Development of a New Medium-wave Radio Transmitter using Hybrid Modulation

Abstract

Described is a new 1kW MF transmitter using a hybrid modulation system which can produce AM waves directly from digitalized audio signals by combining the outputs of switching-type RF power modules and an analogue-type RF power module.
The transmitter consists of 16 switching RF power modules, one analogue RF power module, a 12bit analogue-to-digital (A/D) converter, and a D/A converter which reconverts digital information (LSB group, 8 bits) back to analogue signals to modulate the analogue RF power module.
Putting all of these components together results in an AM transmitter with exceptionally high over-all efficiency (85% or more), reliability, signal-to-noise ratio of 72dB or better, and only about 0.4% total harmonic distortion at 80% modulation.