Difference Between Amplitude Modulation and Frequency Modulation

Amplitude and frequency modulation are the two techniques used to modulate a signal in order to have long distance as well as proper transmission. The major difference between amplitude modulation and frequency modulation lies in the method of modulating the signal. In amplitude modulation, variation in amplitude of carrier signal according to the message signal is noticed. However, in frequency modulation, the frequency of the carrier signal is changed according to the message signal.

In amplitude modulation, simply the amplitude of the carrier is modulated thus its frequency and phase shows no change. Whereas, in frequency modulation, only the frequency of the carrier is modulated hence here amplitude and phase act as constant factors.

Let us now see the contents to be discussed under this article and then we will proceed to understand other major differences between the amplitude and frequency modulation.

Content: Amplitude Modulation Vs Frequency Modulation

  1. Comparison Chart
  2. Definition
  3. Key Differences
  4. Conclusion

Comparison Chart

ParameterAmplitude ModulationFrequency Modulation
Abbreviated asAMFM
OperationAmplitude of carrier is changed according to the message signal.Frequency of carrier is modified according to the message signal.
Constant factorFrequency and phase.Amplitude and phase.
Noise susceptibilityHighLow
Frequency rangeMedium and high frequency range (nearly about 535 to 1705 KHz)Very high and ultra high frequency range (nearly about 88 to 108 MHz)
CostLessComparatively more costly
Circuit complexityThe circuit of amplitude modulation is complex.The complexity of a circuit used for frequency modulation is less as compared to amplitude modulation circuitry.
Bandwidth requirementThe bandwidth requirement is nearly about 30 KHz.The bandwidth requirement in frequency modulation is 80 KHz.
Effect of fadingEffect of fading is severe.In frequency modulation the effect of fading is less severe in comparison to amplitude modulation.
ClassificationDSB-SC, SSB, VSB etc.FSK, offset FSK, BFSK etc.
Transmission rangeHighComparitively less than amplitude modulation technique.
Sound qualityGoodFrequency modulated signal possess better sound quality as compared to amplitude modulated signal.

Definition of Amplitude Modulation

Amplitude modulation is abbreviated as AM. It is a modulation technique in which the amplitude of carrier signal is modified or changed according to the modulating or information bearing signal. Here, the frequency and phase of the signal remain unchanged and only amplitude shows variation.

The carrier signal does not contain any information component in it. Thus, its amplitude is varied according to the message signal.

The figure below represents a message signal, a carrier signal followed by an amplitude modulated signal.

Amplitude modulated waveform

The information signal is a low-frequency signal that is overlapped (superimposed) on a carrier waveform which is mainly a high-frequency wave, by changing the amplitude of the carrier signal.

As we already know that a message signal is a low-frequency signal. And the frequency of the signal shows a direct relationship with the energy of the signal. Thus, we transmit a low-frequency signal directly then the chances of signal distortion will be more severe.

Also, the sender will also become doubtful about the transmission of the signal. Hence, amplitude modulation technique was taken into consideration and adopted worldwide in order to have long distance as well as distortionless transmission.

But several drawbacks were noticed when an amplitude modulated signal is transmitted. Due to which frequency modulation technique was adopted.

Definition of Frequency Modulation

Frequency modulation is abbreviated as FM. In frequency modulation, the frequency of the carrier wave is modified as per the message signal (modulating signal). Here, the other two factors i.e., amplitude and phase show constant behaviour.

Here also, the carrier is informationless waveform whose frequency component undergoes modification according to the message signal.

The figure below represents a message signal, a carrier signal followed by a frequency modulated signal.

Frequency modulated waveform

The above figure clearly indicates that the message signal is a low-frequency signal. The frequency of the carrier signal increases when the amplitude of the message signal rises. Also, the frequency is noticed to be highest when the amplitude of the message signal becomes maximum.

Similarly, with the fall in the amplitude of message signal the frequency of the signal also becomes low.

As we simply modify the frequency of the carrier signal. Thus, it gets less affected by the noise and other environmental factors at the time of transmission. This technique was discovered after the discovery of amplitude modulation and it has overcome various disadvantages of amplitude modulation.

Thus, it is widely used in radio signal broadcasting as well as in the satellite communication system.

Key Differences Between Amplitude Modulation and Frequency Modulation

  1. Amplitude modulation is a technique that was discovered earlier than frequency modulation. However, a signal that is amplitude modulated shows more susceptibility towards noise as compared to frequency modulated signal.
  2. The circuitry involved in amplitude modulation is more complex. However, the circuit complexity is less in case of frequency modulation.
  3. The signal that has been amplitude modulated has the ability to get transmitted to a larger distance. As against, a frequency modulated signal travels comparatively less distance than the amplitude modulated signal.
  4. The amplitude modulation technique is cost-effective whereas the frequency modulation technique is expensive.
  5. Amplitude and frequency modulation technique also shows a variation on the factor of bandwidth requirement. As in the case of amplitude modulation, the bandwidth requirement is less than that of frequency modulation.
  6. Amplitude modulation can be used for medium or high-frequency ranges i.e., in between 35 to 1705 KHz. On the contrary, frequency modulation is used for very high and ultra-high frequency ranges i.e., between 88 to 108 MHz.
  7. The effect of fading is more severe in amplitude modulation rather than frequency modulation technique.
  8. In amplitude modulation, as only amplitude shows variation thus, frequency and phase both remains constant in this case. As against, in frequency modulation, only frequency component shows variation thus amplitude and phase do not any change.
  9. Though an amplitude modulated signal possesses good sound quality, a frequency modulated signal provides somewhat better sound quality than amplitude modulated signal.

Conclusion

So, from the above discussion, we can conclude that the two techniques show their usage in different aspects. In terms of long-distance transmission and cost amplitude modulation is preferred while in terms of better sound quality and fewer distortions frequency modulation technique is more preferable.

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