Two-frequency transmitter with audio modulation phasing - radiates clearance signal into broader angle than course signal for suppression of difference-of-depth-of-modulation interference

摘要

A test receiving antenna (TA) on the centre line (CL) of an aircraft runway (RW), near its end, is wired to a test receiver (TE) and output unit (PL). Course and clearance signals (K,R) are supplied by separate transmitters (S1,S2) to an antenna (LA) which radiates synchronised and phase-shifted 90 and 150 Hz AM beams into unequally broad angles on either side of the flight path. Part of the clearance signal is reflected (RR) from, e.g., a hangar (H) back towards the centre line. USE/ADVANTAGE - In airport's instrument landing system. Transmission is insensitive to interference from strong reflections along glide path and fulfils ICAO requirements for so-called Category III landings.