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.