INTRODUCTION TO RADIO

Keywords

• Radio WaveRadio Wave• WavelengthWavelength• AmplitudeAmplitude• FrequencyFrequency• Communication SystemCommunication System• Transmission SystemTransmission System• Receiver SystemReceiver System• SignalSignal• Electronic EquipmentElectronic Equipment

Communication systems

• Communication was the first requirement for controlling aircraft traffic.

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

Radio Transmitting Equipment

• The transmitter is the device or installation used to generate and transmit ELECTROMAGNETIC WAVES carrying messages or signals, especially those of radio or television.

• The receiver is the part that converts electrical signals into sounds. Example: receiver on radio or television converting broadcast signals into sound or images.

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

Medium for Communication

• For example : telephone and cable television – Medium for transmission signal is

cable and fibre optics• For aircraft or satellite

– Medium transmission signal is AIR using ELECTROMAGNETIC WAVES

What is a Wave

A wave is a disturbance that is produced repeatedly, & transfer energy. Often in the form of vibration & oscillation.

Graphical Presentation of a Wave

Frequency, f

• Frequency is the number of complete waves passing a given point per second. It is measured in Hertz.

• Relationship between frequency, speed and wavelength.

• Frequency f = c

is wavelength, c is speed of light c = 3108

m/s in vacuum

Wavelength

• The distance a radio wave travels during one cycle– One complete change between magnetic and

electric fields.

• Wavelength, = speed of light, c

frequency, f

Amplitude

• Amplitude is the strength, or width, of one wave; it decreases with distance from the transmitting site.

The shorter the wavelength The higher the frequency

What is Electromagnetic Wave

Electromagnetic WaveElectromagnetic Wave

• ElectroElectromagneticmagnetic Wave = Wave =

Electric wave + Magnetic WaveElectric wave + Magnetic Wave• Both waves oscillate at the same frequency

z

x

y

Electric Field

Magnetic FieldDirection of Propagation

Electromagnetic wave

• Electromagnetic wave are used to transmit information by wave motion.

• Invisible Spectrum

Examples of Electromagnetic Wave

• Radio waves (including TV, radio, aircraft communication, radar)

• Microwaves• Infrared radiation• Light • X-rays• Gamma rays

Wavelength (Frequency)

The Electromagnetic Spectrum

• Different frequencies of electromagnetic radiation are better suited to different purposes

• The frequency of a radio wave determines its propagation characteristics

• Radio waves are used to carry the information you want to convey to someone else.

• Radio waves are radiated energy – In free space, they travel in straight lines at

the speed of light.

Radio generally works on AIR waves moving across the ATMOSPHERE.

RADIO WAVES

Radio Waves in Communication

• Radio Wave are everywhere. It is used to Radio Wave are everywhere. It is used to send message to each other (Example: to send message to each other (Example: to broadcast music and TV, aircraft broadcast music and TV, aircraft communication)communication)

• It is possible as Radio Wave can be sent It is possible as Radio Wave can be sent over a very long distance over a very long distance

Radio-wave communications

• Radio-wave communications signals travel through the air in a straight line, reflect off of clouds or layers of the ionosphere, or are relayed by satellites in space.

• They are used in standard broadcast radio and television, short-wave radio, navigation and air-traffic control, cellular telephony, and even remote-controlled toys

Earth Atmosphere

• Earth can cause radio wave to take path other than straight line

• Significant characteristics of earth– Conductor of electricity– Able to conduct low-frequency

• Conductor is a material or device that conducts heat or electricity.

Earth atmosphere

• Another conductor – ionosphere (50-350miles)– Layer of ionized gasses– Act as reflector of radio waves– Low loss– Certain frequencies only (mid range)

Atmospheric Phenomenon

• Three layers:– Troposphere: earth’s surface to about 6.5 mi– Stratosphere: extends from the troposphere

upwards for about 23 mi– Ionosphere: extends from the stratosphere

upwards for about 250mi– Beyond this layer is free space

IONOSPHERE

Atmosphere Layers

As Radio Wave moving in air, They will subject

to?

Radio may be subjected to:

1. Reflection (pantulan/lantuna)

2. Refraction (biasan)

3. Diffrraction (serakan,sebaran)

4. Attenuation (pengurangan)

ReflectionReflection:Reflection: A change in direction of travel of a wave, due A change in direction of travel of a wave, due

to hitting a reflective surface.to hitting a reflective surface.

This is the same characteristic displayed by a radio wave This is the same characteristic displayed by a radio wave as it is reflected from the ionosphereas it is reflected from the ionosphere

A point to remember is that at each point of reflection, A point to remember is that at each point of reflection, the radio wave reverses its phasethe radio wave reverses its phase

Refraction

• Radio waves will bend or refract when they go from one 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 Subject to

• Diffraction:Diffraction: The spreading out of waves, The spreading out of waves, for example when they travel through a for example when they travel through a small opening.small opening.

• Attenuation:Attenuation: The loss of wave energy as it The loss of wave energy as it travels through a medium travels through a medium

Diffraction

• Diffraction is the phenomenon which results in radio waves that normally travel in a straight line to bend around an obstacle.

Direction of wave propagation

Obstacle

Radio Propagation

Depending upon the frequency of the radiated signal

Radio energy is most efficiently propagated by only one of the three main methods:

• Ground wave • Space wave • Sky waves

Transmission of Radio Waves

Effect of ionosphere

• The atmosphere of the earth is concentrated in a think layer about 300 miles thick.

