Post on 19-Jan-2016
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)