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

[Jim Haynes]

There is a publication available on the web titled "The art & Skill of
Radio-Telegraphy" perhaps 3rd edition and it has a chapter on the
high-speed Morse stuff.  Not the short bursts for hiding the signal, but
continuous transmission of messages commercially and military.

The latest edition seems to be available only in hard copy but is quite
inexpensive 
http://n9bor.us/index.php/morse-code/the-art-skill-of-radio-telegraphy