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CBSE NOTES CLASS 12 PHYSICS

CHAPTER 15 COMMUNICATION SYSTEMS

Communication systems

Block diagram of communication system

Modes of communication

Point-to-point communication

Point to multipoint communication-broadcast

Terms related to communication

Transmitter

Receiver

Communication channel

Transducer

Attenuation

Amplification

Repeater

Range of communication

Bandwidth

Bandwidth of some media types

Some wireless frequency bands

Different types of signals

Electrical signal

Noise signal

Analog signal

Digital signal

Coding systems

Rectangular waves

Role of atmosphere in propagation of electromagnetic waves

Different types of waves used in communication

Ground waves

Sky waves

Space waves

Modulation

Demodulation

Baseband signal

Need for modulation

How does size of the antenna related to the frequency of transmitted wave?

How is the effective power radiated by an antenna related to the frequency of transmitted wave?

How does mixing up of signals from different transmitters make modulation necessary?

Mechanism of modulation

Sinusoidal carrier

Pulsed shaped carrier

Amplitude modulation

Modulation index

Side bands

Production and transmission of amplitude modulated wave

Band pass filter

Detection of amplitude modulated wave

Internet

Main applications of Internet

Facsimile (FAX)

Mobile telephony

CBSE NOTES CLASS 12 PHYSICS

CHAPTER 15 COMMUNICATION SYSTEMS

Rectangular waves

Digital signals are in the form of rectangular waves. This rectangular wave can be decomposed into a superposition of sinusoidal waves of frequencies ν0, 2ν0, 3ν0, 4ν0 ... nν0, where n is an integer extending to infinity and ν 0 is fundamental frequency equal to 1To.

To reproduce the rectangular wave shape exactly we need to superimpose all the harmonics ν0, 2ν0, 3ν0, 4ν0 .., which implies an infinite bandwidth.

However, for practical purposes, the contribution from higher harmonics can be neglected, thus limiting the bandwidth.

Received waves are a distorted version of the transmitted one. If the bandwidth is large enough to accommodate a few harmonics, the information is not lost and the rectangular signal is more or less recovered.

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