INTRODUCTION

HISTORY The Airports Authority of India (AAI) is an organization working under the Ministry of Civil Aviation that manages all the airports in India. It was formed under the act of parliament(AIRPORTS AUTHORITY OF INDIA ACT 1994) by merging the INTERNATIONAL AIRPORTS AUTHORITY OF INDIA and NATIONAL AIRPORTS AUTHORITY with a view to accelerate the integrated development, expansion and modernization of the air traffic services, passenger terminals, operational areas and cargo facilities at the airports in the country.The AAI manages and operates 126 airports including 12 international airports, 89 domestic airports and 26 civil enclaves. The corporate headquarters (CHQ) are at Rajiv Gandhi Bhawan, Safdarjung Airport, New Delhi. V.P Agrawal is the current chairman of the AAI.

FUNCTIONS To control and manage the entire Indian airspace (excluding the special user airspace) extending beyond the territorial limits of the country, as accepted by ICAO.

Provisioning of Communication and Navigational aids viz. ILS, DVOR, DME, Radar, etc.

To Design, Construct, Operate and Maintain International Airports, Domestic Airports, Civil Enclaves at Defence Airports.

Development and Management of International Cargo Terminals.

Provisioning of Passenger Facilitation and Information System.

Expansion and Strengthening of Operational areas viz. Runways, Apron, Taxiways, etc.

Provisioning of Visual Aids.

AAI TODAYAAI manages 126 airports, which include 11 international airports, 89 domestic airports and 26 civil enclaves at Defense airfields. AAI also provides Air Traffic Management Services over entire Indian Air Space and adjoining oceanic areas with ground installations at all airports and 25 other locations to ensure safety of aircraft operations. All major air-routes over Indian landmass are Radar covered (24 Radar installations at 11 locations) along with VOR/DVOR coverage (72 installations) co-located with Distance Measuring Equipment (71 installations), 39 runways provided with ILS installations with Night Landing Facilities at 36 airports and Automatic Message Switching System at 15 airports. AAI's successful implementation of Automatic Dependence Surveillance system, using indigenous technology, at Calcutta and Chennai Air Traffic Control Centers, gave India the distinction of being the first country to use this advanced technology in the South East Asian region enabling effective Air Traffic Control over oceanic areas using satellite mode of communication. Use of remote controlled VHF coverage, along with satellite communication links, has given added strength to our Air Traffic Management System. During the first year of the millennium, AAI endeavors to make its operations more transparent and the availability of instantaneous information to customers by deploying state-of-art Information Technology

INTERNATIONAL CIVIL AVIATION ORGANISATION (ICAO) The International Civil Aviation Organization (ICAO), an agency of the United Nations, codifies the principles and techniques of international air navigation and fosters the planning and development of international air transport to ensure safe and orderly growth. Its headquarters are located in the Quartier International of Montreal, Canada. The ICAO Council adopts standards and recommended practices concerning air navigation, its infrastructure, Flight inspection, prevention of unlawful interference, and facilitation of border-crossing procedures for international civil aviation. In addition, the ICAO defines the protocols for air accident investigation followed by transport safety authorities in countries signatory to the Convention on International Civil Aviation, commonly known as the Chicago Convention.

INDIAN AIRPORTS There are 449 airports/airstrips in the country. Among these, the AAI owns and manages 5 international airports, 87 domestic airports and 28 civil enclaves at defense airfields and provides air traffic services over the entire Indian airspace and adjoining oceanic areas. AIRPORT CLASSIFICATION Airports are presently classified in the following manner: International Airports: - These are declared as international airports and are available for scheduled international operations by Indian and foreign carriers. Presently, Mumbai, Delhi, Chennai, Calcutta and Thiruvananthapuram are in this category.

Domestic Airports: Customs Airports with limited international operations: - These have customs and immigration facilities for limited international operations by national carriers and for foreign tourist and cargo charter flights. These include Bangalore (CE), Hyderabad, Ahmedabad, Calicut, Goa (CE), Varanasi, Patna, Agra (CE), Jaipur, Amritsar, Tiruchirapally, Coimbatore, Lucknow. (CE - Civil Enclave) Model Airports:- These domestic airports have minimum runway length of 7500 feet and adequate terminal capacity (400 passengers or more) to handle Airbus 320 type of aircraft. These can cater to limited international traffic also, if required. These include Bhubaneswar, Guwahati, Nagpur, Vadodara, Imphal and Indore. Rest 6 Nos. of airports, developed under Model Airports concept has graduated to the classification of Customs Airports, given above.

Other Domestic Airports:- All other 71 domestic airports are covered in this category.

Civil Enclaves in Defense Airport:- There are 28 civil enclaves in Defense airfields. Twenty civil enclaves are in operation.

ABOUT THE DELHI AIRPORT After its privatization the Delhi airport was handed over to the GMR group. At present the DIAL (Delhi International Airport Ltd.) is responsible for its maintenance. The DIAL group is undertaking many modernization projects to help it to enter the league the most technologically advanced airports of the world. Most of these modernization projects are being done with a view to enhance passenger convenience. The AAI holds 26% shares in the DIAL. Every building and each terminal in the Airport complex is owned by DIAL except for the ATS building which maintained by the government or the contracting state of the UN. DIAL receives all the landing and parking charges whereas AAI receives all the RNFC (Route Navigation Facilities Charges). All the equipments installed in an airport depend primarily on the geographical features of the location. Delhi does not face any adverse weather conditions and lies in the great northern plains region of India. But at the same time it faces extreme foggy conditions during the winter season which reduce the visibly to almost zero which in turn makes landing extremely difficult. Hence to cater to this problem the Delhi airport is equipped with ILS Cat 3(Instrument Landing System Category 3) which enables landing even at zero visibility conditionsREVENUE Most of AAI's revenue is generated from landing/parking fees and fees collected by providing Air Traffic Control services to aircraft over the Indian airspace. Only 16 of the 126 airfields operated by the AAI are profitable while the other airports incur heavy losses due to under utilization and poor management.PRIVATISATION OF AIRPORTS The AAI was involved in a tussle with the Ministry of Civil Aviation over the issue of privatization of its two most profitable airports, Delhi Airport and Mumbai Airport. The Government of India handed over these two airports to private companies for the purpose of modernization in 2006. The privatization for Mumbai has been handed to GVK Group and for Delhi to the GMR Group. The airports which have been privatized are : Cochin- Cochin International Airport Bangalore Bengaluru International Airport Delhi Indira Gandhi International Airport Hyderabad- Rajiv Gandhi International Airport Mumbai- Chhatrapati Shivaji International Airport

ORGANISATION

AIR TRAFFIC CONTROL Air traffic control (ATC) is a service provided by ground-based controllers who direct aircraft on the ground and in the air. The primary purpose of ATC systems worldwide is to separate aircraft to prevent collisions, to organize and expedite the flow of traffic, and to provide information and other support for pilots when able. In some countries, ATC may also play a security or defense role (as in the United States), or be run entirely by the military (as in Brazil). In addition to its primary function, the ATC can provide additional services such as providing information to pilots, weather and navigation information and NOTAMs (Notices to Airmen). In many countries, ATC services are provided throughout the majority of airspace, and its services are available to all users (private, military, and commercial). AIRSPACE Airspace means the portion of the atmosphere controlled by a particular country on top of its territory and territorial waters or, more generally, any specific three-dimensional portion of the atmosphere. Controlled airspace exists where it is deemed necessary that air traffic control has some form of positive executive control over aircraft flying that airspace Uncontrolled airspace is airspace in which air traffic control does not exert any executive authority, although it may act in an advisory manner.

