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  1. PREFACE Practical training is an important constituent of any curriculum and Bachelor of Technology is no exception to this general rule. Practical training…
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  • 1. PREFACE Practical training is an important constituent of any curriculum and Bachelor of Technology is no exception to this general rule. Practical training helps the student in getting acquainted with the manner in which his knowledge is being practically used outside the institution and this is normally different from what he has learned in the books. As one switches from the process of learning to that of implementation of his concepts, he finds an abrupt change. This is exactly why summer training session during the B.Tech. curriculum becomes all the more important. Summer training is prescribed for the student of Technical Colleges as a part of the four year degree course of engineering by the AICTE. We are required to undergo summer training for a period of 30 days after the completion of the 3rd year. There are various technological advances in the field of electronics and communication that the world at large is witnessing. The vaccum tubes have been replaced by small ICs and the transmission medium of wires and cables which have high dielectric and tangent losses has been replaced by negligible lossy medium like the optical fibers. The wired communication has been replaced by wireless communication and even in wireless communication the analog means of communication is getting replaced by digital means of communication for higher accuracy and bit transfer rate and for less susceptibility towards noise. This training report describes in detail the training after the 3rd year session, which I completed successfully at the All India Radio, Jaipur which is the oldest government organization in the field of media and broadcasting. This report also gives the information about the organization and its working along with the vocational training undertaken during the training period. All India Radio provided me an exposure in the field of communication for the first time. It was an honor for me to meet AIR professionals. They taught me about how the organization works and strives to reach the maximum of the population, through its various intricate and complicated technologies of communication. We were made aware of the technologies which are used in AIR for the purpose of broadcasting and communication and of the importance of radio in today‟s world which has still hooked the country into one unit in spite of the popularity of television and internet among the people.
  • 2. ACKNOWLEDGEMENT Exchange of ideas generates the new objects to work in a better way. This report is based on the ideas exchanged among the students and the trainers at AIR, Jaipur and the study materials provided by the AIR professionals. I owe my sincere thanks to Mr. Banerjee, Mr. R.K. Chaturvedi, Mr. Manohar Lal Sharma, trainers at All India Radio, Jaipur for providing me their continuous motivation for the project and whole hearted support in this endeavour, which proved vital for the successful completion of summer training ’10. Without their expert help and guidance it was difficult to develop this report. I would like to thank Mr. H.K.Patsaria (Assistant Engineer) and Mr. ( HR Manager) for accepting my application of summer internship in their esteem organization and also considering my name eligible for the merit list. I would also like to express my gratitude to Mr. Sudhanshu Mathur (HOD- ECE) and other faculties whose kind inspiration and invaluable guidance encouraged me from time to time and helped me in the successful completion of the summer practical training report. I am also thankful to all my colleagues for their co-operation and support. Debojyoti Majumdar (Vll Semester, E.C.E)
  • 3. COMPANY PROFLE All India Radio‟s history dates back to the early 1920s when radio broadcasting started in India. The first programme was broadcasted in 1923 by the Radio Club of Bombay. This was followed by setting up of Broadcasting Services in 1927 with two privately owned transmitters at Bombay and Calcutta. The British Government then took over the radio transmission in India and under its banner it came to be known as The Indian Broadcasting Service. It was all changed to All India Radio (AIR) in 1936 with clear objective to inform, educate and entertain the masses which after independence came to be known as Akashvani from 1957. There are at present 231 radio stations in the country. Each of these radio stations functions as the sub-ordinate office of All India Radio. The main function of these centres is to transmit the programmes produced at nearby local CBS or other studios and also from New Delhi studio. Since its inception All India Radio has