Radio Station Training Report

CONTENTS 1)

INTRODUCTION

2)

BLOCK DIAGRAM DESCRIPTION OF RADIO STATION

3)

RADIO NETWORKING TERMINAL a) SATELLITE b) R.N. TERMINAL

4)

CONSOLE a) ANNOUNCER CONSOLE b) AUDIO SWITCHING CONSOLE c) DOUBLE CONTROL CONSOLE d) PHONE IN CONSOLE

5)

AUDIO RACKS a) DISTRIBUTION AMPLIFIER b) EQUALISER c) MONITORING AMPLIFIER

6)

EQIPMENTS a) CTR’S b) C.D. PLAYER c) TURN TABLE

7)

POWER SUPPLY INCONTROL SYSTEM

8)

ACOUSTIC TREATMENT

9)

TRANSMITTER

10)

CONTROL SYSTEM

11)

STUDIO TRANSMITTER LINK

12)

INTRODUCTION TO C-BAND

INTRODUCTION COMMUNICATION: It is the process where by information is transferred from one point called source to the other point called destination (receiver). RADIO: Radio comes after telephone in the communication history. It means wireless communication by electromagnetic wawes or precisely saying radio wawes. BROADCASTING: Broadcasting comes under the wide definition of communication, it means one way communication, where one speaks and other listens only without interfacing. The basic requirement is that the signal to be broadcast must be distortion free. RADIO STATION: For the purpose of entertainment and NEWS broadcasting, radio stations are established. First radio station started in 1935 in the state of Hyderabad. In Rajasthan first radio station was established on 9th of April 1955 in Jaipur, which was medium wawe station of 1KV power capability. AIR BIKANER STATION: Medium wawe Transmitter of NEC Company having 10KV power capabilities was inaugurated in April 1963 as an auxiliary centre of AIR, Jaipur. Till year 1980-81 the station was originated three hours of program daily, there activity of station was increased and station functioning as full-filled station from 1981-82. In August 1992, 2*10KV transmitter has been installed which increased power of transmission to 20KV. STUDIO CATEGORY: The radio station categorized according to the number of studios in the station. Broadly it is divided into five categories (A) Studio 1 (B) Studio 2 (Having four studios eg Bikaner radio station) (C) Studio 3 (D) Studio 4 (E) Studio 5: This type of studio is present metro cities having two music studios, two drama studios as per requirement. BIKANER STUDIO: Bikaner radio station is II type of radio station having four studios:(A) Music studio (B) Drama studio (C) Talk studio (D) Play back studio

BLOCK DIAGRAM OF RADIO STATION Consoles are the main component in the radio station. Control room is the place from where all features of programs are controlled prior to send to the transmitter for broadcasting. It means the proper programs of appropriate level, the clarity of sound, noise level etc. are monitored before broadcasting. For program monitoring & selection of the proper program to be broadcasted is selected through switching console. Switching console is the main component in the control room. Signal is routed through distribution amplifier while passing from the control room. The purpose of the distribution amplifier is to provide multiple outputs at the same level from single input. Mainly playback studio is used for announcing a program & rest studios are chiefly used recording live & however we can use them as playback in emergency. Main component of playback studio is announcer console. Here input is through mike(-7db) & record players(0db),output is at +4dbu after internal processing. Output signal is selected by fader (variable attenuator) & leads to jack panel , after repeat coil 7 & 4db pad. Repeat coil is 1:1 transformer used for safety purpose to protect one circuit from another circuit fault by separating them electrically. A +4db pad is provided so that input to switching console is 0db. In jack panel various connection are provided, of all studios & six of R.N. frequencies. We can interlink them or connect to switching console through bars. Recording room is for recording & editing of various programs. Switching console is similar in function as announcer console but output of this is send to transmitter after equalized line amplifier. Now signal is send to transmitter by coaxial cables, also both ends are connected to repeat coil. In transmitting station signal is again fed to equalizer line amplifier & then to 14db pad, then -6dbu signal is fed to limiter (6dbu), then a 6db pad. Now signal is fed to transmitter. In Bikaner AIR there are two transmitters having capacity of 10KW each. A combiner is provided to combine their power output, which is fed to antenna (110 meter self-radiating steel tower). A dummy antenna (resistor) is provided to bear the output of other transmitter in case of failure of one transmitter, the selector switch on the combiner control this. Also, there is an emergency studio in the transmitting station to use in emergency created due to difficulty in receiving signal from studio.

RADIO NETWORKING TERMINAL SATELLITE Since the advent of freedom, India has embarked upon a program of national development & has attempted to use very consciously, since technology as an instrument for rapidly accelerating national growth. Radio & television can serve as efficient tools for learning & distortion free information transfer for instruction. The need for developmental information is maximum in rural & economically backward villages, which are remote & isolate from urban centers. The absence of an extensive was ameliorated by the successful launchings of INSAT-1D & INSAT-2D. The first generation India satellite system (INSAT-1D) built by the ford aerospace & communication corporation FACC of USA, to Indian specification & requirements under a contact from the development of space (DOS) is located at 83 degree east longitude INSAT- 1D became operational on June 1990 & INSAT2A during July 1992. Each of the multipurpose INSAT-1 satellites is designed to provide the following capabilities over there individual seven year in orbit life.

Fixed satellites service (FSS): Twelve transponders operating in 5935-6415 MHz (up-link), 3710-4200 (downlink). Utilization for thick route, thin route and remote area communication and TV program distribution.

Broadcast satellite service (BSS): Two transponders in operating in 58555935MHz (uplink) and 2555-2635MHz (downlink). Utilization for direct TV broadcasting to augmented low cost community TV sets in rural areas radio program distribution, national TV networking disaster warning.

R.N. TERMINAL: The various stations of AIR spread throughout the nation are required to relay certain programs and news services, centrally originated at New Delhi. There are also events of popular interests, taking place any where in the country, which need national or regional coverage. The programs for external service also originate at New Delhi and broadcast round the clock from transmitting stations located at Aligarh, Calcutta, Jullunder, Rajkot, Bombay, & Madras. In order to meet these varied requirements, AIR needs an elaborated networking systems, confirming to a set of quality and reliability objectives. Any one of the six carrier signals is selected in one module and is down converted to 5.5MHz in the synthesizer. Now in the demodulator unit original audio signals are extracted.

R.N. Terminal has been developed at Space application centre (SAC) Ahemdabad of ISRO as a joint ISRO program. The uplinks are provided by P & T. Radio networking refers to National networking of AIR stations through the series of satellite for radio programming distribution. The Radio Network terminals (RNT) located at AIR stations receives the S-BAND. R.N. transmission & audio program thus received after processing is fed to transmitter to be broadcasted. The RNT acts as the ground terminal for satellite signal reception. The transponder is INSAT-2 satellite that can accommodate 28 channels. The RNT is thus designed to receive any of these channels and six of them simultaneously. In, addition, the equipment is confined incorporate redundancy. The block diagram of R.N. terminal is shown in figure. The system is considered by the following components:1. 12ft. chickens mesh reflector antenna + helical feed. 2. Low noise amplifier unit (LNA). 3. Front-end converter unit (FEC). 4. Passive frequency translator unit (FTP). 5. Active frequency translator unit (FTA). 6. Synthesized translator unit. 7. Audio demodulator unit (DEM). 8. Power supply (PS). The 12ft. parabolic antenna collects the R.N. carriers transmitted by the satellite and feed them to the feed mounted LNA unit. The LNA unit contains two channels of LNA PCB’s in the redundant mode any of which can be selected by means of an RF switch. The outputs of the LNA’s are combined in powers to give the output of two LNA’s unit. The S-BAND output of two LNA is given to FEC through low loss cable. The FEC contains two channels of down converter & IF pre amplifier. An RF switch does channel selection. The FEC is located close to the antenna & is converted to the indoor unit by means of a coaxial cable for carrying the IF signal & a separate three core cable for the +24 volt DC supply. Power of LNA module is taken from the power connector points of FEC. Power to the normal/redundant sites of the LNA/FEC is switched by a toggle switch provided on the front panel of the FAT unit. In the indoor part of the equipment, the signal from the FBC is fed to the power divider in the passive frequency translator. The two wide band (92MHz) filters in the passive frequency translator, separate the 52MHz components of the IF. Again the 52MHz/92MHz signals are divided.

