Re: ATC on passengers' headsets

From:         Ray Moody <moody@ironwood.cray.com>
Organization: Cray Research Inc.
Date:         30 Aug 95 14:12:50 
References:   1
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>I'd be interested in this, too.  Is it generally possible to listen to
>ATC radio from inside the aircraft on your own battery-powered receiver?

Yes, it is possible.  It is also illegal and even a little bit dangerous.

Most radios operate by generating a signal 10.8Mhz lower than the
frequency that is to be received.  This signal is mixed with the
incoming signal and the resulting superheterodyne is exactly 10.8Mhz.
This signal is presented to a fixed-frequency receiver.  The result is
consistently good reception at all frequencies the receiver is
designed for.

The problem is that radio receivers leak radio waves.  You can easily
observe this by placing two FM receivers close to each other and
tuning one to a frequency 10.8Mhz lower than the other.  Now what if a
pilot is looking for a signal 10.8Mhz higher than a nearby passenger
is tuned in to...

Since the FM band is just below the air traffic band, FM radios are
also illegal and even a little bit dangerous.

--
								Ray