POWER AND MODULATION CONTROL IN AN AMPLITUDE MODULATOR SYSTEM

摘要

1527762 Amplitude modulators WESTING- HOUSE ELECTRIC CORP 15 Sept 1975 [30 Sept 1974] 37809/75 Heading H3R An RF amplitude modulator amplifier arrangement in which control and maintenance of the power output is obtained under varying line voltage conditions without varying modulation percentage comprises a comparator 18 responsive to a modulating signal at 22 and a variable amplitude reference signal at 20 to provide a pulse width modulated output signal whose duty ratio is dependent on the amplitude of the reference signal at 20, a variable biasing circuit 48 for determining the initial gross power output of 16, a control circuit 60-90 generating a control signal in dependence upon feed-back power output of 16 for varying the amplitude of the reference signal and a filter 32 responsive to the pulse width modulated output to provide to 16 a D.C. component of a predetermined level determining the average power output of 16 and an A.C. component i.e. the modulation signal. The pulse width modulated signal turns a switch 30 on and off periodically and signal components at the audio modulating signal alone are passed by the filter. The power output of 16 may be adjusted to a desired value by a remote or local control 80 also influencing the amplitude of the reference signal. A slow start control 90 enables output power to be gradually built up each time the carrier is turned on.