Frequency Modulation or FM is a method of encoding information on one carrier wave by changing the wave carrier frequency. Frequency Modulation technology is used in the fields of computing, telecommunications, and signal processing. In frequency modulation, the frequency of the carrier wave is changed according to the frequency of the modulating signal.
In this article, we will discuss the definition of frequency modulation, its advantages and disadvantages, the modulation index, the differences between AM and FM, and the expressions for frequency modulation.
What is Frequency Modulation?
Frequency Modulation is a process of encoding information on one carrier wave by changing its frequency. The frequency of the carrier wave is changed according to the frequency of the modulating signal. Frequency modulation is used for broadcasting and radio communication. Modulation is the process of converting the carrier signal into an electrical signal. Amplitude and phase remain the same in FM.
Frequency Modulation is used in FM radio broadcasting, magnetic tape-recording systems, monitoring newborns for seizures via EEG, radar, seismic prospecting, sound synthesis, telemetry, two-way radio systems, and video-transmission systems.
Frequency Modulation System
A Frequency Modulation system refers to a communication or signal processing system that utilizes frequency modulation to encode and transmit information. Frequency Modulation system consist of input signal, carrier wave, modulation process, transmission, reception, demodulation and output signal.
Frequency Modulation Deviation
Frequency Modulation Deviation refers to the extent to which the frequency of a carrier wave is changed or deviated from its center frequency in response to change in the amplitude of the modulating signal. It is a key parameter in frequency Modulation systems and determines the amount by which the carrier frequency shifts during the modulation process.
Frequency Modulation Demodulation
Frequency Modulation Demodulation is the process of extracting the original information usually an audio signal from a modulated FM carrier wave. Demodulation is an important step in FM receivers to recover the transmitted information accurately. The goal of FM modulation is to reproduce the original information encoded in the FM signal, ensuring high-quality audio output.
Frequency Modulation Waveform
Frequency Modulation generates a modulated waveform by changing the frequency of a carrier signal in response to change in the amplitude of a modulating signal. The result is s waveform that has characteristic distinct from the original carrier wave. The shape of the waveform is highly dependent on the characteristic of the modulating signal and the specific parameters of the FM modulation process.
The wave form of frequency modulation signal is shown in the image added below,
Representation of Frequency Modulation Signal
Frequencies in Frequency Modulation
In Frequency Modulation, the frequency of the carrier signal is varied in accordance with the instantaneous amplitude of the modulating signal. The parameters associated with FM are carrier frequency, Modulating Signal Frequency, Frequency deviation, Modulation index, Sideband Frequencies and Total Bandwidth. The expression for the instantaneous frequency can be expressed mathematically based on the modulation index, the frequency deviation and the modulating signal.
Expression for Frequency Modulated Wave
The expression for a frequency modulated wave can be derived from the basic equation for frequency modulation. The general form of an FM wave can be written as
s(t) = Ac cos(2πfct + 2πkf ∫t 0 m(τ)dτ
where,
- Ac is the Amplitude of the Carrier Signal
- fc is the Frequency of the Carrier Signal
- kf is the Frequency Deviation Sensitivity
- m(t) is the Modulating Signal
Radio Frequency Modulation
Radio frequency Modulation is a technique of encoding the information on a carrier wave by changing its frequency. It is used in field of telecommunication and employed in radio broadcasting, two-way radio communication, television broadcasting and various wireless communication systems. Radio frequency Modulation is a fundamental concept in the world of wireless communication, enabling the transmission of information over the airwaves efficiently and reliably.
Pulse frequency Modulation
Pulse frequency Modulation is a type of modulation where the information is encoded by changing the frequency of a series of pulses. It is used in field of digital communication and control system. Pulse frequency Modulation is commonly used in applications where resistance to noise is important.
Frequency Modulation Synthesis
Frequency Modulation synthesis is a method of sound synthesis that uses the frequency of carrier waveform, to modulate the frequency of modulator waveform. This is particularly associated with the creation of complex and evolving sounds.
Frequency Modulation Receiver
A Frequency Modulation receiver is a device that is used to demodulate and recover the original modulating signal from an FM modulated carrier wave. The receiver is a crucial part of the communication system and it has various applications such as FM radio broadcasting, two-way radio communication, and various wireless communication system.
Frequency Modulation Music
Frequency Modulation is used in electronic music for creating a wide range of sounds, from classic bell tones to complex textures. FM can generate complex waveforms by modulating the frequency of one oscillator with another. Musicians explore vast sonic possibilities of FM synthesis to create sounds that stand out and contribute to the unique character of track.
Frequency Modulation Broadcasting
Frequency Modulation broadcasting is a widely used method for transmitting audio signals over the airways. FM broadcasting offers several advantages, including higher audio quality and resistance to certain types of interference compared to other modulation methods like Amplitude Modulation. It is commonly used for music, talk show, news and other forms of radio programming.
Advantages of Frequency Modulation
Some of the advantages of Frequency modulation are listed below
- The Amplitude of FM wave remains constant over time. This helps in removing noise from received signal.
- FM is resistant to single strength variation.
- It enhances more efficient use of bandwidth.
- FM is used in radio broadcasting because FM is known for its superior quality compared to other methods of modulation.
- It improves and increase the capacity for communication.
Disadvantage of Frequency Modulation
Some of disadvantages of Frequency Modulation are listed below
- Modulation of wave increases the complexity in implementation.
- It requires specialized equipment and knowledge to implement, which makes it less accessible.
- Sometimes modulation leads to loss in quality of signal received, which reduces the clarity of transmitted data.
- FM has a large bandwidth which makes it costlier.
Application of Frequency Modulation
Frequency Modulation has many applications in science and technological field. Some of its real life uses are mentioned below
- FM is used in radio broadcasting.
