[GreenKeys] FSK Intercept equpment (was something about FRF)

[Jim Haynes]

As I understand it FRF was one of a fairly long line of Navy IF type
diversity RTTY converters beginning with the FRA.

Mention of sending messages on two different tone frequencies - doesn't
the U.S. MD-522 do something like that in one of its modes?

Then speaking of intercept, I can only speculate, having no inside
knowledge, but I've previously noted a similarity of the last generation
of hardware RTTY TUs.  The ST-8000, Frederick 1280, Electrocom 400 family
and Dovetron family all have the ability to tune to any mark and space 
frequencies over a fairly wide range.  That suggests they could be used
to monitor any one channel of a multichannel carrier telegraph system
in addition to single channel systems with all different amounts of shift.

jhhaynes at earthlink dot net