Amplitude Modulation & Frequency Modulation

 

Modulation is the technique of varying some operating characteristic of a sinusoidal signal (amplitude, frequency, or phase). It thus opens up three modulation schemes: amplitude modulation, frequency modulation, and phase modulation. We can say that amplitude modulation (AM) was the first type of modulation adapted for civilian use, and it remained the dominant type of modulation in civilian radio broadcasting until the late 1970s. Then, frequency modulation (FM) took over, and AM radio began a slow decline. Amplitude modulation and frequency modulation seem to be methods of transmitting data that involve modifying a carrier signal. The primary distinction between the two modulations is that in frequency modulation, the carrier wave’s frequency is modified in response to the transmitted data, whereas in amplitude modulation, the carrier wave gets changed in response to the data. For example, if several different sets of data must be transmitted over the same medium, each set is sent using a different frequency wave. This is the method by which radio broadcasts are produced.

Overview

Youngsters may not remember FM radio, where you could listen to the latest pop songs over a jumble of static. Before all this, there was AM radio, which had even worse sound quality. Frequency modulation and amplitude modulation are still being used today, but they are now used to transmit digital data at high speeds over a high-frequency carrier wave. Amplitude modulation is often used in technologies such as the 802.11 standards (a.k.a. WiFi), whereas other radio technologies continue to use digitally modulated frequency modulation.

Somewhere at the system level, it’s fascinating to observe the evolution of amplitude modulation vs. frequency modulation, as well as the transition to all-digital modulation schemes. Even though these two broad modulation methods are well-known among electronics enthusiasts, they are not the most commonly used methods in wired or wireless communications. Rather, when it comes to wireless communication protocols, industry standards reveal that standardised modulation techniques are digitised multilevel signalling schemes that use either amplitude or phase modulation with time division or frequency division multiplexing.

Amplitude Modulation

The concept of broadcasting any audio production over radio waves was discovered in the 1870s, and the AM method was also introduced at the time. In order to explain the definition of Amplitude modulation, it can be stated that in this modulation technique, the amplitude of a carrier varies depending on the information signal. AM radio broadcast signals use lower carrier frequencies, allowing them to travel longer distances than FM.

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

Here,

C stands for the carrier amplitude

φ stands for the phase signal of the initial reference time

M stands for the carrier amplitude

Modulation Index (µ) = Ac / Am

Ac is said to be the amplitude of carrier wave.

Am is said to be the amplitude of modulating signal.

The benefits of AM include its low cost and ease of detection using simple equipment even in weak signals. In addition, compared to frequency modulation, AM has a narrower bandwidth and broader coverage. A few disadvantages include signal degradation due to electrical storms or radiofrequency or noise interferences, low signal quality, and applications that are limited to one-sided communication.

Types of Amplitude Modulation:

• Single Sideband (SSB) Modulation: As in the case of SSB modulation, the amplitude-modulated wave contains one of two components: an upper sideband and a lower sideband.
• Double Sideband-Suppressed Carrier Modulation (DSB-SC): Through DSB-SC modulation, the bandwidth remains constant despite the fact that the transmitted wave only contains upper and lower sidebands.
• Vestigial Sideband (VSB) Modulation: Through VSB modulation, the vestige that is part of the signal is only modulated, including one sideband.

Frequency Modulation

The process of encoding information on a specific analogue or digital signal by varying the carrier wave frequency in accordance with the frequency of the modulating signal is known as frequency modulation. FM is an abbreviation for Frequency Modulation. A modulating signal, as we know, is the transmission of information or a message after it has been converted into an electronic signal.

Now, m (t) = A m cos (ωmt + Ɵ)

Here,

m(t) stands for the modulating signal

Am stands for the amplitude modulating signal

ωm stands for the angular frequency

Ɵ is said to be the phase of the modulating signal

FM has been better suited than AM to the microwave radio relay transmission of stereophonic sound, audio signals for television programmes, and long-distance telephone calls. Promotional FM broadcasting stations have higher frequency allocations than AM stations. The designated frequencies range from 88 to 108 MHz and are spaced 200 kHz apart.

The fact that an FM wave remains constant, as opposed to AM, gives it a significant advantage in terms of sound quality. As a result, encoders can remove received noise, resulting in higher sound quality. Furthermore, frequency modulation can be used for low-power transmitters, and power consumption is kept to a minimum. But on the other hand, FM has some drawbacks, such as the fact that the frequency modulated continuous wave cannot be broadcasted over a longer distance because the signal is more local. Some other requirement for FM is a complicated receiver and transmitter, which automatically raises the cost.

Difference between Amplitude Modulation and Frequency Modulation

Both amplitude modulation and frequency modulation are transmission techniques used to send information from sender to receiver. The similarities between the two, however, end here. Amplitude modulation is the process of modulating the carrier signal based on the amplitude of the baseband signal. The carrier signal’s frequency and phase, however, will not be altered.

Frequency modulation, on the other hand, involves modulating the carrier signal based on the frequency of the baseband or information signal. Thereby, the primary distinction between amplitude modulation and frequency modulation is that amplitude modulation is the process of modulating the amplitude of the carrier signal, whereas frequency modulation is the process of modulating the frequency of the carrier signal.

Some other significant term that distinguishes these two modulation techniques is the bandwidth requirement. When compared to frequency modulation, the bandwidth requirement for amplitude modulation is very low.

Also read: Need for Modulation

FAQs

Which travels farther AM or FM?

FM transmission uses broadcast waves (88-108 MHz) that are shorter and do not travel as far as AM broadcast waves (540 – 1600 kHz). The amplitude of the carrier waves varies in AM transmission to match changes in the electromagnetic waves coming from the radio studio.

What is frequency deviation in FM?

In FM radio, frequency deviation refers to the difference between the minimum and maximum extent of a frequency modulated signal and the nominal centre or carrier frequency.

What is the highest modulating frequency?

Because the maximum bandwidth possible is 10 kHz, the highest modulation frequency typically used in AM broadcast is 5 kHz.