Transcript INTRODUCTION TO RADIO

INTRODUCTION TO
RADIO
Keywords
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Radio Wave
Wavelength
Amplitude
Frequency
Communication System
Transmission System
Receiver System
Signal
Electronic 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
l
l is wavelength, c is speed of light c = 3108
m/s in vacuum
Wavelength
• The distance a radio wave travels
during one cycle
– One complete change between magnetic and
electric fields.
• Wavelength, l = 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 Wave
• Electromagnetic Wave =
Electric wave + Magnetic Wave
• Both waves oscillate at the same frequency
Electric Field
z
y
Magnetic Field
x
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
• 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 in
Communication
• Radio Wave are everywhere. It is used to
send message to each other (Example: to
broadcast music and TV, aircraft
communication)
• It is possible as Radio Wave can be sent
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 (50350miles)
– 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.
2.
3.
4.
Reflection (pantulan/lantuna)
Refraction (biasan)
Diffrraction (serakan,sebaran)
Attenuation (pengurangan)
Reflection
Reflection: A 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
A point to remember is that at each point of reflection,
the 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: The spreading out of waves,
for example when they travel through a
small opening.
• Attenuation: The loss of wave energy as it
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
•
1,000,000,000 Hz = 1 GHz = 1 Gigahertz
(M=10^6)
• 1,000,000,000,000 Hz = 1 THz = 1 Terahertz
(G=10^9)
(T=10^12)
Radio Frequency (RF)
Spectrum
S
E
Exercises
List down the frequency range for HF,
VHF and UHF
Table of Radio Frequencies
Description
Very Low
Frequency
A. RADIO THEORY
Abbreviation
Frequency
Wavelength
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 Carrier
118-121.4 MHz
Air Traffic Control
121.5
Emergency
121.6 – 121.9
Airport Ground control
121.95
Flight Schools
121.975
Private Aircraft Advisory
123.0
Unicom 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
(l)
• 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
more waves from coherent sources
Radio-frequency
Interference
• If the radiated energy comes from another
radio transmitter, then it is considered radiofrequency 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)