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ACKNOWLEDGMENT The feeling of euphoria, I have on the successful completion of the summer training at ALL INDIA RADIO (AIR) is expressible. I take this opportunity to express my profound gratitude and indebtedness to permit me to undertake the training in this esteemed organization. I would like to pay heartfelt thanks to the respected Sujit Roy sir for giving the permission to take the training in this reputed organization. I therefore cherish this informative and educational training in the All India Radio (AIR), Kolkata which enabled me to get hands on experience in the field of Radio Communication both in Analog & Digital process and in telecommunication operation.

About All India Radio ( AIR ) All India Radio (AIR) ,one of the largest radio networks in the world is a division of Prasar Bharti (Broadcasting Cooperation of India) Established in 1936, today it is the sub service of Prasar Bhartis Doordarshan, the national television broadcaster. All India Radio is also known as Akashvani. The head quarter is at the Akashvani Bhavan, New Delhi. AIR today has a network of 237 broadcasting centers with 149 medium frequency (MW), 54 high frequency (SW) and 177 FM transmitters. The coverage is 91.85% of the area, serving 99.18% of the people in the largest democracy of the world. AIR covers 24 Languages and 146 dialects in home services. In External services, it covers 27 languages; 17 national and 10 foreign languages.

HISTORY AND PRESENT SCENARIO : The first license granted for transmitting a broadcast was given on February 23, 1922. The Radio Club of Calcutta was the first radio club to start functioning in Nov-1924The Government run broadcasting set up was called the India State Broadcasting Service (ISBS) which is then turned into AIR (All India Radio) in June 1936. The introduction of the commercial channel Vividh Bharti in October 1957 increased the interest and popularity of radio.AIR today has a network of 232 broadcasting centres with 149 medium frequency(MW), 54 high frequency (SW) and 171 FM transmitters. The coverage is 91.79% of the area serving 99.14% of the people.

PRINCIPAL OF AIR (ALL INDIA RADIO)

Transmitting A radio wave carries information signal; Signals are converted into electrical signals. A carrier wave is then produced from the modulation. The wave is then amplified, and sent to the antenna that then converts signal into an E.M. wave.

Receiving An antenna on receiving the signal send it to the receiver this then converts the electrical signal sends it to the amplifier either a speaker/headphones jack this is then converted into a sound wave.

OBJECTIVES OF ALL INDIA RADIO :

To uphold the unity and integrity of the country and the values enshrined in the Constitution. Present a fair and balanced flow of information of national, regional, local and international interest, including contrasting views, without advocating any opinion or ideology of its own. Produce and transit varied programs designed to awaken, inform, educate, entertain and enrich all sections of the people.MODULATION

Modulation is a process of superimposing information on a carrier by varying one of its parameters (amplitude, frequency or phase). In telecommunications, modulation is the process of conveying a message signal.

Need for Modulation :

Modulating the signal over higher frequency can reduce antenna size.

To differentiate among transmissions (stations) Maximum to minimum frequency ratio can be reduced to minimum by modulating the signal on a high frequency.

Types of Modulation In general, there are three types of modulation: a) Amplitude Modulation b) Angle Modulation c) Pulse Modulation

Amplitude Modulation If the amplitude of the carrier is varied in accordance with the amplitude of the modulating signal (information), it is called amplitude modulation.

Transistor Power Amplifier

Oscillator output is fed to the transistor Power amplifier (TRPA). It gives an output of 12 Watt across 75 ohms. It works on + 20 V DC, derived

from a separate rectifier and regulator. For different operating frequencies, different output filters are selected. (Low Pass Filter). In the first Fig. shows the Qwartz Crystal Oscillator and in the second shows the Elenos-t1800-compact-fm-transmitter-amplifier-1

