Abstract: An efficient circuit for coupling at least three radio frequency transmitters of arbitrary power and frequency to one antenna comprises a three-port circulator connected to the output of each transmitter, a four-port connector and a five-port inphase power combiner, and transmission lines having the same characteristic impedances connecting the circulators through the connector and the combiner to the antenna. The transmission lines interconnecting the components of the circuit have electrical lengths selected to deliver energy in phase to the ports of the connector and to the combiner. In a three-transmitter embodiment, one output port of each circulator is connected to the connector, a second output port of each circulator is connected to the combiner, and the output port of the connector is connected to the combiner. In a four-transmitter embodiment, one output port of each circulator is connected to the connector and the second output port of each circulator is connected to the combiner.

Abstract: Low level amplitude modulated radio transmitting apparatus employing a DC control loop from the output amplifier to the audio modulating stage for maintaining the carrier output level constant. The audio signal to be transmitted is superimposed on the DC control signal and the resulting signal is applied to an operational amplifier that controls a current driver supplying operating potential to the modulating stage. A DC limiter at the input to the operational amplifier limits the DC control signal to the operational amplifier thus preventing continuous overdriving of the RF elements in the event of a disruption in the DC control loop. An audio by-pass permits the audio signal to by-pass the DC limiter and be summed with the limited DC control signal at the input to the operational amplifier.