[Qcwa] WWII RTTY

[Harvey&Bessie]

RTTY signals on the air were frequency-shift keying, the mark and space signals being 850
Hz apart (until much later, when narrower shifts were used.) The receivers were dual
diversity, using two separate antennas and two separate receivers, the audio signals being
combined in a special unit designed to select the signal with the best signal-to-noise
ratio. The audio coming out of the receivers was two-tone mark was 2125 Hz and space,
2975. These audio tones were converted into DC mark and space for the TTY machines. The
TTY machines themselves were very complicated mechanical "marvels." The radio circuits
were full duplex on separate frequencies, the transmit circuits sent all the time and the
receive, received all the time. There was no switching between send and receive.
All message traffic was sent from punched tape, keyboard direct keying was confined to the
"order wire," the circuit where the operators communicated with each other about the
traffic (no rag chewing, strictly business).
I was the Chief Engineer at the tape-relay center in Halemano, Hawaii for over a year,
before I transferred to Signal Corps' Plant Engineering Agency in the Pentagon (1952).

Harvey/W4TG