Analyzing Interference on Aviation Instrument Landing System from Frequency Modulated Broadcasting Systems: the Case of Bole International Airport
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Date
2018-06
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Addis Ababa University
Abstract
An Instrument Landing System (ILS) is a ground-based instrument approach system
that provides precision guidance to aircrafts approaching and landing on a runway
using combinations of radio signals. There are three components of ILS; namely,
localizer (LOC), Glide slope (GP) and Distance Measuring Equipment (DME) or series of
markers. LOC is used by the pilot to determine the location of the airplane relative to the
centerline of the runway; GP provides the slope information (inclination angle) and
DME distance from the beginning of the runway. Among the three ILS subsystems
(components) this thesis focuses on LOC which is operating from 108.1 MHZ to 111.975
MHZ. This frequency range is prone to adjacent channel interference from Frequency
Modulation (FM) broadcasting systems that are operating from 87.5MHZ to 108MHZ.
In the past few years there is an increase in number of FM broadcasting radio stations in
Addis Ababa. FM broadcasting stations are likely to cause intermodulation interference
to the ILS LOC, hence, posing a great risk to aircraft navigation safety. This thesis
addresses interference of Addis Ababa Bole international airport RWY 25 ILS localizers
and analyzes the interference mechanism.
The study accomplished through the establishment and implementation of models
regarding the characterization of the transmitter and its signal, as well the definition of
the aircraft approach path. Model development was done from the bases of field
measurements of ILS LOC power level on a certain approach rout and then translates
each parameter into defining the scenario. Furthermore, the assessments of interference
were performed by using two criteria. One consisted on the raw analysis of the ratio
between the LOC signal power and interfering signals power, and the other is based on
an International Telecommunication Union (ITU) Recommendation. The results verified
the non-existence of any harmful interference generated by Addis Ababa commercial FM
broadcasting networks on ILS LOCs runway (RWY) 25 heading for the time being.
However, the results also indicate that there is interference RWY 07, though it is not
being operational for the time being.
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Keywords
ILS, Localizer, broadcasting, Interference., inter-modulation