Answer / mahesh

the info signal which is needed to b sent is very weak.
hence a strong signal called carrier is used carry the info
signal. this process is called modulation which is done at
transmitter side.
since this carrier does not contain any info it is removed
at at the reciever.this process is called demodulation

Answer / syncopator

In a communication system, other than at audio frequencies,
a so-called carrier is used.

The carrier may be an r.f. transmission or it may be light
transmission.

It is usually said that the carrier itself does not contain
any information. *

Information may be imposed upon a transmitted carrier by
means of a system called modulation.

The information may be recovered at a receiving point by a
system called demodulation.

* Although it is said that an unmodulated carrier conveys
no information, this is not strictly true. It conveys the
informtaion that the transmitter is working.

An unmodulated r.f. carrier could also be use as a beacon,
although this would be most unusual.

Answer / dk

the signal that is transmitted will become weak as it continues to propagate in the communication channel.so high frequency carrier wave is added along with the transmitting signal.this process is called as modulation.after reaching the receiver side the original information has to be obtained.so carrier wave is seperated from signal,this process is called as demodulation.

Answer / anupam bhardwaj

it is the procces in which the low freq s/g is vary
according to the high freq s/g, so it is very importent in
transmitter section.
&
de-modulation is oposite of this so it is used in recever
section

Answer / 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.

Answer / reza r

Modulation is used in order to achieve some of the followings:

1- To put the signal on a carrier frequency we have, for
example we have a channel that can only carry frequencies
between 30~31MHz, an we have to transfer our speech over
this channel (Bandwidth of speech is 0~4KHz), so we use
modulation to mount the signal over the available channel.

2- To minimize the destructive channel effects such as
noise, interference and so on. destructive effects will vary
on the different frequencies.

3- in order to decrease the size of the antenna! (antenna
size depends on the Landa (wavelength of the signal). The
higher the frequency, the lower the wavelength. The lower
the wavelength, the smaller the antenna size!

also there is some other benefits in modulation...

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