become one of the largest broadcasting network in the world serving the ever increasing population of India. At the time of independence there were only 6 radio stations and 18 transmitters, which covered 11% population and 2.5% of total land area of the country. Till December,2007 the network comprises of 231 radio stations and 373 transmitters which provide radio coverage to 99.14% of the population and reaches 91.79% area of the country, a total of 384 channels and transmits in 24 different languages and dialects. In spite of recent penetration by other media such as Cable TV, AIR remains the most common means of gaining access to information and entertainment, as the radio receivers are relatively cheap and affordable. In Rajasthan itself there are 23 transmitters and 5 CBS radio stations and 17 non-CBS stations serving the population of the state of Rajasthan. The main high power transmitter of 50KW is stationed at Ajmer because Ajmer is located at the centre of Rajasthan, from where the programmes are broadcasted to all other parts of Rajasthan. The Jaipur CBS station has got its transmitter of 2KW stationed at Vaishali Nagar, Jaipur, which is used to transmit programmes from the Jaipur CBS station to the Ajmer CBS station so that the programme can be transmitted to all other parts of Rajasthan. For FM transmission, there are 21 FM transmitters of 1KW in Jaipur situated at a distance of 40km from each other. ORGANISATIONAL SET UP The Directorate General, All India Radio functions under the Prasar Bharati. The Prasar Bharati Board functions at the apex level ensuring formulation and implementation of the policies of the organisation and fulfillment of the mandate in terms of the Prasar Bharati. Act, 1990. The Executive Member functions as a Chief Executive Officer (CEO) of the Corporation subject to the control and supervision of the Board. The CEO, the Member (Finance) and the Member (Personnel) perform their functions from Prasar Bharati headquarters at 2nd Floor, PTI Building - Parliament Street, New Delhi-110001. All important policy matters relating to Finance, Administration and Personnel are submitted to CEO and the Board through the Member (Finance) and Member (Personnel) as required, for the purpose of advice, implementation of proposals and decisions thereon. Officers from different streams working in the Prasar Bharati Secretariat assist the CEO, Member (Finance) and Member (Personnel) in integrating action, operations, plans and policy implementation as well as to look after the budget, accounts and general financial matters of the Corporation.
  • 4. Prasar Bharati also has a unified vigilance set up at the headquarters, headed by a Chief Vigilance Officer. The Director General of All India Radio is headed by the Director General. He functions in close association with the Member (Finance) and Member (Personnel) and the CEO in carrying out the day to day affairs of AIR. In AIR there are broadly five different Wings responsible for distinct activities viz, Programme, Engineering, Administration, Finance and News. PROGRAMME WING The Director General is assisted by Deputy Directors General in the Headquarters and Deputy Directors General in the regions for a better supervision of the stations. The Headquarters of the Regional DDGs are situated at Kolkata (ER) Mumbai and Ahmedabad (WR), Lucknow (CR-I), Bhopal (CR-II), Guwahati (NER), Chennai SR-I), Bangaluru (SR- II), Delhi (NR-I) and Chandigarh (NR-II). ENGINEERING WING In respect of technical matters of All India Radio, The Director General is assisted by the Engineer-in-Chief and Chief Engineers posted in the headquarters and the zonal Chief Engineers. In addition, there is a Planning and Development Unit in the Headquarters to assist the Director General in respect of Development Plan Scheme of All India Radio. In respect of Civil Construction activities, the Director General is assisted by the Civil Construction Wing, which is headed by a Chief Engineer. CCW also caters to the needs of Doordarshan. ADMINISTRATIVE WING A Dy. Director General (Administration) assists the Director General on all matters of administration while Dy. Director General (Programme) assists DG in administration of Programme personnel. A Director looks after the Engineering Administration of All India Radio, while another Director (Admin. & Finance) assists DG in matters of administration and finance. SECURITY WING The Director General is assisted by a Deputy Director General (Security), Asstt. Director General (Security) and a Dy. Director (Security) on matters connected with the security and safety of AIR installations, transmitters, studios, offices etc. AUDIENCE RESEARCH WING There is a Director, Audience Research to assist the Director General in carrying out surveys of audience research on the programmes broadcast by various station of All India Radio.
