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RAN LECTURE 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 10 k. Hz to 300’ 000 MHz.
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 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 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 antenna Array Antenna Reflector antenna Wire Antennas
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 of n y ctio ire D tion Electric Field z aga op Pr Magnetic Field x
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 waves are radiated energy. Subject to attenuation & interference Can be reflected, refracted and diffracted Properties of Radio Waves Consist of oscillating electric and magnetic fields In free space, they travel in straight lines at the speed of light c = 3 108 m/s.
Radio Wave In free space, radio wave travel in straight lines at the speed of light c = 3 108 m/s. Frequency is the number of wave cycles that occur within 1 second. It is measured in Hertz. f = c/l [c is speed of & l 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. 5 m? [speed of light c = 3 108 m/s. ] f = c/l f= 3 108 m/s / 2. 5 m f= 120’ 000 Hz f= 120 MHz
Example What is the frequency of Distance Measuring Equipment (DME) operating at a wavelength of 0. 3 m? [speed of light c = 3 108 m/s. ] f = c/l f= 3 108 m/s / 0. 3 m f= 1 x 109 Hz @ 1000 x 106 Hz f= 1 GHz @ 1000 MHz
Example What is the wavelength of ILS Localizer operating at a frequency of 100 MHz? [speed of light c = 3 108 m/s. ]
Example What is the wavelength of an aircraft communications operating at a frequency of 30 MHz? [speed of light c = 3 108 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 is the prevention of reception of a clear radio signal. Interference also means the superposition of two or more waves from same sources. There 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 VLF 3 KHz - 30 KHz 100, 000 m - 10, 000 m Low Frequency LF 30 KHz - 300 KHz 10, 000 m - 1, 000 Medium Frequency MF 300 KHz - 3 MHz 1, 000 m - 100 m High Frequency HF 3 MHz - 30 MHz 100 m - 10 m Very High Frequency VHF 30 MHz - 300 MHz 10 m - 1 m Ultra High Frequency UHF 300 MHz - 3 GHz 1 m - 0. 10 m Super High Frequency SHF 3 GHz - 30 GHz 0. 10 m - 0. 01 m Extremely High Frequency EHF 30 GHz - 300 GHz 0. 01 m - 0. 001 m Very Low Frequency
Band Frequency LF 30– 300 k. Hz MF 300 k. Hz– 3 MHz HF 3 – 30 MHz VHF 30 – 300 MHz UHF 300 MHz– 3 GHz
Wave Propagation There are three principle paths which radio waves may follow over the earth between the transmitter and the receiver: Surface Wave (Ground wave) Wave Propagation Sky wave Space waves
Follows the contour of the Earth Line of Sight: Clear path between transmitting and receiving antennas
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 transmissions Sky Wave A wave that is refracted by the Ionosphere and returned to earth. Propagate Middle Range Frequencies (HF, VHF). Used for long distance transmissions
Wave Propagation Space Wave A wave which is line of sight (reception dependant on altitude). Propagate Upper Range Frequencies. Used for VHF/UHF Transmissions.
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 HF 1 = Typically used for Long-Range ATC communications. HF 2 = Back up to HF 1. (frequently used to listen to the BBC to overcome boredom on longer flights). VHF 1 = Used for ATC communications VHF 2 = Emergency frequency monitoring. VHF 3 = Typically used for Data transmissions
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 – 300 MHz) Normally, VHF between 100 to 200 MHz 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 (300 MHz– 3 GHz) 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 also UHF signals receivable by Television, example, TV 8, TV 3, NTV 7 and TV 9 and ASTRO.