Answer Posted / daniel joel

modulation is the process of changing the characteristics of
high frequency signal (carrier signal) like
amplitude,phase,frequency with reference to a low frequency
signal(message signal).
Need of modulation is 1.To decrease the antenna height
*to transmit a low frequency signal we need height of
antenna to be very large(since wavelength is inversly
proportional to frequency.so if we modulate a low frequency
signal with a high frequency one then it requires antenna
height of just meters,which is practically possible.
2.To avoid interference in the channel we adopt modulation.
3.To overcome noise in the channel.
Demodulation is necessary to retrive back the message signal
from modulated signal.

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