Modulation is the addition of information (or the signal) to an electronic or optical signal carrier.

In electronics, modulation is the process of varying one or more properties of a high frequency periodic waveform, called the carrier signal, with respect to a modulating signal.

In telecommunications, modulation is the process of conveying a message signal, for example a digital bit stream or an analog audio signal, inside another signal that can be physically transmitted.

A carrier frequency is an electronic wave that is combined with the information signal and carries it across the communication channel.

A carrier signal is a single frequency that is used to carry the intelligence (data).

For digital, the intelligence is either a 1 or 0. When we modulate the carrier , we are changing its characteristics to correspond to either a 1 or 0.

There are three aspects of the basic carrier wave that can be modulated:

-Amplitude-Frequency-Phase (or angle)

The three corresponding techniques are as follows:-Amplitude Modulation(AM)-Frequency Modulation(FM)-Phase Modulation(PM)

Other modulation techniques are:- Amplitude shift keying(ASK)- Frequency shift keying(FSK)- Phase shift keying(PSK)

Amplitude modulation (AM) is a method of impressing data onto an alternating-current (AC) carrier waveform.

In the above example, a 1 is represented by the presence of the carrier for a predefined period of 3 cycles of carrier. Absence or no carrier indicates a 0.

In AM, the carrier itself does not fluctuate in amplitude. Instead, the modulating data appears in the form of signal components at frequencies slightly higher and lower than that of the carrier.

Frequency modulation (FM) is a method of impressing data onto an alternating-current (AC) wave by varying the instantaneous frequency of the wave.

Frequency Modulation modifies the frequency of the carrier to represent the 1s or 0s.

In the above example, a 0 is represented by the original carrier frequency and a 1 by a much higher frequency ( the cycles are spaced closer together).

Phase modulation (PM) is a method of impressing data onto an alternating-current (AC) waveform by varying the instantaneous phase of the wave.

The carrier phase is switched at every occurrence of a 1 bit but remains unaffected for a 0 bit.

The phase of the signal is measured relative to the phase of the preceding bit.