What do you understand by modulation ? Explain the need for modulation .

Explanation

The process of combining audio frequency signal with high frequency signal is called modulation .
To transmit an electronic signal in the audio frequency range (20 Hz to 20 KHz) over a long distance directly the following constraints limit the possibility .
(1) Size of the antenna (2) Effective power radiated by the antenna (3) Mixing up of signals from different transmitters .
For 20 KHz signal the height of antenna is about 4km , still a large height. This makes antenna length impractical . Even if we transmit the signal, they may combine with low frequency signals present in the atmosphere and it is impossible to distinguish the signals at the receiving end .
In order to avoid these problems a low frequency audio signal is combined with high frequency signal to transiate the audio signal to high frequencies .