On 9/2/2010 12:51 PM, mm wrote:
On Thu, 02 Sep 2010 07:56:08 -0400, Jeff
wrote:


Jeff
(used to hold a ham license, still remember something.... or part of
something!)

While we're talking about stuff like this.

Long ago when I was in high school I had a Hallicrafters reciever, 4
bands from ?? the table radio band up to shortwave.

And I was listening to the sound from one of the tv stations (even the
radio was AM and tv sound is supposed to be FM, but it matched the
sound coming from our tv on one channel) and every couple minutes I
would have to tune the radio higher. This went on for 40 minutes or
more, with me eventually tuning the radio much higher than it was, so
high I went off the end of the band.

I think there was a higher band so I started at the low end of that,
but couldn't find the same station.

What the heck was going on?

I'll guess that you had to chase the tuning up the band because the
superregenerative oscillator in the Hallicrafters was drifting as the tubes
warmed up the resistors and capacitors in the circuit. I don't know enough to
even guess how you were picking up an FM audio signal on an AM receiver unless
the transmitter was broadcasting some sort of spurious subharmonic that was
amplitude modulated or unless the FM signal and the IF section of the receiver
created a beat frequency (analagous to tuning in a single side band audio signal).