From: "Michael A. Terrell"
Subject: Re: Re-amplifying filtered-out TV channel?
Date: Fri, 13 Dec 2002 21:56:44 -0500
Organization: Have you seen my bench? No, really! Where is it?
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Nico Coesel wrote:
> Is this for real? I've read about bypassing filters to get more
> channels in the US, but I always thought this was a hoax.
> Over here the cable companies are already using second generation
> encoders/decoders in which the video and audio are digitally
> encoded/decoded. This system hasn't been fully cracked yet (AFAIK),
> recovering the sounds seems to be the biggest problem.
> Before that, a circuit to restore sync and colorburst was already
> necessary to make a coded TV channel give a decent picture.
> Reply to nico@nctdevpuntnl (punt=.)
> Bedrijven en winkels vinden? Adresboekje.nl
There are tuned traps that will remove a single, or multiple
channels, or even a block of channels. This is called "Negative
trapping", because it removes channel (s) when installed. It was popular
20 years ago, and were made by companies like Eagle and Comsonics. They
were popular before digital scrambling was popular and worked ok, as
long as they weren't physically removed. They destroyed a TV channel by
brute force, and had horrible ripple in the passband that would be very
hard to duplicate in reverse, plus they drifted with temperature
Another system used a hi Q trap to remove a jamming signal in the NTSC
guard band between the audio and video carriers, These were referred to
as "Positive traps, because you had to add the trap to get the channel.
The jamming signal was modulated, and caused the AGC to screw up both
video and audio.
A lot of cable companies here are going digital for HDTV, but there
are still some mom and pop systems with 1000 customers. or less who use
what they already have on old 36 or 45 channel systems. Some landlords
have private systems for large apartment complexes who still use this,
Michael A. Terrell