It is a shortened form of radiotelegraph - apparatus for transmitting or receiving radio broadcasts. Derived from Radiophone and Radiotelography, words coined in the 1890's
AM on a radio stands for amplitude modulation.
Alpha
Radio
RAdio Detecting And Ranging
Prgenet radio corn
National Public Radio
Delta
Tela
Amplitude modulation.
Radio wave fequency....
Xtra
Radio