An amplitude modulation system that is acheived by suming phase modulated carriers. Orignially marketed by RCA for AM broadcast transmitters. Amplitude modulation (AM) is a form of modulation in which the amplitude of a carrier wave is varied in direct proportion to that of a modulating signal. ... RCA, formerly an initialism for the Radio Corporation of America, is now a trademark used by two companies for products descended from that common ancestor: Thomson Consumer Electronics, which manufactures RCA-branded televisions, DVD players, video cassette recorders, direct broadcast satellite decoders, camcorders, audio equipment, telephones, and related accessories; and...

RCA BTA-50H circa 1960s

How it works

1) The system takes a carrier frequency and splits it into two identical signals.
2) The signals are first phase shifted a few degrees from each other (to provide a base power output with zero modulation from the transmitter).
3) Each signal is then phase modulated by the audio signal, one signal is positively phase modulated while the other is negatively phase modulated.
4) The two signals are then amplified to a desired power.
5) Finally, the two signals are summed in the final output filter stage of the transmitter.

The result is that when the signals are closer in phase, the output amplitude is larger and when the signals are more out of phase, the output is low.

Links

Ross Revenge - Transmitter Room - Ampliphase Theory