Communication Systems

Bandwidth of Signals and Transmission Medium

  • The TRANSMITTER processes the message and makes suitable for transmission through a channel.
  • The unwanted signals which tend to disturb the transmission of message signals are called NOISE.
  • The RECEIVER extracts the message from the received signals at the channel output
  • The loss of strength of a signal while propagating through a medium is known as ATTENUATION.
  • AMPLIFICATION is the process of increasing the amplitude of a signal using an amplifier Amplification is necessary to compensate the attenuation of the signal
  • RANGE is the largest distance between a source and destination up to which the signal is received with sufficient strength.
  • BANDWIDTH refers to the frequency range over which an equipment operates or the portion of the spectrum occupied by the signal.
  • The original low frequency message signal cannot be transmitted to long distances. Therefore, at the transmitter the original low frequency message signal is super imposed on high frequency wave, which acts as the carrier. This process is knows as MODULATION.
  • The process of retrieval of information from the carrier wave at the receiver is termed as DEMODULATION.
  • The distance between transmitting antenna and the horizon, \tt D_{t} = \sqrt{2Rh_{t}} (R- radius of earth)
  • The distance between receiving antenna and the horizon, \tt D_{r} = \sqrt{2Rh_{r}}
  • The maximum distance between the transmitting antenna and receiving antenna is denoted as Dm
  • Dm = Dr + Dt
    \tt =\sqrt{2 Rh_{r}} + \sqrt{2 Rh_{t}}
  • The radius ‘d’ of the area covered by a single transmitting tower of height h is given by \tt d = \sqrt{2 R_{e}h}
  • If the Population density around the tower is given,
    Number of persons covered = Area covered by tower × Population density = πd2 × Population density.

View the Topic in this video From 00:23 To 11:26

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1. Range is limited due to curvature of earth. If h be the height of the transmitting antenna, then signal can be received upto a maximum distance
d = \sqrt{2Rh}

2. If height of transmitting and receiving antennas be hT and hR respectively. The effective range will
d = \sqrt{2Rh_{T}} + \sqrt{2 Rh_{R}}