Amplitude , Frequency and Phase Modulation

Amplitude Modulation (AM)



-> Method of broadcasting radio signals. it was discovered in 1870s.

-> 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.

Frequency Modulation (FM)


FM is another, a relatively advanced method of transmitting information through radio waves. In FM, the frequency of the carrier wave is modified in accordance with the input signal to send the information, e.g. the instantaneous frequency of the carrier wave increases when the amplitude of the carrier wave increases, and vice versa. It is invented in the 1930s by Edwin Howard Armstrong.

It is also used in telemetry, radar, seismic prospecting. In radio transmission, an advantage of frequency modulation is that it has a larger signal-to-noise ratio and therefore rejects radio frequency interference better than an equal power amplitude modulation (AM) signal. For this reason, most music is broadcast over FM radio.




Phase Modulation (PM)

Phase modulation (PM) is a modulation pattern that encodes information as variations in the instantaneous phase of a carrier wave.

Phase modulation is widely used for transmitting radio waves and is an integral part of many digital transmission coding schemes that underlie a wide range of technologies like WiFi, GSM and satellite television.


Phase modulation is closely related to frequency modulation (FM); it is often used as an intermediate step to achieve FM. Mathematically both phase and frequency modulation can be considered a special case of quadrature amplitude modulation (QAM).

Difference between AM and FM:-

AM (Amplitude Modulation)	FM(Frequency Modulation)
The amplitude of the carrier wave is modified in order to send the data or information.	The frequency of the carrier wave is modified in order to send the data or information.
It works in a frequency range of 535 to 1705 Kilohertz (KHz).	It works in a frequency range of 88 to 108 Megahertz (MHz).
It has two sidebands.	It has an infinite number of sidebands.
In this method, the frequency and phase remain the same.	The amplitude and phase remain the same.
Its modulation index varies from 0 to 1.	Its modulation index is always greater than one.
It can transmit over long distances, have a large range.	It cannot transmit over long distances, have a smaller range.
poor sound quality.	better sound quality.
In AM, if two or more signals are received at the same frequency, both are demodulated which causes interference.	In FM, if two or more signals are received at the same frequency, the receiver captures the stronger signal and eliminates the weaker one.
It has simple circuit design.	It has complex circuit design.
It is a less costly method.	It is more costly than AM.
It requires low bandwidth in the range of 10 kHz.	It requires high bandwidth in the range of 200 kHz.
The received signal is of low quality	The received signal is of high quality