Airspace may be further subdivided into a variety of areas and zones, including zones where there are either restrictions on flying activities or complete prohibition of flying activities. HISTORY OF AIR TRAFFIC CONTROL In 1919, the International Commission for Air Navigation (ICAN) was created to develop General Rules for Air Traffic. Its rules and procedures were applied in most countries where aircraft operated. The United States did not sign the ICAN Convention, but later developed its own set of air traffic rules after passage of the Air Commerce Act of 1926. This legislation authorized the Department of Commerce to establish air traffic rules for the navigation, protection, and identification of aircraft, including rules as to safe altitudes of flight and rules for the prevention of collisions between vessels and aircraft. As more aircraft were fitted for radio communication, radio-equipped airport traffic control towers began to replace the flagmen. Increases in the number of flights created a need for ATC that was not just confined to airport areas but also extended out along the airways. In the subsequent years many organizations were established with a view to provide air traffic services in various regions. But all these organizations constituted in different regions and countries worked independent of each other which made air transportation extremely unmanageable especially for international flights. Hence, the need of the hour was an international organization which would lay standard specifications for international civil aviation. Hence the INTERNATIONAL CIVIL AVIATION ORGANISATION was constituted.

. AIR TRAFFIC MANAGEMENT An information service and alerting service are the basic levels of air traffic service, providing information pertinent to the safe and efficient conduct of flights and alerting the relevant authorities should an aircraft be in distress. These are available to all aircraft through an FIR. FLIGHT INFORMATION REGION (FIR) The airspace of the world has been divided into homogeneous regions called FIRs. A Flight Information Region (FIR) is an aviation term used to describe airspace with specific dimensions, in which a Flight Information Service and an alerting service are provided. It is the largest regular division of airspace in use in the world today. Any portion of the atmosphere belongs to some specific FIR. Smaller countries' airspace is encompassed by a single FIR, larger countries' airspace is subdivided into a number of regional FIRs. Some FIRs may encompass the territorial airspace of several countries. Oceanic airspace is divided into Oceanic Information Regions and delegated to a controlling authority bordering that region. The division among authorities is done by international agreement through ICAO.There is no standard size for FIRs, it is a matter for administrative convenience of the country concerned. The FIR is responsible for providing air traffic services to all the flights that are: Entering (overhead) Leaving (overhead) Taking off Landing

In India there are five such FIRs namely: Delhi Mumbai Chennai Calcutta Guwahati

The region of airspace over which an FIR is responsible for providing air traffic services is broadly classified as:

Area Approach Tower

An FIR may include many airports within itself. For example the Delhi FIR includes Jaipur, Varanasi, Nagpur, Amritsar airports etc. The delhi airport is connected to all these stations through various media links to enable the effective management of air traffic services in the Delhi FIR.

ATS ORGANISATION

AIR TRAFFIC MGT.AIR TRAFFIC CONTROLCNSCOMMUNICATIONNAVIGATIONSURVEILLANCEFLIGHT CONTROLAREA CONTROLcAERODROME CONTROL SURFACE MVMENT CONTROLHFRT,AIS,NOTAM, AMSS, VHF,ASBSILS, VOR, DME ,NDBPRIMARY AND SECONDARY RADAR

AIR TRAFFIC MANAGEMENT It can be broadly categorized as CNS ATC

CNS Communication, navigation and surveillance which are the three basic facilities which aid civil aviation. Thus, CNS are the building blocks of ATM. COMMUNICATION is a process of transferring information from one source to another. Communication is commonly defined as "the imparting or interchange of thoughts, opinions, or information by speech, writing, or signs". Communication can be perceived as a two-way process. But in civil aviation it is one-way process. At any time either the controller can speak or the pilot can speak.

COMMUNICATION in civil aviation can be further classified as : Ground to ground: This enables various stations in the AFTN (aeronautical fixed telecommunications network) to communicate via low or high speed links. Various messages containing important information are exchanged. The communication is based on store and forward principle.

Ground to Air: This includes all the communication between the controllers and the pilot. It may include voice communication or DATIS or any other form of messages. Ground to Air communication generally uses either VHF of HF frequencies. Communication takes place through transmitters and receivers installed o the ground as well as on board the aircraft. VHF and HF are used for voice communication. VHF transmitters have short range while HF can be used for communicating over long distances.

Air to Air: This may include communication between the pilots of two aircrafts in the air. Such type of communication also uses VHF and HF frequencies.

NAVIGATION is the process of reading, and controlling the movement of a craft or vehicle from one place to another. It is also the term of art used for the specialized knowledge used by navigators to perform navigation tasks. Navigation in civil aviation was earlier accomplished by means of various equipments such as NDB, ILS, DVOR, DME. NDB is the oldest known navigational toll. It works on the basic principle of the magnetic compass. Nowadays, advanced equipments such as the VOR and DME are used as navigational aids.

DVOR is the directional very high frequency omni radio range which measures the azimuth angle with respect to the north. It radiated lines across 360 deg each of which are spaced 1 deg apart. There may be several VORs installed in an FIR. When an aircraft comes overhead a VOR it gives the pilot the direction it must move in order to reach the next VOR on the air route to its destination.

ILS is the instrument landing system which helps the aircraft to land safely. DME gives the slant distance of the aircraft.

SURVEILLANCE is the monitoring of the behavior of a person or group of people, often in a surreptitious manner. The word surveillance is commonly used to describe observation from a distance by means of electronic equipment. In civil aviation surveillance equipment is installed in each airport to monitor the movement of all the aircrafts within its region of operation. Primary and secondary radar are used to aid surveillance in civil aviation.

