There are two basic modes of communication

1. Point to Point Communication: It is a type of communication in which message is transmitted over a link b/w a single transmitter and a receiver. For example Telephone
2. Broad Cast Mode:  It is a type of communication in which there is large number of receiver corresponding to single transmitter. For ex. Radio and TV.

Basic Terms used in Communication System

1. Signal It is a single value of function of time that carries information .It has unique value at any instant. A signal is usually electrical and is of two types

Analog Communication è  In this signal current or voltage varies with time continuously .For example Speech, Music, Sound, produced by a vibrating tuning fork.

 Digital Signal:  It is a discontinuous function of time in which current or voltage is in the form of pulses. In digital signal each pulse has two level) and 1. I.e. open and closed circuit.

0 and 1   are also referred as bits. For example letters printed in book ,  output of a digital computer , fax , listing of any data .Analog and digital are interconvert able and there are various coding schemes for digital communication such as BCD(Binary Coded Decimal) , ASCII ( American Standard Code for Information Interchange )  

1. It is a device that converts one form of energy into another. For example

1. Microphone – It converts speech signal into electrical signal.
2. Piezoelectric sensor   è it converts pressure variations into electrical signal.
3. Photo detector It is that device that converts light signal into electrical signal

2. Repeater è A Repeater is a combination of receiver amplifier and a transmitter. Its function is to extend the range of communication.

Repeaters are erected at suitable location in between transmitter and receiver.

3. Transmission Medium and Communication Channel: It is a link through which the information of message is propagated from the source to the destination without any noise. These are of two types

1. Guided Transmission medium
2. Un Guided Transmission medium

Guided Transmission medium: The communication medium used in point to point communication between a single transmitter and receiver. These are used in line transmission. For example free space used for space communication & Satellite Communication (T.V., Radio)

4. Antenna – An antenna is a structure that is capable of radiating and receiveing E.M Waves . It may be metallic Object  collection of wires. The antenna may be transmitting or receiving . These are of two typesè i) Hertz Antenna – It is a straight conductor of length half of the wavelength of radio signal to be transmitted or receive .  l= l /2    ii) Marconi  Antenna è It is a straight conductor of length one quarter of wavelength of radio signal to be transmitted or received … l= l /2……..

The design of antenna depends upon the frequency of carrier wave and directivity of the beam. The antenna may be dipole antenna or dish type antenna(directional antenna).

 

Antenna

Dipole antenna  → omni directional.