Tuesday, 28 February 2012

Need for modulation

Reduction in antenna height:
  • Minimum antenna height for a signal of wavelength ‘λ’ is λ/4.
  • At low frequencies, wavelength is high. Hence antenna height is more. By modulating the signal at high frequency, wavelength can be reduced there by antenna height)
Avoids mixing of signals:
All sound signals are in the frequency range of 20Hz to 20 KHz. If baseband transmission is used to transmit these signals directly from source, then all signals are in same frequency range, hence signals mix with each other. To avoid this each transmitted signal needs to be transferred to different frequency range. This is achieved through modulation.  

Increases range of communication:
At low frequencies radiation is poor as well as attenuation is high. Therefore base band signal transmission can’t be used for long distance communications. Modulation increases the frequency of the signal, hence it increases radiation and also attenuation is less.

Allows multiplexing of signals:
 Multiplexing means transmission of two or more signals through same channel. Signals coming from different sources can be translated to different frequency range through modulation. They can be separated at receiver using filters.

Allows bandwidth adjustment:
Modulation can reduce the bandwidth required for signal transmission.

Improves quality of reception:
Modulation reduces the effect of noise, and hence S/N ratio is improved. So quality of reception is high.

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