  • 5. ACTIVITIES OF SUBORDINATE OFFICES OF AIR There are a number of subordinate offices of All India Radio performing distinct functions. Broad activities, in brief, are given below. NEWS SERVICES DIVISION News Services Division works round the clock and broadcasts over 500 news bulletins both in the home and external services. The bulletins are in Indian and Foreign languages. It is headed by Director General, News Service. There are 44 regional News Units. The bulletins vary from region to region according to news interest. EXTERNAL SERVICE DIVISION As a 'Voice of the Nation', External Services Division of All India Radio has been India's "Authentic Window to the World". With growing importance of India in the world, an increasingly important role is envisaged for External Broadcast for times to come. External Services Division of All India Radio broadcasts in 16 foreign and 11 Indian languages for approximately 72 hours in a day covering more than 100 countries. TRANSCRIPTION & PROGRAMME EXCHANGE SERVICE This service looks after exchange of programmes among the stations, building and maintenance of sound archives and commercial release of prestigious recordings of music maestros. RESEARCH DEPARTMENT The functions of the Research Department include Research and Development of equipment required by AIR and Doordarshan, investigation and studies relating to AIR and Doordarshan, development of prototype models of R&D equipment for limited use, field trials in the network of AIR and Doordarshan. CENTRAL STORE OFFICE The Central Store Office located at New Delhi performs functions relating to procurement, stocking and distribution of engineering stores required for the maintenance of technical equipment at All India Radio Stations. STAFF TRAINING INSTITUTE (PROGRAMME) The Staff Training Institute (Programme) started with Directorate since 1948 has presently two main branches functioning from Kingsway Camp, Delhi and Bhubaneshwar. It imparts in-service training to programme personnel and administrative staff and induction course for the newly recruited staff and short duration refresher courses. It conducts examinations for administrative staff. In addition, at present five Regional Training Institutes at Hyderabad, Shillong, Lucknow, Ahmedabad and Thiruvananthapuram are working.
  • 6. 1 INTRODUCTION Communication is a term which means a process of transferring information from one place to the other. That place can be anywhere within the earth. But the earth atmosphere and the other surrounding objects are a lossy medium which absorbs the signals that is being transmitted with the help of the transmitter. As a result of this the signal that is received by the receiver is of very weak strength. Further more noise is also added in a considerable amount to the signal. In order to reduce the addition of noise to the signal and the signal could be transmitted to a longer distance from antenna of adequate width various modulation schemes have been employed which are discussed below. 1.1 Modulation Modulation is a process of superimposing information on a carrier by varying one of its parameters (amplitude, frequency or phase). 1.2 Need for Modulation  Modulating the signal over high frequencies can reduce antenna size.  To differentiate among transmissions (stations).  Maximum to minimum frequency ratio can be reduced to minimum by modulating the signal over high frequency. 1.3 Types of Modulation In general there are two types of modulation: a) Amplitude Modulation b) Angle Modulation 1.31 Amplitude Modulation If the amplitude of the carrier is varied in accordance with the amplitude of the baseband signal, it is called amplitude modulation. This modulation is shown in figure 1.1. We can see this on the screen of oscilloscope. 1.32 Spectrum of AM Signal The spectrum of AM signal is shown in figure 1.2. If fm = modulating frequency fc = Carrier frequency. The Spectrum of AM signal will be as below: Power in the carrier, Pc = (Ac / 2 ½ ) 2 = (Ac) 2 / 2 Power in sideband, Plsb = Pusb = (ma 2 Ac 2 )/8 Power in upper sideband (Pusb) = Power in lower sideband (Plsb) Hence total power, Pt = Pc + Pusb + Plsb = Ac 2 {1+ (ma 2 )/2} / 2 = Pc {1+ (ma 2 )/2} Where, Ac = Amplitude of the carrier Am = Amplitude of the modulating signal ma = Modulation index = Am/Ac Bandwidth, BW = (fc + fm) – (fc + fm) = 2fm
  • 7. 1.33 Angle Modulation Variation of the angle of carrier signal with time results in angle modulation. It is of two types a) Frequency Modulation b) Phase Modulation 1.33.1 Frequency Modulation If the frequency of the carrier is varied in accordance with the amplitude of the modulating signal (information), it is called frequency modulation. This has been shown in figure given below. 1.33.2 Spectrum of FM signal with sinusoidal modulation A frequency modulated signal has a large number of frequency components even when the modulating signal is a single frequency signal. The adjacent frequency components are spaced just fm apart. These components lie on both sides of the carrier and are symmetrically placed about it. The amplitudes of the corresponding component are equal. The components, with frequencies (fc + fm) and (fc - fm) are called the first order side bands. The amplitude of each of the first order side bands is AJ1 (mf). The components with frequencies (fc - nfm) and (fc - nfm), where n is an integer, are called the nth order side bands. The amplitude of carrier is AJ0 (mf). The relative amplitudes of various side bands, therefore, depend upon the index of modulation alone, the amplitude of a particular side bands being equal to the Bessel function of the corresponding order. The spectrum is shown in figure given below. From the above we find that the process of frequency modulation results in a reduction of carrier amplitude and generation of an infinite number of side bands. Generally, a limited number of side bands closer to the carrier frequency will have significant amplitudes. Power Pc = Ac 2 /2 = Power of the unmodulated carrier This holds true for any type of modulating signal and for any value of modulation index. Where, Ac = Amplitude of the carrier Am = Amplitude of the modulating signal mf = df / fm = Modulation index df = Frequency deviation fm = Frequency of the modulating signal Bandwidth of FM signal Band width can be defined as that frequency range which accommodates the carrier and the closest side bands contributing at least 98% of the total signal power. (Carson rule). BW = 2(mf + 1) fm = 2(mf fm + fm) = 2(df + fm) 1.33.3 Phase Modulation If the Phase of the carrier is varied in accordance with the amplitude of the modulating signal (information), it is called phase modulation. This modulation has got minimum use.
