Difference Between AM and FM

Radio broadcasting started on this planet in 1905 on an experimental basis. Around 1920, it became a commercial broadcast too.


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Amplitude Modulation (AM) and Frequency Modulation (FM) are the two different modes of radio broadcast. Both modes help transmit information in the form of Electromagnetic Waves.

Key Takeaways

  1. AM (Amplitude Modulation) radio signals transmit information by varying the amplitude of the carrier wave, which is more susceptible to noise and interference, resulting in lower sound quality.
  2. FM (Frequency Modulation) radio signals convey information by altering the frequency of the carrier wave, providing better sound quality and resistance to interference, but with a more limited range compared to AM signals.
  3. The key difference between AM and FM lies in their modulation techniques, with AM adjusting the amplitude and FM altering frequency, which affects signal range, sound quality, and susceptibility to interference.

AM vs FM

AM radio transmits by varying the amplitude of the radio wave, while FM radio transmits by varying the frequency of the radio wave. FM provides better sound quality, while AM has a more extended range and is less prone to interference. AM stations have a stronger signal during the night, while FM stations have a stronger signal during the daytime.

AM vs FM

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Amplitude Modulation came into existence earlier than Frequency Modulation. The discovery of FM radio signals is an upgrade in signal clarity compared to AM radio signals.


Comparison Table

Parameter of ComparisonAmplitude Modulation (AM)Frequency Modulation (FM)
ModulationIn AM, the carrier wave is modulated in amplitude, keeping phase and frequency constant.In FM, the carrier wave is modulated in frequency, keeping phase and amplitude constant.
Cost FactorAM transmission and reception are of low cost.FM transmission and reception are relatively costlier than the AM systems
Quality of SoundThe Sound Quality is relatively poor in the case of AMThe interference in the case of FM is less, thus making the sound quality the best.
Complexity in FunctionalityThe Transmission and reception functionality is straightforwardThe Transmission and reception functionality is highly complex
Distance of BroadcastAM signals can be transmitted over a long distance.FM signals cannot be transmitted over long distances. Many FM radio stations are required for this purpose.


What is AM (Amplitude Modulation)?

Amplitude modulation is a process by which the radio wave signal is transmitted by modulating the amplitude. AM is used in the form of electronic communication.

AM is the oldest and earliest method of transmitting information as radio signals. While the carrier does not vary in amplitude, the modulating data transforms it for transmission.

Amplitude Modulation is very simple to implement compared to other radio transmission and reception forms. AM requires limited bandwidth too.

AM is not expensive, and this makes it useful for long-distance transmissions. The transmitter and receiver components are also not complex, making them economical for usage.

AM consumes more power for transmission as well as the reception. AM signals require very high bandwidth, at times equivalent to the highest frequency.

The signal is constantly interfered with noise, making the quality consistently poor. However, it is most sought after as it can be transmitted long distances.

The AM radio transmitters can transmit sound waves with a frequency range of up to 15KHz. But the receiver can reproduce the signals only up to 5KHz or sometimes even Less. AM signal transmission and reception can be affected by external factors.

Storms and Sunspots can duly affect the signal quality, usually with a lot of noise in the background.

amplitude modulation

What is FM (Frequency Modulation)?

Frequency Modulation is the process by which the radio wave signal is transmitted by modulating the frequency. This method is considered a versatile mode of radio signal transmission and reception.

It is indeed a fact that the amplitude changes in FM also. However, it is not noticeable compared to AM. FM is most desirable for its signal quality.

The transmitter and receiver components are complex, thus making them expensive. The functionality of FM is also not that simple.

FM signals cannot travel long distances because it requires many radio stations to receive and reproduce at a minimal distance. More importantly, FM consumes less power.

The geographical interference between two neighbouring stations is also limited. Even the man-made interference of Cellphone towers and other towers is considerably less, making the signal quality undisturbed.

FM transmission and reception require very high bandwidth. FM is considered the premium broadcasting technology that gives the perfect sound quality.

FM radio stations sprung into action in the 1990s to offer high-quality music over the radio. The FM receiver accepts the correct transmitting station and rejects the unwanted signals, thus making it picture-perfect.

frequency modulation

Main Differences Between AM and FM

  1. The noticeable difference between AM and FM is the disturbance factor, AM is a lot noisier and easily affected by external environmental changes, whereas FM offers disturbance-free reception. AM has poor sound quality than FM.
  2. It is indeed to be accepted on the terms of an economy that AM radio signals can be propagated to a long distance without any need for intermediate radio stations. In contrast, FM cannot be transmitted to a longer distance; if done, it requires multiple stations to receive and reproduce.
  3. Another factor to note is that AM transmitter and receiver components are simple and less expensive. At the same time, FM components are expensive.
  4. The technical difference in the modulation is that the amplitude is modulated in AM, keeping the phase and frequency as constants. In contrast, the frequency is modulated in FM, keeping phase and amplitude as constants.
  5. The bandwidth required by FM is more when compared to AM. FM requires twenty times more bandwidth than AM.
Difference Between AM and FM
  1. https://www.osapublishing.org/abstract.cfm?uri=ol-31-15-2254
  2. https://arxiv.org/pdf/1808.08589
  3. https://pure.tue.nl/ws/files/2235569/Metis174587.pdf
  4. https://apps.dtic.mil/docs/citations/ADA446837
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