Amplitude: An Ultimate Guide

Sound waves require a medium to travel and have several characteristics of their own; one of them is amplitude. It measures loudness, volume, power or strength. For example, in an electrical circuit working on alternating current or AC, the amplitude is measured in terms of the voltage level, expressed as positive or negative by the direction of the current flow. 

The article discusses the different types of amplitude modulation with particular advantages and disadvantages. It also gives information about the term ‘frequency’, commonly used in Physics. 

Amplitude 

• For a transverse wave, the amplitude is defined as the maximum distance or displacement of a vibrating object or a wave from its equilibrium position. The periodic function phase is also called an amplitude.
• It can also be defined as the distance measured from rest to crest.
• The waves generate from vibrating bodies or sources in which the amplitude is directly proportional to the amplitude of the source.
• The intensity of waves is proportional to the square of amplitudes.
• The length of the shortest interval, which contains only one copy of the repeating pattern of a wave cycle, is known as the Period.
• The amplitude of the sound is in direct proportion with loudness.
• Therefore, if the loudness is more, the wave’s amplitude would be more, and if the loudness is feeble, the amplitude will be below.
• The term semi-amplitude means half-peak to peak amplitude.
• Peak-to-peak (p-p) amplitude varies between the peaks or the highest amplitude values of a wave.
• An oscilloscope is used to measure peak-to-peak amplitude.
• The energy by a pulse of a transverse wave transported through a medium is directly proportional to its amplitude.

Wave equation of amplitude

• x = A sin [ωt – kx] + b is the wave equation

where A is the wave’s amplitude, t is time, ω is the angular frequency, x is the oscillating frequency, and k – time offset and b – displacement offset are the arbitrary constants.

Amplitude Modulation

Amplitude Modulation is the linear modulation of the amplitude of the carrier signal concerning the instantaneous message signal.

Types of Amplitude Modulation

1. Double Sideband Suppressed Carrier (DSB SC)

• In this type of modulation, the message signal’s frequency spectrum is situated symmetrically above and below the frequency spectrum of the carrier wave.
• The sidebands are the lower and the upper frequencies of the modulated signals.
• The lower sideband or LSB has lesser frequency components than carrier frequency, while the upper sideband or USB has higher frequency components than the carrier frequency wave.
• The bandwidth of the message signal is half of the bandwidth of the DSB-SC signal.

Advantages :

There is no need for filtering out during the modulation of sidebands, and the process of modulation is quite simple.

Disadvantages :

The envelope detection is impossible and has high bandwidth compared to VSB and SSB; also, the carrier power is not utilised.

2. Traditional Amplitude Modulation or Double Sideband Full Carrier (DSB FC)

• In this type of modulation, there is demodulation of the carrier signal.
• The envelope of the modulation signal contains the message signal.
• In the modulated signal, the amplitude of the message signal should not drop below zero to attain this envelope.
• At the receiver end, the modulation index should range between 0 and 1 to detect the envelope.

Advantages

Broadcasting can be done efficiently while the receiver has a low cost with a simple operating model.

Disadvantages

The noise and its waste power significantly affect the amplitude modulation and have low efficiency of around 33%.

3. Quadrature Amplitude Modulation (QAM)

• In the QAM modulation type, the same frequency carrier transmits two different forms of message signals with a variation in the phase shift.
• The problem with DSB modulated signal is the excessive double bandwidth of the modulating signal. At the same time, QAM can be used by sending two varying messages in the same frequency carrier signal with a phase difference of 90 degrees.
• As the QAM modulated signal contains two message signals, it cannot be demodulated using the envelope detection technique.

Advantages :

It can carry more than a single message signal and use low bandwidth compared with the transmitted information.

Disadvantages:

The envelope detection technique does not work; it also has a highly complex transmitter design.

4. Single Sideband Modulation (SSB)

• In this particular modulation type, a single sideband communication occurs in which only one sideband can be transmitted through the antenna.
• It has either a lower sideband or the upper sideband, unlike SSB and DSB.
• The modulated signal of SSB is passed through a bandpass filter. Here, the bandpass filter removes the DSB at wc; there is filtration of either the lower or the upper sideband.
• The message signal’s bandwidth is identical to the bandwidth of the SSB signal.

Advantages :

This modulation type saves around half of the power transmitted by a single sideband, and the message signal is similar to the bandwidth.

Frequency of a wave

• The frequency of a wave is defined as the total number of waves passed through in a specific period. For example, if a wave passes in ½ seconds, its frequency would be 2 Hz per second.
• To determine the frequency of a particular wave, we need to divide the velocity of that specific wave by the wavelength. The unit for frequency is Hertz.
• The vibrations caused by the waves are equal to the frequency of that wave. Frequency depends mainly on the features of the object’s material, which affects the velocity of the wave, and the length of the material, which further affects the wavelength of that wave.
• The wavelength and the frequency are inversely proportional to one another; one quantity increases while the other decreases.

Conclusion

This article gives an insight into the term amplitude and its definition. It also describes the wave equation of the amplitude and frequency of a wave. Moreover, there is a detailed explanation of amplitude modulation and its types with a few advantages and disadvantages. The different types are – Double Sideband Suppressed Carrier (DSB SC), Traditional Amplitude modulation or double Sideband full carrier (DSB FC), and Quadrature Amplitude Modulation (QAM).