[GreenKeys] FRF FSK conv. (was - Two eBay Novelties)

[David Burns]

On 2/9/2014 8:12 PM, Nick England wrote:
> This "dual channel" FRF unit is just dual diversity....The FRF wasn't an intercept
> unit.
Indeed, dual diversity.  I wasn't suggesting it was an intercept unit, 
but yes, diversity and not analogous to the Russian system.
> I believe the Soviet system you are thinking of was DFSK running two
> different TTY signals on a pair of frequencies.
The NSA units I had decoded four audio frequencies each separated (from 
the next lower) by a standard shift (determined by a plug-in filter 
group encased in a metal can about the size of a TV B+ capacitor with an 
octal plug on one end of the assembly), and when both channels were 
running the scope presented a square pattern. (As I recall, I only saw 
that once.)  It had a plug-board (associated with the filter plug-in) to 
allow for dynamically assigning M-M, M-S, S-M and S-S to different 
frequencies.  My NSA buddy said it didn't take long to determine the 
correct mark-space frequency assignments once a transmission started.  I 
only used the standard 850 shift single-channel decoding.  It was a 
single monolithic unit (scope, power supply, decoding logic, filters) 
about two feet tall in the rack.  I think I had 5 or 6 of them, and two 
that worked (using about $100 in tubes [each] at the time.)  It output 
keyed tones for each channel.