Modulation & Demodulation
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| Modulation and Demodulation (image searched from google image) |
In radio or wireless communication systems audio signal is first converted into corresponding electrical signal with the help of a microphone. This electrical signal has frequency in the audible range (20 Hz to 20 kHz) and can not be directly and efficiently radiated into space in the form of EM radio wave by using a transmitting antenna. For direct radiation of audio frequency electrical signals through antenna, We require an antenna of impractical size.
[ Let a signal of 1 kHz. Then the wavelength,
]
To overcome this problem, the audio frequency signal is used to modulate some characteristics (usually amplitude or frequency) of a high frequency wave called Carrier wave. This high frequency carrier wave can now be efficiently radiated into space by using smaller antenna of convenient sizes. At the receiving end the original signal is recovered from the modulated carrier wave by a process known as Demodulation.
The need for Modulation Arises out of the Following
1. Direct transmission is limited to any small distances.
2. Direct transmission requires antenna of sub-normal size.
3. In direct transmission there is the possibility of signals from different stations getting mixed and lost.
Modulation
The process of producing a wave in which some characteristics of high frequency carrier wave varies in accordance with the instantaneous value of a low frequency information signal is known as Modulation.
Carrier Wave
The high frequency wave on which the modulating wave is superimposed is called Carrier wave.
Demodulation
The process of recovering the original modulating signal from the modulated carrier wave is known as Demodulation or Detector.
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