What is a Modulation?
Definition: Translation of Low Frequency signal to high frequency signal is generally referred as modulation. By doing so, we transfer the low frequency message signal to longer distances. This can be illustrated with paper and stone example as discussed below.
Take a paper of some size and try to through it to 5-10meter distance. It is impossible to through a plain paper to such longer distance, because the weight of that paper is very less. Now take a stone of some size and place the stone in the paper and enclose the stone. Now through the paper enclosed stone and then observe the distance travel by it. Obviously, the paper enclosed stone travels long distance than a plain paper because, the weight of the plain paper translated to higher weight of stone.
|Modulation analogy with paper throw|
The same analogy can be applied to our communication systems, where message signal of lower frequency can be sent to longer distance by translating the message signal frequency to higher frequencies. This technique is called “frequency translation or modulation”.
If f1(t) is the message signal (paper) contains information to be transmitted and f2(t) as carrier signal (stone), then the modulated signal will be given as f1(t) X f2(t). The carrier signal is enclosed by the message signal.