The power dividers are used to get normal and redundant channels, which can be selected by changing the cable connection. The four outputs are then fed to the audio frequency translator. The signal of 92 MHz band undergoes frequency down conversion, amplification and power division in the active translator. Also 52MHz band signals undergo power division in the translator unit. The output signal of the active translator, which is now in the 52MHz band and fed to the synthesized translator via coaxial cables. Each such translator has six numbers of synthesizer + translator plug in modules. Any of the channels can be selected/tuned by varying the entry of front panel thumb wheel switch of the synthesized plug-in. The selected input signals are down converted to 5.5 MHz in the synthesized translator output signal is undergone demodulation, de-emphasis filtering (L.P.) in the demodulator plug-in module in the demodulator unit. The outputs of these are in a demodulator unit. The output of this audio is across 600 ohm (balanced). In the active frequency translator facility is provided to monitor the carrier levels on the front panel level meter. The power supply unit for the R.N. terminal is meant to cater the power supply requirement of R.N. terminal equipment. This 19th rack is mountable unit, provides both +24 volt and -24 volt tracking regulated DC output, the positive supply has a current rating of 5 A., while the negative supply output is rated for 3 A. The power supply unit features over voltage and short circuit protection. The unit operates at 230 volt, 50 Hz singlephase mains.

CONSOLE: The console has been specially designed for broadcast application, keeping in mind the stress for high reliability and continuous operations. The console is ideally suited for any broadcast studio, which requires efficient use of its facility while maintaining the highest subjective audio quality throughout the transmission process. Types of console:Announcer console (8 channel audio mixer) Audio switching console Dubbing control console Phone in console ANNOUNCER CONSOLE (8 CHANNEL AUDIO MIXER) Keltron mono audio mixer is designed and developed to meet AIR specification. It is used in transmission studios and talk’s announcer room of AIR for mixing and controlling of audio program. Keltron audio mixers have eight input modules and

talk back module. It has been configured into two types: M162 A:-Two of the input channels have mike/line input with self- illuminated selection switch. Rest of the input channels has two numbers of input channels. M162 B: - Four of the input channels have mike/line input with self-illuminated selection switch. Rest of the input channels has two numbers of input channels. Selection switch: - Rest of the four channels has two number of input channel with self –illuminated selection switch for each of the input channel. The block diagram of both the types and internal circuit diagram of announcer console is shown in the figure. The microphone signals which reaches the input module through the XLR connector in the connector module is amplified to required level by microphone amplifier stage. The signal is then passed on to the phone splitter stage, which provides phase inversion to the signal, if desired and passes the output to MIC/Line selector stage. Line signal which is fed to the input modules reach to the line amplifier through the XLR connectors in the connector module and comes to the MIC/Line selector stage after proper gain selection. For microphone stage the rest oscillator can be injected to the chain from the “OSC OUT” socket provided on the talk back module using the patch cord provided along with the console. For line stage the oscillator test signal can be selected using the “OSC ON” switch provided on the same module. The output from the MIC/Line selector stage is fed to the channel fader. The post fade signal is again amplified to the required level & forms the main channel output. The pre fade signal is fed to the module for PFL monitoring using the “PFL ON” switch. The pre fade & post fade signals are also “or” amplified & fed to the overload indications circuit that gives an LED indicator scanning the full signals patch. This module also gives the DC control voltage for routing the signals to Master 1 & Master 2 channels. The module also contain the hardware for channel ON indicator LED which lights when the fader is faded IN from the off position with master output routing & with the corresponding master fader is also faded IN from infinity. The module also gives a DC voltage for “LIVEMIC” indicator. This control signal is further routed to the talkback module for energizing the relay actuation circuit for ON AIR indication. This signal also affects the PFL & main monitor channel when microphone channel is faded in. For M162 A, the monitoring speaker & PFL speaker of transmission studio will be muted and WLR outside A/R & outside S/L will be operated when the microphone channel is faded in.

For M162 B, the monitoring speaker for announcer room will be muted when the microphone channel is faded in. PFL speaker will be muted & WLR outside A/R will be operated in this condition. Monitoring speakers for studio will be outside S/L, will be operated in this condition. This signal output is not available for line inputs as muting/warning signals are not required along with the line signal. Other input channel have functions similar to input channel on except for the fact that modules IP02 MB have only line inputs & hence contains the circuitry for line signal processing only. The main channel outputs from the input channels 1 to 3 are connected to the corresponding signal input of master output channels 1 & 2. The signal can be routed to either one or both of the master channels using the routing switches on the input modules. In the master module the output of mixer stage is fed to the program selector switch that selects either of the master mixer or oscillator signal used for calibration. The output of selector goes to channel fader. The post fade signal is fed to the line amplifier which amplifies to the required level & feeds to unbalanced converter which is connected to the main channel output socket (XLR connector on the connector module). Besides the main channel also gives the auxiliary outputs (2 outputs per channel). This module also provides the pre fade & post fade monitor output signals for the purpose of monitoring. The PFL monitor signal can be switched on the pre fade & post fade signal & gives an LED indication under overload condition. The channel “ON” indicator LED of this module becomes ON when the fader is faded in from infinity position. The Master 2 output module is similar in function to the Master 1 output module. Nominal = 0dbu Maximum = +20dbu Adjustable in range of (-10dbu) to (+10dbu) continuous with center defined for middle position. OUTPUT LEVEL Main master output Nominal = +4dbu Maximum = +24dbu

Auxiliary output Nominal = +4dbu Maximum = +24dbu IMPEDANCE (Electrically Balanced) Input Impedance:Mike input > or = 2kohms Line input > or = 2kohms Output Impedance:Master output < or = 50ohms Auxiliary output < or = 50ohms OVERLOAD MARGIN (HEADROOM) Input:Microprocessor unit = 20db Line input = 20db Overload margin at channel fader = 1db Output:Overload margin at master fader = 1db Frequency response:+ 0.5db for 40 Hz to 15 KHz w.r.t to 1 KHz

TOTAL HARMONIC DISTORTION Mike channel:With nominal input max 0.3% (40 Hz to 15 KHz) Line channel:With nominal input max 0.1% (40 Hz to 15 KHz) For driving different relays connected to the console, the different types of indicators provided to the console are given below:ON AIR This indicator becomes ON when the console receives ON AIR logic input from the switching console. When LED is ON it indicates that the program from this console is selected by switching console for ON AIR transmission.

LINE MIC This indicator becomes ON when any of the microprocessor channel is faded in with proper routing to the master output channel. The fader of the routed master channel should also be faded in for lighting of microprocessor signal path from the announcer’s console. READY This indicator becomes ON using the ‘ready’ signal provided on the talkback module. This indicator when ON gives a signal to the switching console illuminating the ‘READY’ LED for the corresponding input channel. This indicator when ON, shows that operator is ready for transmission of program. PFL OFF This indicator (blinking type) becomes ON when the PFL monitor channel is switched OFF using the PFL OFF” switch. TB CALLING This indicator (blinking type) becomes ON when there is any signal present on the talk back input port. Under audio monitoring muted condition this indicator will inform the operator the presence of a TB call that can be monitored using the headphone if required OSC ON This indicator (blinking type) becomes ON when any of the input/output Module is in the oscillator mode.

