Why is it necessary to modulate a signal onto a carrier wave?

Answer 1

There are two basic reason for modulation..... 1) It is extremely difficult to radiate low-frequncy signals from an antenna in the form of electromagnetic energy. 2)Information signals often occupy the same frequency band and if two or more sourses were transmitted at the same time they would interfere with each other.

Answer 2

modulation is required from energetic viewpoint: you can't directly send electrical oscillations of sound frequency! You have to modulate - to "seat sound signal" on high frequency electromagnetic oscillations & send!

Answer 3

The purpose of radio communication is to move information from one place to another.

The carrier wave by itself carries no information. The information has to be added to it

somehow. When the electrical signal that carries the information is added onto the

carrier, that's the process loosely called "modulation".

Answer 4

"Modulation" is the process of changing the pure radio wave in some way,

for the purpose of causing it to carry information.

If a physicist on one side of the laboratory generates a radio wave and another

physicist across the room is able to detect the wave, that's very nice, and if the

year is 1860, then it's very exciting and they publish a paper and become very

famous and get invited to scientists' parties. But they still don't have anything

that they can use to carry a news bulletin, a weather forecast, or rap music from

one place to another, not even across the laboratory.

In order to carry any information on the radio wave, it has to be changed in some

way from time to time, according to some kind of pattern that the people on both

ends have worked out.

The easiest way to do that is to turn the wave on and off, according to some

system of patterns. Make a different pattern for each letter of the alphabet,

and then you can spell out any message you want to send from one end to

the other. That's exactly how information was sent over radio waves, at the

beginning and for quite a long time. The most widely used set of patterns for

letters and numbers was the Morse Code. To use it, the radio waves only had

to be switched on and off. Anybody anywhere who could detect the wave just

clearly enough to be able to tell when it's on and when it's off, and knew the

code, could "copy" the message.

Later on, with the development of more advanced electronic components,

methods were developed that could change the amplitude or frequency of the

radio waves, very rapidly, and those changes could be used on the receiving

end to construct sounds, that could almost duplicate sounds used to cause

the changes at the sending end. At that point, you then had a way to send

a speech by the president, a weather report, the sound of a live orchestra,

a church sermon, or the voice of a professional singer, over great distances.

Anyway, we're wandering far from a short answer to the question.

"Modulation" is the process of changing the pure radio wave in some way,

for the purpose of causing it to carry information.

Answer 5

Modulation is applied to a carrier.

If the carrier wasn't modulated it wouldn't carry any information other than that the transmitter was working. Not very useful.

It is the modulation which contains the "information" which we want to send.

Answer 6

Some characteristic of the radio wave is changed corresponding to the information,

according to a pattern that has been agreed between the sender and receiver.

The receiver then observes the changes, interprets them according to the agreed

pattern, and reconstructs the information.

Simplest example: Radio wave is turned on and off, representing each letter, digit,

and punctuation with a unique pattern of long and short 'on' and 'off' periods that

the sender and receiver have agreed on. The receiver monitors the patterns of

on/off and short/long, compares them to the agreed patterns, and reconstructs

the message out of letters, digits, and punctuation. The most popular and widely-used

set of on/off patterns is called the "Morse Code".

Other widely-used methods of adding information to radio waves consist of varying

the amplitude, frequency, or phase of the waves according to an agreed pattern.