LECTURE 3

Objectives

Introduction to various types of antenna used in aviationIntroduction to frequency used in aviation and their characteristics

AntennaAntenna

An antenna is a device which provides means for radiating or receiving radio waves.

In communication link, the transmitter is connected through a cable to one antenna, the signal is radiated to another antenna, and then passes through another cable to the receiver.

Communication between aircraft and airfields must use free space propagation, as do radar and navigation systems.

Broadcast systems such as TV or radio can used one transmitter to serve many receivers via a free space link.

Illustration

Transmitting antenna

Receiving antanna

FREE SPACE

Electromagnetic Wave propagates

Tx lineTx line

Antenna as transition deviceWire Antennas

Printed Circuit Antenna

Types of antennaArray Antenna

Reflector antenna

Aperture antennas

Why choose a correct antenna?

Other than receiving and transmitting energy, an antenna in an advanced wireless system is usually require to optimize the radiation energy in some directions.

For wireless communication systems, the antenna is one of the most critical components.

A good design of the antenna can relax system requirements and improve overall system performance

e.g: A TV for which the overall broadcast reception can be improved by utilizing a high performance antenna.

Antenna on Aircraft

Type and size of antenna varies with the different types of aircraft.The location of antenna depends on the design of aircraft.

Discussion on frequencies used for aviation

Frequency Band

Band Frequency

LF 3 0– 300kHzMF 300kHz– 3MHzHF 3 – 30MHz

VHF 30 – 300MHzUHF 300MHz– 3GHz

S E

The use of the various Radio Frequencies all over the World is allocated by ITU (International Telecommunications Union.The Radio Frequencies are being used in various field, amongst them include :

FM Radio BroadcastTelevision BroadcastLand Mobile Stations (Emergency, Business, and Military)Amateur RadioMarine CommunicationsAIRCRAFT COMMUNICATIONSAIR TRAFFIC CONTROLAIR NAVIGATION SYSTEMS (e.g.VOR/DME,NDB)

VLF-Very Low Frequency

Can be used for communication with submerged submarines and they have some use for this purpose aboard aircraft.

VLF were very important to air navigation years ago, but became increasingly less important as more reliable systems operating at higher frequencies were developed and became widely available.

HF-High Frequency (3– 30 MHz)

HF: This is the basic band for long-range communications, mainly because its transmissions are reflected from the ionosphere.

HF1 = Typically used for Long-Range ATC communications

HF2 = Back up to HF1. (frequently used to listen to the BBC to overcome boredom on longer flights)

HF undergoes the “Skywave” phenomena where ionosphere refracts the HF radio waves and can be utilized for medium and long range radio communications,

HF transmissions are reflected from the ionosphere.

Disadvantage of HF

Efficiency of HF is affected by:All kinds of electrical interference caused by ionosphere disturbances such as thunderstorms. This provides the typical radio noise.Other weather phenomena:

SunlightSeasonSolar Activity

VHF: Very High Frequency

VHF-Very High Frequency (30 – 300MHz)

Normally, VHF between 100 to 200MHz are used for ATC communications, emergency and navigational aids (VOR, DME, ILS).

VHF1 = Used for ATC communicationsVHF2 = Emergency frequency monitoring.VHF3 = Typically used for Data transmissions (ACARS).

Characteristics of VHF Characteristics of VHF RadiosRadios

The propagation characteristics of VHF are optimized for short range communications.The range varies depending the atmospheric conditions but normally is about 180. nautical miles.However it is more prone to blockage by Land Features, buildings, and its lower spectrum frequencies.

Specific UsageVHF Voice communication Source Carrier

118-121.4 MHz Air Traffic Control

121.5 MHz Emergency

121.6 – 121.9 MHz Airport Ground control

123.1 MHz Search And Rescue

123.675-128.8 MHz Air traffic control

128.825-132.0 MHz En Route

132.05-135.975 MHz Air traffic control

The use of VHF for Aeronautical The use of VHF for Aeronautical Communications in MalaysiaCommunications in Malaysia

In Malaysia the use of VHF Radio Systems for Aviation purposes are wholly owned by DCA Malaysia and are stationed on various Hill Stations owned by Telekom Malaysia

UHF-Ultra High Frequency (300MHz– 3GHz)

UHF: similar to VHF, but is restricted mainly for military aviation use.

In Malaysia, UHF is mostly used by Combat Aircraft of the Royal Malaysian Air Force (RMAF).

Other applications includes Navigations/Landing Aids such as the Glide path component of the ILS(Instrument Landing Systems).

UHF broadcasting was used outside Kuala Lumpur and the Klang Valley by private TV station TV3 in the late 80’s with the Government stations only transmitting in VHF (Bands 1 and 3).

At current count, there are 4 distinct UHF signals receivable by an analog TV set in the Klang Vall, Channel 25 (8TV), Channel 29 (TV3 UHF Transmission), Channel 37 (NTV7) and Channel 39 (TV9). Channel 35 is usually allocated for VCR,s, decoder units (i.e.the ASTRO and MiTV set top boxes) and other devices that have an RF signal generator (i.e. consoles).

Question

Names two types of two way communication radios (frequencies) used on an aircraft?What are their purposes?List the benefit of the new communication system for passengers.(broadband for surfing the net,SMS,and phones.)

Benefit of the new communication system for passengers

Some of the benefits of passengers are the broadband, SMS, Phones, these are good to keep business travelers well into their schedules, this allows them to work while they fly, and this alleviates the problems once they land, they can track their flights, know exactly when they will land, etc...

Onboard Communications

Radio is the choice of communications medium for air to ground communications, but there are requirements for considerable onboard communications. such applications as voice communications among flight crew members between flight crew members and passengers.

This communication is provided by a system called an interphone and usually works in conjunction with an audio panel, which not only provides the interphone function but switches speakers and headphones between the various communications and navigation systems aboard the aircraft.

Audio PanelA number of audio sources in the aircraft that the flight crew should monitor

Different transceivers for communicationNavigation equipment (for station identifier)

ADF, VOR, DME, MLSSurveillance equipment – TCAS

Method of selecting which navigation systems will be heard on headphones/speaker Use audio control panel

Example of a control panel