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Describe and explain how a simple radio receiver and transceiver works and then explain one of its uses in an ILS (Instrument Landing System).

Extracts from this document...


Chris Tootell

Physics Coursework 2003

ILS (Instrument Landing System)

Chris Tootell

0743 (HN)







How Does It Work?

UHF and VHF Equipment:

The Aerials:

The Localiser Transmitter:

Glide Path Transmitter:

Autoland Capabilities:

Problems Of The ILS:



In this reading and research project I am going to describe and explain how a simple radio receiver and transceiver works and then explain one of its uses in an ILS (Instrument Landing System). I am then going to go on and explain its application and importance around the world in everyday usage. In the description the main three sections involved in how the ILS works will be covered as well as the background to the use of the ILS and the uses of it.


Now I have covered the way in which radio waves are transmitted and received and the construction of the devices needed I am going to move onto the application of there use. I am going to use an ILS as the use of radio and will describe how it works.

ILS is short for Instrument Landing System. The ILS is basically a pilot interpreted runway approach aid. This means that it will ‘help’ the pilot of an aircraft fitted with ILS equipment to make an approach to an airport that is equipped with ILS transmitting equipment. Although it sounds very simple a design it is actually rather more complicated and uses many different methods of communications that I will discuss later.

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Below I have described two different types of radio waves and how they are transmitted.

Amplitude Modulation - In amplitude modulation, the amplitude of the sine wave (its peak-to-peak voltage) changes. So, for example, the sine wave produced by a person's voice is overlaid onto the transmitter's sine wave to vary its amplitude.


Frequency Modulation- FM radio stations and hundreds of other wireless technologies (including the sound portion of a TV signal, cordless phones, cell phones, etc.) use frequency modulation. The advantage to FM is that it is largely immune to static which is very important when dealing with very accurate electronic devices. In FM, the transmitter's sine wave frequency changes very slightly based on the information signal.

Once you modulate a sine wave with information, you can transmit the information.


The receiver is then simply tuned in to the specific frequency that the transmitter is transmitting on and then the information is fed into the instruments where it is decoded. Once the instruments decode the information that is sent out by the transmitter it is displayed on the instrument face, which can be viewed by the pilot.

The Aerials:

All transmitters of any kind require an aerial to transmit the signal through the air. There are quite a few different types of aerial including the ferrite aerial that is used

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Problems Of The ILS:

Although now the ILS is an almost essential piece of technology on aircraft it didn’t use to be so accurate and many aircraft would attempt a landing in zero visibility only to find that the runway wasn’t where the ILS said that it was. image09.jpg

When the company Airbus came into the aviation market they thought that it would be a good idea to incorporate the ILS system into their new aircraft, which meant that the computer expected the aircraft to land on the runway that the ILS was tuned into. This worked very well until the aircraft wasn’t actually landing. On the 26th June 1988 a new airbus A320 was displaying at an air show, when the onboard computer decided to land. The pilots attempted to climb but the computer kept pushing the nose down. The consequences of which were the aircraft overran the runway into the near by forest.


http://www.allstar.fiu.edu/aero/ILS.htm - A site dedicated to Navigation Systems and avionics for aircraft.

Advanced Physics Text Book; S. Adams - Used as a resource for information about antenna arrays.

Ground Studies For Pilots Book; S.Taylor - A very detailed book dedicated to explain radio aids in aircraft and on the ground.

Avionics, Past & Present; Honeywell – This book gave some good information about avionics in aircraft.

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