Amplitude and Frequency Modulation

Introduction:

The method of modifying the carrier signal in response to the message signal is known as modulation. In the process of modulation, the high-frequency sine wave signal is referred to as the carrier signal. The modulating signal is the name given to the output signal. Modulation is a signal processing technique that involves shifting the signal’s frequency range. Modulation is used to enhance the range of the signals and also for fast transmission. Sinusoidal wave is a generally used curve that ensures smooth repetitive oscillations. The modulation uses sinusoidal waves. Modulation is a branch of science in electronics and communication systems. One example of modulation is seen in radio signals.

Types of modulation

• Amplitude Modulation: In this type of modulation, a carrier signal with a different amplitude is superimposed with a base signal to change the amplitude of the base signal or modulate that, but the frequency of both signals remains the same.
• Frequency Modulation: In this type of modulation, the carrier signal with a different frequency is superimposed with the base signal so that the frequency of the base signal can be changed or modulated. The amplitude of both of the signals remains the same.
• Phase Modulation: In this type of modulation, the phase of the base signal changes or modifies after it is superimposed with the carrier signal.

Amplitude Modulation

In analogue modulation, if the amplitude and duration of a pulse are made to vary by the instantaneous values of any baseband modulating signal, then this is called Pulse Amplitude Modulation or Pulse Duration/Width Modulation or Pulse Position Modulation.

In digital modulation, the modulation technique used is known as Pulse Code Modulation, where the analogue signal is converted into a digital form of 1s and 0s. The resultant is a coded pulse train known as PCM. This is also being developed as Delta Modulation (DM).

Frequency Modulation:

 If the frequency of any carrier wave is varied according to the instantaneous value of a modulating signal, then such a method is known as Frequency modulation. The basis for switching a signal with a network signal at different frequencies but with the same amplitude, even if the frequency signal is normal, can be done.

Benefits of frequency modulation:

Noise-resilient: Reducing background noise is one of the key advantages of frequency modulation, which the broadcasting sector has extensively embraced. Because most noise is amplitude-based, it may be eliminated by sending the signal through a limiter, which only causes frequency changes to be seen.

Signal strength fluctuations are unaffected: Any changes in signal intensity may be removed in the same way as amplitude noise can be removed. Frequency modulation is especially well suited for mobile applications where signal levels often fluctuate since it does not suffer from audio amplitude fluctuation due to signal level changes.

It is more efficient than a variety of other modalities. Because linear amplifiers are inherently inefficient, the use of non-linear amplifiers, such as class C and other related devices leads to higher levels of transmitter efficiency.

Why is modulation needed in communication systems?

We live in a digitally evolved era where using wires to stay connected to everyone is no longer necessary. Within minutes, messages, information, and signals are sent from one part of the planet to another. To transmit messages quickly, the modulation procedure is crucial. 

Some of the reasons why we need modulation are as follows:

• It is not possible to build an antenna to radiate the base signal provided, to be in the order of the magnitude of the wavelength of the transmitted signal. For example, if there is a signal of wavelength λ, the length of the antennae should be λ/4 at least so that smooth transmission could be possible.
• If we directly transmit the signal, the ratio of highest to lowest frequency becomes very high. Hence, transmission is very difficult. But with the modulation of transmission with the carrier signal, the ratio of highest to lowest frequency becomes low and hence transmission becomes possible.
• Wireless communication is possible due to modulation. Modulation helps in the long-distance transmission of signals. Hence, this technology is used in mobile phones nowadays so that effective mobile communication could be possible. 
• Modulation is also important to differentiate between two different message signals. After carrier signal modulation, every signal is given with specific amplitude, frequency and wavelength so that it can be transmitted and could be received only by those for whom the message is supposed to be.
• Before transmission, the original low-frequency baseband message or information signal must be translated into a high-frequency wave so that the translated signal retains the information included in the original signal. To do so, we use a high-frequency signal called the carrier wave and a procedure called modulation to attach information to it. The carrier wave can be either continuous (sinusoidal) or pulsed. 
• The power radiated increases with decreasing, i.e., the increasing frequency for the same antenna length. As a result, the effective power emitted by a baseband signal with a long wavelength would be low. We require high power for good transmission. Hence, there is a need for a high-frequency transmission. 

Conclusion :

In this article, we learned about frequency modulation. The carrier signal with a different frequency that is superimposed with the base signal so that the frequency of the base signal can be changed or modulated. This technology is used in telecommunications, radio broadcasting, signal processing, computing, etc.  We also learnt the different modulators and the application of frequency modulators. To gain a better understanding of this chapter, other topics such as Amplitude modulation, propagation of EM waves, and ground or surface wave propagation are suggested to the user.