Signal Science, Inc.

John P King

Joseph S Friedman

Joseph P Pride, Iii

Joseph T DeWitte, Jr

James D Orndorff

Dorothy A Shannon

A method and apparatus for ultrasonic frequency expansion is characterized by expanding audiometric frequencies before translation into the ultrasonic range. The audiometric signals are first expanded in time by a factor of 1/.beta. where .beta.&lt;1 while generally maintaining the frequency content of the audiometric signals. Next the frequency of the signals is expanded by a factor 1/.beta. while compressing the time scale to that of the original signal. The frequency expanded signal is processed via a single-sideband upconverter to translate the frequency expanded signal into a single sideband signal in the ultrasonic range.

Ultrasonic frequency expansion processor

A direction finding method and apparatus for a radio signal source, modulated by a digital information signal and existing in a heavy interference environment, is based on cyclic crosscorrelation. The direction finding technique exploits the second order periodicity of a transmitted signal having digital modulation, whereby the technique is immune to narrow-band interference. Radio frequency signals are received by two spaced antennas, and the signal of interest can be considered as a cyclostationary process. The signal time of arrival difference between the two antennas is determined using a cyclic crosscorrelation method. This is implemented by sending the electrical signals, developed by the antennas, through a variable delay device, then to a balanced mixer. The composite signal from the mixer is sent to a band-pass filter whose center frequency is equal to the baud rate of the signal of interest. The output energy of the filter is proportional to that portion of the cyclic crosscorrelation function where the cyclic frequency corresponds to the baud rate. With the use of a peak detector, which finds the peak values of the cyclic crosscorrelation function, the time difference of arrival between the two antennas is determined. This, in turn, determines a line of position to the radio source.

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Ellicott City, MD, United States of America

John P King