SUPPLY STATUS This indicator shows the status of the Power Supply unit. This indicator will be steady when all the supply rails are normal and it will start blinking when there is fault in any one of the supply rails. The PPM meter panel is also provided with one 20db attenuation switch for each PPM meter & PPM meter program selector switch for the Master 2 PPM meter. The ‘PPM ATTEN’ switch when operated gives 20db attenuation to the PPM signal. The PFL amplifier & console speaker are located in the PPM meter box. The main power supply is a standard 19” unit. The master monitor amplifier is also housed in the unit. PA91 MB used for the studio & fold back. M162A has only one monitor amplifier inside it, but there are two monitor amplifiers in PA92 MB module that are used for M162B. There is a small motherboard in the backside of power supply. The input & output connectors of monitoring amplifier are fixed to it. The supply is connected to the console. The main power ON/OFF switch is located on the power supply unit.

MIC/LINE channels Balanced MIC/LINE each has the following facilities:MIC/LINE selection switch with self illuminated push button phase reversal function with switch & indicator ON while use. Sensitivity control in steps with continuous fine adjustment between steps, which is PCB mounting type & conductive plastic. Independent output selection to main master output 1 as well as master 2 prefade listening facilities. Mute indications while when fader is faded in from infinity position. Remote starting facility for starting the line level sources. High level input channels Balanced high level line input channels have the following facilities:MIC/LINE Input selection switches between line1/linr2 with self illuminated push button switch. Continuously varying sensitivity. Control for line level output selection to main master output 1 as well as master 2. Output channels Two master output channels each have the following facilities:Two auxiliary outputs channel/each master. Overload indication. Prefade listening facility. Switch selection of master 2 on master 1. Channel ON indication. Input level Mike level Nominal = -70dbu Maximum = -40dbu Adjustable with sensitivity control in steps of (10 db) each. Remote selector selects one out of eight connected to its input through the back panel terminal. The output from the ADA is fed to the channel fader. The postfade signal is again amplified to the required level and forms the main channel output. The prefade signal is fed to the Monitor Module for PFL monitoring using the “PFL ON” switch. This module also gives the DC control voltages for routing the signals to Master 1, 2, 3 & 4 Output channels. The input Module also contains the hardware for the channel ON indicator LED which lights when the fader is faded IN from the OFF position. This module also has a “ON AIR” LED mounted above the “CH:ON” LED which is lighted when the channel fader is faded IN with proper routing and the corresponding Master channel fader is also ON. This module also gives a DC signal for ON AIR LOGIC output which is meant for further routing to Announcer’s Console for lighting of ON AIR indicator and actuation of the ON AIR relay.

Other Input channels have functions similar to Input channel. The main channel outputs from the Input channels 1 to 8 are connected to the corresponding signal inputs of Master Output channels 1, 2, 3 & 4. The signals can be routed to either one or all of the Master channels using the routing switches on the Input Modules. The output of the mixer stage is fed to the input of the Limiter. The output of the Limiter varies linearly with the input till the threshold level and it remains constant at the threshold setting. A three position rotary switch is used to control the threshold setting of 9 dB, 12 dB and 15 dB. A gain reduction meter indicates the reduction in gain effected by the limiter. The limiter can be switched IN or OUT of the signal path using the “LIMITER ON” switches provided on the output module. The output of this selector goes to the channel fader. The postfade signal is fed to the Line Amplifier which amplifies the signal to the required level and feeds the output transformer, the secondary of which is connected to the main channel output socket (XLR connector on the back panel). Besides the main channel output this module gives the auxiliary outputs (four outputs per channel). This module also provides the prefade and postfade monitor output signals for the purpose of monitoring. The PFL monitor signal can be switched on using the “PFL ON” switch on the module. The overload indicator circuit provides LED indication sensing the prefade and postfade signals. The VU meter drive signal is derived from the main output signal. The “VU ATTN” switch provides 10 dB attenuation for the VU meter signal. The channel ON indicator LED of this module becomes ON when the fader is faded IN from the OFF position.

The Master 2 Output Module is similar in function to the Master 1 Output Module. Provision is given for expanding the console by adding two more output Modules (master 3 & 4) which are similar in function to the Master 1 Module. The Monitor Module of the console contains the hardware for selection and monitoring of different signals of the console. The Monitor Module has two separate channels, one for monitoring the PFL channel and the other for monitoring the main channel. The PFL monitoring is effected by a mix bus which takes all the Input channel and Output channel PFL signals. Any of these signals can be selected for monitoring using the “PFL ON” switch provided on the corresponding modules. The output of the PFL monitor mixer is fed to the PFL level control. The signal from the level control goes to the PFL amplifier through the “PFL OFF” control which can be used to switch off the PFL monitor channel. This status will as indicated on the VU meter panel by a red flashing LED designated as “PFL OFF”. This facility can be used for defeating the DIM control which attenuates the Master monitor channel by sensing the presence of signal in the PFL channel when monitoring the Master Monitor Channel. The input to the headphone amplifier is taken prior to this control so as to enable the continuous monitoring even under the PFL OFF condition. The talk back signal is mixed along with the level controlled PFL signal and is available for monitoring on the PFL monitor amplifier.

The main monitor channel is built around a 8 x 1 program selector which selects the signal for monitoring from “EXT:1”, “EXT:2”, “EXT:3”, “MASTER 1”,”MASTER 2”, “MASTER 3”, “MASTER 4”, and “PFL” signal. Any one of the above signal can be selected using the program selector push button switch on the Monitor Module. The output from this selector is fed to the main monitor level control. The signal from the level control goes to the main monitor amplifier through the DIM control. The DIM control attenuates the main monitor channel signal by 20 dB when signal is present on the PFL channel or when the “PRESS TO SPEAK” switch is pressed to as to enable clear monitoring of PFL signal and talkback signal.

The Monitor Module also gives the signal for driving the monitor VU meter. This signal is routed from the top of the main monitor channel level control and is not affected by the DIM control. The level of any signal selected by the 8 x 1 program selector can be monitored on this VU meter. The talkback Module of the console houses the hardware for to and fro talk back signal processing, signal senses and the test oscillator. The output from the talk back microphone is fed to the microphone pre-amplifier, the gain of which can be varied using the “TB SEND” level control. The output of the pre-amplifier is fed to the TB signal distributor through a “PRESS TO SPEAK” switch, gating circuit, buffer amplifier and an ADA. The ‘PRESS TO SPEAK” switch is used to enable the TB MIC. The talkback signal can be routed to any one of the eight destinations using the 8 x 1 push button selector switch provided on the Talkback Module. The output of the TB signal distributor is terminated on the back panel of the console. The oscillator circuit of the module provides 0 dbu signal required for testing the line inputs of the Input channels. The input signal is directly fed through the mother board to the oscillator injection points of the Input/Output Modules. Besides this, the high level signal is also available at the back panel XLR connector for external use.

