High-Efficiency Modulation System

A descriptive and mathematical treatment is given of a means for obtaining modulated radio-frequency power with good conversion efficiency from the usual direct-current source. The method employed is to modify the load line on a saturated radio-frequency amplifier to take care of positive peaks and to grid modulate the amplifier for negative peaks. Load modification is accomplished by absorption and in this system the absorbed power is not dissipated in heat but is returned to the direct-current source for the power-amplifier tube and thereby reduces the drain from the supply. This results in direct-current-to-carrier conversion efficiencics in the order of 50 to 60 per cent when average tubes are used.