Frequency Modulation Vs. Amplitude Modulation

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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 -

Amplitude Modulation

Frequency Modulation

In this case, while sending the data, the amplitude of the carrier wave is modified.  

In the case of FM, while sending the information, the frequency of the carrier wave is modified.  

The frequency range of AM is between 535 to 1705 Kilohertz. 

The frequency range is 88 to 108 megahertz in this case.

Consists of two sidebands. 

Consists of an infinite number of sidebands.

The modulation index of AM may vary from 0 to 1.

The modulation index of FM stays greater than 1. 

It delivers low sound quality since it is susceptible to noise.

Due to being less susceptible to noise, it delivers better sound quality.

Issues like signal distortion can be noticed in AM.

There is less chance of signal distortion in frequency modulation.

The circuit design is simple and less expensive. 

The circuit design is intricate, and it is on the expensive side as compared to AM.

In the case of AM, power consumption becomes an issue since a bulk amount of power gets used by the carrier that does not contain the data. 

Since the information signal carries all transmitted power, it does not involve wastage of power. 


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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FAQ (Frequently Asked Questions)

1. What are the purpose of Amplitude and Frequency Modulation?

Ans. To transmit information from a specific place to another place, modulation and demodulation are required. Mainly used in electronic communication, amplitude modulation helps to transmit messages through the radio carrier wave. 

On the other hand, frequency modulation is widespread in FM radio broadcasting as it provides a clear sound quality. In case of frequency modulation, there are fewer disturbances during signal transmission, especially when the priority is transmitting the wave to a longer distance.  

2. What is the application of Frequency Modulation?

Ans. Due to its resiliency to signal level variations, frequency modulation is ideal for a lot of high-quality applications, including mobile communication systems and two-way radio communication. Some of the applications include FM radio broadcasting where FM helps to provide a larger signal. It is further used in seismic prospecting, telemetry, sound synthesis, etc. Due to the improved signal and better sound quality, FM is preferable for high-quality audio broadcasts.

3. What are the advantages of an RF amplifier?

Ans. There are certain advantages of using an RF amplifier – (1) It helps to amplify weak signals that are received by the receiver, and it also chooses better signals among them (2) RF amplifiers are better in terms of signal-to-noise ratio than several other amplifiers (3) The sensitivity is also better in RF amplifier.  

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