-----Original Message-----
From: Gerry Cox
Sent: 17 August 1998 09:08
To: 'paulb@midcoast.com.au'
Subject: RE: comunication to tv with coax cable


An alternative method of determining the channel is to pick up the line
timebase radiation with a high gain amplifier and small antenna and to
compare the phase of the signals with the line synch of all the broadcast
signals of interested. This is how the TV licence evasion detection systems
work here in the U.K.

Another simpler method is to detect and measure the frequency of the local
oscillator of the TV's tuner. This will have a frequency displaced from the
tuned frequency by the first IF frequency, which is often about 39MHZ. It
can be detected by loosely coupling to the sets antenna cable.

Regards,
Gerry Cox

-----Original Message-----
From: Paul B. Webster VK2BZC [mailto:paulb@MIDCOAST.COM.AU]
Sent: 16 August 1998 05:23
To: PICLIST@MITVMA.MIT.EDU
Subject: Re: comunication to tv with coax cable


Nihat DAGDEMIR wrote:

> in my project I want to determine which channel in use on Tv set at
> hotel's rooms

> is there any projects comunication to tv with coax cable ?.

  Well, co-ax is used to carry supply current to antenna amplifiers and
you could certainly use it to carry a 1-wire bus using, say, a slow
wire-OR-ed serial protocol resembling RS-232.

  You have to consider two problems, as well as making sure all
splitters have direct DC pass-through.  1} How do you figure out which
channel the TV is set to?  (Monitor the tuning voltage presumably)
2} TVs may be "live chassis".  Ouch!
--
  Cheers,
        Paul B.