VHF UNITCommunication is the process of sending, receiving and processing of information by electrical means. In Radio communication, for transmission information/message are first converted into electrical signals then modulated with a carrier signal of high frequency, amplified up to a required level, converted into electromagnetic waves and radiated in the space, with the help of antenna. For reception these electromagnetic waves received by the antenna, converted into electrical signals, amplified, detected and reproduced in the original form of information/message with the help of speaker.Frequency band and its uses in communicationsBand NameFrequency Band

Ultra Low Frequency (ULF)3Hz - 30 Hz

Very Low Frequency (VLF)3 kHz - 30 kHz

Low Frequency (LF)30 kHz - 300 kHz

Medium Frequency (MF)300 kHz - 3 MHz

High Frequency (HF)3 MHz - 30 MHz

Very High Frequency (VHF)30 MHz - 300 MHz

Ultra High Frequency (UHF)300 MHz -3 GHz

Super High Frequency (SHF)3 GHz - 30 GHz

Extra High Frequency (EHF)30 GHz - 300 GHz

Infrared Frequency3 THz- 30 THz

Name Of The EquipmentFrequency BanD

NDB200 450 KHz

HF3 30 MHz

Localizer108 112 MHz

VOR108 117.975 MHz

VHF117.975 137 MHz

Glide Path328 336 MHz

DME960 1215 MHz

UHF LINK0.3 2.7 GHz

RADAR0.3 12 GHz

The allocated frequency range for VHF communication is 108-156 MHz. Of this, AAI operates in the range of 117.975-136 MHzs. Each airport operational under AAI has been designated a frequency range. This division is termed as horizontal division. The Safdarjung Airport communicates at 122.3 MHzThe administration of the Indian Air Space is divided into Flight Information Regions (FIRs). There are four major FIRs New Delhi, Kolkata, Chennai and Mumbai. Each of the FIRs extends till about 200 nautical miles.Administration within these 200 nautical miles is also subdivided into Area, Approach and Tower Control. Maximum catering of Air Traffic is in Approach Region.

Each subdivision sends signals at a particular frequency to avoid any kind of interference. In the Approach subdivision, the aircraft is placed in different Air Flight levels to avoid any clash. Hence, approach needs more frequencies. In order to have an uninterrupted communication, each level is allocated multiple frequencies, to be used as standby.Two basic equipments required for VHF communication:a) Transmitterb) ReceiverThe transmitter and receiver consist of two tuned circuits each, all four tuned to the same frequency.

Transmitter:The transmitter is an electronic device, which usually with the aid of the antenna propagates an electromagnetic signal. A normal radio frequency transmitter uses a balanced modulator. In a balanced modulator, a signal is modulated using two carriers that are 180 degrees out of phase. The resulting signals are then combined in such a way that the carrier components cancel, leaving a DSB-SC (double sideband, suppressed carrier) signal.A balanced modulator is a device that modifies a signal; usually in the form of amplitude modulated (AM) radio signal. It takes the original signal that has both sidebands and a carrier signal, and then modulates it so that only the sideband signals come through the output of the balanced modulator. This creates a balanced signal, as there is less noise because the carrier signal has been removed. Amplitude modulation is a way for a signal to be transmitted over distances. It is the most commonly modified signal for use with a balanced modulator. Understanding how it works will demonstrate how a balanced modulator works. The AM signal is originally sent with a carrier signal in the form of a wave. The wave is then modulated, or changed, by an audio signal that is also in the form of a wave. This produces a signal that has the original carrier signal plus two bands, one on top of the original signal and one on the bottom. These are referred to as sidebands and are exact copies of each other. A signal like this is called a double-sideband amplitude modulated (DSB-AM) signal. The sidebands, because they were modified by the originating audio waveform, are the signals responsible for carrying the information that is being transmitted. Once modulated, the carrier signal doesnt serve a real practical purpose anymore, and it only shows that a signal is being sent. It does, however, take up a larger chunk of power than the two sideband signals, and also creates a less-clear signal. To remedy, or modulate, this situation, a balanced modulator would be used. The balanced modulator removes or suppresses the carrier signal, so that only the two sideband signals remain. The signal that remains now has several times more power because the carrier signal is not there to drain it away. This type of signal is referred to as double-sideband suppressed-carrier (DSBSC). In addition to being more powerful, the signal is also cleaner as it has less signal noise, which the carrier signal can often create. At some point, a DSBSC signal needs to have its carrier signal regenerated. This will allow for the signal to be put back into its original form for reception. In the case of an AM signal, it allows the signal to be received on the proper frequency and be heard. This can be taken care of by a device such as a beat frequency oscillator.

Receiver:The receiver units used for the radio communication purposes of AAI typically use a Super heterodyne Receiver.In electronics, a *super heterodyne receiver*(sometimes shortened to *superhet*) uses frequency mixing or heterodyning to convert a received signal to a fixed intermediate frequency , which can be more conveniently processed than the original radio carrier frequency. Virtually all modern radio and television receivers use the superheterodyne principle. The principle of operation of the superheterodyne receiver depends on the use of heterodyning or frequency mixing . The signal from the antenna is filtered sufficiently at least to reject the "image frequency and possibly amplified. A local oscillator in the receiver produces a sine wave which mixes with that signal, shifting it to a specific intermediate frequency (IF), usually a lower frequency. The If signal is itself filtered and amplified and possibly processed in additional ways. The demodulator uses the IF signals rather than the original radio frequency to recreate a copy of the original modulation (such as audio). The following essential elements are common to all superhet circuits: a receiving antenna , a tuned stage which may optionally contain amplification (RF amplifier), a variable frequency local oscillator , a frequency mixer , a band pass filter and intermediate frequency (IF) amplifier, and a demodulator plus additional circuitry to amplify or process the original audio signal (or other transmitted information).To receive a radio signal, a suitable antenna is required. This is often built into a receiver; especially in the case of AM broadcast band radios. The output of the antenna may be very small, often only a few micro volts. The signal from the antenna is tuned and may be amplified in a so-called radio frequency (RF) amplifier, although this stage is often omitted. One or more tuned circuits at this stage block frequencies which are far removed from the intended reception frequency. In order to tune the receiver to a particular station, the frequency of the local oscillator is controlled by the tuning knob. Tuning of the local oscillator and the RF stage may use a variable capacitor, or varicap diode. The tuning of one (or more) tuned circuits in the RF stage must track the tuning of the local oscillator.The signal is then fed into a circuit where it is mixed with a sine wave from a variable frequency oscillator known as the local oscillator (LO). The mixer uses a non-linear component to produce both sum and difference beat frequencies signals, each one containing the modulation contained in the desired signal. The output of the mixer may include the original RF signal at fd, the local oscillator signal at fLO, and the two new frequencies fd+fLO and fd-fLO. The mixer may inadvertently produce additional frequencies such as 3rd- and higher-order inter-modulation products. The undesired signals are removed by the IF band pass filter , leaving only the desired offset IF signal at fIF which contains the original modulation (transmitted information) as the received radio signal had at fd. The stages of an intermediate frequency amplifier are tuned to a particular frequency not dependent on the receiving frequency; it greatly simplifies optimization of the circuit. The IF amplifier (or IF strip) can be made highly selective around its center frequency fIF, whereas achieving such a selectivity at a much higher RF frequency would be much more difficult. By tuning the frequency of the local oscillator fLO, the resulting difference frequency fLO - fd (or fd-fLO when using low-side injection) will be matched to the IF amplifier's frequency fIF for the desired reception frequency fd. One section of the tuning capacitor will thus adjust the local oscillator's frequency fLO to (fd + fIF) while the RF stage is tuned to fd. Engineering the multi-section tuning capacitor (or varactors ) and coils to fulfill this condition across the tuning range is known as Tracking. Other signals produced by the mixer (such as due to stations at nearby frequencies) can be very well filtered out in the IF stage, giving the superheterodyne receiver its superior performance. However, if fLO is set to fd + fIF, then an incoming radio signal at fLO + fIF will also produce a heterodyne at fIF; this is called the image frequency and must be rejected by the tuned circuits in the RF stage. The image frequency is 2fIF higher (or lower) than fd, so employing a higher IF frequency fIF increases the receiver's image rejection without requiring additional selectivity in the RF stage. Usually the intermediate frequency is lower than the reception frequency fd, but in some modern receivers it is more convenient to first convert an entire band to a much higher intermediate frequency; this eliminates the problem of image rejection. Then a tunable local oscillator and mixer convert that signal to a second much lower intermediate frequency where the selectivity of the receiver is accomplished. In order to avoid interference to receivers, licensing authorities will avoid assigning common IF frequencies to transmitting stations. Standard intermediate frequencies used are 455 kHz for medium-wave AM radio, 10.7 MHz for broadcast FM receivers, 38.9 MHz (Europe) or 45 MHz (US) for television, and 70 MHz for satellite and terrestrial microwave equipment. In early superhets, the IF stage was often a regenerative stage providing the sensitivity and selectivity with fewer components. Such superhets were called super-gainers or regenerodynes.The IF stage includes a filter and/or multiple tuned circuits in order to achieve the desired selectivity. This filtering must therefore have a band pass equal to or less than the frequency spacing between adjacent broadcast channels. Ideally a filter would have a high attenuation to adjacent channels, but maintain a flat response across the desired signal spectrum in order to retain the quality of the received signal. This may be obtained using one or more dual tuned IF transformers, or a multipole ceramic crystal filter.The received signal is now processed by the demodulator stage where the audio signal (or other baseband signal) is recovered and then further amplified. AM demodulation requires the simple rectification of the RF signal (so-called envelope detection), and a simple RC low pass filter to remove remnants of the intermediate frequency. FM signals may be detected using a discriminator, ratio detector, or phase-locked loop. Continuous wave (Morse code) and single sideband signals require a product detector using a so-called beat frequency oscillator, and there are other techniques used for different types of modulation. The resulting audio signal (for instance) is then amplified and drives a loudspeaker. When high-side injection has been used, where the local oscillator is at a higher frequency than the received signal (as is common), then the frequency spectrum of the original signal will be reversed. This must be taken into account by the demodulator (and in the IF filtering) in the case of certain types of modulation such as single sideband.Generally, instead of using a separate transmitter and receiver and a constricted version called a Transceiver is used on either sides. This can be used to both transmit and receive the amplitude modulated signal.

