COMMUNICATION COMMUNICATION

SYSTEMSYSTEM

ELEMENTS OF ELEMENTS OF COMMUNICATION SYSTEMCOMMUNICATION SYSTEM

• Communication system have three essential Communication system have three essential elements transmitter, medium/channel, receiver.elements transmitter, medium/channel, receiver.

BAND WIDTH OF SIGNALSBAND WIDTH OF SIGNALS

• The type of communication system needed for a The type of communication system needed for a given signal depends on the band of frequencies given signal depends on the band of frequencies witch is considered essential for communication witch is considered essential for communication process.process.

• For speech signals, frequency range 300Hz to For speech signals, frequency range 300Hz to 3100 Hz is considered adequate. for commercial 3100 Hz is considered adequate. for commercial telephonic communication speech signal requirs telephonic communication speech signal requirs a band width of 2800 Hz. a band width of 2800 Hz.

BAND WIDTH OF SIGNALSBAND WIDTH OF SIGNALS

• A T.V signal contains both voice and picture A T.V signal contains both voice and picture and is usually allocated 6 MHz of band width for and is usually allocated 6 MHz of band width for transmission. video signals for transmission of transmission. video signals for transmission of pictures require about 4.2 MHz of band width pictures require about 4.2 MHz of band width for transmission.for transmission.

• To transmit music an approximate band width To transmit music an approximate band width of 20 KHz is required because of the high of 20 KHz is required because of the high frequencies produced by musical instruments.frequencies produced by musical instruments.

BAND WIDTH TRANSMISSION BAND WIDTH TRANSMISSION MEDIUMMEDIUM

• The commonly used transmission media are The commonly used transmission media are wire, free space and fiber optic cable.wire, free space and fiber optic cable.

• Band width of coaxial cable 750 MHz.Band width of coaxial cable 750 MHz.• Optical communication using fibers is Optical communication using fibers is

performed in the frequency range of 1 THz to performed in the frequency range of 1 THz to 1000 THz.1000 THz.

• An optical fiber can offer a transmission An optical fiber can offer a transmission bandwidth in excess of 100 GHz. bandwidth in excess of 100 GHz.

PROPAGATION OF PROPAGATION OF ELECTREROMAGNATIC WAVESELECTREROMAGNATIC WAVES• In communication using radio waves, an antenna In communication using radio waves, an antenna

at the transmitter radiates the electromagnetic at the transmitter radiates the electromagnetic waves, witch travels through the space and reach waves, witch travels through the space and reach the receiving antenna at the other end. Earth’s the receiving antenna at the other end. Earth’s atmosphere plays a vital role in the propagation atmosphere plays a vital role in the propagation of E.M waves. of E.M waves.

SKY AND SPACE WAVES SKY AND SPACE WAVES PROPAGATIONPROPAGATION

• Space waves are used for lines-of-sight (LOS) Space waves are used for lines-of-sight (LOS) communication as well as satellite communication as well as satellite communication.communication.

SKY AND SPACE WAVE SKY AND SPACE WAVE PROPAGATIONPROPAGATION

• Long distance communication can be achieved Long distance communication can be achieved by ionosphere reflection of radio waves back by ionosphere reflection of radio waves back towards the earth, this this mode of propagation towards the earth, this this mode of propagation is called sky wave propagation.is called sky wave propagation.

example-A Transmitting antenna at the top of a example-A Transmitting antenna at the top of a tower has a height 32 m and the height of the tower has a height 32 m and the height of the receiving antenna is 50m.what is the maximum receiving antenna is 50m.what is the maximum distance between them for satisfactory distance between them for satisfactory communication in LOS mode?communication in LOS mode?

• Dm=sq root of 2*64*100000*32 + sq root of Dm=sq root of 2*64*100000*32 + sq root of 2*64*100000*50 m2*64*100000*50 m

• Dm=64*100*3.162+8*1000*3.162 mDm=64*100*3.162+8*1000*3.162 m• Dm=144*100*3.162mDm=144*100*3.162m• Dm=45.5 kmDm=45.5 km

NEED FOR MODULATIONNEED FOR MODULATION

• There is a need for translating the original low There is a need for translating the original low frequency base band message or information frequency base band message or information signal into high frequency wave before signal into high frequency wave before transmission such that the translated signal transmission such that the translated signal continues to possess the information contained continues to possess the information contained in the original signal. in the original signal.

NEED FOR MODULATIONNEED FOR MODULATION

• The purpose of a communication system is to The purpose of a communication system is to transmit information or message signals, transmit information or message signals, message signals are also called base band signals.message signals are also called base band signals.

• For transmitting a signal we need an antenna For transmitting a signal we need an antenna should have a size comparable to the wavelength should have a size comparable to the wavelength of the signal.of the signal.

Mixing up of signals from different Mixing up of signals from different transmitterstransmitters

• Another important argument against Another important argument against transmitting base band signals signal directly is transmitting base band signals signal directly is more practical in nature. For translating the more practical in nature. For translating the original low frequency base band message or original low frequency base band message or information signal into high frequency wave information signal into high frequency wave before transmission such that the translated before transmission such that the translated signal continues to possess the information the signal continues to possess the information the information contained in the original signal. information contained in the original signal.

PRODUCTION OF AMPLITUDE PRODUCTION OF AMPLITUDE MODULATIONMODULATION

• In amplitude modulation the amplitude of the In amplitude modulation the amplitude of the carrier is varied in accordance with the carrier is varied in accordance with the information signal.information signal.

DETECTION OF AMPLITUDE DETECTION OF AMPLITUDE MODULATED WAVEMODULATED WAVE

• The transmitted message gets attenuated in propagating The transmitted message gets attenuated in propagating through the channel. Receiving antenna is therefore to through the channel. Receiving antenna is therefore to be followed by an amplifier and a detector. In be followed by an amplifier and a detector. In addition ,to facilitate further processing.addition ,to facilitate further processing.

• Detection is the process of recovering the modulating Detection is the process of recovering the modulating signal from the modulated carrier wave.signal from the modulated carrier wave.

• The modulated signal of the form is passed through a The modulated signal of the form is passed through a rectifier to produce the output .rectifier to produce the output .

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