There are two signal sensor circuits in the Talk back module. One is used for sensing the coming TB signal and lights the “TB CALLING” indicator provides on the VU meter panel. The other signal sensor senses the presence of any signal on the PFL channel and the actuation of the “PRESS TO SPEAK” switch and switches on the 20 dB attenuator inside the monitor module which dims the main monitor channel output by 20 dB for clear listening of the PFL/talk back signals. The different type of indicators provided on the console are given below. PFL OFF This indicator (blinking type) becomes ON when the PFL monitor channel is switched OFF using the PFL OFF” switch. TB CALLING

This indicator (blinking type) becomes ON when there is any signal present on the talk back input port. OSC ON This indicator (blinking type) becomes ON when any of the input/output Module is in the oscillator mode. SUPPLY STATUS This indicator shows the status of the Power Supply unit. This indicator will be steady when all the supply rails are normal and it will start blinking when there is fault in any one of the supply rails. DUBBING CONTROL CONSOLE:Weber manufactures dubbing control console for use in dubbing / editing rooms. This console has state – of – art technique, built with exponential flexibility and variety of features to enhance the creativity of sound engineers. This is basically a 12 channels console ideally suited for dubbing, editing and recording. The unit is designed table recessed type. The input module has provision for two separate electronically balance line input. Each input channel can be separately made ON/OFF through individual FET operated switches common mode rejection at balanced input can be optimized at high and low frequency. The console has 6 input 6 modules that constitute 12 input channels. The master module constitutes the output channel for the console. It contains summing amplifier for the entire input channel. There are 31 outputs and the output is varied through long throw (104mm) weigh highly conductive plastic track with a reverse gain of fader. All outputs are electronically balanced with low output impedance. Output from CTR’s & a spare input can be selected through the playback selector for gang switch. The PCB C-004 can serve as buffer amplifier. It is a unity gain amplifier having high input impedance and low output impedance balanced to unbalanced converter can serve as input PCB for monitoring and buffer amplifier. Convert the balanced signal output from the console and then it is fed to amplifiers through individual going switches. This PCB incorporates three separate sections for balanced to unbalanced conversion. All inputs are electronically balance arrangement is provide to optimize the common mode rejection at high to low frequencies for all the section. PHONE IN CONSOLE The phone in program console is generally used for the used production of listener interactive radio/TV program. This is used to interface telephone lines with the broadcasting mixing console, which in turn interfaces with the expert sitting in the studio. This has provision for receiving three telephone lines at a time. The incoming calls on the telephone lines are indicated by LED’s corresponding to each telephone line and a common ring flasher ring LED. The coordinator can talk to the listener by using the telephone switcher of each telephone line and telephone handset. Then he can hold the telephone line for the listener and feed music to the listener during the waiting period. The listener can

be connected to the expert sitting in the broadcast studio by using telephone switcher. The listener’s query is the expert and the conversion between the listener and the expert can be broadcast live. When this interaction is on, the phone in program coordinator can coordinate with other listener on the other telephone lines and hold the line. Then he can transfer them to the arrival of there turn. The handset incorporates dialer facility and dialing is possible using built in push button switches for external telephone line connection. AUDIO RACKS Audio racks are installed in control room. They consist of jack panel. Distribution amplifier, equalizer, monitoring amplifier and s-band generator. The signal comes in these audio racks and from racks back to studio. All connections of studio are coming on the jack panel, for four studios four different jack panels are connected and on these jack panels every connection of that studio is present. The signal is routed through distribution amplifier. S- Band generator is used to check any wave and is not frequently used. DITRIBUTION AMPLIFIER:When audio signals are need to be routed to multiple distribution at line level without introducing inflexible, lossy multiple pads. Meltron ME201 series distribution amplifier is the best solution. A 20X series distribution amplifier has transfer balanced /electronically balanced input output via professional grade locking Din5-pole 240drg sockets on rear panel. These are wired so as to prevent input and output connections from being interchanged. All the signals processing circuitry is on plug card for quick service, should the need ever arise this design feature also allows field up grading of performance in the switch mains fuse and pilot lamps are located on front panel. Distribution amplifier 201-1/2 series:This type of distribution amplifier can be used where audio signals will be available at many locations. ME201 provide 4 mono distribution channels for one audio signal. Where ME201-2 provides for impendent distribution channels for 2 audio signals. These versions have a gain adjustment of +/- 5db. These versions can provide maximum 8 distances. Channels with a level indicator for monitoring ME 201-1s/2s series. It has one stereo input consisting of balanced output available at 25-pin din connector. It provides 2 stereo output with each one is consisting of L&R balanced output available at 25 pin din connectors. ME201-2s provides for one stereo signal, 4 stereo distribution channels each one is consisting of L&R output. Distribution amplifier is ME201-1mitu (buffer amplifier) series:This version act as a buffer amplifier with a gain adjustment of +5db.

EQUALISER:-

The programmes are fed from the studios to the transmitter on special telephone lines. Underground cable is laid for these lines. At time, these lines can be ten to twenty kilometers long. The lines have resistance which causes some losses, reducing the strength of the signal. These also have some distributed capacitance and distributed inductance which cause greater losses at high and low frequencies. Thus, when a signal is transmitted over long lines, there is greater attenuation at high and low frequencies resulting in poor quality. For correcting this, equalized line amplifier is used. Equalized line amplifiers are amplifiers with adjustable gain and adjustable high and low frequency boost. These are used at the feeding end or at the receiving end or at both ends to provide the required gain and to give the required boost at high or low frequencies, thus providing flat response. This amplifier gives two outputs, one with low and high frequency equalization for outgoing programmed on telephone lines and a second unequalised output for monitoring. The normal input level is -20 dbm and the output level for both channels is +27dBm. The equalised output is capable of giving about 10 dB boosts at 40 Hz with respect to 300 Hz and 20 dB boosts at 10 KHz with respect to 1 KHz or about 25 dB with respect to 300 Hz. However equalised line amplifiers are not used when microwave system (STL) is used for feeding the programmed to transmitter.

MONITORING AMPLIFIER:The output available from the program amplifier is however, not enough to drive loudspeaker. Therefore, monitoring amplifiers are provided to boost these signals further. A part of the output signal from the program amplifier is given to the monitoring amplifier. The output of the monitoring amplifier is usually fed to a monitoring bus for further feeding to the loudspeakers. A separate monitoring amplifier is used for a group of loudspeakers which are located in studios, control room, duty room and other selected places. Monitoring amplifiers of different wattage ratings are used in AIR. But 8 watt monitoring amplifier is very common. Normal input level to the monitoring amplifier is about -12 dbm in matching condition and 0 dbm in bridging condition. Matching input impedance is 600 ohms and bridging input impedance is 10 k ohms. Load impedance values of 8, 50 and 150 ohms are usually provided.

EQUIPMENTS CTR’s (Cassette Tape Recorder) The studer B67 is easily transportable & versatile unit. Its matching font dimension with the 169 mixing console makes it ideally suitable for mobile work for incorporation in a compact studio design as well. A rigid die cast chassis for the tape transport mechanism, state of art electronics for all audio & motor control circuit. The tape transport is equipped with 3 electronic regulated heavy duty AC

motor. The speed of the capstan motor governed by quartz referenced source circuit. There by ensuring out standing speed accuracy regardless of power line frequency or voltage fluctuation motor runs phase locked to the quartz reference and lock on is indicated by illumination of the depressed speed selector button, separate controller provided for each spooling motor to permit individual adjustment of the tape tension during play recording . Electrically non containing tape tension sensors working the induction principle control the tape transport electronics to ensure safe tape handing during any operating mode. An electronic with positive & negative read out is standard equipment it receives its count signal from tape motion sensors. A sinusoidal driving current for both spooling motors ensure stable now & flutter performance from start to end of a tape reel. The electronically interlocked tape transport logic consists of one large scale integrated circuit, which stores all internal and external commands. Transport functions requiring the stop mode before the next commands can be carried out, are released only after the tape has reached stand still. This sequence results in smooth tape handling and ensures agreeable operations. The control logic indicates each transport function by illuminating the corresponding push button. All transport can be fully remote controlled.

