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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

Mechanism of modulation

The carrier wave may be continuous (sinusoidal) or in the form of pulses.

Sinusoidal carrier

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Sinusoidal carrier

A sinusoidal carrier wave can be represented as

c(t ) = Ac sin (ωct + )

where c(t) is the signal strength (voltage or current), Ac is the amplitude, ωc ( = 2πνc) is the angular frequency and φ is the initial phase of the carrier wave.

During the process of modulation, any of the three parameters, that is, Ac, ωc or φ of the carrier wave can be controlled by the message or information signal.

Accordingly there are three types of modulations using a sinusoidal carrier ,

  1. Amplitude modulation (AM),

  2. Frequency modulation (FM)

  3. Phase modulation (PM).

Pulsed shaped carrier

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Pulsed shaped carrier

Pulse characteristics which can be modified are, amplitude, duration or width of pulse, position. Different types of pulse modulation are,

  1. pulse amplitude modulation (PAM),

  2. pulse duration modulation (PDM) or pulse width modulation (PWM),

  3. pulse position modulation (PPM)
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