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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

Facsimile (FAX)

It scans the contents of a document (as an image, not text) to create electronic signals. These signals are then sent to the destination (another FAX machine) in an orderly manner using telephone lines. At the destination, the signals are reconverted into a replica of the original document. Note that FAX provides image of a static document unlike the image provided by television of objects that might be dynamic.

Mobile telephony

The concept of mobile telephony was developed first in 1970’s and it was fully implemented in the following decade. The central concept of this system is to divide the service area into a suitable number of cells centred on an office called MTSO (Mobile Telephone Switching Office).

Each cell contains a low-power transmitter called a base station and caters to a large number of mobile receivers (popularly called cell phones). Each cell could have a service area of a few square kilometers or even less depending upon the number of customers. When a mobile receiver crosses the coverage area of one base station, it is necessary for the mobile user to be transferred to another base station. This procedure is called handover or handoff. This process is carried out very rapidly, to the extent that the consumer does not even notice it. Mobile telephones operate typically in the UHF range of frequencies (about 800-950 MHz).

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