Plus Two Physics Notes Chapter 15 Communication Systems is part of Plus Two Physics Notes. Here we have given Plus Two Physics Notes Chapter 15 Communication Systems.
|Text Book||NCERT Based|
|Chapter Name||Communication Systems|
|Category||Plus Two Kerala|
Kerala Plus Two Physics Notes Chapter 15 Communication Systems
Simplified Detailed Notes
Communication: The process of transmission and reception of some information.
Communication System: It comprises of a transmitter, communication channel and a receiver.
Transmitter: It is a set up that transmits the message to the recieving end through the communication channel.
Receiver: It decodes the original signals. This process of recovering the original signal is called demodulation.
Two basic modes of communication:
- Point to point communication. It involves a single transmitter and receiver, eg., telephony.
- Broadcast mode. It involves multiple recei-vers which are linked to a single transmitter, eg., television, radio.
Some basic Terminologies
- Transducer: Any device which converts one form of energy into another, eg., microphone. Signal. Information which is converted in electrical form and is suitable for transmission: Noise. Unwanted electrical signals. Transmitter. It is a device which processes a message signal so as to make it suitable for transmission.
- Attenuation: It refers to loss of strength of a signal during its propagation through transmission medium.
- Amplification: It is the process by which amplitude of a signal is increased using an electric circuit called amplifier.
Range: Largest distance between a source and destination upto which the signal is recieved with sufficient strength.
- Base band: Band of frequencies representing the original signal.
- Repeater: It picks up a signal from the transmit-ter, amplifies and retransmits it to the receiver.
- Message signals: It is a time varying electrical signal generated by a transducer out of original signal.
These are of two types:
(i) Analog signal: A signal in which current or voltage varies continously with time.
(ii) Digital signals: A signal in which current or voltage can take only two discrete values is called a digital signal.
Bandwidth of signals: In a communication sys-tem, the message signal can be voice, music,picture or computer data.
|Types of signal||Frequency range||Bandwidth|
|Speech signal||300-3100 Hz||2800 Hz|
|Music signal||20-20000 Hz||20 KHz|
|Video signal||4.2 MHz|
|TV signal||6 MHz|
Ground wave propagation (f< 2MHz): In ground wave propagation the radio wave trav-els along the surface of the earth. It follows the curvature of the earth.
Sky wave propagation (2MHz < f < 30MHz): A radiowave directed towards the sky and re-flected by the ionosphere towards the deisred location of the earth is called a sky wave. It is used for long distance communication. Space wave
communication (f > 30 MHz): A space wave travels in a straight line from transmitting antenna to the receiving an-tenna. They are used for Line-of-Sight (LOS) communication as well as satellite communication.
Radio horizon for a signle antenna, d =
R = radius of earth (6400 km), h = antenna height, d = distance to radio horizon
Range of line of sight distance between two antennas: dM = +
where hT and hR are heights of transmitting and recieving antennas respectively.
Modulation: It is the process by which the amplitude, frequency or phase angle of a high frequency carrier wave is varied in accordance with the value of low frequency signal.
Need for modulation
- The height of the antenna should be aleast λ/4 in length for good transmission. For lower frequencies, wavelength (λ) will be high and thus height of the antenna will be high. It is not practically feasible to construct antennas of great height.
- Effective power radiated by an antenna is ∝()2. Thus for same antenna ‘l’ lenth for low frequency signal wave length will be more and thus effective power radiated by will be less.
- Another reason is mixing up of signals. The solution is communicating at high frequencies and alotting a band of frequencies for transmission.
Amplitude modulation: It is the process in which the amplitude of high frequency carrier wave changes in accordance with the value of modulating signal.
Waveform of AM voltage
AM can be represented by the expression:
Note: Amplitude of the carrier wave changes according to the modulating signal.
Ac = amplitude of carrier wave
Am = amplitude of modulating wave
µ =Ac/Am is the modulation index
fc = frequency of carrier wave
fm = frequency of modulating wave
Note: µ is always keep less than 1 to avoid distortion.
Production of AM wave: It is shown by,
Block diagram of a transmitter and reciever:
Detection of Amplitude Modulated Wave
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