Performance of a Medium-wave Radio Transmitter Using Hybrid Modulation.
Kazuhisa Hayeiwa, Hisashi Naka · The Journal of The Institute of Image Information and Television Engineers · 1994
The transmitter whose performance is described here uses hybrid modulation to produce an AM wave directly from the digitalized audio signal.In the prototype transmitter, the efficiency of the analogue-type power amplifier was too low for transmitters with much higher output because the analogue signal from the D/A converter was amplified linearly Using a carrier PWM modulator resulted in a module efficiency of 80%, twice that of the conventional one Since this transmitter has no modulator module like that in conventional transmitter, an overall efficiency of 84-93% (RF output/DC input) is obtained in the MF band.And because transient overvoltages do not occur when the output of the transmitter is shorted, power devices can be protected from breakdowns.In addition, using the serial-type combiner could greatly suppress impulse surges from the output.When a 10-kV (peak) impulse surge was impressed at the output transmitter, only a few volts (peak) appeared at the output of the RF power modules.This means that this tramsmitter is 30-40 times more resistant to lightning surges than conventional transmitters are.1.