- It is used by many radio stations to broadcast music over the radio (One must have heard the term FM in radio while listening it).
- FM is used in radar.
- It is used in seismic prospecting.
- It is used in Electroencephalogram (EEG) , which is a test of brain activity.
- Frequency modulation is superior than other modulations. That’s why it has many applications in various fields.
Modulation Index
Modulation index is denoted by μ. It is the ratio of the amplitude of modulating signal to that of the carrier signal.
μ = Am/ AcÂ
The mathematical representation of an FM signal can be expressed by using the formula. The instantaneous frequency , of the FM waveform at any given time is given by
F(t) = Fc + Kf . m(t)
where, f(t) is instantaneous frequency at time t of the modulated signal
Fc is the carrier frequency, representing the unmodulated frequency
Kf is the frequency sensitivity of the modulator, often referred to as the modulation index
m(t) is the message signal, which contains the information to be encoded into the carrier signal.
Frequency Modulation Width
The frequency modulation index is denoted by Δf or Δfmax and is defined as the maximum deviation of the instantaneous frequency from the carrier wave.
It is expressed as
Δf = kf . Am
where,
- Δf is the Frequency Deviation
- Kf is the Frequency Sensitivity of Modulator
- Am is the Amplitude of Message Signal
Expression For Frequency Modulation
We can represent the expression for frequency-modulated wave by using a sine or cosine work for the vitality of the baseband signal.
We know wave equation as:
m(t) = Am cos(ωmt + ϴ)
- m(t) is Balancing Signal
- Am is Amplitude of Balancing Signal
- ωm is Angular Recurrence of Tweaking Signal
- Ï´ is is Period of the Balancing Signal
when we try to modulate an input signal, we need an expression for carrier wave also
C(t) = AC cos(wct + Ï´)
From amplitude modulation , we need two sine or cosine waves for modulation
m(t) = Am cos (ωmt) and
c(t) = Ac cos (ωct)
or
m(t) = Am cos (2Ï€ fmt)
c(t) = Ac cos (2Ï€fct)
Then frequency modulated wave will be:
fm(t) = fc + k A cos (2Ï€ fmt )
fm (t) = fc + k m(t)
where,
- fm(t) is Frequency Modulated Wave
- fc is Frequency of Carrier Wave
- m(t) is Modulating Signal
- k is Proportionality Constant
Frequency Modulation Transmitter
A Frequency Modulation transmitter is a device that modulates a carrier wave’s frequency with an input signal, typically an audio or data signal. This device is used in broadcasting, two-way radio communication, and various wireless applications. FM transmitters are regulated, and their use may be subjected to licensing depending on the frequency and power at which they operate.
Difference between FM and AM
The differences between FM and AM can easily learnt form the table added below,
| AM has a bad sound quality as compared to FM |
FM has a good sound quality as compared to AM |
| It is cheaper |
It is expensive |
| AM can be sent over a large distance |
FM can be blocked by things like walls |
| Less power efficient |
More power efficient |
| Shorter broadcast range |
Longer broadcast range |
| Modulates amplitude of the carrier signal |
Modulates frequency of carrier signal |
| Demodulation is relatively straightforward |
Demodulation is more complex than AM |
Also, Check
Frequency Modulation IIT JEE Questions
Q1: What is the modulation index of an FM signal having a carrier of 100 kHz when the modulating signal has a frequency of 8 kHz ?
Solution:
Modulation Frequency, fm = 8 kHz
Carrier Swing = 2 × Δf
2 × Δf = 100 kHz
Δf = 50 kHz
Modulation Index = Δf/fm
= 50/8
= 6.25
Q2: Calculate percentage modulation of the signal if it is broadcast in the 88-108 MHz and FM transmission has a frequency deviation of 20 kHz ?
Solution:
For FM broadcast (Δf)max = 75 kHz
%M = (Δf)actual/(Δf)max
%M = 20kHz/75kHz
%M = 26.67%
Q3: A signal of 5 kHz frequency is amplitude modulated on a carrier wave of frequency 2 MHz. The frequencies of the resultant signal are.
Solution:
Fm = 5 kHz
Fc = 2 MHz = 2000 kHz
Frequencies of Resultant Signal are = Fc + Fm = ( 2000 + 5)kHz = 2005 kHz
Fc – Fm = (2000 – 5) = 1995 kHz
Q4: Consider telecommunication through optical fibers. Which of the following statements is not true ?
- (a) Optical fibers can be of graded refractive index
- (b) Optical fibers are subject to electromagnetic interference from outside
- (c) Optical fibers have extremely low transmission loss
- (d) Optical fibers may have a homogenous care with a suitable cladding
Solution:
Option (b) is correct
Frequency Modulation-FAQs
What is full form of FM and AM?
Full form of FM and AM is
- FM: Frequency Modulation
- AM: Amplitude Modulation
What is Modulation of Signal?
Modulation is process of changing a characteristic of a waveform, such as its amplitude or frequency.
Why Value of Modulation Index is kept less than 1 in General ?
Its value is kept less than 1 to avoid overmodulation which leads to distortions in the modulated signal and makes it very hard to demodulate and extract the modulating signal.
What is Modulation Index ?
Modulation index is the ratio of the amplitude of modulating signal to that of the carrier signal.
What is Demodulator?
Demodulator is the device which is used for extracting the original information from a modulated carrier wave.
What is Frequency Modulation?
Frequency modulation is a way of changing frequency of the carrier signal in accordance to the amplitudes of the signal.
What are the Uses of Modulation?
Various uses of Modulation are,
- It reduces the height of Antenna
- It avoids mixing of signal.
- It increases communication range.
- It is improves reception quality.
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