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 method for calibrating and correcting circuit errors induced in an aircraft ILS receiving system is disclosed herein. The spectral components of the input signal are processed through bandpass filters and then rectified and integrated in order to produce an output signal representative of the deviation from the desired centerline course. First and second test signals are generated corresponding to first and second known positions. These test signals are sequentially processed in the same manner as the operational input signals in order to develop first and second position errors which represent distortion and circuit induced errors within the processing system. A corrective function is then derived for a range of operational input signals by interpolating from the first and second position errors. All subsequently processed signals are adjusted by applying the corrective function.

Abstract: A receiver includes demodulator, squelch gating and squelch circuit for controlling the gating. A blanking circuit, responsive to impulse type noise, prevents impulse noise energy from contributing to the control of the gating.