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.



--
Chuck Forsberg www.omen.com 503-614-0430
Developer of Industrial ZMODEM(Tm) for Embedded Applications
Omen Technology Inc "The High Reliability Software"
10255 NW Old Cornelius Pass Portland OR 97231 FAX 629-0665