Antennas:Two types of antennas are used:1. Omni directional Antenna2. Directive AntennaIn order to avoid a black zone and simultaneous loss of communication, each operational frequency has a Directive and an Omni - directional antenna.

Directive AntennaOmni-directional Antenna

VCCS:

The VHF unit also contains Voice Communication Control and Switching equipment (VCCS). The Voice Communications and Control System (VCCS) is a solid state, modular, and flexible system which has provided reliable ATC communications for over twenty years. The basic premise of the design is to provide the Air Traffic Controller with a functional system tailored to his needs. The system provides the controller with single button selection of radio channels for transmit and receive. It also provides 'monitor only' as well as headset and/or microphone loudspeaker functions. Use of intercoms, hot line, and airport telephone access are also part of the system. Channel selected and channel in use are readily visible day and night. Interposition lockout is available to prevent two operators inadvertently using the same radio channel at the same time. Incoming RF signals are visually and audibly apparent with the frequency displayed. The following is a list of the VCCS sub-systems: Radio Channel Control

Intercommunications

Telephone

Crash Alarm & Control

Clock

Test Unit

Power Supply

Meteorological

Figure : Voice Communication Control System

RCAG:

While VHF communication due to being line-of-sight is restricted only till the 200 nautical miles region, sometimes even less, the intermediate communication between the aircraft and ground stations takes place using Extended VHF, also called Radio Communication Air to Ground (RCAG).In this case, the original frequency and message transmitted from the base station is also transmitted from an intermediate station and is fed to the intermediate stations via trunk lines. Hence, the intermediate station also requires a local transmitter. The trunk line used is an optical fiber cable which provides a negligible delay of 20ms.The other specifications kept in mind while transmitting AM signals are that there Voltage Standing Wave Ratio (VSWR) must remain in between 1 and 2, generally, 1.3. Also, according to the ICAO specifications, the modulation percentage is no more than 30%.The Safdarjung Airport incorporates low level modulation and uses an OTE receiver. The advantage of an OTE transmitter over others is that it can transmit both voice (audio) as well as data signals.All such communication between the pilot and the controller is duly recorded for future references. Two companies provide equipments for these services Marathon and Ricochet. Marathon can only record the audio communication while Ricochet is capable of recording both audio as well as the visual data. One more important feature at the Safdarjung Airport is that it uses Vertical Polarization.

AMSS UNITAMSS Stands for Automatic Message Switching System as its name suggest there is automatic switching of networks through which information is send and distributed among various stations with in a network or in different networks.AMSS works on the Amplitude Modulation technique use to increase the strength of the transmitted signal in relation to the information being sent. It is based on the point to point communication.INTRODUCTION AMSS is installed at AFTN (Aeronautical Fixed Telecom Network) centers to send and distribute messages for exchanging aeronautical information among Civil Aviation Authority of Vietnam, airlines companies, air traffic management service, meteorological service, aeronautical information service providers and Air Traffic Control Centers.

The system provides the functions of receiving, storing, analyzing and sorting based on priority of messages to specific addresses. The system provides functions to assign channels, control channels, organize queues based on priority, monitoring operation of the system and encoding messages. The system conforms to AFTN practice standards and recommendations of ICAO, including: Annex 10 Vol II; DOC 8259 - AN/936; DOC 4444-RAC/501 The system fully conforms to all standards and regulations in respect of technical design and AMSS operational standards Version 1.0 that were approved under Decision 947/Q-QLB. The system is manufactured in accordance with ISO 9001:2008 management approach.

DESCRIPTION Stable and precise performance makes it convenient for operation and maintenance. AMSS consists of 2 dedicated Servers and PCs operating on LAN based Hot Stand-by structure. AMSS is an open system. It has modular design with hot backup mechanism, therefore, it is highly reliable and easy to maintain and expand.

The design of application interface is simple, visualized and consistent throughout the system. Requirements on installation conditions are below specified: Power supply 220V 10%; 50 Hz via UPS. Working temperature 22 2C, humidity below 65%.

TECHNICAL SPECIFICATION Message switching capacity: 100,000 messages per day. Able to connect, manage and process 40 communication channels simultaneously. Communication support systems: RS-232/422/485, Ethernet, Fast Ethernet, using auto-connect and dial-up modem. RS-232/422/485 channel speed can reach from 50 bps 230 kbps.

