If an input signal’s height varies with the loudness of a user’s voice and then adds this to the carrier, then the carrier’s amplitude will change corresponding to the input signal that’s been fed into it. This is called amplitude modulation or AM. Frequency of an input signal can also be changed.

The number of complete wavelengths in a given unit of time is called frequency (f). As a wavelength increases in size, its frequency and energy (E) decrease. From these equations you may realize that as the frequency increases, the wavelength gets shorter. As the frequency decreases, the wavelength gets longer.

The amplitude of a variable is the measure of how far, and in what direction, that variable differs from zero. Thus, signal amplitudes can be either positive or negative. The time-domain sequences in Figure 1–3 presented the sample value amplitudes of three different waveforms.

Signal strength or amplitude is measured by the distance of each curve from the zero axis (or red (black in print versions) line in the figure). The direct signal is very much stronger than those of the target area.

Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting messages with a radio carrier wave. In amplitude modulation, the amplitude (signal strength) of the carrier wave is varied in proportion to that of the message signal, such as an audio signal.

Amplitude modulation (AM) signals are easy to demodulate and the radio receivers can demodulate AM signals effortlessly. AM signals are used for long distance transmission since it is less complicated and is also economical.

In amplitude modulation, the carrier is varied in accordance with the message signal. The higher the amplitude, the greater is the magnitude of the signal. So it’s easy for noise to disturb the amplitude modulated signal. Hence, amplitude modulation gives noisy reception.