Amplitude Modulation
Amplitude modulation (AM) is a method of impressing data onto an alternating-current (AC) carrier waveform. The highest frequency of the modulating data is normally less than 10 percent of the carrier frequency.
The instantaneous amplitude(overall signal power) varies depending on the instantaneous amplitude of the modulating data.
Amplitude modulation (AM) is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave.
In amplitude modulation, the amplitude (signal strength) of the carrier wave is varied in proportion to the waveform being transmitted.
That waveform may, for instance, correspond to the sounds to be reproduced by a loudspeaker, or the light intensity of television pixels.
This technique contrasts with frequency modulation, in which the frequency of the carrier signal is varied, and phase modulation, in which its phase is varied.
Amplitude modulation applications
Amplitude modulation is used in a variety of applications. Even though it is not as widely used as it was in previous years in its basic format it can nevertheless still be found.
• Broadcast transmissions:
AM is still widely used for broadcasting on the long, medium and short wave bands. It is simple to demodulate and this means that radio receivers capable of demodulating amplitude modulation are cheap and simple to manufacture. Nevertheless many people are moving to high quality forms of transmission like frequency modulation, FM or digital transmissions.
• Air band radio:
VHF transmissions for many airborne applications still use AM. . It is used for ground to air radio communications as well as two way radio links for ground staff as well.
• Single sideband:
Amplitude modulation in the form of single sideband is still used for HF radio links. Using a lower bandwidth and providing more effective use of the transmitted power this form of modulation is still used for many point to point HF links.
• Quadrature amplitude modulation:
AM is widely used for the transmission of data in everything from short range wireless links such as Wi-Fi to cellular telecommunications and much more. Effectively it is formed by having two carriers 90° out of phase.
These form some of the main uses of amplitude modulation. However in its basic form, this form of modulation is being sued less as a result of its inefficient use of both spectrum and power.
Difference between amplitude and frequency
The frequency is a measurement of cycles per second whereas amplitude is a measurement of how large a wave is and Amplitude represents the wave's energy.
Difference between amplitude and frequency modulations
In frequency modulation, the frequency of the carrier wave is modified as per the transmit data.
In amplitude modulation, the carrier wave is modified according to the data. For example:
In AM radio communication, a continuous wave radio-frequency signal (sinusoidal carrier wave) has its amplitude modulated by an audio waveform before transmission.