NCERT Solution Class 12th Physics Chapter – 15 Communication Systems Notes

NCERT Solutions Class 12th Physics Chapter -15 Communication Systems

NCERT Solutions Class 12th Physics Chapter – 15 Communication Systems

?Chapter -15?

✍Communication Systems✍

?Notes?

A basic communication system consists of information source, transmitter, receiver, and the link between transmitter and receiver.

The setup used for exchanging information between a sender and a receiver is called a communication system.

The transmitter is a part of the communication system which sends out the information.

The receiver is a part of the communication system that picks up the information sent by the transmitter.

The communication channel is a medium or link which transfers the message from the transmitter to the receiver of a communication system.

Low frequencies cannot be transmitted to long distances.

Pulse modulation is of four types:

1. Pulse amplitude modulation (PAM)
2. Pulse duration modulation (PDM)
3. Pulse position modulation (PPM)

Transducer: It is a device that converts energy in one form to another.

Bandwidth: It is defined as the frequency range of a signal. The information-bearing signal is called a baseband signal.

Sampling converts an analog signal into a digital signal.

The number of samples of the analog signal taken per second is called the sampling rate.

Sampling rate = 1T, where T = time period of sampling of the analog signal.

The discrete signals having only two levels are called digital signals.

The signals which vary continuously with time are called analog signals.

Modulation – It is defined as the process of superposing an audio signal on a high-frequency carrier wave.

Demodulation – It is the process of separating the audio wave from a modulated wave.

The degree to which a carrier wave is modulated is measured in terms of modulation index.

Quantization – It is the process of dividing the maximum amplitude of the voltage signal into a fixed number of levels.

The electronic transmission of a document to a distant place via telephone line is called FAX (Facsimile). It scans the contents of a document to create electronic signals.

The Internet permits the communication and sharing of all types of information between two or more computers connected through a large and complex network.

E.mail – It allows the exchange of text/graphic material using e¬mail software.

File transfer is done through a file transfer program (FTP). It allows the transfer of files or software from one computer to another connected through the internet.

Hypertext – It is a powerful feature of the web which automatically ‘ links relevant information from one page on the web to another
using HTML.

E-commerce – It is the process of using the internet to promote business using electronic means such as credit cards etc.

Chat – It is a real-time conversation among people with common interests through typed messages. Everyone belonging to the chat group gets the message instantaneously and can respond rapidly.

FAX provides images of a static document unlike the image provided by television of objects that might be dynamic.

Mobile telephones operate typically in the UHF (Ultra High Frequencies) range of frequencies about 800 – 950 MHz.

The central part of the mobile telephony system is to divide the service area into a suitable number of cells centered on an office called MTSO (Mobile Telephone Switching Office).

Base Station: It is a low-power transmitter contained in each cell. It caters to a large number of mobile receivers.

Pulse modulation – It is the process of producing a train of the pulse; of the carrier, some characteristics of which vary as a function of the instantaneous value of the message signal.

Pulse amplitude modulation (PAM) – It is the process in which the amplitude of the pulses of carrier pulse train varies in accordance with the instantaneous value of the message signal.

Pulse width Modulation (PWM) – The process of pulse modulation in which the width of the pulses of the carrier pulse train varies in accordance with the instantaneous value of the message signal.

Pulse code modulation (PCM) – It is the process of converting an analog signal into a digital signal by sampling it in time, then quantizing and coding it.

Atmosphere – It is defined as the gaseous envelope surrounding the earth.

The radio waves from the transmitting antenna to the receiving. antenna propagate either by ground waves (i.e., space wave or surface wave) or sky waves.

The T.V. signals are frequency modulated.

The maximum distance up to which TV signals can be received is given by d = 2hR−−−−√, where h is the height of the TV antenna and R is the radius of the earth.

The modulation index (m_f) of a frequency modulated wave is defined as the ratio of maximum frequency deviation to the modulating frequency.
i.e., m_f = δmaxfm=fmax−fcfm=±kVmfcfm
where f_m = modulating frequency, E_m = amplitude of modulating wave.

A Hertz antenna is a straight conductor of length equal to half the wavelength of radio signals to be transmitted or received i.e., l = λ2

A Marconi antenna is a straight conductor of length equal to a quarter of the wavelength of radio signals to be transmitted or received i.e., l = λ4

Amplitude modulated signal contains frequencies (W_c – W_m), Wc, and (W_c + W_m).

Attenuation – It is the loss of strength of a signal while propagating through a medium.

Noise – It is defined as the unwanted signal that tends to disturb the transmission and processing of message signals in a communication system.

Amplification is the process of increasing the amplitude of a signal using an electronic circuit.

For demodulation i.e. detection of a signal, 1fc < < τ where f_c frequency of classier wave,
τ = time constant of the circuit.