I have a sneaking suspicion that the main reason that commercial airliners
don't allow cellular phone use is so that you'll have to use the expensive
one they provide in the back of the headrests. But then, I'm a cynical kind
of guy ;^)

-- Stinger
"Brenda Ann" wrote in message
...

"starman" wrote in message
...

Anyone built a passive receiver for VHF or UHF? Could you listen to an
aircraft's communications as a passenger on the same plane? What does
the law say about using any aircraft receiver on a plane, whether it's
passive or active?


There was a circuit, very simple, for a germanium diode receiver for the
FM
broadcast band. Basically, it consisted of a large loop and variable
capacitor making up the tuned circuit, a germanium diode, a resistor, a
100
pF disc cap, and a crystal earphone. Tuning was by slope detection,
although I can't see why such a device could not be made into a ratio
detector by center tapping the coil (or making two identical coils, and
tapping between them). Also no reason that you could not listen to an
airplane's broadcasts on such a device with the loop cut to those
frequencies.

As for the law, I don't think there actually IS one, only a convention
disallowing use of radio receivers/transmitters onboard commercial
flights.
The reason for this is because the local oscillator of an FM radio falls
directly in the aircraft comms band anywhere above 97.4 MHz. A crystal
radio would not interfere, and would be impossible to detect. One for such
close proximity to the transmitter could be just a small coil, instead of
the loop, and could be built into something like a pocket radio case.

"Stinger" ) writes:
I have a sneaking suspicion that the main reason that commercial airliners
don't allow cellular phone use is so that you'll have to use the expensive
one they provide in the back of the headrests. But then, I'm a cynical kind
of guy ;^)

-- Stinger

Huh? There were rules in place a long time before cellphones to deal
with the issue of electronic equipment being used by passengers on airplanes.

At some point, it became an issue, or someone forsaw it being an issue.
That was back in the days when the average person would only have
an AM/FM radio. But it was in place by the early seventies; definitely
before but that's when I first started hearing about it. Radio equipment,
and more recently many pieces of non-radio electronic equipment, could
radiate signal that might interfere with with airplane communication
and/or navigation, so better to be safe than sorry.

Michael


"Brenda Ann" wrote in message
...

"starman" wrote in message
...

Anyone built a passive receiver for VHF or UHF? Could you listen to an
aircraft's communications as a passenger on the same plane? What does
the law say about using any aircraft receiver on a plane, whether it's
passive or active?


There was a circuit, very simple, for a germanium diode receiver for the
FM
broadcast band. Basically, it consisted of a large loop and variable
capacitor making up the tuned circuit, a germanium diode, a resistor, a
100
pF disc cap, and a crystal earphone. Tuning was by slope detection,
although I can't see why such a device could not be made into a ratio
detector by center tapping the coil (or making two identical coils, and
tapping between them). Also no reason that you could not listen to an
airplane's broadcasts on such a device with the loop cut to those
frequencies.

As for the law, I don't think there actually IS one, only a convention
disallowing use of radio receivers/transmitters onboard commercial
flights.
The reason for this is because the local oscillator of an FM radio falls
directly in the aircraft comms band anywhere above 97.4 MHz. A crystal
radio would not interfere, and would be impossible to detect. One for such
close proximity to the transmitter could be just a small coil, instead of
the loop, and could be built into something like a pocket radio case.

A tunnel diode?

That's it, Frank. Thanks.

Were they used in early TV UHF tuners?

Bill, K5BY

"WShoots1" wrote in message
...

Were they used in early TV UHF tuners?

Bill, K5BY

I don't think so. As I understand, they did work well at UHF
frequencies, but the circuits were very touchy to keep working. There
was alot of excitement for the tunnel diode in the old magazine articles
of around 1960, but it was quickly overshadowed by improved conventional
transistors.

Frank Dresser