RF Driver

A 4-1000 A tetrode is used as a driver which operates under class AB condition, without drawing any grid current. About 7 to 10 Watts, of power is fed to the grid of the driver through75: 800 ohms RF Transformer, which provides proper impedance matching to the TRPA output and also provides the necessary grid voltage swing to the driver tube.fig shows 4-1000A 1 KW power tetrode in an amateur radio transmitterPARALLEL OPERATION OF TRANSMITTERSNeed for Parallel Operation At times it may not be possible to get the required power from the single transmitter for the required coverage of the broadcast service. In such conditions, it is essential to combine two or more transmitters to get the required power.COOLING TECHNIQUES IN TRANSMITTERIntroduction In modern A.M. transmitters power valves are used in the power amplifiers (PA)and modulator stages, which are condensed vapour cooled ceramic tetrodes. In the old generation transmitters, triodes are used in the PA, modulator and exciter stages. Both the tetrodes and triodes tubes are capable of being operated at high voltages (11 kV DC) and large anode current of the order of 50 Amps. Different types of cooling are used in AIR transmitter at present. Fig in the left side showing the Air-cooled transmitters for 100 W to 2.5 kW and in the below showing AUDIO CARD Transmitter BEL 2x10 kW.

a) Air cooling b) Vapour cooling system c) Condensed vapour cooling

Air Cooling :At present forced air cooling is used in AIR transmitters. A blower sucks the air through an Air filter and a guided duct system and the forced air is passed on to the required transmitting tubes. There has to be minimum air flow to cool the valves. Hence there will be an air operated Air Flow Switch (Relay).

Vapour Cooling System :This system is used in 100 kW BEL Transmitters. For very high power valves and efficient cooling, air cooling is not sufficient.

Condensed Vapour Cooling in HMB-140BEL 100 kW MW XTR:

In BEL/BBC solid state transmitter of 100 KW/300 kW MW and 50 KW/100KW/500KW SW transmitters, condensed vapour cooling is used for the PA and modulator valves. A high velocity water flows through the valve jacket and transforms into vapour due to the dissipation of power in anodes. The tubes are fitted with a specially formed anode which sits in a cylindrical cooler. The temperature of water coming from the transmitter can theoretically reach about 900 C, but in practice, it is desired to about 700 C in normal modulation. Fig showing the Condensed vapour cooling is used for the PA valve and the coils are cooled with forced air.

FM TRANSMITTER A personal FM transmitter is a low-power FM radio transmitter that broadcasts a signal from a portable audio device. Most of these transmitters plug into the device's headphone jack and then broadcast the signal over an FM broadcast band frequency, so that it can be picked up by any nearby radio. Being low-powered, most transmitters typically have a short range of 100300 feet (30100 metres), depending on the quality of the receiver, obstructions and elevation. Typically they broadcast on any FM frequency from 87.5 to 108.0 MHz in most of the world (or 88.1 to 107.9MHz in the US and Canada).PRINCIPLES OF ANTENNA SYSTEM :Introduction

Antenna is usually a metallic device (as a rod or a wire) used for radiating or receiving electromagnetic waves.This travels in the free space in the form of radio waves (electromagnetic waves). The receiving antenna picks up the radio waves and delivers useful signal at the input of a receiver for reception of signals.

The Function of an Antenna :The purpose of a transmitting aerial is to convert the power delivered by the transmission line into a wave called an "Electro-magnetic wave." This electromagnetic wave is then radiated through space.

How an Aerial Works :

If the wires of an open-ended transmission line are bent back at right angles to the line, at a point one quarter wavelength back from the open end, a simple aerial is formed which is called either a "half-wave dipole," a "doublet," or a "Hertz aerial." The voltage and current distribution on this aerial are the same as on the original transmission line. Fig. showing working of half wave dipole

Basic aerials: Hertz aerial: The half wave dipole or Hertz aerial is used for Short Wave (SW) frequencies in All India Radio network. This can be used at other high frequency also. Since at high frequency the overall length becomes smaller.

Marconi aerial:

Another basic aerial is a vertical quarter-wave grounded aerial sometimes called a "Marconi aerial." If one of the arms of a hertz aerial is removed, and the wire which went to that element is earthed or grounded, the result is a Marconi aerial.

