The Instrument Landing System Calibrator employs a combined analog radio frequency downconverter with a digital control system for analysis of difference in depth of modulation of tones generated by an instrument landing system localizer and glide slope transmitters. Signal sensitivity and accuracy is increased by elimination of system and phase noise present in purely analog designs and hybrid analog digital designs where digital signal processing is conducted at audio frequencies. Digital signal processing is conducted at video frequency with a single heterodyne from VHF and UHF frequency through selectable crystals. Selection of ILS channels is extended by the use of high speed video digital processing in conjunction with the use of selectable filters and selectable crystals to include all ILS channels. Interference between channels and from other radio navigation transmitters and FM stations is avoided by image rejection filtering employed by single radio frequency heterodyne and the increased selectivity of the video digital signal processing.