Modulators – Amplitude modulator – Nonlinear device controlled by modulating signal
Patent
1977-07-29
1979-04-03
Griffin, Robert L.
Modulators
Amplitude modulator
Nonlinear device controlled by modulating signal
325159, 325152, 332 37D, H04B 104
Patent
active
041479858
ABSTRACT:
A low level modulation circuit for use in a radio transmitter obviates the needs for an audio transformer device heretofore required for high signal level modulation of the final stages of a multistage radio frequency amplifier by modulating an initial amplifier stage using a conditioned, low level modulation signal, but yet eliminates additional distortion and noise imposed upon the modulated audio signal by the initial and intermediate amplification stages, through the use of a single, negative feedback circuit. The feedback circuit novelly employs a directional wave coupling device and envelope detection circuitry for deriving signal information from the modulated radio frequency carrier wave just prior to radio transmission of the latter, and functions to combine the derived signal information with the output of a modulating signal source in order to produce a conditioned, low level modulating signal input to the initial amplification stage which modulates the transmitter in a manner to maintain the radio frequency power output of the transmitter at a nearly constant level in spite of variations in supply voltage or amplifier gain, while also reducing noise and distortion in the modulating portion of the transmitted radio output wave. The effects of reflected waves on the antenna line are also sensed by the feedback circuit which uses a shunting diode to drain energy from the initial radio frequency amplification stage and prevent overdriving or burnout of the radio frequency amplifier in the event that abnormally high reflected waves are sensed.
REFERENCES:
patent: 2243221 (1941-05-01), Quilter
patent: 3422356 (1969-01-01), Fritts
patent: 3891926 (1975-06-01), Ishman et al.
patent: 3961287 (1976-06-01), Cacciola et al.
Chin Tommy P.
Griffin Robert L.
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