Isotropic Antenna It is an imaginary (non-existent) point (dimensionless) antenna which radiates equally with unity gain in all directions in three dimensional planes.

Radiation Pattern (Polar Diagram) Graphical representation of the directional radiation properties of the antenna as a function of space coordinates in three dimensions is called the radiation pattern. Such a representation will be usually very complicated to interpret. It is usual practice to represent the same in two dimensions for both horizontal and vertical planes.

Polarizations The plane containing the electric vector in the electromagnetic wave describes the polarization of the radiated wave. Ideally maximum signal is coupled if the antennae (both transmitting and receiving) are oriented in the plane of polarization of the electro -magnetic wave.fig. showing 3-D Radiation Pattern of Dipole Antenna.

WAVE PROPAGATIONPropagation of radio waves takes place by different modes, the mechanism being different in each case. Based on that, it can be classified as:1. Ground (Surface) waves2. Space (Tropospheric) waves3. Sky (Ionospheric) waves

The entire globe has been split into three regions by the International Telecommunication Union. India falls in Region 3 in the above classification.Short WaveThe signal laid at any receiving point using HF propagation must be above the noise field at that place by a specific amount of RF signal-to-noise ratio in absence of interference from other transmissions.FM BandAreaMonoStereo

Rural48 dBV/m54 dBV/m

Urban60 dBV/m66 dBV/m

Large Cities70 dBV/m74 dBV/m

Television BroadcastingMaximum signal requirements for satisfactory reception with receiving antenna at 10 m height are as follows:

Band 1*48 dBV/m Band 355 dBV/m Band 465 dBV/m Band 570 dBV/mSporadic layer (Es) interference

The sporadic E layer is sporadic in its existence as its name implies. It is an ionospheric layer whose ionization density is comparable to that of F layer of the ionosphere, but, usually occurs at the E layer height of 100 to 120 kms. By virtue of its high density odd ionization, the layer is able to reflect VHF frequencies, i.e., the band 40 to 68 MHz over long distances. However, Doordarshan has adopted 40 dBV/m. Co-Channel Interference

If the wanted TV signal exceeds the interfering signal by a voltage ratio of 55 dB or more, no interference will be noted. When the desired signal becomes weaker, Venetian blind interference occurs.

Adjacent Channel Interference

Stations occupying adjacent channels present a different problem. Adjacent channel interference may occur as the result of beats between any two of these carriers. The difference of 1.5 MHz produces a coarse beat pattern.

STUDIO CHAIN IN A TYPICAL AIR STATIONIntroduction

The broadcast of a programme from source to listener involves use of studios, microphones, announcer console, switching console, telephone lines / STL and Transmitter. Normally the programmes originate from a studio centre located inside the city/town for the convenience of artists. The programme could be either live or recorded. All these programmes are then selected and routed from studio to transmitting centre through broadcast quality telephone lines or studio transmitter microwave/VHF links.

Studio Centre

The Studio Centre comprises of one or more studios, recording and dubbing room, a control room and other ancilliary rooms like battery room, a.c. rooms, switch gear room, DG room, R/C room, service room, waiting room, tape library, etc. The size of such a centre and the number of studios provided depend on the programme activities of the station. The studio centres in AIR are categorised as Type I, II, III and IV. Fig showing the Studio Centre.

MixingAs already mentioned, various equipments are available in a studio to generate programme as given below:

Microphone, which normally provides a level of 70 dBm. Turntable which provides an output of 0 dBm.Announcer Console :

The Announcer Console is used for mixing and controlling the programmes that are being produced in the studio using artist microphones, tape playback decks and turn tables/CD players. This is also used for transmission of programmes either live or recorded. The technical facilities provided in a typical announcer booth, besides an Announcer Console are one or two microphones for making announcements, two turn tables for playing the gramophone records and two playback decks or tape recorders for recorded programmes on tapes.

