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INTRODUCTIONINTRODUCTION Communication:Communication: Transference of data from Transference of data from

transmitting station to receiving station via channel is transmitting station to receiving station via channel is called communication.called communication.

The The transmittertransmitter modifies the baseband signal for modifies the baseband signal for efficient transmission.efficient transmission.

The The channelchannel is a medium – such as wire, coaxial cable, is a medium – such as wire, coaxial cable, a waveguide, an optical fiber, or a radio link – through a waveguide, an optical fiber, or a radio link – through which the transmitter output is sent.which the transmitter output is sent.

The The receiverreceiver reprocesses the signal received and the reprocesses the signal received and the output is fed to the output transducer, which converts output is fed to the output transducer, which converts the electrical signal to its original form – the message.the electrical signal to its original form – the message.

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MODULATIONMODULATION Modulation is a process of superimposing information on a carrier by

varying one of its parameters (amplitude, frequency or phase).

Need for Modulation -> Modulating the signal over higher frequency can reduce antenna size.

To differentiate among transmissions (stations)

Maximum to minimum frequency ratio can be reduced to minimum by modulating the signal on a high frequency.

Types of Modulation -> In general, there are three types of modulation:

a) Amplitude Modulation b) Angle Modulation c) Pulse Modulation

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AMPLITUDE MODULATIONAMPLITUDE MODULATION If the amplitude of the carrier is varied in accordance with the

amplitude of the modulating signal (information), it is called

amplitude modulation.

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ANGLE MODULATIONANGLE 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 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.

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ANGLE MODULATIONANGLE MODULATION(cont..)(cont..)

Phase ModulationPhase 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.

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ANTENNA SYSTEMANTENNA SYSTEM Antenna is usually a metallic device (a rod or a wire) used for radiating or receiving

electromagnetic waves. The radio frequency power developed in the final stage of a transmitter is delivered

through cables/feeders, without themselves consuming any power to the transmitting antenna

The RF energy gets converted into electromagnetic waves and travels in the free space at the speed of light.

The receiving antenna picks up the radio waves and delivers useful signal at the input of a receiver for reception of signals.

The transmitting and receiving antennae are reciprocal in the sense, any characteristics of the antenna in general applies equally to both.

Antenna Radiation Resistance The input impedance ‘Zin’ of an antenna is the ratio of voltage to current at its input

terminals, where the power is fed to the antenna. Zin = Ra + jXa, where Ra = Resistive part of impedance Xa = Reactive part of impedance Ra = Rr+Ri Rr = Radiation resistance of the antenna Ri = Ohmic loss resistance of the antenna.

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DISH ANTENNADISH ANTENNA

All India Radio , Chetak udr.All India Radio , Chetak udr. Height: 55mtrsHeight: 55mtrs

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MASTMAST All India Radio All India Radio

Station, chetak udr.Station, chetak udr. Height of mast: 73.4 Height of mast: 73.4

mtrs.mtrs. Base impedence: Base impedence:

154.8154.8 Mast current: 13 ampMast current: 13 amp Feeder current : 9.3 Feeder current : 9.3

ampamp Input resistance: 104 Input resistance: 104

ohmsohms

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VISIT TOVISIT TO

ALL INDIA RADIO,ALL INDIA RADIO,

CHETAK (Udaipur)CHETAK (Udaipur)

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CONTROL ROOMCONTROL ROOM

It includes-It includes- Console designing:Console designing: high reliability and high reliability and

continous operation.continous operation. Digital control- min Digital control- min

signal path gives low signal path gives low distortion and noise.distortion and noise.

Mechanical dimension:Mechanical dimension:

820*515*280mm. 820*515*280mm.

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CONTROL ROOMCONTROL ROOM For two or more studios set up, there would be a provision for

further mixing which is provided by a control console manned by engineers. Such control console is known as switching console.

Broad functions of switching console in control room are as follows:

Switching of different sources for transmission like News, O.Bs. other satellite based relays, live broadcast from recording studio.

Level equalisation and level control.

Quality monitoring.

Signaling to the source location.

Communication link between control room and different studios.

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SOUND RECORDING AND SOUND RECORDING AND DUBBING ROOMDUBBING ROOM

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SOUND RECORDING AND SOUND RECORDING AND DUBBING ROOMDUBBING ROOM

Recording room: Recording room: Three numbers of receptacles for cassette outputs have been provided.

The output impedance of the cassette recorder to 600 ohm.

Red and green lamps are provided on the control panel for indications from and to control room and studios.

Dubbing room:Dubbing room: The arrangement is similar to the

recording room except that an additional tape deck and a mixer unit have been provided. This arrangement allows mixing of programmes.

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TALK ROOMTALK ROOM

Designing: It depends upon frequency or Designing: It depends upon frequency or time of required specification.time of required specification.

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VISIT TOVISIT TOALL INDIA RADIO,ALL INDIA RADIO,

MADRI (Udaipur)MADRI (Udaipur)

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ANTENNA TRANSMITTER ANTENNA TRANSMITTER UNIT (ATU)UNIT (ATU)

Function: used for impedance and Function: used for impedance and capacitance matching.capacitance matching.

Antenna impedance coverage equals Antenna impedance coverage equals to 10 to 900 ohm.to 10 to 900 ohm.

It should be housed inside a It should be housed inside a building ,surrounding ground level building ,surrounding ground level and constructed at the base of the and constructed at the base of the antennaantenna

Monitoring facilities are provided to Monitoring facilities are provided to monitor feeder current and antenna monitor feeder current and antenna current while tuning and for continuos current while tuning and for continuos monitoring of radiated transmitter.monitoring of radiated transmitter.

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COMBINING COMBINING UNIT/COMBINERUNIT/COMBINER

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COMBINERCOMBINER

To combine RF output of two 10kw mw To combine RF output of two 10kw mw transmitter provide higher output power.transmitter provide higher output power.

Parallel operation ensures greater reliability upto Parallel operation ensures greater reliability upto

5kw power reduced.5kw power reduced.

Power Specification: Input power = 2*10kw. Power Specification: Input power = 2*10kw. Output power = 20kw. frequency= 525kHz to Output power = 20kw. frequency= 525kHz to 1605kHz.1605kHz.

In combiner: Solid state-valves. Three valves in In combiner: Solid state-valves. Three valves in transmitter 1.transmitter 1.

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AUTOMATIC VOLTAGE AUTOMATIC VOLTAGE REGULATOR (AVR)REGULATOR (AVR)

It contains steady ac supply from fluctuating mains. It contains steady ac supply from fluctuating mains.

Two for each transmitter ,used to control voltage.Two for each transmitter ,used to control voltage.

Features:Features: High frequency.High frequency. Zero waveform distortion.Zero waveform distortion. Low internal impedance.Low internal impedance. Zero phase shiftZero phase shift Frequency range:47-63Hz.Frequency range:47-63Hz.

Operating Principle:Operating Principle: Induced voltage either in phase or Induced voltage either in phase or out of phase with supply voltage.out of phase with supply voltage.

Voltage in first winding added or subtracted from mains Voltage in first winding added or subtracted from mains depending on phase w.r.t line voltage.depending on phase w.r.t line voltage.

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??QUERIESQUERIES

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THANK YOUTHANK YOU