This invention relates generally to signal oscillators and more particularly to an offset local oscillator for use with a tracking servo bridge detector which is utilized as part of a system for precision bridge-type measurements on quartz crystal resonators.
Apparatus of this type is disclosed in a publication entitled "Implementation of Bridge Measurement Techniques For Quartz Crystal Parameters" by E. Hafner et al. which appeared in Proceedings of The 30th Annual Symposium on Frequency Control (2-4 June, 1976). On p. 96 of this publication there is described an offset local oscillator unit which is powered and controlled by a main tracking bridge detector wherein the offset is produced at half-frequency by phasing type single sideband techniques and then filtering by means of a phase-locked voltage controlled oscillator at the local oscillator frequency.
The following references are typically illustrative of means for generating single sideband signals.
U.s. pat. No. 3,243,731 -- J. W. Erickson PA1 U.s. pat. No. 3,605,017 -- A. B. Chertok et al.
The present invention is directed to another means for providing a signal offset by a fixed frequency from a generator input for use as the local oscillator in the receiver section of a tracking servo bridge detector.