Radio and Navigational Aids LECTURE 3

Objectives Introduction to various types of antenna used in aviation Introduction to frequency used in aviation and their characteristics

Antenna An antenna is a device which provides means for radiating or receiving radio waves. In communication link, the transmitter is connected through a cable to one antenna, the signal is radiated to another antenna, and then passes through another cable to the receiver. Communication between aircraft and airfields must use free space propagation, as do radar and navigation systems. Broadcast systems such as TV or radio can used one transmitter to serve many receivers via a free space link.

Electromagnetic Wave propagates Illustration Electromagnetic Wave propagates Transmitting antenna Receiving antanna FREE SPACE Tx line

Antenna as transition device Wire Antennas Printed Circuit Antenna HF notch antenna is a portion of metal at the base of the tailfin is replaced by fibreglass so that a loop antenna can be formed. It is clearly aerodynamically suitable. At UHF and VHF, ‘blade’ antenna are used, which are essentially monopoles made with a a flat sheet rather than a cylinder. The antenna is encased in a fibre glass shell which is shaped for minimum aerodynamic resistance. This shell also acts as the antenna ‘radome’. Radome = protect an antenna from weather or wind erosion while still allowing antenna to radiate. Usually placed at the top tail fin Printed antenna are often used for satellite communications and navigation systems, because they can be mounted on aircraft skin. An aircraft nose cone may be replaced by a fibre glass radome containing a small microwave reflector antenna which can be rotated vertically and horizontally for use as a forward-looking radar antenna.

Types of antenna Reflector antenna Array Antenna Aperture antennas

Why choose a correct antenna? Other than receiving and transmitting energy, an antenna in an advanced wireless system is usually require to optimize the radiation energy in some directions. For wireless communication systems, the antenna is one of the most critical components. A good design of the antenna can relax system requirements and improve overall system performance e.g: A TV for which the overall broadcast reception can be improved by utilizing a high performance antenna.

Antenna on Aircraft Type and size of antenna varies with the different types of aircraft. The location of antenna depends on the design of aircraft.

Discussion on frequencies used for aviation

Frequency Band LF 3 0– 300kHz MF 300kHz– 3MHz HF 3 – 30MHz VHF S E Band Frequency LF 3 0– 300kHz MF 300kHz– 3MHz HF 3 – 30MHz VHF 30 – 300MHz UHF 300MHz– 3GHz These adjectival designations are convenient in referring to transmission in those bands allocated for radiocommunication by aircraft.

Frequency Band The use of the various Radio Frequencies all over the World is allocated by ITU (International Telecommunications Union. The Radio Frequencies are being used in various field, amongst them include : FM Radio Broadcast Television Broadcast Land Mobile Stations (Emergency, Business, and Military) Amateur Radio Marine Communications AIRCRAFT COMMUNICATIONS AIR TRAFFIC CONTROL AIR NAVIGATION SYSTEMS (e.g.VOR/DME,NDB)

VLF-Very Low Frequency Can be used for communication with submerged submarines and they have some use for this purpose aboard aircraft. VLF were very important to air navigation years ago, but became increasingly less important as more reliable systems operating at higher frequencies were developed and became widely available.

HF-High Frequency HF-High Frequency (3– 30 MHz) HF: This is the basic band for long-range communications, mainly because its transmissions are reflected from the ionosphere. 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) High Frequencies were widely used for domestic aircraft voice communications years ago. Nearly all that traffic moved to Very High Frequencies long ago and domestic aircraft use of Medium Frequencies is now very rare. However, international flights still use the High Frequencies bands routinely for voice communications, because of the much longer distances over which they can be used. All these frequencies can be received by the receiver at this website.

HF transmissions are reflected from the ionosphere. HF-High Frequency HF undergoes the “Skywave” phenomena where ionosphere refracts 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 Solar Activity

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). VHF1 = Used for ATC communications VHF2 = Emergency frequency monitoring. VHF3 = Typically used for Data transmissions (ACARS). VHF: This is the standard air traffic control band using speech modulation. It is limited to LOS, ‘line of sight’ range, normally about 200km. The lower end, 108-118MHz, is restricted to VOR/ILS functions, the remainder is used for civil aviation. All VHF can be used interchangeably for any VHF purposes.

Characteristics of VHF Radios 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, and its lower spectrum frequencies.

Airport Ground control 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 Shows block diagram of AM radio transmitter for speech communication. Source carrier and information (voice) are modulated

The use of VHF for Aeronautical Communications in Malaysia In Malaysia the use of VHF Radio Systems for Aviation purposes are wholly owned by DCA Malaysia and are stationed on various Hill Stations owned by Telekom Malaysia

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 UHF broadcasting was used outside Kuala Lumpur and the Klang Valley by private TV station TV3 in the late 80’s with the Government stations only transmitting in VHF (Bands 1 and 3). At current count, there are 4 distinct UHF signals receivable by an analog TV set in the Klang Vall, Channel 25 (8TV), Channel 29 (TV3 UHF Transmission), Channel 37 (NTV7) and Channel 39 (TV9). Channel 35 is usually allocated for VCR,s, decoder units (i.e.the ASTRO and MiTV set top boxes) and other devices that have an RF signal generator (i.e. consoles).

Question Names two types of two way communication radios (frequencies) used on an aircraft? What are their purposes? List the benefit of the new communication system for passengers.(broadband for surfing the net,SMS,and phones.)

Benefit of the new communication system for passengers Some of the benefits of passengers are the broadband, SMS, Phones, these are good to keep business travelers well into their schedules, this allows them to work while they fly, and this alleviates the problems once they land, they can track their flights, know exactly when they will land, etc...

Onboard Communications Radio is the choice of communications medium for air to ground communications, but there are requirements for considerable onboard communications. such applications as voice communications among flight crew members between flight crew members and passengers. This communication is provided by a system called an interphone and usually works in conjunction with an audio panel, which not only provides the interphone function but switches speakers and headphones between the various communications and navigation systems aboard the aircraft.

Audio Panel A number of audio sources in the aircraft that the flight crew should monitor Different transceivers for communication Navigation equipment (for station identifier) ADF, VOR, DME, MLS Surveillance equipment – TCAS Method of selecting which navigation systems will be heard on headphones/speaker Use audio control panel

Example of a control panel The figure shows two rows One row selects sources for speaker Another row selects sources for the headphones Other sources that does not require any switching includes Voice warning signals from the collision avoidance system and the marker beacon used of instrument landing Audio control panel must provide switching for the communications transceiver transmit function Normally there are 2 transceiver and on can be controlled from the microphone The audio panel is a very critical piece of equipment aboard the aircraft. Since all the audio sources pass through the audio panel, a failure in the audio panel can cause a serious problem. Therefore, many audio control panels have an emergency mode. The emergency mode permits bypassing the audio panel and allows one transceiver to be operated. In many cases, since the speaker amplifier is in the audio panel, there will be no cabin speaker and headphones must be used. To reduce the likelihood of an audio panel failure, many larger aircraft provide two audio panels, one for the pilot and a second for the first officer