Modifying configurations of online system through parameterization without resetting the system (Adding, removing, modifying channel sorting table) Vast storage capacity (depending on hardware capacity). It has backup and raid mechanism to ensure message data safety. Easy and convenient message management and access by parameter. Provide private reception and transmission queue for more than 500 messages. Have view, delete and print functions for each channel. Able to switch messages in a queue to another. AMSS handles messages by 2 modes: Auto and Semi, supports ITA-2 and IA-5 message format. It supports TCP/IP via Non-Protocol communication protocol. AMSS displays, monitors, manages, list and report message switching operations It monitors and manages operational status of hardware and communication channels. Its terminals synchronize time with those from 2 servers and standard time received from GPS.AERONAUTICAL TELECOMMUNICATION NETWORK ATN is a global aviation standard telecommunications network recommended by ICAO to provide seamless Air/Ground and Ground/Ground communication services It is a dynamic telecommunications network designed to support projected traffic growth due to Air/Ground Service advances and other new emerging Ground/Ground applications. In the new CNS/ATM system, communications with aircraft for both voice and data (except for polar region) will be by direct aircraft to satellite link and then to air traffic control (ATC) centre via a satellite ground earth station and ground-ground communication network. Voice communication (HF) will be maintained during the transition period and over polar region until such time satellite communication is available. In terminal areas and in some high density airspaces VHF and SSR mode S will be used. In computer data networking terminology, the infrastructure required to support the interconnection of automated systems is referred to as an Internet. Simply stated, an Internet comprises the interconnection of computers through sub-networks, using gateways or routers. The inter-networking infrastructure for this global network is the Aeronautical Telecommunication Network (ATN). The Data transfer through an Aeronautical internet will be supported by three types of data communication sub-networks. The ground network AFTN,ADNS,SITA Network The Air-ground network Satellite, Gate-link, HF, VHF, SSR Modes The Airborne network the Airborne Data Bus, Communication management unit. THE GROUND NETWORKIt is formed by the Aeronautical Fixed telecommunication network (AFTN), common ICAO data interchange network (CIDIN) and Airline industry private networks.

THE AIR-GROUND NETWORK The Air-Ground sub networks of VHF, Satellite, Mode S, gate link, (and possibly HF) will provide linkage between Aircraft-based and ground-based routers (Intermediate system). The available/planned air-ground communication systems are- Satellite Gate link HF radio SSR Mode S VHF

SATELLITE Voice and data using the Aeronautical Mobile Satellite Services (AMSS) will be the new main feature of future aeronautical communication systems. The use of communication satellites will provide global coverage and could support both high and low speed data links as well ashigh quality voice link between aircraft and ground stations. Once implemented AMSS(satellite) will outcast the need of conventional modes of message passing and every station will depend on satellite link for transfer of messages. GATELINK The gate link is a high speed two way data communication link between a parked aircraft and a ground based communication system. The link is either physical or short-range directed transmission (such as infra red). Data can be passed to flight management computer data bus for updating purpose. The design is based on a data transfer of 100Mbps. High Frequency (HF) High Frequency Radio communication is mostly used in long distance communication by the phenomenon of reflection. High frequency EM waves have the property of being reflected by the ionosphere. This method is extensively used in polar areas of over oceans where communication centers cannot be established. SSR MODES In addition to its use for surveillance the mode S option of SSR also makes available an air-ground data link, which could be used for ATS purposes in high density airspace. Very High Frequency (VHF) VHF will remain in use in many continental and terminal areas. THE AIRBORNE NETWORK It consists of Communication Management Unit (CMU) and the Aeronautical radio incorporation data buses (ARINC). Interconnectivity to and inter operability with the Public data Network (PDN) will be achieved using gate-ways to route information outside the Aeronautical environment. THE AIRBORNE COMMUNICATION NETWORKThe function of the airborne communications network is to transfer information between the various airborne systems and the systems on ground. The airborne network contains the two following elements. Airborne Data Bus Communication Management Unit (CMU) AIRBORNE DATA BUS The airborne data bus is the physical connection between avionics system elements carrying the digital data. AFTN SWITCHING SYSTEM INTRODUCTION In AFTN, information is exchanged between many stations. The simplest form of communication is point-to-point type, where information is transmitted from a source to sink through a medium. The source is where information is generated and includes all functions necessary to translate the information into an agreed code, format and procedure. The medium could be a pair of wires, radio systems etc. is responsible for transferring the information. The sink is defined as the recipient of information; it includes all necessary elements to decode the signals back into information. CLASSIFICATION OF AFTN SWITCHING SYSTEM A switching system is an easy solution that can allow on demand basis the connection of any combination of source and sink stations. AFTN switching system can be classified into3 (three) major categories: Line Switching Message Switching Packet Switching. LINE SWITCHINGWhen the switching system issued for switching lines or circuits it is called line-switching system. Telex switches and telephones exchanges are common examples of the line switching system. They provide user on demand basis end-to-end connection. As long as connection is up the user has exclusive use of the total bandwidth of the communication channel as per requirement. It is interactive and versatile. MESSAGE SWITCHINGIn the Message Switching system, messages from the source are collected and stored in the input queue which are analyzed by the computer system and transfer the messages to an appropriate output queue in the order of priority. The message switching system works on store and forward principle. It provides good line utilization, multi-addressing, message and system accounting, protects against blocking condition, and compatibility to various line interfaces. PACKET SWITCHING SYSTEM This system divides a message into small chunks called packet. These packets are made of a bit stream, each containing communication control bits and data bits. The communication control bits are used for the link and network control procedure and data bits are for the user. A packet could be compared to an envelope into which data are placed. The envelope contains the destination address and other control information. Long messages are being cut into small chunks and transmitted as packets. At the destination the network device stores, reassembles the incoming packets and decodes the signals back into information by designated protocol. It can handle high-density traffic. Messages are protected until delivered. No direct connection required between source and sink. Single port handles multiple circuits access simultaneously and can communicate with high speed. ICAO MESSAGE FORMATNOTAM NOTAM is the acronym for Notices to Airmen containing information or change in any aeronautical facility, service, procedure or hazard the timely knowledge of which is essential to personal concerned with the flight operation. The conditions which necessitates origination of NOTAM are mentioned in the "Guidance Manual for Aeronautical Information Services in the Asia/Pacific Region" kept in the International NOTAM office-Delhi. Five series are used to issue NOTAM. Each series is separately identified by a letter. Each NOTAM in series of NOTAM is allocated a serial number, that number is consecutive and based on the calendar year. Series A: Contains information in respect of changes/un-serviceability of aeronautical facility likely to last for more than 2 hrs and given general international distribution. Series B: Contains information in respect of changes/un-serviceability etc. of aeronautical facilities likely to last for more than 30 min. but less than 2 hours and given limited international/national distribution to adjacent states only. Series G: Contains information of a general and lasting character affecting aircraft operation in general and this series is operated only by International NOTAM Office(NOF) Delhi and issued under the authority of AIS-AAI Headquarters and given wide publicity by dissemination to all recipients of NOTAM from the four international offices in India. Series C: Contains information in respect of changes/un-serviceability etc. of aeronautical facilities in respect of location utilized by domestic flights only. Series D: Contains information in respect of changes/un-serviceability of aeronautical facilities under defense authorities and utilized by domestic scheduled flights only. NOTAMN: NOTAM containing new information. NOTAMR: NOTAM replacing a previous NOTAM. NOTAMC: NOTAM canceling a previous NOTAM. LOCATION INDICATOR DEFINITION: Four letter code groups formulated in accordance with the rules prescribed by ICAO and assigned to a location of an aeronautical fixed station. FORMULATION: Four letter location indicator formulated and assigned to a geographical location where there is situated a station forming a part of aeronautical fixed service. ICAO DOC7910 contains a list of four letter code group location indicator for use in aviation only as a location of an aeronautical fixed station in address, originator text etc. and not repeat not as a radio call sign of ships which is only four letter one. ESTABLISHMENT OF AERONAUTICAL FIXED SERVICE (AFS) ROUTING AREAS The world is divided into 22non over lapping AFS routing areas, each of which is assigned a separate identifying letter. I, J, Q and X are not allocated. The boundaries of these areas need not necessarily coincide with the boundaries of any state, territory or FIR but are decided solely from a consideration of the requirements of the AFS, so as to assist message traffic routing processes to the maximum possible extent. Each separate state or territory is assigned a separate identifying letter to permit differentiation between that state or territory and other states or territories in the same AFS routing areas. Separate identifying letters are assigned to parts of a state or territory. Where a separate state or territory is itself an AFS routing area and Where routing uncertainties can exit at stations feeding traffic into that states or territory and Where by so doing these routing uncertainties can be removed or alleviated. No separate identifying letter is assigned where a separate state or territory contains only tributary stations. Unallocated letters within each AFS routing area may be assigned as additional letters, by ICAO, at the request of a state having jurisdiction at location(s) within such area, in instances where additional assignment will facilitate the processes of message routing. ASSIGNMENT OF LOCATION INDICATORS Assignment of the first letter of a location indicator: The first letter of the location indicator shall be the letter assigned to the AFS routing area within which the location is situated except that where the location is served only by a single communication centre situated in another AFS routing area, the first letter shall be that assigned to the area in which that communication centre is situated. Assignment of the second letter of a location indicator: The second letter of the location indicator shall be letter assigned to the state or territory (or portion thereof) within which the location is situated, except that where the location is served only by a single communication centre situated in another state or territory in which that communication centre is situated. Assignment of the third letter of a location indicator: Where in a state or territory, aeronautical fixed telecommunication stations are connected to a communication centre, the third letter of the location indicator should be so assigned as to assist in the process of routing to that communication centre. Assignment of the fourth letter of a location indicator:In respect of the fourth letter, and in instances where assignment of the second and third letters is not prescribed under 1.3 and 1.5 the state concerned shall assign the letters as desired, except that those states assigned the identifying letter N in accordance with 2.2 should arrange their national allocation of specific four letter location indicators so as to avoid the use of the combination NN for the third and fourth letters.LIST OF THE SOME IMPORTANT INTERNATIONAL LOCATION INDICATORS OBBI BAHRAIN OYAA ADEN OOMS MUSCAT OMAA ABU-DHABI OMDB DUBAI OEJD JEDDAHOEDR DAHRAN OPLA LAHOREOPKC KARACHI OAKB KABULOAKN KANDHAR OIII TEHRANORBS BAGDAD OKBK KUWAIT OLBA BAIRUT OTBD DOHA EGLL LONDON FIMP MAURITIUS FJDC DIEGO GARCIA FSIA SEYCHELLES HAAB ADDIS- ABABA HECA CAIRO HKNA NAIROBI HSSS KHARTOUM HTDA DAR ES-SALAAM LCNC NICOSIA LFPO PARIS/ORLY LTBA ISTANBUL RJTT TOKYO UUEE MOSCOW UTTT TASKENT VTBD BANGKOK VCBI COLOMBO VHHH HONGKONG FVHA HARRARE INTL FACT CAPE TOWN INTL FADN DURBAN INTL FAJS JOHANNESBURG FAPE PORT ELIZABETH INTL

