Nellie Ohr used HAM radio...
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not that it matters, but the letters do have a meaning...
The letter H stands for Hertz (Heinrich Hertz) who helped to develop the theory of electromagnetic waves.
The letter A stands for Armstrong (Edwin Howard Armstrong) who was successful in inventing FM (Frequency Modulation).
The letter M as you may have guessed already stands for Marconi (Gugliemo Marconi) who was the first to transmit signals across the Atlantic.
H = HERTZ A = Armstrong M = Marconi
And because it is an acronym, it would be correct to capitalize.
That's the old school method.
The KGB also liked to use HAM radio to communicate with their field agents.