TWO-FREQUENCY TRANSMITTING APPARATUS WITH TONE-MODULATION PHASING FOR AN INSTRUMENT LANDING SYSTEM

摘要

Two-Frequency Transmitting Apparatus with Tone-Modulation Phasing for an Instrument Landing System Two-frequency transmitting apparatus (S1, S2, LA) for instrument-landing systems is disclosed which is insensitive to DDM (difference in depth of modulation) distortions caused by reflections of the clearance signal from obstacles (H) located near the runway (RW). This insensitivity is achieved by providing different phase shifts of the equal modulation frequencies (90 Hz and 150 Hz) used for the course and clearance signals. The different phase shifts correspond to a phase shift of a common fundamental frequency (30 Hz). The twofrequency transmitting apparatus can be used to specify a localizer course or a glide path. Fig. 1