Category Archive: communication

Nov 28

Communication Systems : Revision Test

One mark questions

What is the meant by the term attenuation ? Why ground wave transmission is restricted to 1500 kHz? Define critical

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Mar 11

COMMUNICATION SYSTEMS

IMPORTANT POINTS TO REMEMBER

  • Communication system is a system that transmits information from one point to another. The three basic components of a communication system are :
  1. Transmitter
  2. Communication channel
  3. Receiver
  • Transmitter is a device that transmits the receiving end through a communication channel.It basically transforms a message signal into a suitable form for transmission to the receiver. A transmitter consists of :
  1. A signal generator
  2. A modulator
  3. An antenna
  • Message signal is a time varying electrical signal produced by a transducer,a device that converts energy in one form to another. This signal carries information. There are two types of message signals:
  1. Analog, and
  2. Digital
  • A signal has two important characteristics-(a) amplitude ,and (b) frequency or phase.Analog signal is a continuous function of time.It may take any value in a given range. Digital signal is a discrete signal discontinuous in time.They are sampled with time.
  • Bandwidth is the range over which frequencies in a signal vary
  • Base band is the range of frequency representing the original signal;the one delivered by source.
  • Modulation is the modification of a message signal by varying some of the characteristics of a wave to transmit information. The radio frequency carrier wave is superimposed by an audio frequency signal.
  • There are three types of modulation:  
  •     (a)Amplitude modulation
  •     (b)Frequency modulation
  •     (c) Pulse modulation,

(a) Amplitude modulation: The amplitude of the carrier wave is varied in proportion to amplitude of modulating signal.

(b) Frequency modulation: The frequency of a carrier

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