AM vs. FM: Differences between Amplitude and Frequency Modulation

Amplitude Modulation (AM) and Frequency Modulation (FM) are two types of radio waves. They are the ways of broadcasting audio signals which is achieved by transmitting the information in the form of electromagnetic waves. They may sound similar but they are not the same thing.
In this write-up, we are sharing the major differences between AM and FM.

Definition of AM

Amplitude Modulation is a radio wave that works by modulating or varying the amplitude of the audio signal while keeping the frequency and phase constant.

Definition of FM

Frequency Modulation is a radio wave that works by modulating or varying the frequency of the audio signal while keeping the amplitude constant.

Differences between AM and FM

Table of differences between AM and FM Modulations
# Basis of Difference Amplitude Modulation Frequency Modulation
1. Definition AM is a radio wave that works by modulating the amplitude of the signal. FM is a radio wave that works by modulating the frequency of the signal.
2. Origin The origin of AM radio waves can be traced back to the mid of 1870s. It was in that period that AM method of audio transmission was used successfully. The origin of FM radio waves goes back to the 1930s. It was developed and successfully used in the United States and the development is mainly credited to Edwin Armstrong.
3. Modulation of Carrier Waves In AM, the carrier waves are modulated in amplitude while the frequency and phase remain constant. In FM, the carrier waves are modulated in frequency while the amplitude and phase remain constant.
4. Sound Quality AM waves have poorer sound quality as compared to FM waves due to lower bandwidth. FM waves have better sound quality than AM waves due to higher bandwidth.
5. Cost-effectiveness AM waves are cost-effective in comparison to FM waves. They are cheaper and can be transmitted over long distances. FM waves are costlier in comparison to AM waves and are more local i.e. they cannot be transmitted to very long distances.
6. Interference AM radio waves are prone to interference and hence not very secure. They easily get affected by electrical storms and other radio frequency interference. FM radio waves are lesser prone to interference by electrical storms or other radio frequency interference. But, they can be affected by physical barriers. Tall buildings and other such physical barriers can affect the coverage and quality of FM radio waves.
7. Complexity Transmitter and receiver in the case of AM are simple. Transmitter and receiver are more complex for FM radio waves.
8. Noise susceptibility AM is comparatively more susceptible to noise as amplitude is affected by noise. As already discussed the information in the case of AM is transmitted by modulating amplitude. FM is not susceptible to noise as the information in FM signals are transmitted through altering the frequency and not amplitude.
9. Spectrum Range AM radio waves range from 535 to 1705 kilohertz. FM radio waves have higher bandwidth which ranges from 88 to 108 megahertz.
10. Stations More stations can be available in any frequency range in the case of AM. It is possible to create radio stations every 10kHz. For FM radio stations can be made every 200kHz. The number of available stations is much less as compared to AM.
11. Detection AM radio waves are relatively easy to detect with simple equipment. They can be detected even when the signal is not very strong. FM radio waves are comparatively tough to detect with simple equipment. There need to have a strong signal to be detected.
12. Zero crossings Zero crossings i.e. the rate of sign-changes of the signal during a frame is equidistant in the case of AM. Zero crossings is not equidistant in the case of FM.
13. Efficiency AM is considered less efficient as power is wasted in transmitting the carrier signal. FM is considered more efficient as all power is utilized and not wasted in transmitting the carrier signal.
14. Multiple signals at the same frequency When two signals are received at the same frequency in AM both are demodulated causing interference. When two signals are received at the same frequency in the case of FM, the receiver captures the stronger signal and the weaker signal is eliminated.
15. Use AM is used for video signals like television and other motion pictures. FM is used for audio signals like radio and voice signals.
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