  • 8. 2. MW TRANSMITTER All India Radio uses various MW transmitters in its network. They are from 1 kW to 500 kW power. Various power and make of transmitters used are: 1. 1 kW MW Transmitter – BEL, Harris, BE 2. 10 kW/20 kW Transmitter – BEL, Harris 3. 100/200 kW BEL – HMB 140. 4. 100 kW – Thales (Fully Solid state) 5. 200 kW/300 kW – Thales (Fully Solid State) 6. 300 kW – BBC – Tube Version. 7. 500 kW BBC/Russian Transmitter. 2.1 10 KW MW TRANSMITTER (HMB 163) 2.11 SALIENT FEATURES  Identical type of valves both for PA and Modulators.  Except in the final stage, all other stages are solid state operated.  Valves are ceramic metal tetrode permits full range operation upto 110 MHz.  PA is in Class C amplitude modulated which is one of the oldest and yet most popular modulation technique used in India and elsewhere in the world.  Microprocessor controlled system with self diagnostic facility.  Efficiency is better than 50%.  A compact and modular system with everything in a single cabinet. 2.12 TECHNICAL SPECIFICATION 1. Emission : Double side band broadcasting on MW. 2. Rated Carrier output kW : 10 kW however it can go upto 15 kW (max.) 3. Output Impedance : 230 ohm for open line and 50 ohm for cable feed type. 4. AF response : -1.5 dB 5. Distortion : Less than 4% 6. Noise Level : -60 dB 7. Audio Input Level : 0 dbm for 100% modulation 8. Audio Input impedance : 600 ohm bal 9. Power consumption : 20 KVA on carrier 22 KVA on 40% modulation 30 KVA on 100% modulation 2.2 100 KW HMB 140 MEDIUM WAVE TRANSMITTER AIR has 52 transmitters of this type and is the back bone of MW service. So let us discuss this transmitter in detail.
  • 9. RF circuits consists of a crystal oscillator, transistor power amplifier, RF. Driver and Power Amplifier of 100 kW HMB 140 MW transmitter are shown in Fig. 7. Block Diagram of RF Chain (HMB-140) 2.21 CRYSTAL OSCILLATOR To oscillate at a consistent frequency, the crystal is kept in a oven. The temperature of the oven is maintained between 68 to 72o C and the corresponding indication is available in the meter panel. Crystal oven is heated by + 12 V. One crystal oscillator with a stand by has been provided. It gives an output of 5 V square wave which is required to drive the Transistor Power Amplifier. The crystal oscillator works between 3 MHz and 6 MHz for different carrier frequencies. Different capacitors are used to select different frequency ranges. In addition, variable capacitor is used for varying the frequency of the crystal within a few cycles. The oscillator frequency is divided by 2, 4, or 8 which is selected by jumpering the appropriate terminals. The oscillator Unit gives 3 outputs, one each for RF output, RF Monitoring and RF output indication. 2.22 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). 2.23 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 through a 75 : 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. Various Pin Voltages The cathode of the driver : - 600 V Control grid : - 650 V Screen grid : + 100 V Plate Voltage : + 1900 V Because the cathode is at -600 V, the effective grid to cathode bias voltage (fixed) is -50
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