Frequency Modulation Vs. Amplitude Modulation

Frequency modulation (FM) and amplitude modulation (AM) are used to transmit data in the form of electromagnetic waves. While AM follows the process of modulating the amplitude of the carrier wave where frequency remains constant, in case of FM, the wave frequency varies, and amplitude remains constant.  

Both these methods work to encode and broadcast radio signals, but the way that happens makes the actual difference. To understand how both these modulation process works, let us find out their differences.

Amplitude modulation (AM)

Back in the 1870s, the concept of broadcasting any audio production through radio waves was discovered, and that is when the AM method was also introduced. To explain the Amplitude modulation definition, it can be mentioned that, in this modulation technique, depending on the information signal, the amplitude of a carrier varies. Radio broadcast signals under AM use lower carrier frequencies, and thus they can travel long distances, and that is larger than FM.

Types of Amplitude Modulation

Three types of amplitude modulation can be found -

1. Single Sideband (SSB) Modulation

In case of SSB modulation, between an upper sideband and lower sideband, the amplitude-modulated wave contains either one of two. 

2. Double Sideband-suppressed Carrier Modulation

In the case of DSB-SC modulation, bandwidth remains constant even though the transmitted wave contains only upper and lower sidebands. 

3. Vestigial Sideband (VSB) Modulation 

In the case of VSB modulation, vestige which is a part of the signal is only modulated, including one sideband. 

Amplitude Modulation Equation

The equation of Amplitude Modulation is –

Y(t) = A.sin(ωct)+ A M2[sin((ωc+ωm)t+ φ)] + A M2[sin((ωc-ωm)t- φ)]

[Here, C stands for the carrier amplitude 

φ stands for a phase of the signal at the beginning of the reference time 

M stands for carrier amplitude 

Modulation Index (µ) = Ac/Am 

Ac= amplitude of carrier wave 

Am= Amplitude of modulating signal] 

Frequency Modulation (FM)

On the other hand, to explain the frequency modulation definition, it is required to mention that, carrier wave which carries information is modified according to the signal. Invented in 1930, FM was considered as an advanced technique of transmitting information (sound) through radio waves. The bandwidth of FM radio signals is larger than the AM ones, which also helps them with better sound quality. 

Frequency Modulation Formula

The formula of frequency modulation is –

m(t) = Am cos (ωmt + Ɵ)

[Here, m(t) stands for modulating signal 

Am stands for the amplitude of the modulating signal 

ωm stands for the angular frequency of the same 

Ɵ stands for the phase of the modulating signal] 

Difference Between Amplitude Modulation and Frequency Modulation

Being an advanced method of transmitting information, FM is different from AM in a lot of aspects. Some critical differences between amplitude and frequency Modulation are given below -

Pros and Cons of Amplitude Modulation

The advantages of AM include its affordability, ease in detecting using simple equipment even in a weak signal. Also, AM has a narrow bandwidth and broader coverage as compared to frequency modulation. Some of the disadvantages include signal getting affected by electrical storms, or any radiofrequency or noise interferences, low signal quality, and also the applications are restricted to one-sided communication. 

Pros and Cons of Frequency Modulation

A significant advantage found in FM is that it possesses better sound quality since an FM wave remains constant, unlike AM. Therefore, encoders can remove the received noise, and better sound quality can be achieved. Also, frequency modulation can be used for low power transmitters, and power consumption also remains limited. On the other hand, some disadvantages can also be found in FM, such as the frequency modulated continuous wave cannot be broadcasted over the longer distance since the signal is more local. Also, another requirement for FM is a complicated receiver and transmitter, and the cost becomes automatically high because of that. 

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