Jim Lux wrote:
Chuck Forsberg WA7KGX N2469R wrote:
On Mon, 13 Dec 2004 08:47:43 -0600, Richard Harrison wrote:

Some Guy wrote:
"I have no trouble receiving FM radio broadcasts on a small am/fm radio
I sometimes listen to while onboard commercial jet sirliners (flying at
cruise altitude), but I bever seem to be able to pick up AM radio
stations. It`s just static across the AM band.

Any explanation for this?"

Fuselage of the airliner acts as a waveguide below cutoff frequency
(where diameter is at least 1/2-wavelength). Below cutoff, attenuation
soars rapidly.

FM wavelength is about 3 meters. AM wavelength is about 300 meters.
Propagation of FM inside the fuselage is OK. Propagation of AM inside
the fuselage vanishes quickly.

You need to stick the suction cups of your Zenith portable`s Wave Magnet
to a window to get AM reception.

Best regards, Richard Harrison, KB5WZI

Years ago I could get some shortwave reception by placing the
radio's whip antenna across the window and lowering the shade
to keep in place (and hide the radio). MW stations were generally
too weak to listen to. FM was a jumble at altitude.

These days RFI from the cabin entertainment systems completely
blanks out everything so don't bother trying. Be thankful MP3 players
still work.




One notes that you need to have permission from the plane's pilot to
operate any sort of radio (including a receiver) while in flight. With
receivers, the concern is with things like Local Oscillator or other
leakage signals.

Whether this is a legitimate concern is a topic of discussion (e.g.
they've flown commercial planes with an antenna and logging spectrum
analyzer in an overhead bin, and discovered that lots of folks forget to
turn off their cell phones), but the fact remains that the regulations
say no radios, except those permitted by the pilot in command.

And the reality is the pilot in command of commercial aircraft has to
follow the policies of his employer, most of which take the safe
route of banning everything that might even remotely cause a problem.


--
Jim Pennino

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