CD PLAYER:The compact disc is an excellent medium for professional audio recording. The compact disc stores enormous digital data in a thin metallic foil in the form of microscopic droplets known as ‘pits’ which is further covered with thin layers of polycarbonate type plastic at both surfaces. It is rugged convenient to handle & economical. The disc also provides many additional data recorded on the disc under sub code which is exploited in the CD player to evolve various feathers for variety of applications. While a low cost CD player for consumer market utilizes a part of such information a professional grade player provides elaborate control on CD transport utilizing additional sub code information. The CD02MK11 designed by the R & D. AIR meet all typical requirements of professional grade CD player and provides a very simple and user friendly control panel & display. There are many main function keys and sub function keys in this CD player. TURN TABLE:This is the oldest equipment for playing long players. Main power connection: Each unit is set at the factor to the mains voltage specified with the order. The unit may be switched to a main voltage of either number-120v or 200v or240v. Grounding connection: The grounding wire of the main power cable is permanently converted to the chasses of the turn table. Audio connections: These are located on the rear of unit. Switch function: The main switch functions are power switch, start switch, tone/arm lift, speed selector.

For testing these equipments, we use standard measuring tapes and CDs. The signal to noise ratio and distortion of the equipment are measured through these measuring tapes and CDs.

POWER SUPPLY IN CONTROL ROOM Power supply in the station from RSEB is 250V, 32A unregulated supply. It is regulated using AVR. The regulated supply is provided to main switch along with unregulated supply. There are three indicator lamps in the section for indicating light, studio input power & control room power. The power supply section has studio room fuse box having 16A, 240V essential light, fuse & main switch for control room. The control room has frequency meter and voltmeter indication power supply in the audio racks is regulated power supply. The block diagram of power supply system in control is shown in the figure.

ACOUSTIC TREATMENT A broadcasting studio is a room in studio complex which has been specially designed and constructed to serve the purpose of originating broadcasting programs. Whenever any musician sings and we sit in front of a performing musician to listen to him, we enjoy the program by virtue of the superb qualities of our sensory organs namely ears. However, when we listen to the same program over the broadcast chain at our home though domestic receivers, the conditions are entirely different. We as broadcasters are continuously engaged in the task of ensuring the maximum pleasure for the listener at home when the artists are performing inside the studios. In order to achieve our goal we must thoroughly understand the characteristic of the different components involved in the broadcast chain, and in this process we must preserve the original quality of sound produced by the artists inside the studio. The science of sound is often called “Acoustics”. Good acoustics is a pre-requisite of high quality broadcasting or recording. Acoustic treatment is provided in studios, control rooms, and other technical areas in order to achieve the acoustic conditions which have been found from experience to be suitable for the various types of programmes. In this section problems and design aspects of internal acoustics of a broadcast studio are explained.

PROPAGATION OF SOUND WAVES Sound waves emanating from a sound source are propagated in all directions. These sound waves are subject to reflection, absorption and refraction on encountering an obstacle. Extent to which each of these phenomenon takes place depends upon the structure and shape of the obstacle, and also on the

frequency of sound waves. In close rooms, the sound would be reflected and rereflected till the intensity weakens and it dies down. Physical characteristics of sound waves are thus modified in various ways before they reach the human ear. These reflected waves can create echo effect in the room. To achieve the desirable effects of the reflected sound, the dimensions and shape of the room are decided with due care and acoustic treatments are also provided on the various surfaces.

REVERBERATION TIME (R/T) In any enclosed room when a sound is switched off, it takes a finite length of time to decay to inaudibility. The ‘hanging-on’ of the sound in a room after the exciting signal has been removed, is called ‘reverberation’ and the time taken for the sound to decay to one millionth of its initial value, i.e. 60 dB, after the source has stopped, is termed ‘Reverberation Time’(R/T).

FACTORS COVERING REVERBERATION TIME R/T of a room depends upon shape and size of room and on the total absorption offered on boundary surfaces. For a room of given volume and surface area, the R/T can be derived by Eyring’s formula R/T

Where

=

R/T V S α

= = = =

0.049 V − S × ln (1 − α )

Reverberation time in seconds Volume in cubic ft. Total surface area of room in Sq.ft. Average absorption coefficient

Average absorption coefficient ( α ) is given by

α

=

S1α 1 + S 2 α 2 + .........+ S n α n S1 + S 2 + .......+ S n

Where S1, S2…….Sn are the areas (in sq. ft.) of different materials provided, and α 1, α 2 ……α n are the absorption coefficients of these materials. α of acoustic material is defined as the ratio of absorbed sound to the total incident energy of sound. An open window absorbs/allows to pass all of the sound energy striking it and reflects none. Thus it has α of unity.α of practically all acoustic materials vary with frequency.

EFFECTS OF R/T ON PROGRAMME Reverberation is the most important single parameter of a room. influences the audio programs in following ways:-

It

(a) Volume of program increases due to reverberation of sound. This is a desirable feature, however, too much of reverberation may impair the quality of program and, therefore, should be controlled. (b) Reverberation results in prolongation of sound inside the room. This leads to ‘blending of one sound with the next and produces a very pleasant continuity in the flow of music. Too much of prolongation, however, may create loss in intelligibility of program due to decrease in clarity. (c) Reverberation time of a room is dependent on frequency. Therefore, it modifies the frequency characteristics of the total sound field inside the room. High R/T at mid and high frequencies lead to increased ‘live ness’ and that at low frequencies increases ‘warmth’. This effect can be used judiciously for desirable qualities.

OPTIMUM REVERBERATION TIME R/T value at each frequency of sound is fixed for most desirable results for different type of programmes. Larger the room size the longer it takes for the sound to travel to the boundary surfaces and get reflected. Therefore, optimum R/T increases with the increase in the room size. Optimum R/T values at other audio frequencies are dependent mainly on the type of programme for which the studio will be used. For drama programmes, the optimum R/T is taken as an average of talks and music values at each frequency.

ACOUSTIC ABSORBERS:Acoustic absorbers are provided on the inner surfaces of the room to achieve optimum R/T characteristics. Different absorbers have different absorption characteristics. No single absorber generally provides uniform absorption over the complete frequency spectrum. Some of the commonly used absorbers are:

(1) Porous Materials: Mineral wool, glass wool, etc. are members of this class. These materials are very good absorber and are most effective in mid and high frequencies, however, these cannot be used without some facing material. Carpets and curtains also fall in this category.

(2) Fibrous Materials: Celotak, insulation boards, perfotiles, jolly-lowtone tiles etc. fall in this category. Absorption of these materials depends upon their softness. Absorption efficiency of these materials depends upon the trapping and dissipation of sound energy in tiny pores. Absorption gets reduced if the surfaces pores are filled with paints etc.These materials have very poor absorption on low frequencies. However appreciable improvement at these frequencies is possible by providing air-gap behind.

(3) Panel Absorbers: Panel absorbers are thin sheets/membranes with an air cavity behind. The mass of the panel and the springiness of the air in the cavity resonant at some particular frequency. Panel absorbers with 3mm teak ply-facing + 50mm air gap + 25mm mineral wool resonate at about 125Hz. This is generally used as low frequency absorber (LFA). (4) Perforated Panel Absorbers: Perforated hardboard (PHB) spaced from the wall constitute a resonant type of sound absorber. The absorption can be considerably enhanced by inserting a suitable porous/fibrous damping materials in the air cavity. The absorption pattern can be varied by adjusting the front and rear air gap from the damping material. Absorption coefficient of this absorber depends on the percentage open area of PHBs also.