Control Room

For two or more studios set up, there would be a provision for further mixing which is provided by a control console manned by engineers. Such control console is known as switching console. Broad functions of switching console in control room are as follows:

Switching of different sources for transmission like News, O.Bs. other satellite based relays, live broadcast from recording studio. Level equalisation and level control. Quality monitoring. Signalling to the source location. Communication link between control room and different studios.FACILITIES IN STUDIO CENTREIntroductionIn addition to control room and studios, dubbing/recording rooms are also provided in a studio complex. The fig below showing Serimux Secure SSH Console Switch Application. Following equipments are generally provided in a recording/dubbing room :i) Console tape recordersii) Console tape decksiii) Recording/dubbing panel having switches, jacks and keys etc.

The above equipments can be used for the following purpose. The fig. below showing Radio Cassette Deck Recorder Stereo System Console.

For recording of programmes originating from any studio. For recording of programmes available in the switching consoles in control room. For dubbing of programmes available on cassette tape. For editing of programmes For mixing and recording of programmes

HARD DISK BASED RECORDING SYSTEMIntroductionThe computer system deals mainly with texts and digits. These texts and digits are in digital form and are recorded on the hard disk of the computer. So, if the analog audio or video is converted into digital form, it can be recorded on the hard disk of the computer. Then the computer can manipulate the audio/video in the similar way as it manipulates texts and digits. This is what is known as hard disk based recording system. Fig. above showing Zoom HD16CD Hard Disk Recording Studio.Analogue System - The constraints Quality - It degrades with usage. Compression technique is not possible. Signal quality degrades due to tape hiss, modulation noise, dropouts, wow and flutter, cross talk, distortion etc.Digital System - The benefits No quality degradation with multiple usage. Complete automation is possible. It is possible to use compression technique. This results in bandwidth saving.

SATELLITE COMMUNICATION

Satellites are basically reflectors in sky. Satellite Communication is the outcome of the desire of man to achieve the concept of global village.1st satellite named as Sputnik -1 was launched in 1957 by USSR from Bikonour Cosmodromme in Kazakhstan. Due to following advantages satellite communication is generally used: This is only means which can provide multi access two way communication. Within the coverage area, it is possible to establish one way or two way communication between any two points. It is possible to provide large coverage using satellite. For example geostationary satellite can cover about 42% of earth surface using global beam.

Radio Networking Terminal The various All India Radio stations spread throughout the nation are required to relay certain programs which are originating from Delhi.In order to link Delhi and capital stations with other AIR stations, RN through INSAT is not only cost effective but also provide the good technical quality as compared to DOT lines and SW linkage. Thus RNT acts as the ground terminal for satellite signal reception.

STUDIO TRANSMITTER LINK:The programs produced at the Studios are not transmitted from the same complex with intention of preventing the problems due to interference and radiation. The high quality sound programmes from AIR studio centre are normally transported to the AIR transmitting centre with the help of a transmission link named as the STUDIO TRANSMITTER LINK (STL). fig showing studio to transmitter link with backup

AIR is having three types of STL called STL-01, STL-02 and STL-05. For quality transmission of the programmes, STL is realised using four methods. They are: A microwave link ISDN link BSNL dial up linkEARTHING SYSTEM Earthing : Earthing is the connection of electrical equipment and wiring systems to earth by a wire or other conductor. The primary purpose of grounding is to reduce the risk of serious electric shock from current leaking into uninsulated metal parts of an appliance, power tool, or other electrical device. In a properly grounded system, such leaking current (called fault current) is carried away harmlessly. Ground stationA ground station, earth station, or earth terminal is a terrestrial radio station designed for extra planetary telecommunication with spacecraft, or reception of radio waves from an astronomical radio source. Ground stations are located either on the surface of the Earth or in its atmosphere.

Conclusion It has been a matter of immense pleasure, honor and challenge and opportunity to take up this project and complete it successfully. While developing this project I have learnt a lot about the Radio Communication (Analog and Digital). I have also learnt how the progress in technology and science made the radio communication far easier by reducing little errors. During the training session and while completing the project report I have learnt the importance of the Radio communication.

SAJIB NATH DURGAPUR INSTITUTE OF ADVANCED TECHNOLOGY & MANAGEMENT