper report awhile back. It was part of a discussion
involving revising CVI's contract, in addition to adding capability.
Just because it's in the contract now doesn't mean it won't disappear
in future revisions (but I'm glad it's there now).

As far as Cary and HBO: there are several different methods of stopping
or allowing channels into your home:

1) scrambling via sync inversion/sync stripping/signal inversion.
Cary CVI does this for premium channels other than HBO.
The descrambler is either a box on your TV (typical), or a box on the
pole (or ground unit). Either method MAY allow remote authorizations
by the cable company via sending a signal down the cable itself to your
box (addressable convertors). Older units had a programmed key built 
in which had to be changed manually by the cable company if you changed
your service level. When I first moved to Cary, Alert used this method.
You had to take your box to the cable office to upgrade or downgrade
service level. The box on the pole is more expensive because it must
be able to decode ALL channels and pass them ALL through to your house
at once (so you can tune to any given one). The box on your TV just
has to descramble ONE channel at a time, which it typically puts out
on channel 3 or 4. 

2) jamming. Cary CVI does this for HBO. They overlay a jamming signal on
the unscrambled channel signal. The jamming keeps your TV/VCR from 
processing the video and/or audio into a picture. They typically have to
drive out to your house to turn this on or off at the pole.

3) trapping: this is mostly not used anymore, but may be how they block
MTV for the smaller set of people that specifically want it OFF.
What is referred to as a "notch" filter (one or more) is placed in the
cable running to your house (or at the pole). The filter removes the signal
for the specific channel they are blocking. Multiple traps may be used,
but the signal is degraded for each trap added, so normally only one
or two are used.

stuff deleted

>   CVI can block any channel from your house (if you consider the
>   programming offensive) I know MTV blocking is free, don't know
>   about the others.

See above...

>|>
>|> >Why do we need those boxes on top of our TV?  They look ugly, they

 stuff deleted

>    Only if you want a premium channel, PAY-PER-VIEW, or do not have
>    a cable ready TV/VCR, else, your paying for a restrictive device.

Amen.

>-- 
>--------------------------------------------------------------------------------
>David S. Tyree                  SAS Institute Inc.         sasdst@mvs.sas.com
>Publishing Programmer Analyst   SAS Campus Drive           (919) 677-8000 x7405
>Publications Services           Cary, NC 27513             (919) 677-8123 FAX
>--------------------------------------------------------------------------------
>   The opinions expressed are my own and not those of SAS Institute Inc.,
>   Town of Cary, State of North Carolina, United States of America, or Earth.
--
Steve Holzworth
sch@unx.sas.com
x6872
SAS Institute - Open Systems R & D
Cary, N.C.
Newsgroups: triangle.general