Ahhhh, yes, I know that sound! Many years ago (let's not ask...) I was a
Navy ET and had to work on those FDM systems. The ones we had were good for
24
channels, 4 KHz wide.
jbt
In a message dated 2/19/2008 11:35:46 P.M. Eastern Standard Time,
[EMAIL PROTECTED] writes:
Mario Filippi wrote:
> The idea to play SW noises sounds great. As long as I can remember
> there was the sound of something like an airplane engine on shortwave,
> never could figure out what that was, maybe when I attend the 'fest
> someone will know what it is.
>
> */s/*
Hello,
It is a Voice Frequency Telegraphy. I know it as FDM for Frequency
Division Multiplex. It sounds like a aircraft engine when tuned on AM.
Most of the activity in the US is Military for point-to-point links.
It is a method of transmitting multiple RadioTeletype channels within a
3 KHz voice radio channel. It uses very narrow shifts for the RTTY
signals and up to about 12 channels can be sent. Most of the military
signals are encrypted but on some FDM there is one channel of Aviation
Weather or News in the clear.
This web page has a good description.
http://crackmonkey.org/pipermail/crackmonkey/2001-July/021165.html
I copied some FDM in my time. It takes a very stable receiver, good
audio filter, good RTTY demodulator, and a steady hand on the tuning
knob. 10 Hertz off frequency can turn good copy into bad.
73 Eric
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**************Ideas to please picky eaters. Watch video on AOL Living.
(http://living.aol.com/video/how-to-please-your-picky-eater/rachel-campos-duffy/
2050827?NCID=aolcmp00300000002598)
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