[BC] FM Band other used for 19 kHz.

[Thomas G. Osenkowsky]

The second generation Oak cable boxes used a 15.75 kHz
signal to jam the video. That same signal was amplitude modulated
on the FM sound carrier at a low level. To decode you demodulated
the 15.75 kHz signal, used an all pass filter to vary phase which
controlled side shading and amplitude which controlled brilliance.
This could modulate the TV AGC which descrambled the station.

Tom Osenkowsky, CPBE

----- Original Message ----- 
From: <nakayle at gmail.com>
To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
Sent: Wednesday, January 18, 2006 12:14 PM
Subject: Re: [BC] FM Band other used for 19 kHz.


  This reminds me of the terrible waste of using 25% of TV's modulation just
to transmit a sync pulse when modern sets could lock on far less.   In fact,
there no need to transmit a sync pulse at all now since it can be generated
internally in the TV using the color burst as reference. Many cable
descramblers do just this- regenerating missing sync that was removed in the
scramming process.  This would leave almost the whole envelope left for
video modulation greatly improving S/N.  Ofcourse all this will soon be mute
anyway as analog goes the way of the dinosaur.