Difference between AM and FM

Amplitude modulation and frequency modulation are used to transmit data using the method of modifying a carrier signal. The main difference between both modulations is that in frequency modulation, the carrier wave frequency is modified as per the transmit data. In contrast, in amplitude modulation, the carrier wave is modified according to the data.

For instance, if several sets of data are required to be transmitted using the same medium, then each set off is sent using different frequency waves. This is the process of how radio broadcasts are done.


Table of Contents

Amplitude Modulation

Amplitude modulation is a modulation technique where the amplitude of a carrier varies depending on the information signal. AM radio broadcast signals use lower carrier frequencies, which helps them travel long distances. Sometimes AM signals can be able to bounce off the ionosphere. The distance travelled by the AM is much larger than the FM.

Read More: Amplitude Modulation

Frequency Modulation

In this module, the carrier wave frequency is modified according to the signal that carries information. The radio signals have large bandwidth than AM radio signals, which helps to offer much better sound quality. Frequency modulation also enables to transmit stereo signals.

Difference Between AM and FM

Amplitude Modulation (AM) Frequency Modulation (FM)
The first successful audio transmission was carried out in the mid-1870s Developed in 1930 by Edwin Armstrong, in the United States
The radio wave is called a carrier wave, and the frequency and phase remain the same The radio wave is called a carrier wave, but the amplitude and phase remain the same
Has poor sound quality, but can transmit longer distance Has higher bandwidth with better sound quality
The frequency range of AM radio varies from 535 to 1705 kHz The frequency range of FM is 88 to 108 MHz in the higher spectrum
More susceptible to noise Less susceptible to noise

Read More: Frequency Modulation

Frequently Asked Questions – FAQs


What is the need for modulation and demodulation?

There is a need for modulation and demodulation to transmit the information from one place to another. Modulation is used for sending information over long distances as low-frequency signals cannot be used in covering large areas.  Demodulation helps in receiving the information sent through modulation. Demodulation takes place at the receiving end.


What are the various techniques used in analog modulation?

Following are the three techniques that are used in analog modulation:

  • Amplitude modulation (AM)
  • Frequency modulation (FM)
  • Phase modulation (PM)

What are digital modulation and its types?

Digital modulation is the modulation technique that uses discrete signals for modulating a carrier wave. It is used to transmit signals over an analog channel with a high frequency. Following are the four types of digital modulation:

  • PSK which stands for Phase Shift Keying
  • ASK which stands for Amplitude Shift Keying
  • FSK which stands for Frequency Shift Keying
  • QAM which stands for Quadrature Amplitude Modulation

Differentiate between a detector and a demodulator.

A detector is defined as the device that recovers information of interest which is contained in a modulated wave.

The demodulator is the device that is an updated form of a detector used for extracting the original information from a modulated carrier wave.


What are the advantages of using an RF amplifier

Following are the advantages of using an RF amplifier:

  • The sensitivity of the RF amplifier is better.
  • The signal-to-noise ratio of RF amplifiers is better than other amplifiers.
  • The rejection rate when compared to other amplifiers, RF has better selectivity.
Test your knowledge on AM and FM difference


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