DESIGN OF ROOM ACOUSTICS Design for correct reverberation time consists of estimating the total absorption which must be present in the studio. This is calculated by Eyring’s Formula, some of the absorption is offered by windows, doors, flooring and artists inside the studio. For the balance requirement sound absorbing materials are provided on walls and ceiling surfaces. Calculations are generally made at six spot frequencies of 125, 250, 500, 1000, 2000 and 4000 Hz. Quantities of materials of known absorption coefficients are selected by trial and error method so that R/T requirements are met within +5% of the optimum R/T at all these frequencies. Computer aided design for the same has also been involved.

SOUND INSULATION The ‘unwanted sound’ or ‘noise’ in the studios spoils the quality of recorded programmes. Sound insulation of walls doors etc. and layout of the studio building is therefore, decided for acceptable background noise level in the studios.

ACCEPTABLE BACKGROUND NOISE LEVEL It is not possible to specify an acceptable background noise level in the studios as a single weighted figure, because the noise normally present is spread over a wide range. Excessive noise energy over a small bandwidth could be very disturbing without very much affecting the weighted noise figure.

SOURCES OF NOISE AND SOUND Noise in studios may be either air-borne or structure borne. Background noise in a studio can originate from (1) (2) (3)

Outside the building Inside the studio itself and /or Outside the studio but within the building

(a) Noise originated from outside the building Noise from outside the studio building are mostly due to aircraft, road and rail traffic etc.These noise can be avoided/minimized by locating the studio building in a quiet environment away from the railway lines highways and aerodromes. In case studio centre is located in noisy street, sufficient set-back distance is provided between the street kerbed and the main building. Sometimes a multistoreyed office building is built in between the studio building and the sound source to act as a sound barrier for the studio building.

(b) Noise from inside the studio Noise from inside the studio itself consist of air-conditioning noise due to air flow, the noise from fluorescent lights, from cooling fans in tape recorders etc. Noise due to airflow in the studios is controlled by creating slow diffusions of air. To avoid noise of fluorescent lights, ballast chokes are not mounted with the light fittings in the studio. These are mounted separately in a ballast niche outside the studio. Cooling fans in tape recorders are generally of low noise type.

TRANSMITTER Transmitter HMB 163 operates in the medium wave radio broadcast band (5251605 KHz) with proper output of 10KW on carrier. Type of emission – A3 (DSB Broadcasting) 525 – 1602 KHz Frequency range – 525 – 1605 KHz, presently operated at 1395 KHz. The ALLINDIA RADIO, BIKANER has two numbers (2*10) of medium wave transmitter HMB 163, which operates on 1395 KHz in the medium wave radio broadcast band. The transmitter is self contained cabinet with minimum of outside components. Valves (tetrode tube 4C*15,000A) are used in the final RF and modulator stage only. The 10KW medium wave transmitter uses only three beam power tetrode tubes 4C*15,000A, 1 in RF power amplifier stage & 2nos. in modulator stage. The transmitter uses a standard class B high level modulation & the final power amplifier is class C. Solid state amplifiers are used in only power audio & radio frequency stages. The control system is microprocessor based & the rectifiers are solid state devices. Transmitter has two stages:(1) RF stage (Radio – frequency stage) (2) AF stage (Audio – frequency stage) BRIEF DESCRIPTION:The RF chain consists of a crystal oscillator at 2/4/8times the carrier frequency followed by a divider. This is followed by a solid state RF amplifier delivering an output impedance of 230 ohms for mobile applications and 50 ohms for static applications. This modulator is a conventional class B push full stage with a modulation transformer. A tertiary winding modulates the screen of the PA stage. The transmitter works on forced air cooling using the single blower to cool the RF & modulator valves. The control system using microprocessor provides for the following (1) Sequential interlocking & HT switch ON (2) Protection against high VSWR & over current (3) Status information & fault indication in the display (4) Facilities for remote operation & remote monitoring

TECHNICAL SPECIFICATION:(a) Type of emission (b) Frequency Range (c) Rated carrier output (d) Output Impedance Modulation capability (A) Program (B) Sinusoidal Tone

- A3 (DSB Broadcasting) - 525 – 1605 KHz - 10 KW - 230 ohms Continuous with peak to 100% modulation. 1 10mts. Any one frequency between 100Hz to 500Hz at 100% modulation. 2 50mts. At 70% modulation at 2 frequency for 2 Hrs.

3 Short term test 100% modulation on any frequency between 50Hz to 7.5 KHz for one minute. 4 Over modulation should withstand a level 3 times as

High as input level required for 100% modulation at 1 KHz, 3 times momentarily. (C) Type of modulation High level plate modulation (D) Overall efficiency 75% (E) Cooling system Forced air cooling (F) Power Supply 415V, 3phase, 50Hz, 4 wire. (G) Main Voltage +10% or – 10% AVR (H) P.F. Better than 90% (I) Tube Complement 3*4C*15,000A (J) Overall Dimension Width – 1800mm Depth – 1000mm Height – 2100mm (K) Max power consumption 20 KVA on carrier 22 KVA at 40% modulation at 1Hz 30 KVA at 100% modulation at 1Hz Frequency and base impedance are measured by vector impedance meter. The 10KW medium wave transmitter uses only 3 beam power tetrode tubes 4C*15,000A, one in RF power amplifier stage & second in modulator stage. The transmitter uses a standard class B high level modulation & the final power amplifier is class C. Solid state amplifiers are used in only power audio & radio frequency stages. The control system is microprocessor based & the rectifiers are solid state devices. RF STAGE Fixed frequency crystal oscillator serves as a main drive source. Two oscillators are provided out of which one stand by. In order to have frequency stability, crystals in the range of 3 – 6 MHz are used. The oscillator output is a square wave of 5V amplitude and is fed to a solid power amplifier, which is capable of delivering about 200W to the grid of the final preamplifier. The final preamplifier uses 4C*15,000A air cooled tetrode tube. It is a conventional grounded cathode circuit, operating in class C with plate modulation. The screen grid is modulated along with the plate with an audio voltage from a tertiary winding in the modulation transformer. A current transformer & voltage divider step down the RF current & voltage respectively. A comparator to trip the transmitter during high VSWR senses the rectifier RF voltage & current. AUDIO STAGE The AF input for transmitter is standard 600 ohm balanced impedance. The preliminary stages are all solid state & direct coupled audio exciter contains four power transmitters in series in each channel & is designed to deliver a peak AF output of 200V to the modulator grids. The modulator uses two numbers of 4C*15,000A & is designed to work with no grid current & delivers the required output for 100% modulation of the 10KW carrier. RECTIFIER SYSTEMS

