Transmitter with low-level modulation and minimal harmonic emissions

Abstract

An AM radio transmitter utilizes a push-pull MOSFET based design that rejects even-ordered harmonics, and therefore produces minimal electromagnetic radiation. The transmitter contains a low level modulating circuit and a feedback modulation arrangement which linearizes the modulation of the transmitter, and also senses reverse power in the transmitter antenna line, so that the power and modulation can be reduced if the transmitter has a less than optimal load condition existing on an antenna port. A unique modulation amplifier utilizes a Darlington RF pair having an input stage including the collector of the first transistor of the pair, and a pin diode connected to the base of the first transistor of the pair. A radio signal is modulated by varying a voltage on the collector of the input stage, and simultaneously maintaining a constant voltage at an output stage of the Darlington RF transistor pair. Additionally, a bias of the pin diode is simultaneously varied by the audio signal, thereby changing attenuation characteristics of the radio signal.

Dependencies are inferred from the claim text.