Abstract: Apparatus for searching for range indicating pulse signals received as part of distance measuring equipment which first form a list of distance indications in a first search time. The distance indications obtained in a second search time are then logically combined with those indications in the first list and any combination that results in a difference value of less than a prescribed amount is retained for list updating purposes until there is only a single distance indication left in the list. The apparatus can then change to a track mode by placing a search window around the single distance indication thereby reducing the amount of extraneous information to be manipulated by the receiving apparatus.

Abstract: Phase shifting apparatus is illustrated using a feedback loop to monitor the frequency and correct the phase shifting mechanism so that the desired amount of phase shift will occur at all frequencies. The phase shifter comprises a multistage storage means which samples the incoming signal periodically and outputs this information after a time delay. This time delay will vary for a given amount of phase shift depending upon the frequency. Thus, the feedback loop adjusts the sampling time whereby the time period of the sample times is electrically correct.

Abstract: An approach to measuring the phase difference between two signals which automatically compensates for errors due to unequal DC offsets between the two channels of phase derived signal circuitry due to aging or temperature variations of components in these circuits by measuring the positive and negative half cycle time periods of the two signals whose phase is being compared as well as measuring the time difference between the same phase point on each of the two signals and combining this information in accordance with an algorithm set forth herein to obtain a phase measurement. The swapping of the signal paths on a periodic basis and averaging of the results is also used to eliminate errors due to signal processing variations in one of the signal paths as compared to the other signal path.

Abstract: A phase controlled signal generator using a cyclical counter with preset and reset control terminals to provide a continually advancing digital signal. This digital signal is converted in a sine table PROM and D to A converter to a sine wave signal which signal has a phase shift with respect to a reference in accordance with a phase control preset input and which signal can be periodically synchronized to a given starting phase to maintain signal stability or Doppler frequency shift.

Abstract: A VOR bearing measurement scheme wherein the received 30 hertz reference signal is delayed a fixed time to produce an approximately 90 degree phase shifted reference signal. The reference is multiplied by the phase shifted, itself and the variable signals to produce first, second and fourth signals. The variable signal is then multiplied by the phase shifted signal to produce the third signal. The bearing is then indicative of the ratio of filtered third and fourth signals less the ratio of filtered first and second signals.