Abstract: An antenna matching apparatus tunable to different frequencies is disclosed for use with a high frequency transmitter that is rapidly switchable between different transmitting frequencies by a control unit according to a predetermined frequency scheme. This apparatus which is tunable as quickly as the transmitter, includes two or more antenna tuning means tuned to different frequencies which are tuned to different frequencies and switched rapidly by the control unit.

Abstract: A transmitter control system for transmitters having means for selectively switching one channel to another in the multiple channels and means for controlling the transmitter output so as to deactivate, activate and reduce the transmitter output. The system comprises comparator means for comparing a start signal from the transmitter output control means with a detected signal of the transmitter output, the output of the comparator means being adapted to selectively drive at least one of the channel switching means for switching channels and a transmitter power reduction control circuit included in the transmitter output control means upon occurrence of a detected signal of the transmitter output indicative of a failure of the transmitter.

Abstract: An FM receiver includes a varactor tuned RF filter to which is applied a bias voltage and a 20 Hz sinusoidal signal for varying the varactor capacitance and the resonant frequency of the filter. As a result, an FM broadcast signal in the pass-band of the filter is phase-modulated by the filter. The second harmonic of the phase modulation is recovered and coupled to a synchronous detector driven at a 40 Hz rate to provide an error voltage. The bias voltage is related to the integral of the error voltage. A difference between the frequency about which the tuned circuit periodically varies and the carrier frequency of the FM signal cause the bias voltage to vary so as to reduce the magnitude of the difference, thereby fine-tuning the receiver.

Abstract: A trailing wire antenna coupling and control method for providing maximum voltage limited power output from power amplifiers of a high power low frequency RF transmitter system while varying the inductance of the coupling circuit to present a high resistance load having practically zero reactance to the power amplifiers, all during extension and retraction of the antenna toward and from its optimum length, as well as at the optimum length.

Abstract: An antenna coupler samples the power transferred between the transmitter and the load, and at two equal distance points from the load. The coupler, based upon the value of the samples, connects a tuning stub to the transmission lines that ensures matched impedance conditions between the transmitter and the load.

Abstract: A high power, high frequency radio transmitter is connected to an antenna through an adjustable impedance coupling device which comprises a helical coil having a number of straight-sided triangular turns. Remotely operable, pneumatic cylinders are mounted on each side or segment of the coil turns in electrical contact therewith and have piston rods which can be moved into and out of electrical contact with a respective fixed conductive member or bus disposed alongside the coil. Additionally, a number of capacitors can be connected into the coupler circuit as required by the similar movement of piston rods into contact with a similar bus, each such piston rod being housed within a pneumatic cylinder electrically connected to a respective one of such capacitors.

Abstract: Apparatus for automatically tuning a circuit to a radio frequency signal. The apparatus has a signal supply for supplying the radio frequency signal to the circuit. A frequency counter and variable impedance are also connected in the circuit. A motor changes the setting of the variable impedance to vary its impedance. The frequency counter is connected to the signal supply means and produces a digital signal representative of the frequency of the radio frequency signal for controlling operation of the motor. The impedance of the circuit is thus varied in relation to the frequency of the radio frequency signal to provide coarse tuning of the circuit.

Abstract: The local oscillator frequency in a communication tuning system is selected to either high side mix or low side mix as appropriate to place the local oscillator frequency and image frequency outside the bandpass range of the bandpass filter. This allows bandpass filters having a frequency range equal to approximately twice the IF frequency in a transmitter, and approximately four times the IF frequency in a receiver.