[GreenKeys] on-off radio teletype (not FSK)

[Jim Haynes]

And, I might add, while the two-tone limiterless demodulator has well
known advantages over the limiter-discriminator design, it may be that
the poor design of ham limiter-discriminator TUs accentuates the
apparent superiority of two-tone designs.

If I were still playing with hardware I would build a 
limiter-discriminator TU along the Don Wiggins ideas and see how well it
does.

One thing we have to keep in mind is that the mechanical Teletype is 
really awful compared with an electronic emulator of any kind.  The
reason is mainly that a missed STOP pulse lets the selector cam keep
rotating, which results in several errored characters before things
get back to normal.  The same happens with a false START pulse.  The
literature suggests that this problem costs about 15dB in signal to
noise ratio.  So if you are serious about using a mechanical Teletype
on the radio, by all means put an electronic regenerator between the
demodulator and the machine.