[Milsurplus] "mystery" modem on 8780/7160 kHz

[D C *Mac* Macdonald]

I would suggest that those who have info
on this contact the ARRL's "Intruder Watch."

I have only heard about it, but know nothing more.

Mac, K2GKK/5



----Original Message Follows----
From: "John Vendely" <jvendely at cfl.rr.com>
To: <milsurplus at mailman.qth.net>
Subject: [Milsurplus] "mystery" modem on 8780/7160 kHz
Date: Sat, 6 Aug 2005 07:21:47 -0400

Greetings,

Can anyone identify the modems in use on 8780 and 7160 kHz USB, and who the 
users might be?  THey appear to be some kind of parallel multitone modem, 
occupying a nominal voice bandwidth, distinguished by an unusually long 
synch sequence of just under 3 seconds at the beginning of the transmission. 
  Signals have been heard at various times in the late afternoon and evening 
at moderate to strong levels here on the Florida space coast, up the east 
coast, and throughout the midwest.  Transmissions seem to be most common 
around the top of the hour, and around the half hour.  Alas, at present I 
have no directional antenna facility on these frequencies.  Apparently 
operating in frequency diversity, transmissions take place simultaneously on 
both frequencies.  As I first heard them on 7160 kHz, I assumed they were 
digital voice operations by ham operators. However, no call signs or other 
activity are ever heard, and upon discovering the second channel at 8780 
kHz, it became obvious that this wasn't the explanation.

73,

John
K9WT