AMSS-OPERATIONS To run the workstations, user-friendly application software on windows 2000 has been designed by ECIL in accordance with ICAO Annex-10 Vol. II. The application supports new and old AFTN message format. The application has been divided into two parts viz. FRONTEND and BACKEND application.

AMSS HARDWARE CONFIGURATION & COMPONENTSThe basic AMSS configuration consists of Server (s) as a host message-switching computer, data server for storing and access data and agent workstation (s) for message input. The message switching system in major stations like Chennai or Kolkata configured as below AMSS Server with hot standby. AMSS server console VDU and console printers Data Base Server (s) ADC/FIC Server Communication Server LTU Units CCM Box Router Fast Ethernet Switch Power Supply Unit MODEM (s) Line Drivers Windows-2000 Adv. Ser for Database Server Windows-2000 professional for workstation Different workstations (NODES) Audio Visual Alarm (AVA) Drop Printers Report Printers Workstation Printers. AMSS SERVER (ONL) It receives messages, analyses routes, stores messages in duplicate schedules and transmits messages. It gives health signals to SOLC and monitors its own sub-systems for generating console messages. It also takes a snap shot of the System Status from which the system can roll back in case of failure. AMSS SWITCH SERVER H/W CONFIGURATION AMSS is based on Intel PIII 1.13MHz microprocessor and the main system is fully duplicated and each server consists of Intel SDS2 Mother board integrated with 2 serial and 1 parallel port, 1GB memory, ultra2 SCSI controller, 52XIDE CD ROM , 2Ethernet NIC adapters, 1.44MB FDD,40GB disk drive. DAT DRIVE 12GB,24GB, Color monitor, key board and mouse. 64 port communication controller card Disk switch SOLC card SCSI Active termination LVD.

