[GreenKeys] Ham RTTY and military RATT

[Jim Haynes]

Yeah.  Well in the early days we were just frequency shifting the 
transmitter VFO, nobody was using SSB, and mark was what you got
when you were not typing, so it made some sense to specify the mark
frequency as the operating frequency.  850 shift was chosen because
that's what most of the military and press and others were using.
Far wider than necessary, except that equipment was so drifty in those
days that it allowed you to copy without constantly retuning the receiver.
And of course separate transmitters and receivers that drifted
independently.

I suppose even then purists would specify a channel with a center 
frequency and a width, corresponding to FM for voice and music, but
for RTTY you never got the center frequency coming out so you couldn't
tune to it.

Once we got into SSB of course there is the frequency of the suppressed
carrier which you set on the radio, and then the matter of which tone
frequencies you put into and get out of the radio.  As long as we were
using analog filters the tone frequencies had to be pretty well 
standardized.

Now that we have DSP demodulation it's rather arbitrary what tone 
frequencies are used in SSB.

 	---

 	"Ya can argue all ya wanna, but it's dif'rent than it was."
 	"No it ain't! No it ain't!  But ya gotta know the territory."
 		Meredith Willson, The Music Man