The entire rectifier used in the transmitter for providing DC supplies to the various stages employs silicon diodes. The HT rectifier supplying 5KW to the final RF amplifier & the modulators also uses silicon diode rectifiers. CONTROL & PROTECTION CIRCUIT An electronic control system is adopted for the transmitter. The system uses Z80 microprocessor. Connectors switch ON the power circuits. Both auto & normal operation are provided, the selection being carried out with a switch mounted on the control panel. Pressing the appropriate push button switching commands carries out individual switching operations & transmitter states are automatically supervised. Two commands are not carried out in certain requirements of interlocking are not through & until such requirements are met. Provisions for visual indication of fault are made. Acoustic alarms in case of monetary over loads supplement the visual indication. The stand by allows the transmitter to be maintained in operational stage up to filament ON. Recycling operations in the event momentary overload is provided. In case, if cycling take place 3 times in 16 sec. the transmitter is automatically taken in to stand by condition. COOLING & VENTILATION SYSTEM The PA & modulator valves employ forced air cooling. The blower is mounted at the bottom of PA cubicle. Air intake is from the bottom, left hand side of the transmitter through & air filter. The air is ducted to an air chamber, on which valves bases are mounted. The grid components of the PA and modulator valves are mounted in the air chamber. The air at required volume and pressure is forced through the valves providing cooling of the valves. Hot air is let out from top of the transmitter rack. External air ducts duct the air out of the transmitter building. Provision for monitoring the airflow & the exhaust air temp. are provided. These are interlocked with control system of the transmitter. The blower is capable of providing air at 35M/min. at static pressure of 60mm WC. The approximate airflow for individual valves is given below:(a) PA = 10m/min. modulation 1 – 6 m/min. modulation 1 – 8 m/min. (b) The blast motor is 3 phase at 415 & is rated for 1HP. The air temperature sensing thermostats should be set at 70 degree C during normal program modulation & 85 degree C while 100% with continuous tone for more than one minute. AIR FLOW CIRCUIT SAFETY SYSTEMS (a) Mechanical key exchange (b) Electrical interlocking CRYSTAL OSCILLATOR INTERFACE The RF output from the 2nd crystal oscillator is fed to the RF IN and of the crystal interface PCB. The oscillator A/B select signal in given by the microprocessor based control system. RF EXCITER

The class E type power amplifier is designed to generate 220W of drive power to drive the grid of final RF power stage value 4C*15,000A. The RF amplifier assembly consists of (a) RFamplifier driver (b) RF amplifier comprising 1 RF 440 power MOSFET impedance matching transformer interface. (c) RF amplifier interface. Switch Mode Power Supplies (SMPS) are used for regulated DC supplies to the 200W RF exciter stage. FINAL POWER AMPLIFIER It is a class C power amplifier. It uses 4C*15,000A air cooled tetrode tube. It is a conventional grounded cathode circuit operating in class C with plate modulation. Biasing of valve is done at - 400V. The screen grid is modulated along with the plate with an audio voltage from a tertiary winding in the modulation transformer. A current transformer & voltage divider step down the RF current & voltage respectively. A comparator to trip the transmitter during high VSWR senses the rectifier RF voltage & current. AUDIO FREQUENCY STAGES Audio signal as comes from the control through PNT’s lines having signal level 1 – 2 db (approximately) is passed through equalizer and level limiter, now it come into audio stage components, firstly high pass filter. The AF input for the transmitter is at 600 ohm balanced impedance. The final stage of the audio exciter contains four power transistors in series in each grid. An overall feedback is employed from the primary of the modulation transformer. The standing feeds for the modulator are kept to the minimum in order to conserve power at low level of modulation, by incorporating a linearity corrector in the audio preliminary stages. The modulator uses 2nos. of 5C*15,000A value & is designed to work with no grid current & delivers the required output for 100% modulation of the 10KW carrier. High Pass Filter The audio input from the speech rack is fed to active High Pass Filter. It cuts off all frequencies below 50 Hz. This also has the audio attenuator and audio muting relay. The Hum compensator provides for the introduction of controlled amount of signals at 50, 100 and 150 C/s which can be varied from 0 to 360o into the pre amplifier stage APA 302 so as to cancel the Hum components due to the power frequencies present in the system. This will help to raise the S/N ratio of the transmitter.

AF Pre-amplifier The output of the High Pass Filter is fed to the AF Pre-amplifier, one for each balanced audio line. Signal from the negative feed back network from the

secondary of the modulation transformer and the signals from the compensator also are fed to this unit. AF Pre-Corrector

This card corrects the audio for the non-linearity of modulator tubes. It uses an op-amp and switching circuits which will distort the audio for different audio levels, opposite to that of tube distortion. AF Driver 2 AF drivers are used to drive the two modulator valves. The driver provides the necessary DC Bias voltage and also AF signal sufficient to modulate 100%. The output of AF driver stage is formed by four transistors in series as it works with a high voltage of about -400 V. The transistors are protected with diodes and Zener diodes against high voltages that may result due to internal tube flashovers. There is a potentiometer by which any clipping can be set such that the maximum modulation factor will not exceed. POWER SUPPLIES: The transmitters has been provided with the power supplies required for the value circuit as well as transistorized sub units as listed below 1. High Tension power supply – 5KV, 6A this provides anode power supply to PA and modulator valves. 2. 750V, 400mA supply, this provides screen voltage to PA value. 3. 750V, 50mA supply, this provides screen voltage to modulator value. 4. -650V supply, this provides grid bias supply to PA and modulator value. Apart from the above, the following power supplies has been provided for the sub units 1. An SMPS unit providing DC voltage which can be set from 25V to 45V for the RF exciter stage. 2. +5V, 5A-/15V, 1A. For the control electronic and interface PCB’s. 3. +12V relays. 4. A battery supply with out 12V rechargeable batteries are provided for backup of microprocessor based control in the event of power failure the battery enables the status of transmitters to be stored for two minutes in the event of power failure. HT Power Supply:The HT supply consists of a 3phase power transformer T101 and 3phase full wave rectifier; it provides a DC output voltage of the 5KV at 2136 tap. The HT voltage can be adjusted from 3.5KV to 6KV by the tap changing on the secondary of T101. Silicon avalanche diodes have been used for rectification. Totally 84 diodes are connected in 3phase full wave connection, each one phase comprising of 28 diodes mounted on 1 mounting plate. A total of 3 such set are mounted on the rear of the PD cubical. Resistors and capacitors are connected in parallel across each diode for the purpose of preventing abnormal voltage due to surges for equalizing the distributed voltage etc. The power transformer used for HT power supply is installed at the rear of PD cubicle, the DC voltage after rectification is

filtered by smoothing choke of L102 and capacitors C122 A, B, C. These components are located at the bottom of PA cubicle. 750 DC for PA screen: This supply provides the screen voltage of RF power amplifier tube 4C*15,000A. It employs 3 phase full wave rectifier followed by a choke input filter. The 2 phase transformer provides the necessary AC voltage to the rectifier formed by CR503 to CR514. The DC output is filtered by 3H choke followed by capacitors C201, C202. R519 is a shunt for monitoring PA screen current. R501, R502, R503 are used for meter multiplier for voltmeter located on the front panel. 750V DC for modulator screen: This supply provides screen voltage for modulator tubes 4C*15,000A and is identical to the screen supply of PA tube. The audio fed to the transmitter from input equipment is set to oddball (1mW at 600 ohm) and the modulation of the transformer brought to 100% means of the adjustable control in the AF input attenuate. CONTROL SYSTEM The 10KW medium wave transmitter is provided with a microprocessor based control monitoring unit. Optional facility to connect a remote control unit for remote operation and a printer for data logging are provided. An 8*5 matrix keyboard and a 3*40 character LCD unit are provided to help the operator to effect control and monitoring functions. Selections of oscillator are performed by the control system on suitable commands. Facility to monitor a selected parameter is also incorporated on suitable operation from the keyboard. The system scans all the operating parameters and checks for both cut off and warning limits. If a parameter exceeds a cut off limit, the transmitter is tripped off. A hooter circuit is turned ON to give audio alarm whenever the system detects any parameter exceeding cut off limit. The control system records the error as a coded number and updates the error counter. The operation can read the error number and refer the error list to find out the explanation for each error number. A display of real time information is provided on the LCD. Organization of control unit: The following topics broadly cover the organization of control unit Block diagram and principle of operation. Z 80 CPU: The control system uses Z 80 microprocessor and its family of peripheral devices. The CPU and the peripheral devices are linked by a vectored interrupt system, which may be daily chained to allow the implementation of priority interrupt scheme. Clock Circuit: An external circuit generates the system clock of 2.5MHz. Program Memory: The system software is stored on program memory of 22K bytes. Data Memory: The data memory of 6K bytes is provided to store temporary data like measured values.

