[Physics Class Notes] on Frequency Modulation Vs. Amplitude Modulation Pdf for Exam

People of this generation may not be aware of this thing called FM radio, where people listen to the newest pop songs over blur and static. Before FM radio it was AM radio, which has the worst sound quality ever. Both FM and Am are still with us till today. But they are used to send high-speed digital data over high-frequency carrier waves. Amplitude modulation is used in technologies like WiFi, while other radio technologies still use digital frequency modulation.

Amplitude Modulation

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.

Amplitude modulation is the process in which the wave signals are transmitted by modulating the amplitude of the signal. The amplitude modulation is often called AM. This technique was established by Landell de Moura and Reginald Fessenden in the 20th century when conducting radiotelephone experiments. It is used to transfer information through a radio wave. It is mostly used in electronic communications like portable two-way radios, citizens band radio, VHF aircraft radio, etc.

Y(t) = A sin (ωct) + A M2sin((ωc + ωm) t + φ) + A M2sin((ωc − ωm) t − φ)

Where, 

C is the carrier amplitude 

φ is the phase signal of the initial reference time 

M is the carrier amplitude 

Modulation Index (µ) = Ac / Am 

Ac is the amplitude of carrier wave 

Am is the amplitude of modulating signal

Types of Amplitude Modulation

Three types of amplitude modulation can be found –

1. Single Sideband (SSB) Modulation

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

Frequency Modulation

Frequency modulation is the process of encoding information on a particular analogue or digital signal by varying the carrier wave frequency in accordance with the frequency of the modulating signal. The Frequency Modulation is often called FM. As we know, a modulating signal is the transmitting of information or message after being converted into an electronic signal.

m (t) = A m cos (ωmt + Ɵ)

Where,

m(t) is the modulating signal 

Am is the amplitude modulating signal 

ωm is the angular frequency

Ɵ is the phase of the modulating signal

Difference between Amplitude Modulation and Frequency Modulation

Frequency Modulation is the advanced method of transmitting information when compared to Amplitude Modulation in various aspects. Here are some of the differences between Frequency Modulation and Amplitude Modulation.

 

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 being 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 a 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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