ITM UNIVERSITYPRESENTATION ON INDUSTRIAL TRAINING All India Radio (Akashvani) PRESENTED BY:- MOHIT MAKHIJA BETN1EC11083 Introduction to AIR All India Radio has been a distinctive part of the Indian way of life since 1937. Its also known as Prasar Bharti It is responsible for public service broadcasting in India through All India Radio All India Radio has emerged as one of the largest broadcasting networks in the world. . .5% area of the country. regional and local to cater to the needs of the audience through a large number of centers in the country. At the time of independence there were six radio stations with 18 transmitters covering merely 11% population and 2. AIR Gwalior is at its 50th year (on 15th August 1964) of service now and its transmitter is situated at Rairu . the transmitter 10 KW MW transmitter was replaced by 2 x 10 KW MW . AIR have three tier system of broadcasting: national. ) 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. The wave is then amplified. wave. SW and FM bands to serve the home including external service. and sent to the antenna that then converts signal into an E. (Low power to super power transmitters are working in MW.M.Principle of AIR Transmitting A radio wave carries information signal Signals are converted into electrical signals. A carrier wave is then produced from the modulation. • Modulation • Amplification Reception • Demodulation • Amplification Transmission . Modulating signal Microphone Carrier Wave Modulated Wave .Methodology of Radio How radio electromagnetic waves are changed to Radio Waves • The sound wave is equivalent to a pressure wave. ROOM s in AIR • Studio Centre • Broadcast Studio • Mixing • Control Room . III and IV. Music Studio. II.Broadcasting chain: Studio Centre A studio is a room in studio complex which has been specially designed and constructed to serve the purpose of originating broadcasting programs. Control Room. The number of studios and facilities provided in each type are different. . The Station consists of Talk Studio booth and sound lock and playback Studio. Recording-Cum Dubbing Room. The studio centers in AIR are categorized as Type I. the microphone which is the first equipment that picks up the sound. It is necessary that the place where a program for broadcast purposes is being produced should be free of extraneous noise The area of room is insulated from outside sound . The studios are to be specially treated to give an optimum reverberation time and minimum noise level. . is not able to distinguish between wanted and unwanted signals and will pick up the sound not only from the artists and the instruments but also reflections from the walls marring the quality and clarity of the program.Broadcast Studio A broadcast studio is an acoustically treated room. Mixing The level from microphone is quite low and need to be amplified so as to bring it to the levels of tape recorder. Mike Mixer Amplifier . Audio mixing is done in following two ways: Low level mixing High level mixing Low level mixing Required equipments are selected and then outputs are mixed before feeding to an amplifier. This is called low level mixing. High level mixing Low-level output of each equipment is pre-amplified and then mixed. low level mixing Low level seems to be economical because we will be using a single amplifier but the Quality of sound suffers in this system In low level mixing. All India Radio employs High level mixing. there is signal loss of about 10 to 15 dB in mixing circuits. High level mixing system requires one pre-amplifier in each of the low level channels but ensures a S/N of better than 50 dB. This is called high level mixing Mike Amplifier Mixer High level vs. . Quality monitoring. Signaling to the source location.Bs. Broad functions of switching console in control room are as follows: Switching of different sources for transmission like News. Such control console is known as switching console. live broadcast from recording studio.Control room For two or more studios set up. O. . other satellite based relays. Communication link between control room and different studios. Level equalization and level control. there would be a provision for • • • • • further mixing which is provided by a control console manned by engineers. . The output from a microphone which is at very low level is fed to its input.Amplifiers used in AIR The following are some of the audio amplifiers used in AIR. A special feature of this amplifier is that the noise contributed by this is very low. In some pre -amplifiers a variable gain between 40 to 50 dB is provided. The normal gain of this amplifier is about 50 dB. The amplified signals obtained from this amplifier are given to the program amplifier through a mixing console. Pre-Amplifier Pre-amplifier is the first amplifier in the broadcast chain. The output obtained from the program amplifier is of a sufficiently high level and can be handled without the risk of picking up electrical noise.Program Amplifier Program amplifier provides second stage of amplification. The normal input level to this amplifier varies from -45to 20 dB It has a gain of 70 dB which is variable from 0 to 70 dB. . The output obtained from the fader box or mixing console is fed to the input of this amplifier. Therefore. The output of the monitoring amplifier is usually fed to a bus for further feeding to the loudspeakers Monitoring amplifiers of different wattage ratings are used in AIR.Monitoring Amplifier The output available from the program amplifier is however. But 8 watt monitoring amplifier is very common . monitoring amplifiers are provided to boost these signals further. not enough to drive loudspeaker. A part of the output signal from the program amplifier is given to the monitoring amplifier. Harris. BE 2. 200 kW/300 kW – Thales (Fully Solid State) 6. Various power and make of transmitters used are: 1. 7. Harris 3. 4. 1 kW MW Transmtiter – BEL. 100/200 kW BEL – HMB 140. They are from 1 kW to 500 kW power. 100 kW – Thales (Fully Solid state) 5. 10 kW/20 kW Transmitter – BEL.Transmitter AIR has its tranmitter located at Rairu (18 km from GWL) All India Radio uses various MW transmitters in its network. 300 kW – BBC – Tube Version. . 500 kW BBC/Russian Transmitter. •It gives an output of 5 V square wave which is required to drive the Transistor Power Amplifier. Transistor Power Amplifier •Oscillator output is fed to the transistor Power amplifier (TRPA).) . •It gives an output of 12 Watt across 75 ohms. typically for driving the antenna of a transmitter. the crystal is kept in a oven. It works on + 20 V DC (An RF power amplifier is a type of electronic amplifier used to convert a low-power radio-frequency signal into a larger signal of significant power.Block Diagram of transmitter 100 kW HMB 140 Medium Wave transmitter Crystal Oscillator •To oscillate at a consistent frequency. transmitter. a) Air cooling b) Vapour cooling system c) Condensed vapour cooling . lot of power is dissipated in the valve as the input power is not fully converted into output RF power due to the efficiency of the amplifier which never reaches 100% Different types of cooling are used in AIR transmitter at present.M.Cooling System Used in Transmitter In high power A.