ran lecture 2: radio theory. learning outcomes at the end of this lecture, the student should be...
TRANSCRIPT
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.