Abstract: A local oscillator null circuit and method for use in tuning a wideband, heterodyne receiver relatively close to zero frequency without experiencing excessive feedthrough from a local oscillator to an associated IF stage in the receiver. The local oscillator is connected to circuit means for generating a derivative signal proportional to the local oscillator signal and shifted in phase with respect thereto by a desired amount determined by the phase difference between the local oscillator signal and the signal in the mixer output spectrum which is at the local oscillator frequency. The null circuit combines the derivative signal with the mixer output signal proportionally to produce a null at the local oscillator frequency.

Abstract: A wideband, microwave regenerative divider with varactor tuning in which a double-balanced mixer is incorporated in a feedback loop with a varactor-tuned filter and an RF amplifier in the forward loop, with the RF amplifier output fed directly back to the mixer. A series resonant circuit formed by two serially connected back-to-back varactors interconnected by an inductor is tuned by application of a DC tuning voltage to a center tap of the inductor. In the preferred embodiment two regenerative dividers are connected in series in a YIG oscillator system which includes a programmable tuning circuit connected between the VCO tuning signal input for the YIG oscillator and the tuning voltage inputs of the respective regenerative dividers.

Abstract: A system and method for continuous tuning of a YIG oscillator over its entire operating range by control of a resolver in a feedback loop around the oscillator. The resolver and a delay line form a phase shift network the output of which is compared in phase with the output of the oscillator, which is also coupled to the input of the resolver, and the phase-difference signal resulting from the phase comparison is coupled to an integrator connected in turn to the tuning signal input of the oscillator. Repetitive operation of the resolver over its operating range enables continuous tuning of the oscillator over its entire operating range.

Abstract: Magnetic recording tape has groups of coded marks which successively identify successive portions of the tape. An optical reader is positioned to read the marks on the tape as the tape travels through the sound reproduction system, and a decoder decodes the marks and identifies, in numerical form, the specific portion of the tape which is in position for sound reproduction. The system has the capability of identifying the specific portion of the tape in position for sound reproduction irrespectively of the speed or direction of travel of the tape within the system, or the position of the tape when operation of the system is initiated.

Abstract: An automatic direction finding (ADF) system including a direction finding antenna array which connects to a radio receiver to process an audio output signal selectively illuminating a segment of a segmented circular visual directional display indicating the direction from which the received signal arrived. In an FM version, the ADF system electronically switches between antennas in the direction finding antenna array alternately incorporating vector information onto the received carrier in a manner that can be phase detected to produce an audio frequency signal within the normal pre-audio bandpass of the receiver. The audio frequency is then demultiplexed to produce separate vector signals. These separate vector signals are then processed for selectively illuminating a segment of the segmented circular visual directional display.