AMSS SERVER HOT-STANDBY (HSB) It receives the messages, preprocesses it and buffers received blocks with message identification. It also gives health signals to SOLC. Hot standby on receiving signal from SOLC, that online server has failed, it initiate recovery from the roll back point ledger by ONL server in the last successful batch of operations. It then analyses the buffer of received block to re-input into the system. The reception in HSB continues during all these activities. SYSTEM CONSOLE PRINTERThe system console is a VDU, which is used for booting, loading the OS, start up, date time input and recovery. The console is basically a UNIX Terminal which can be used for any program development activities also thro user friendly shell commands e.g. Editing source program, Copying of programs, Diagnostics running etc., The system console printer attached with both the servers printers all the commands used by the supervisor terminal and also logs the server activity, which helps the system administrator to analyze the trouble. DATABASE SERVER/ADC-FIC SERVER The dual redundant servers supports the required data base support for the AMSS System for various applications like ASBS, NOTAM office automation, HFRT, OPMET Data bank, YA automation, ADC/FIC application etc., These servers are fully redundant and work infail safe mode. The database gets replicated in the Hot standby system based on events. Back end software running on these servers supports the replication and transmission of messages from/to the AMSS system and also supports the Workflow and automation application. Supports the query and report request generated from the front-end GUI applications. COMMUNICATION SERVERThis server supports various line protocols like X.25, HDLC, PPP, SLIP, TCP/IP etc., basically this server works as a gateway to remove stations connected in the X.25 and TCP/IP cloud. All the messages received from the remote stations will be passed to the AMSS switch through Ethernet connectivity and vice-versa. This server supports a minimum of four-eight channels and both servers put together supports 8-16 channels. HW CONFIGURATION OF APP. FIC/ADC & COM SERVERS These servers consist of Intel SDS2 mother board with 2serial and one parallel port 1GB memory, integrated dual ultra2 SCSI controller, dual channel RAID SCSI controller. 3 x 36GB Hot swappable disk drives Color monitor, with key board and mouse 52 X IDE CD ROM 3.5,1.44MB FDD X.25 Card ( for comm. Server) NIC(Ethernet adapter) Dual channel RAID SCSI controller( for App and FIC/ADC Servers) LINE TERMINATION UNIT (LTU) LTU rack with a capacity to support 64 channels is provided in view of the future expansion. By adding additional line termination cards (LTU-B/C) and associate communication multiplexers the system capacity can be enhanced. The software supplied supports up to 128 lines. By simple updating the database, routing directory, the system capacity can be enhanced to 128 channels. There is one LTU for each line. LTU B/C interface supports two types of channels. LTUB serves the function of converting Baudot code interface to RS232C interface. This unit also provides line isolation, over voltage, current protection etc; LTU-C is basically RS232 to RS232 with functions of line isolation TX signal selection (online systems TX signal only allowed to the external line) and other protection facilities.VARIOUS NETWORKS AND EQIPMENTS USED IN AMSS LOCAL AREA NETWORK (LAN): A local area network (LAN) is usually privately owned and links the devices in a single office, building, or campus. Depending on the needs of an organization and the type of technology used, a LAN can be as simple as two PCs and a printer in someone's home office. Currently, LAN size is limited to a few kilometers. LANs are designed to allow resources to be shared between personal computers or workstations. The resources to be shared can include hardware (e.g., a printer), software (e.g., an application program), or data. One of the computers may be given a large capacity disk drive and may become a server to the other clients (for example Database Server of AMSS). Software can be stored on this central server and used as needed by the whole group. METROPOLITAN AREA NETWORK (MAN): A metropolitan area network (MAN) is a network that connects two or more local area networks or campus area networks together but does not extend beyond the boundaries of the immediate town/city. Routers, switches and hubs are connected to create a metropolitan area network. WIDE AREA NETWORK (WAN): wide area network (WAN) provides long-distance transmission of data, voice, image, and video information over large geographic areas that may comprise a country, a continent, or even the whole world. WANs may utilize public, leased, or private communication equipment, usually in combinations, and can therefore span an unlimited number of miles. A WAN that is wholly owned and used by a single company is often referred to as an enterprise network. WANs technology such as X.25 and TCP/IP used in AAI AMSS. HUB: A network hub is a fairly unsophisticated broadcast device. Hubs do not manage any of the traffic that comes through them, and any packet entering any port is broadcast out on every other port. Since every packet is being sent out through every other port, packet collisions result which greatly impedes the smooth flow of traffic. ETHERNET SWITCH: A network switch is a computer networking device that connects network segments. The term commonly refers to a Network bridge that processes and routes data at the Data link layer (layer 2) of the OSI model. ROUTERS: Router is a networking device whose software and hardware are usually tailored to the tasks of routing and forwarding information. For example, on the Internet, information is directed to various paths by routers. Routers connect two or more logical subnets, which do not necessarily map one-to-one to the physical interfaces of the router. NIC CARD: A network interface controller (NIC) is a hardware device that handles an interface to a computer network and allows a network-capable device to access that network. The NIC has a ROM chip that contains a unique number, the multiple access control (MAC) Address burned into it. The MAC address identifies the device uniquely on the LAN. FRAME RELAY: X.25 is a protocol that the CCITT developed to provide reliable data communications on public data networks. It uses packet switching and virtual circuits, and provides a data rate up to 64kbps. It provides very robust error checking features, which makes it a good choice for older networks. Because of its extensive error checking, it not only works well on these older networks that are more susceptible to physical interference RS-232 SERIAL TRANSFER PROTOCOL: In telecommunications, RS-232(Recommended Standard 232) is a standard for serial binary data signals connecting between a DTE (Data Terminal Equipment) and a DCE (Data Circuit-terminating Equipment). POWER SUPPLY UNITS: Dual power supply units for supply of (+/-60V, +/-12V and +5V) is provided in LTU rack. 60V is provided for remote lines, 12V for RS232C serial communication and 5V for supply to LTU cards. LINE DRIVERS: Line drivers are used as a device to make long distance connectivity where the capacity of a line fails to transfer the data from one terminal to another terminal. The line drivers are fixed in between two points of a serial line RS232 (one at output end and other at input end).

AUDIO VISUAL ALARM (AVA) The Audio Visual Alarm (AVA) software monitors and displays the status of the entire message switching system including its various allied sub-systems. The AVA displays Switch status- MS1 and MS2 Device Status-Disks and Tapes Power Supply status Real time Channel status The AVA obtains all the status information from the ONLINE AMSS system through LAN and displays them graphically. The graphical representation enables quicker and easier interpretation of current status of the entire network. The status of all systems and sub-systems are displayed in the form of rectangular blocks. The background color of a block indicates the current status of the system/sub-system concerned. The date and time of failure are shown wherever they are relevant. In case of failure of message switches or disks which are critical, the software Comes to the foreground if it had been minimized Gives visual effect to the block concerned (in red color) Generates alarm sound The AVA software can also be run in any WS running Windows NT. The AVA terminal will have special hardware to monitor LTU power status. If it is run on a WS other than AVA terminal, then the status of all systems/sub-systems except LTU power status can be monitored. A typical AVA screen for monitoring of Servers & Workstations is shown below.

SRP- This printer is used for auto printing of various reports generated by the system. SRJ- This printer is used for printing logging details of rejected messages by the system. Also it logs the header summary of the messages transacted through LTU. DROP printer (RS-232) used as a drop circuit through LTU. Printer is used for printing messages to drop messages directly to an addressee as per address indicator for the drop printer. WORK STATION PRINTER This printer is connected through the COM port of workstation and messages are printed according to the address of the workstation. Messages can also be printed by selecting the particular message and executing print command. AMSS Software Configuration AMSS switch servers: Operating system: switch server works on UNIX operating system. The advantage of using UNIX is the stability of the system. Since the two servers are the heart of the AMSS, uninterrupted working is necessary in every case. Also the chance of virus attack is less as compared to WINDOWS based system. UNIX version 5.05 is currently being used here. Application: application for the switch servers are written in C language. The application presently used is designed by ECIL and maintained by AAI. The application manages four files used in routing the messages to desired channel. These being: Ai8.data: maps address to route. Gi8.data: maps group address to route. Route. data: maps rote to logical address. Line. data: maps logical to physical address. Database server: Operating server: database servers work on WINDOWS 2000. Application: SQL 2000 is used for the database application. Databases contain tables which hold the messages received from various inputs. A copy is retained for 30 days. Workstations: Operating server: workstations are loaded with windows XP OS. Application: applications based on visual Care run on these stations.