Counter and timer circuit: Counter/timer contains four programmable 8 – bit counter/timers. Each of which has 9 – bit pre scalar. Each of four channels may be configured to operate in either counter/timer mode. Serial I/O ports: Serial input output controller contains two serial ports one of them is connected to a modem, which can be connected to a remote terminal through a telephone line. Second part is connected to RS 232C interface, which can be connected to a printer for data logging. Real time clock: This keeps updating the parameters seconds, hours, date, month & year. These parameters can be set by suitable commands. Digital input interface: Twenty one input state signals are read by the system through parallel input output ports system check this digital input before switching ON operation & also checks whether the system is normal working condition after it is switched ON. Control output interface: This section provides ON/OFF control signals for various stages, oscillator and really control signals parallel input output ports the signals. LCD units: 2*40 character LCD unit display information like date, time, message, user prompts, parameter, error codes etc. Keyboard, Keyboard interface & bar graph display: 8*5 matrix keyboard through a keyboard interface device providing input device with which operator can effect controls & other function on the transmitter, the bar graph display unit displays 100% of modulation. Analog input interface: The12 analog parameter is monitored periodically or on command from keyboard. They are connected through analog input interface circuit. It consists of multiplexer, A/D converters & A PIO. The PIO port sends the address of the parameters to be measured & the multiplexer connects to the selected parameters. The A/D converter provide an 8 bit word corresponding to the parameter value that can be read & further processed for control or display function.

SUMMARY OF TRANSMITTER :Finally we can say that audio signal of level 8 db from control room is send to transmitter through co-axial cables. The level of this audio signal is equalized & also passed through limiter to balance the loss faced by audio signal transmission through co-axial cables. This was the first AF stage, after second AF stage in which it is further amplified on higher level, this signal employed in final PA valve through modulation transformer for plate modulation & power amplification. After this stage the amplitude modulated signal of 10KW power from individual transmitter is combined in the combiner unit, which is passive device. This combined signal of 20KW is sent to antenna through 230ohm unbalanced open wire feeder line. After impedance matching to antenna tuning unit (ATU), this signal is broadcasted through air.

STARLINK SL 9003Q DIGITAL TRANSMITTER LINK SYSTEM INTRODUCTION:STARLINK 9000 is the first all digital, open architecture, modular system for CD quality audio transmission. The versatility and power of the STARLINK 9000 comes from a complete range of “plug and play” personality modules. The SL 9003Q Digital Studio Transmitter Link (DSTL) system is a transmitter/receiver pair that conveys high quality digital audio across a microwave radio path. Typically program material is transmitted from a studio side to a remote transmitter site, or to a repeater site. Utilizing especially efficient Quadrature Amplitude Modulation (QAM) technology, the SL 9003Q delivers four 16 bit linear audio audio channels and is especially compatible with existing FCC part 74 frequency allocations. ASE/EBU digital audio I/O, combined with a built in variable same rate converter, provided seamless connection to the all digital air chain without compression, plug in MPEG audio modules and synchronous data channels. User selectable 16, 32 or 64 QAM, achieves the high special efficiency of the SL 9003Q. Powerful Read Solomon error correction, coupled with a 20 tap adaptive equalizer, provide unsurpassed signal robustness in hostile RF environments. An ultra linear one watt average transmitted power is achieved with redundant RF power hybrid modules. The system also has provisions for two asynchronous auxiliary data channels (up to 38,400 bands) that are used for communication in remote control applications. SYSTEM FEATURES:In addition to establishing a new industry standard for studio transmitter link performance, the SL 9003Q incorporates many new and innovative features, including:(1) Linear 16 bit digital audio performance. (2) Higher system gain, 26db more than composite STL. (3) Degradation free multiple hops. (4) Configurable for up to 4 linear audio program channels per STL systems. (5) No background chatters from co-channel or adjacent channel interface. (6) No crosstalk between channels. (7) Built in AES/EBU digital audio interface. (8) Operation through fractional T1 network. (9) Extensive LCD screen status monitoring. (10) Selectable RF spectral efficiency. (11) Sample rate converter for digital audio operation from 30-50 KHz. (12) Peak reading LED bar graph display for all audio channels. (13) Adjustable bit error rate threshold indication for monitoring transmission quality. (14) Important status functions implemented with bi-color LED indication. INTRODUCTION TO C-BAND:-

The AIR broadcasting stations spread throughout the country are required to relay certain programs which are originated from Delhi and from other regional stations in the state capitals. In order to link Delhi and other capital stations with other stations for the purpose of these relays AIR uses satellite radio networking through INSAT series of satellites. The RN receiver terminals to be located at AIR stations act as ground terminals to receive S-band, C-band or both depending on the receiver system configuration. These programs thus received through RN terminals are fed to the terrestrisial transmitters for broadcast purpose. SYSTEM SPECIFICATION C-BAND ANTENNA AND FEED:(1) Type and size parabolic dish antenna 6.2mts diameter (2) Material of dish perforated aluminium alloy (3) Received band C-band (4) Feed prime focus (5) Polarization linear (6) Frequency band 3.7 to 4.2 GHz (7) Gain >45 db (nominal) at 4 GHz C-BAND LNBC:(1) Input frequency (2) Input impedance (3) Input/output return loss (4) Output frequency (5) Noise temperature (6) Conversion gain CABLE:(1) Cable loss (2) Impedance

3.7 to 4.2 GHz 50 ohms > 12db 450-1450 MHz < 45 Kelvin 50 db or more 6 db / 100 feet 75 ohms

SYSTEM CONFIGURATION The main building blocks of system are:(1) (2) (3) (4) (5) (6) (7)

6.2mts antenna and feed. C-band LNBC Power divider Analog receiver Digital receiver Wired indoor rack PC dump terminal

The CB and block down converter convert the C-band signal collected at the antenna to the L-band. A low loss cable (50 meter) carries the IF signal and DC supply to the LNBC.

PRACTICAL TRAINING REPORT

ALL INDIA RADIO, BIKANER SUBMITTED BY – Surendra kumar Roll No 1203/06 B.Tech. 2nd YEAR ELECTRONICS & COMMUNICATION ENGINEERING NIT KURUKSHETRA

CERTIFICATE This is to certify that Mr. Surendra kumar NIT KURUKSHETRA has successfully completed his training from 9/6/2008 to 6/7/2008 at All India Radio Station, Bikaner. During this his behaviour was very good.

ALL INDIA RADIO, BIKANER

ACKNOWLEDGEMENT To excel in any field, practical training is an integral part of study. The theory does not really cater to the complete need; therefore on the job training is unavailable. Needless to add that it is an excellent opportunity to acquaint oneself of first hand experience of working environment, management & motivation of human resources along with operational skills. I wish to express my humble gratitude to the management & staff of All India Radio, Bikaner for extending their co-operation to me during my practical training at their esteemed organization. My training will not be completed unless I mention my thanks particularly to the following guides:Mr. PRATAP SINGH

Assistant Station Engg. All India Radio, Bikaner

Mr. S. R. Suthar

Assistant Engg. All India Radio, Bikaner

Mr. S. V. Rao

Junior Engg. All India Radio, Bikaner