Amplitude Modulation - Amplitude Modulation Applications

Amplitude Modulation, or AM as it is often called is an electronic communication systems technique wherein the baseband signal is superimposed with the amplitude of the carrier wave i.e. the amplitude of the carrier wave varies with proportion to the base waveform that is being transmitted. Amplitude Modulation has been in use since the earliest days of radio technology. One of the main reasons for the use of amplitude modulation was its ease of use. The system mainly required the carrier amplitude to be modulated, additionally, the detector required in the receiver could be a simple diode-based circuit. This meant that complicated demodulators weren’t required and as a result, the costs were reduced – a key requirement for the use of radio technology in the early days when ICs weren’t available.
Amplitude Modulation

What is Amplitude Modulation (AM)?

When an amplitude modulated signal is created, the amplitude of the created signal represents the original baseband signal to be transmitted. This amplitude forms an envelope over the underlying high-frequency carrier wave. Here, the overall envelope of the carrier is modulated to carry the audio signal. AM is the simplest way of modulating a signal. In short, amplitude modulation is defined as the modulation in which the amplitude of the carrier wave is varied in accordance with some characteristic of the modulating signal.

Amplitude Modulation History

The first recorded instance of amplitude modulation of the baseband wave harks back to 1901 when a Canadian man Reginald Fessenden used a continuous spark transmission to create the first amplitude modulation ever. Into this continuous spark transmission, he puts a carbon microphone in the antenna lead. The sound waves impacting on the microphone varied its resistances and this, in turn, varied the intensity of the transmission.

Though the accuracy and the signal-to-noise ratio in this earlier method of transmission were very low, with the advent of a continuous sine wave generator, the audio quality was greatly improved. This led to Amplitude modulated waves becoming the standard for voice transmission.

Amplitude Modulation Formula

Amplitude Modulation expression is given by:

\(s(t)=[A_{c}+A_{m}cos(2\pi f_{m}t)]cos(2\pi f_{c}t)\)

Where,

  • Am is the amplitude of the modulating signal
  • Ac is the amplitude of the carrier signal
  • fm is the frequency of the modulating signal
  • fc is the frequency of the carrier signal

Amplitude Demodulation

Demodulation or detection is a process where the signal that is a mixture of the amplitude of the baseband signal and the frequency of the carrier signal, is deconstructed to yield the original signal that is to be transmitted. Simply, it is the recovery of the modulating signal from the modulated wave.

Detection Of Amplitude Modulated Wave (Demodulation)

The amplitude modulation and demodulation are equally simple to perform. The amplitude modulated signal needs just a simple diode detector circuit to demodulate. The diode rectifies the incoming signal, allowing only one-half of the signal waveform to pass through. The capacitor then is used to remove the radio frequency parts of the signal, leaving just the original waveform. As you see, the equipment for demodulation is very cheap, and this enables the cost of the receivers to be kept low.
Detection of Amplitude Modulated Wave
Thus, amplitude modulated wave can be demodulated in two steps:

  • Rectification of modulated wave
  • Elimination of the RF component of the modulated wave

Advantages And Disadvantages Of Amplitude Modulation

Given below in a tabular column are the various advantages and disadvantages of amplitude modulation.

Advantages

Disadvantages

It can be demodulated using a circuit with fewer components

It is not efficient in terms of its use of bandwidth, requiring a bandwidth equal to twice of the highest audio frequency

It is easy to implement

Not efficient in terms of power usage

AM receivers are cheap and there is no requirement of specialised components

Prone to high levels of noise as most noise is amplitude based and AM detectors are sensitive to it.

 


 

Applications Of Amplitude Modulation

With the improvement of the technology, the uses of amplitude modulation waves has become somewhat less prevalent, nevertheless it can still be found playing an important role in;

  1. Broadcast Transmission: AM is still widely used for broadcasting either long or medium or short wave bands. The received signal is simple to break down into the baseband signal and hence the equipment cost to the user is very little and it is easy to manufacture
  2. Air band Radio: The use of AM in the aerospace industry is widespread. The VHF (Very High Frequency) transmissions made by the airborne equipment still use AM. The radio contact between ground to air and also ground to ground use AM signals.
  3. Quadrature Amplitude Modulation: Believe it or not, AM is used in the transmission of data of pretty much everything, from short range transmissions such as Wi-Fi to cellular communications and etc. Quadrature amplitude modulation is formed by mixing two carriers that are out of phase by 90o.

The need for modulation was sky high and the invention of Amplitude modulation has changed the way in which we communicate.

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What is the current (I) in the circuit?

 

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