RANLECTURE 2:

RADIO THEORY

Learning Outcomes

At the end of this lecture, the student should be able to: Describe about radio principles Explain the applications of HF, VHF, UHF in

aviations

What is RADIO?

Radio is wireless transmission through space of ELECTROMAGNETIC WAVES in the approximate frequency range from 10kHz to 300’000MHz.

Why learn radio theory?

Radio theory is essential knowledge for the understanding of the reasons why particular frequencies are used for particular navigational aids system (DME,VOR & etc)

What is Communication

Communication is a process of transmitting INFORMATION from one location to another

MEDIUM is required for the delivery of the information to be exchanged.

For example,Transmission medium for television or telephone is cable or fiber optics

History of Communication

Radio transmission starts in US in 1920 with the invention of RADIO TRANSMITTING EQUIPMENT that capable of transmitting voice and music.

Radio Transmitting Equipment

TRANSMITTER : a device used to generate and transmit radio signals [ELECTROMAGNETIC WAVES].

RECEIVER : a device that receives incoming radio signals and converts them to sound or light. Example: receiver on radio or television converting broadcast signals into sound or images.

Radio Transmission

In communication link, the TRANSMITTER is connected through a cable to one ANTENNA.

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

The signal is radiated to ANOTHER ANTENNA, and then passes through another cable to the RECEIVER.

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

Types of antennaArray Antenna

Reflector antenna

Wire Antennas

Electromagnetic Wave

Electromagnetic Wave

Electromagnetic Wave = Electric wave + Magnetic Wave Electromagnetic wave are used to transmit information

by wave motion. Both waves oscillate at the same frequency

z

x

y

Electric Field

Magnetic FieldDirection of Propagation

Electromagnetic Wave

The types of electromagnetic wave including: RADIO WAVES (for TV, radio, aircraft

communication) Microwaves (radar, microwave oven) Infrared radiation (Body screening, remotes) Visible Light (Bulb) Ultraviolet (Medical Equipments) X-rays (Medical X-rays, Baggage Screening) Gamma rays (Space Observations)

Radio waves

Everyday technologies that depend on radio waves:

Standard broadcast radio and television Wireless networks Cell phones GPS receivers Aircraft Communications ATC communications Satellite communications Police radios, Wireless clocks, Cordless

phones , Garage door openers

Properties of Radio Waves

Radio Wave

In free space, radio wave travel in straight lines at the speed of light c = 3108 m/s.

Frequency is the number of wave cycles that occur within 1 second. It is measured in Hertz.

f = c/c is speed of & is wavelength

Wavelength is the distance a radio wave travels during one cycle.

Amplitude is the strength of the signal. THE HIGHER THE FREQUENCY, THE

SHORTER THE WAVELENGTH

Example

What is the frequency of an Air Traffic Control operating at a wavelength of 2.5m? [speed of light c = 3108 m/s.]

f = c/f= 3108 m/s / 2.5mf= 120’ 000 000 Hzf= 120 MHz

Example

What is the frequency of Distance Measuring Equipment (DME) operating at a wavelength of 0.3m? [speed of light c = 3108 m/s.]

f = c/f= 3108 m/s / 0.3mf= 1 x 109Hz @ 1000 x 106 Hzf= 1 GHz @ 1000 MHz

Example

What is the wavelength of ILS Localizer operating at a frequency of 100MHz? [speed of light c = 3108 m/s.]

Example

What is the wavelength of an aircraft communications operating at a frequency of 30MHz? [speed of light c = 3108 m/s.]

RADIO WAVE can be reflected.

Reflection is the change in direction of travel of a wave, due to hitting a reflective surface.This is the same characteristic displayed by a radio wave as it is reflected from the ionosphere.When reflection of wave happen, the wavelength, frequency and speed do not change.

RADIO WAVE can be refracted

Refraction occurs when the radio waves go from one medium to another medium.

Refract means change the direction of radio propagation of by causing them to travel at different speeds and at different direction along the wave front.

RADIO WAVE can be diffracted. Diffraction of waves is spreading out of waves when

they move through a gap or around an obstacle. Frequency, wavelength and speed of waves do not

change. The direction of propagation and the pattern of waves

are change.

Direction of wave propagation

Obstacle

Radio Wave subject to attenuation Radio wave can pass through an opaque

object, but may suffer attenuation. Attenuation is the loss of wave energy as it

travels through a medium . Or in short word the strength of the radio

wave is reduced.

Radio wave subject to Interference

Interference is the prevention of reception of a clear radio signal.

Interference also means the superposition of two or more waves from same sources.

There are a large number of users of radio communication

How can these users coexist without interfering with each other?

How to avoid interference

Radio communicators can operate without interfering by choosing different radio frequency

To eliminate confusion and facilitate international understanding the majority of the countries of the world have joined in establishing standard classification systems.

The use of the various Radio Frequencies all over the World is allocated by ITU (International Telecommunications Union).

Exercise

• Why do you think airline attendants ask passengers to turn off electronic devices including phones, radios, TVs and computer during take-off and landing?

Radio Frequencies Classification System

Table of Radio Frequencies

Description Abbreviation Frequency Wavelength

Very Low Frequency VLF 3 KHz - 30 KHz 100,000m - 10,000m

Low Frequency LF 30 KHz - 300 KHz 10,000m - 1,000

Medium Frequency MF 300 KHz - 3 MHz 1,000m - 100m

High Frequency HF 3 MHz - 30 MHz 100m - 10m

Very High Frequency VHF 30 MHz - 300 MHz 10m - 1m

Ultra High Frequency UHF 300 MHz - 3 GHz 1m - 0.10m

Super High Frequency SHF 3 GHz - 30 GHz 0.10m - 0.01m

Extremely High Frequency EHF 30 GHz - 300 GHz 0.01m - 0.001m

Band Frequency

LF 30– 300kHz

MF 300kHz– 3MHz

HF 3 – 30MHz

VHF 30 – 300MHz

UHF 300MHz– 3GHz

Wave Propagation

There are three principle paths which radio waves may follow over the earth between the transmitter and the receiver:

Wave Propagation

Line of Sight: Clear path between transmitting and receiving antennas

Follows the contour of the Earth

Wave Propagation

Surface Wave (Ground Wave) A wave which follows the contours of the

earth’s surface. Propagate Low Frequencies (LF,MF) Used for short distance radio transmissionsSky Wave A wave that is refracted by the Ionosphere

and returned to earth. Propagate Middle Range Frequencies

(HF,VHF). Used for long distance transmissions

Space Wave A wave which is line of sight (reception

dependant on altitude). Propagate Upper Range Frequencies. Used for VHF/UHF Transmissions.

Wave Propagation

Application of HF, VHF & UHF

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

HF and VHF Usage on Aircraft 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).

VHF1 = Used for ATC communications VHF2 = Emergency frequency

monitoring. VHF3 = Typically used for Data

transmissions

HF-High Frequency

HF-High Frequency (3– 30 MHz)

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

HF is widely used for domestic aircraft voice communications.

HF-High Frequency

HF undergoes the “Skywave” phenomena where ionosphere reflects 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: Sunlight Season

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).

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.

Specific Usage VHF 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

UHF: Ultra High Frequency

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: Ultra High Frequency

• At current count, there are also UHF signals receivable by Television, example, TV8, TV3, NTV7 and TV9 and ASTRO.