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
