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CBSE Class 12 Physics Notes

Communication Systems

Communication Systems

  1. Analog and Digital Mode of Transmission. An analog message is physical quantity that varies with time usually in a smooth and continuous fashion.

    A digital message is an ordered sequence of symbols selected from a finite set of discrete elements

  2. Operational advantages of digital communication system over analog communication systems are:
    1. An improved security message
    2. Increased immunity to noise and external interference.
    3. A common format for encoding different kinds of message signals for the purpose of transmission.
    4. Flexibility in configuration digital communication system.
  3. Attenuation, Distortion, Interference and Noise are the undesirable effects in the source of signal transmission.
  4. Modulation : Process of changing some characteristic e.g. amplitude, frequency or phase of a carrier wave in accordance with the intensity of the signal is known as modulation.
  5. Types of Modulation
    1. Amplitude modulation
    2. Frequency modulation
    3. Phase modulation.
  6. Amplitude Modulation : The amplitude of the carrier wave changes according to the intensity of the signal. The amplitude variation of the carrier wave is at the signal frequency. 
  7. Modulation Factor " The ratio of change of amplitude of carrier wave to the amplitude of normal carrier wave is called modulation factor (m).
  8. Pulse modulation could be classified as: Pulse Amplitude Modulation (PAM), Pulse Duration Modulation (PDM) or Pulse Width Modulation (PWM) and Pulse Position Modulation (PPM).
  9. Demodulation: Demodulation is the process of recovering the signal intelligence from a modulated carrier wave.
  10. FAX : Facsimiles of FAX means exact reproduction of the documents, a picture, letter, map etc. at receiver end.
  11. MODEM : The term modem means modulator and demodulator. It converts a series of binary pulses of digital information into an analog signal and transmits across the phone lines.

Block Diagrams

Generalized Communication systems

Generalized Communication systems

Simple Modulator for obtaining AM signal

AM signal

Transmitter

Transmitter

Receiver

Receiver

Detection of an AM signal

Detection of an AM signal
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