John. I thought those multiplexed systems were 16 channels? I worked on them too as an ET probably 150 years ago. Then again, I've slept a LOT since then!
-Tim On Wed, Feb 20, 2008 at 5:20 PM, <[EMAIL PROTECTED]> wrote: > 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 > _______________________________________________ > Swlfest mailing list > [email protected] > http://montreal.kotalampi.com/mailman/listinfo/swlfest > > To unsubscribe: Send an E-mail to > [EMAIL PROTECTED], or visit the URL > shown above. > > For more information on the Fest, visit: > > http://www.swlfest.com > http://swlfest.blogspot.com > > > > > ------------------------------ > Delicious ideas to please the pickiest eaters. Watch the video on AOL > Living.<http://living.aol.com/video/how-to-please-your-picky-eater/rachel-campos-duffy/2050827?NCID=aolcmp00300000002598> > > _______________________________________________ > Swlfest mailing list > [email protected] > http://montreal.kotalampi.com/mailman/listinfo/swlfest > > To unsubscribe: Send an E-mail to > [EMAIL PROTECTED], or visit the URL > shown above. > > For more information on the Fest, visit: > > http://www.swlfest.com > http://swlfest.blogspot.com > >
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