Abstract: A highly stable variable frequency oscillator is disclosed which employs a ultitap surface acoustic wave device as a frequency standard. A feedback path which includes a voltage controlled switch for selecting a desired output tap drives a differential amplifier, phase detector, low pass filter, voltage controlled oscillator and phase splitter for driving the input tap of the surface acoustic wave device. Various additional feedback paths are also employed. The variable frequency signal is taken from the output of the voltage controlled oscillator.

Abstract: A standby microwave transmitter power amplifier tube is switched into a mowave power distribution system for a phased array in microseconds when any transmitter tube feeding any one of the radiating elements fails and all the radiating elements continue to be fed by respective transmitter tubes after the switching is completed, the switching being accomplished by changing electrical length of a quarter-wavelength waveguide stub to one-half wavelength by switching a reciprocal latching ferrite phase shifter in the stub, in response to termination of microwave power from one of the feed tubes.

Abstract: The described signal receiving system includes control apparatus for making system phase angle track the orientation angle of linear polarization of a radiated carrier, and for keeping substantially small any phase and amplitude distortions of the carrier which result from undesired polarization modulation.

Abstract: A seismic surveillance system for detecting intruders, and the like. A seic transmitter coupled to the trunk of a tree establishes a seismic field in the earth via the roots of the tree. A seismic receiver similarly coupled to another tree detects the field and the presence of an intruder on the earth in which the field is established is detected by noting changes in the phase, amplitude, or frequency of the seismic field.

Abstract: A battery charging circuit which monitors the terminal voltage of the battery being charged and when the terminal voltage drops off, which occurs at full charge, the circuit operates to terminate the charging.