Duncan,
same audio channel. We were using TMC MMX-2 ISB exciters with the optional
6kHz bandwidth filters. We needed the extra audio bandwidth because we were using
the ISB transmitters at Greenville for program feed to the stations in Europe and Africa,
before we got into satellite program distribution.
One tone pair was lower, maybe between 700 and 1000 Hz, the other tone pair was
maybe somewhere in the lower 2kHz range.
I wish I have taken far more copious notes about the RTTY, had I known we'd have
discussions like this 35 years after the fact!!
73
Sheldon