Apparatus for computing the change in bearing of an object

Claim 1

Means to compute the change in bearing of an object during a time period T from continously-received signals E x and E y having amplitudes proportional to x and y components of the bearing of the object, comprising a two-phase clock, a summer, switch means operated under control of the two outputs in different phases of said clock to apply said signals E x and E y in respective phases to said summer, a filter to derive a sine wave from the output of said summer, means to translate the sine wave from said filter to a square wave, whereby the phase difference between said square wave and an output of said clock is a measure of the bearing of the object, and means to determine the change in phase of said square wave during said time period T to provide a measure of the change in bearing of the object, said means to determine the change in phase of said square wave including a counter operated for an integral number of cycles of said square wave during the time period T, and said means to determine the change in phase of said square wave including a high-speed clock having an output coupled to the input of said counter, and coupled through a frequency divider to control said two-phase clock.