Aircraft Communication System PDF

Aircraft Communication System Radio Theory  Radio theory emphasizes the transmission and detection of communication signals consisting of electromagnetic waves that travel through the air in a straight line or by reflection from the ionosphere or from a communications satellite....

Aircraft Communication System Radio Theory  Radio theory emphasizes the transmission and detection of communication signals consisting of electromagnetic waves that travel through the air in a straight line or by reflection from the ionosphere or from a communications satellite. Wave  A progressive disturbance in a medium.  Moves outward, possesses energy.  Energy is lost due to friction. Electromagnetic Wave  Electromagnetic waves are formed when an electric field comes in contact with a magnetic field. They are hence known as ‘electromagnetic’ waves. The electric field and magnetic field of an electromagnetic wave are perpendicular (at right angles) to each other. Radio wave  Radio wave is a type of Electromagnetic Wave.  Radio wave is from the portion of the electromagnetic spectrum at lower frequencies than microwaves. They are used in standard broadcast radio and television, shortwave radio, navigation and air-traffic control, cellular telephony, and even remote-controlled toys.  The SI unit for wave frequency is the hertz (Hz), where 1 hertz equals 1 wave passing a fixed point in 1 second. A higher-frequency wave has more energy than a lower- frequency wave with the same amplitude. Radio wave Low Frequency  Long Wavelength  Low Energy  Poor Quality High Frequency  Short Wavelength  High Energy  Good Quality Factors affecting radio waves Diffraction  Occurs in low frequency radio waves, it is the bending of a radio wave. Reflection  Occurs in high frequency radio waves, it is the bouncing back of a radio wave. Refraction  Occurs in high and low frequency radio waves, it is the changing in direction of a radio wave caused by a disturbance. (E.g. Rain) Attenuation  It is a reduction of signal strength during transmission, it is the loss of energy of a radio wave, friction may cause attenuation. Radio Wave Propagation  A radio wave is transmitted via omni directional, directional or pulse & echo method. From the antenna it moves out along three paths, depending primarily upon its frequency. These paths are surface waves, sky waves, and space waves. Radio Wave Propagation Omni directional  Radio wave is propagated in all directions. Directional  Radio wave is propagated in one direction. Pulse & echo  Bouncing back of radio waves. Types of Radio Waves Ground waves / Surface waves  Follows the curvature of the Earth, this wave is restricted by gravity.  VLF, LF, and MF Sky wave  This type of radio wave is stronger than the ground waves and it can overcome gravity, but it cannot penetrate the ionosphere.  HF Space wave  This type of radio wave can overcome gravity and can penetrate the ionosphere, its limitation is line of sight.  VHF, UHF, SHF, EHF Frequency band limits Radiotelephony  Pilots, engineers and air traffic controllers communicate by using the radiotelephony phraseology that consists of a set of standardized words and phrases approved for the radiotelephony communications by ICAO in all routine aircraft situations.  The communication is made possible due to their common and work-related topics. HF and VHF Communication  VHF and HF communication systems use transceivers.  A transceivers is a self contained transmitter and receiver.  The transmitter and receiver both operate at same frequency, and the microphone button determines when there is an output from the transmitter.  In the absence of transmission the receiver is sensitive to incoming signals.  This combination of transmitters and receivers saves a lot of space and weight and are hence largely used. VHF Communication  Very High Frequency is a term used to describe the 30MHz to 300MHz portion of the radio spectrum.  This range of frequencies will provide short-range LOS (line of site) communications.  The range for VHF communications depends on equipment used, antenna height, and terrain(typically 2 to 20 miles). HF Communication  The frequency range is 3-30 MHz  This is used for long range communications because of its longer transmission range.  This is the basic band for long-range communications, mainly because its transmissions are reflected from the ionosphere.  HF transmitters have higher power outputs than VHF transmitters.  A Tuner is used to match the impedance of the transceiver to the antenna.  Use and installation of the HF communication system is same as that of the VHF communication system.  The advantage of using HF communication system over VHF communication system is that it can transmit information over long distance as the output power of the HF transmitter is higher than that of the VHF transmitter. Service Interphone System  The service interphone system provides ground crew personnel and all aircraft crewmembers with facilities that enable two-way voice communications during aircraft servicing or during normal flight operations.  Handset jacks are located throughout the aircraft, internally and externally, for use by ground crew personnel to facilitate aircraft servicing and maintenance. The service interphone switch on pilots' overhead panel P5 is used to disconnect these jacks from the system when they are not in use. Communication  Transmitting information from one party to another.  Using different methods such as radio, METAR, ATIS, etc. Basic communication equipment  VHF Radio  Transponder  ELT VHF Radio  VHF communication systems are the most widely used for maintaining contact between ground and aircraft. This employs "Line Of Sight" transmission. Transponder  A device that receives a radio signal and sends out a signal in response. Mode A  Identification (Squawk Code) Mode C  Identification and altitude (Pressure Altitude) Mode S  Identification, altitude, data exchange. Transponder  “Squawk” assigning a transponder code  Right to left  0-7 Basic Squawk Codes  1200 – VFR  7500 – Unlawful Interference  7600 – Radio Failure/Lost Communications (NORDO)  7700 – Emergency (SOS, MAYDAY) Transponder  OFF Button  ON Button  STBY Button  ALT Button  IDENT Button Emergency Locator Transmitter (ELT)  An equipment which broadcasts distinctive signals on designated frequencies and, depending on application, may be automatically activated by impact or be manually activated.  Self contained and self powered. Transmits on distress frequencies:  121.5 MHz (civilian)  406 MHz for new ELTs  243 MHz (military) Emergency Locator Transmitter (ELT)  Automatic on impact (5G’s).  Battery should be enough to power it for at least 48 hours.  Batteries should be changed or recharged at 50 percent of the battery’s useful life. Categories of Messages Weather Reports ATIS  Automatic Terminal Information Service METAR  Meteorological Aerodrome Report TAF  Terminal Aerodrome Forecast Light Gun Signals