3 Jan 2018

Amplitude Modulation Vs Frequency Modulation | AM Vs FM | Advantages and Disadvantages of AM and FM

What is Amplitude Modulation (AM)

Definition:-

Amplitude Modulation, is a system, where the maximum amplitude of the carrier wave varies, according to the instantaneous value (amplitude) of the modulating (message or baseband) signal.

What is Frequency Modulation (FM) 


In case of Frequency Modulation (FM) the frequency of the carrier wave varies according to the instantaneous value of the modulating (message) signal.

Comparison of AM and FM (AM vs FM)

Why FM is better than AM


Following reasons make the Frequency Modulation (FM) better than Amplitude Modulation (AM)

1.FM broadcasts operate in upper VHF (Very High Frequency) and UHF (Ultra High Frequency) ranges, while MF (Medium Frequency) and HF (High Frequency) ranges are used by AM broadcasts. This is a big advantage for FM, since in VHF and UHF frequency ranges there is less noise interference.


AM vs FM Video (Comparison of AM and FM) Video


 

2.FM receivers are more immune to noise in comparison to AM receivers. since FM receivers may be fitted with amplitude limiters. These amplitude limiters can remove the amplitude variations caused by the noise.

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3.In FM, it is possible to further reduce noise by increasing frequency deviation. This is not possible in case of AM, since in AM, we can not exceed 100℅ modulation without Severe distortions.

4.Standard Frequency allocations provide a guard band between commercial FM stations. This leads to less interference between adjacent channels in FM in comparison to AM.

5.In case of FM, all the transmitted power is useful but in AM, most of the power is present in carrier, that does not contain any information.

6.In FM Amplitude is constant, so does not depend on modulation depth. But in case of AM, the transmitted power is governed by the modulation depth.
This allows the use of low level modulation in FM transmitter and also we can use efficient class C amplifiers in all stages following the modulator.

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7.The average power handled equals the peak power, since all the amplifiers handle constant power. But in case of AM transmitter, the maximum power is 4 times the average power.

Disadvantage of FM over AM


1.Transmitting and receiving equipment used in FM mainly for the purpose of modulation and demodulation are more Complex and so more costly in comparison to AM.

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2.A channel of 200 kHz is required in FM broadcast in comparison to only 10 kHz in case of AM broadcast which is really a big drawback of FM.

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