L-BAND RADAR UNIT

RADAR

DEFINITION-: RADAR (Radio Detection And Ranging) is a way to detect and study far off targets by transmitting a radio pulse in the direction of the target and Radarstands forRADIO DETECTION AND RANGING. It is basically an echo ranging system in which electromagnetic energy in the form of high power short duration pulses are sent out at distant targets. After this an echo is received at the transmitting station. This echo is the received signal from the long distant object. The echo is then analyzed to obtain information regarding the location of targets.

COMPONENTS OF A RADAR SYSTEM:It consists of a transmitter and a receiver. Both the elements are connected to a directional antenna through a duplexer. Now what is a duplexer? It is a switching arrangement. It is excited by a small portion of the pulse power generated by the transmitter. The duplexer disconnects the receiver from the antenna and connects the transmitter to the antenna. The function of the antenna is to rotate in order to direct the radiated beam as necessary. When the transmitted pulse is over, the duplexer reconnects the receiver to the antenna. Now the reflected pulses are received and processed at thesuperheterodyne receiver. The demodulated pulses are then fed to theindicatorfor display purpose and analysis.The main function of radar is to provide information on theelevation(vertical direction) andazimuth(horizontal direction) of the antenna, thus the position of the target can be found.The distance of the target can be calculated by from total time (t) taken by the pulse to travel to the target and return to its original initial point. Assuming c to be the velocity of light in free space, the distance traversed by pulse is ct meters. Now this is 2times the target distance, hence the distance to the target is ct/2 meters.

APPLICATIONS OF RADAR:

Radar finds its applications in various fields like:c) MILITARY USES: enemy ships can be detected by radar which helps in direct targeting of the enemy ships or even aircrafts. Moreover radar displays are used in bomb ships or in cities at night. We are well aware of the satellites revolving in space used for communication purposes, but do we know that radar placed on a satellite helps in detecting the ballistic missiles.d) IN SUBMARINES: Radars are also used in finding submarines and in directing guided missiles.e) CIVILIAN USES: Useful information about navigations can be obtained from radars. Radar located or fixed in ships can be used to locate marker buoys, other ships, land etc.f) SCIENTIFIC USES: Map positions of islands can be found out using radars. Furthermore information regarding the distance and motions of different planetary bodies can be obtained with the help of radar.g) OTHER USES: Radars are used in mapping, meteorology, air traffic control at airports providing landing facilities. Radars are also used by police forces for traffic speed control and prosecution of offenders.

INTRODUCTION TO L-BAND RADAR

L-BAND RADAR is located at Bijwasan, New Delhi. It has a Football-like shape (with dipole antenna over it) as shielding is done to protect the radar from the unwanted winds and unwanted overlapping of signals.The L-Band Radar has frequency band (1 to 2 GHz) is preferred for the operation of long-range air-surveillance radars out to 250NM (400km). They transmit pulses with high power, broad bandwidth and an intrapulse modulation often. Due to the curvature of the earth the achievable maximum range is limited for targets flying with low altitude. These objects disappear very fast behind the radar horizon.In Air Traffic Management (ATM) long-range surveillance radars like the Air Route Surveillance Radar (ARSR) works in this frequency band. Coupled with a Monopulse Secondary Surveillance Radar (MSSR) they use a relatively large, but slower rotating antenna (speed~5 rpm) with Peak Power (40kw) has antenna area of about 2metre square. The designator L-Band is good as mnemonic rhyme as large antenna or long range. Another radar used by AAI is S-Band Radar has frequency range is 2-4 GHz (220 nautical mile) with fast rotating antenna (speed~12 rpm) with peak power (40 kw) than L-band Radar .

TWO TYES OF RADAR h) PRIMARYi) SECONDRY PRIMARY RADARThe following figure shows the operating principle of a primary radar set. The radar antenna illuminates the target with a microwave signal, which is then reflected and picked up by a receiving device. The electrical signal picked up by the receiving antenna is called echo or return. The radar signal is generated by a powerful transmitter and received by a highly sensitive receiver.

All targets produce a diffuse reflection i.e. it is reflected in a wide number of directions. The reflected signal is also called scattering.Backscatteris the term given to reflections in the opposite direction to the incident rays.Radar signals can be displayed on the traditional plan position indicator (PPI) or other more advanced radar display systems. A PPI has a rotating vector with the radar at the origin, which indicates the pointing direction of the antenna and hence the bearing of targets.TransmitterThe radar transmitter produces the short duration high-power rf pulses of energy that are into space by the antenna.DuplexerThe duplexer alternately switches the antenna between the transmitter and receiver so that only one antenna need be used. This switching is necessary because the high-power pulses of the transmitter would destroy the receiver if energy were allowed to enter the receiver.ReceiverThe receivers amplify and demodulate the received RF-signals. The receiver provides video signals on the output.Radar Antenna The Antenna transfers the transmitter energy to signals in space with the required distribution and efficiency. This process is applied in an identical way on reception.Indicator The indicator should present to the observer a continuous, easily understandable, graphic picture of the relative position of radar targets.Video displayThe radar screen (in this case a PPI-scope) displays the produced from the echo signals bright blibs. The longer the pulses were delayed by the runtime, the further away from the center of this radar scope they are displayed. The direction of the deflection on this screen is that in which the antenna is currently pointing.

SECONDARY RADARThe objectives of this chapter of the homepage Radar Basics are to indicate the principles of the operation of Secondary Surveillance Radar (SSR). Firstly, the functional block diagram of the SSR (Mode A/C) system will be described, including both the Up Link formats and the Reply Messages. Secondly, the main aspects of the forthcoming Mode S system will be described.

As well as seeing hostile aircraft it soon became apparent that Radar was a good tool to see friendly aircraft and hence control and direct them. If the friendly aircraft is fitted with atransponder(transmitting responder), then it sends a strong signal back as an echo. An active also encoded response signal which is returned to the radar set then is generated in the transponder. This proved very useful for the military in seeing their own aircraft clearly. In this response can be contained much more information, as a primary radar unit is able to acquire (E.g. anAltitude an identification code or also any technical problems on board such as a radio contact loss ...).

Mode S MSSRIntheinterrogator on the ground:The secondary radar set needs a synchronous impulse of the (analogous) primary radar set to the synchronization of the indication.3. The chosen mode is encoded in theCoder. (By the different modes different questions can be defined to the airplane.)4. Thetransmittermodulates these impulses with the RF frequency. Because another frequency than on the replay path is used on the interrogation path, an expensive duplexer can be renounced.5. Theantennais usually mounted on the antenna of the primary radar set and turns synchronously to the deflection on the monitor therefore.In the aircrafts transponder:Areceiving antennaand atransponderare in the airplane.

Thereceiveramplifies and demodulates the interrogation impulses. Thedecoderdecodes the question according to the desired information and induces the coder to prepare the suitable answer. Thecoderencodes the answer. Thetransmitteramplifies the replay impulses and modulates these with the RF reply-frequency.

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