• Ionized layers within this span have the ability to reflect high frequency radio waves .

Radio Propagation

Ground Waves: Part of the transmitted radiation that follows the surface of the earth

Sky Waves Part of the transmitted radiation that is reflected or refracted from the ionosphere.

Space Waves: Part of the transmitted radiation that does not follow the curvature of the earth

Ground Waves

• Radio wave that travels along the earth’s surface (surface wave)

• Vertically polarized• Changes in terrain have strong effect• Attenuation directly related to surface

impedances– More conductive the more attenuated– Better over water

Ground Waves• Two types: Direct & Ground reflected

Sky wave

• Radio waves radiated from the transmitting antenna in a direction toward the ionosphere

• Long distance transmissions• Sky wave strike the ionosphere, is refracted

back to ground, strike the ground, reflected back toward the ionosphere, etc until it reaches the receiving antenna

• Skipping is he refraction and reflection of sky waves

Finding where you are on the radio dial

• There are two ways to tell someone where to meet you on the radio dial (spectrum)– Band– Frequency

Radio Frequency (RF) Spectrum

• The Radio Frequency Spectrum is divided into segments of frequencies that basically have unique behavior.

Frequency of Radio Wave

• Frequency. Radio waves are classified according to their frequency; that is, the number of cycles that occur within 1 second.

• In radio communications the term Hertz (Hz) is equivalent to the term cycle.

• 1,000 Hz = 1 kHz = 1 Kilohertz (k=10^3)

• 1,000,000 Hz = 1 MHz = 1 Megahertz (M=10^6)

• 1,000,000,000 Hz = 1 GHz = 1 Gigahertz (G=10^9)

• 1,000,000,000,000 Hz = 1 THz = 1 Terahertz (T=10^12)

Radio Frequency (RF) Spectrum

S E

Exercises

List down the frequency range for HF,

VHF and UHF

A. RADIO THEORYTable 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

Frequency Usage

• There are a large number of users of radio communication

• How can these users coexist without interfering with each other?

• Radio communicators can operate without interfering by choosing different radio frequency

• Each frequency generated by electromagnetic waves modulated with information on carrier

• Each carrier are distinguished between each other and communication that takes places on one frequency do not interfere with each other

Frequency Spectrum

• The use of filters can filter out any possible frequencies and leaving the frequency desired for communication to take place.

• E.g. standard broadcast radio – channels (assignment of specific radio channels)

• Spectrum = distribution of radio energy as a function of frequency e.g. plot of the strength of radio stations

Frequency Bands

• Allocation of frequencies by international treaty the responsibility of the International Telecommunications Union (ITU). Geneva Frequency Band nomencalture is defined in the ITU Radio Regulations, sext. 2.1. in decade steps of 3 to 30 Hz upwards.

• Aircraft communication is carried out by radio in the following frequency bands:

Specific Usage

• VHF Voice communication Source Carrier118-121.4 MHz Air Traffic Control

121.5 Emergency

121.6 – 121.9 Airport Ground control

121.95 Flight Schools

121.975 Private Aircraft Advisory

123.0Unicom controlled

airports

123.1 Search And Rescue

123.675-128.8 Air traffic control

128.825-132.0 En Route

132.05-135.975 Air traffic control

So, Where am I?

• Back to how to tell where you are in the spectrum

• Bands identify the segment of the spectrum where you will operate– Wavelength is used to identify the band

• Frequencies identify specifically where you are within the band

Another use for frequency and wavelength

• For the station antenna to efficiently send the radio wave out into space, the antenna must be designed for the specific operating frequency– The antenna length needs to closely match the

wavelength of the frequency to be used– Any mismatch between antenna length and

frequency wavelength will result in radio frequency energy being reflected back to the transmitter, not going (being emitted) into space

Encoding Information on Radio Waves

• What quantities characterize a radio wave?

• Two common ways to carry analog information with radio waves– Amplitude Modulation (AM)– Frequency Modulation (FM): “static free”

Modulating Radio Waves

• Modulation - variation of amplitude or frequency when waves are broadcast– AM – amplitude modulation

• Carries audio for T.V. Broadcasts• Longer wavelength so can bend around hills

– FM – frequency modulation • Carries video for T.V. Broadcasts

Types of Modulation

• Amplitude Modulation- In A.M. the amplitude of the carrier wave is made to vary in accordance with the audio frequency.

• In Frequency Modulation, the Frequency of the carrier wave is made to vary in accordance with the Audio wave.

AM vs. FM

• FM is not inherently higher frequency than AM– these are just choices– aviation band is 108–136 MHz uses AM

technique

Frequency Allocation

Question 1: wavelength ()

• What is the wavelength of a standard broadcast station operating at a frequency of 1000kilohertz (kHz)?

What is Interference

• Interference: The superposition of two or Interference: The superposition of two or more waves from coherent sourcesmore waves from coherent sources

Radio-frequency Interference

• If the radiated energy comes from another radio transmitter, then it is considered radio-frequency interference (RFI)

• The transmitting antenna should be specifically designed to prevent the energy from being returned to the circuit.

• It is desirable that the antenna “free” the energy in order that it might radiate into space

Electromagnetic Interference

• If the energy comes from else where, then it is electromagnetic interference (EMI)