Localizer receiver proximity and capture

There are times when it is necessary to locate two localizer systems in close proximity of each other. When this is done the two systems have the potential to interfere with each other and the flyability of the localizer can be impaired. In fact when two systems are located at the opposite end of the same runway, interference through mere brute force does occur. To minimize this interference FAA Order 6750.16d requires interlocks to be installed to ensure that only one ILS can radiate at a time. Usually this interlock is operated from the control tower. In Airports where there is no control tower the issue becomes a little more complicated. The intent of this paper is to analyze this interference and develop a model that can predict the effect of one system over the other. How well the receiver discriminates between the radiations of the system that are in proximity to each other depends on the receiver selectivity. The response of these receivers under the capture effect conditions will then depend on the capability of the receiver to reproduce the beat frequency waveform that results when the carrier from one system adds to the carrier from the other. Model results do indicate that the receiver capture systems do perform very well in these circumstances however a slight deviation of the aircraft from the centerline will result in excessive perturbations on course information for approaching aircraft during over flight of the opposite end localizer antenna array.