[GreenKeys] 170 hz - cast in stone ?

[WA5CAB at cs.com]

Most of the early (through the 60's I think except for multi-channel or MUX) 
military terminal units (receiving converters) were FM rather than filter.  As 
such, if you tuned the system to center midway between Mark and Space, they 
would continue to copy if the shift were not 850 Hz.  Some would hang in pretty 
well down to 170 but not well at 85.  

Boehme also built (for ASA I think) an audio receiving converter of the 
filter type where one filter was fixed and the other tunable.  This was the Model 
5C (maybe there were also Models 5, 5A and 5B but I never saw or heard of any). 
 It would work at 170 shift but not terribly well.  The 5C would also copy 
high-speed Morse, and had two input channels for diversity operation (so did 
several of the other military sets, for that matter).

In a message dated 1/10/2007 10:37:24 AM Central Standard Time, 
jhhaynes at earthlink.net writes: 
> U.S. hams could never use 1300 Hz shift because of the FCC rule.
> And early on if you used anything other than 850 or 170 you were
> not likely to make any contacts because the receiving station
> would have filters for only those two shifts.  Today you might
> be able to use other shifts, depending on what the receiving software
> allows.

Robert Downs - Houston
<http://www.wa5cab.com> (Web Store)
MVPA 9480
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