Types of MCW
editI see mention of AM-modulating a carrier with audio Morse code, perhaps even leaving the carrier on while the tone turns on and off, although I would shoot for keying the carrier, also, to save electricity. Either way, the author comments that this is an inefficient transmission method, indubitably referring to the amount of radio spectrum used.
What I've never seen is keying two RF frequencies, equal amplitude, 700 Hz apart. That would provide MCW that could be heard with an AM receiver. It would be more efficient, spectrum- and transmitter-power-wise than AM-modulating a carrier with a tone.
Has that type of MCW ever been used? In applications that use (or used) A2A, wouldn't a "double carrier" have been an improvement? Does it have an official modulation designation? Would we have to "assume" that it would be legal above 50.1 MHz (except 219-220 MHz), or are rules for this type of MCW specifically mentioned in the FCC's Part 97?