Wideband frequency modulation applications and techniques. Know the relationship of carrier frequency, modulation frequency and modulation index to efficiency and bandwidth. Phase modulation, and frequency modulation are both the modulation techniques analyzed in angle modulation. Glavieux a, thitimajshima p 2010 near shannon limit errorcorrecting pdf. But we are getting ahead of ourselves, as we have not yet even defined what am is. During this lab you will create an fm signal by modulating an audio waveform onto a carrier, examine the spectrum of the modulated carrier, evaluate the modulated carrier when the modulation index is varied and. Below we illustrate an fm modulated signal in which the center frequency is 500 khz. Frequency modulation if the modulating signal is mt and then the modulated signal st is where, b is the modulation index. Fm is in contrast with amplitude modulation where amplitude of the carrier waves is modulated with frequency remaining. Frequency multiplier is a nonlinear device, which produces an output signal whose frequency is n times the input signal frequency. This article includes a list of related items that share the same name or similar names.
In chapter1, we investigated the way of modulating a sinusoidal carrier wave using am technique. What is modulation index modulation index in am and fm. In telecommunications and signal processing, frequency modulation fm is the encoding of. Fm and pm the that such set signal sinusoidal a is mt when. Modulation index is defined as the ratio of the fundamental component amplitude of the linetoneutral inverter output voltage to onehalf of the available dc bus voltage. The modulation takes place by varying the three parameters of the sinusoid carrier.
The mathematical representation of frequency modulation consists of a sinusoidal expression with the integral of the baseband signal added to the argument of the sine or cosine function. Hence, the spectrum of narrow band fm consists of the carrier and upper sideband and a lower sideband. Explain the difference between narrow band fm and wide band. Amplitude modulation index frequency modulation index phase modulation index. Mar 01, 2016 a narrow band fm is the fm wave with a small bandwidth. Frequency modulation fm is the encoding of the information in a carrier wave by varying the instantaneous frequency of the wave. The deviation ratio is the maximum frequency deviation divided by the maximum modulating frequency. The term wbfm is used in applications where the modulation index is equal to or larger than 1. This shout can be heard only up to a certain distance. For the fm signal, the change rate of the instant phase. Pdf modulation index estimation of frequency and phase. Discuss the differences between am and angle modulation. Phase modulation is similar to frequency modulation and is an important technique in digital communication systems.
The modulation index can be used to make the frequency deviation more sensitive or less sensitive to variations in the baseband value. The modulation index or modulation depth of a modulation scheme describes by how much the modulated variable of the carrier signal varies around its unmodulated level. In the graph below, the fm deviation has been selected as 425 khz. The averate power of such as signal developed across a 1ohm resistor is also constant. Million communications systems and research section in pulse code modulation phase modulation systems, the nonreturntozero or biphase data are directly modulated onto the residual carrier. Phase modulation is another type of angle modulation very similar to frequency modulation. However, in this article, we are going to address applications and techniques for wbfm with modulation indexes much larger than that, going up to 100 and.
What is fm, frequency modulation electronics notes. Looking for a comprehensive article on fm modulation, here it is what you are looking for. The subsystem that takes the information signal and processes it prior to transmission. There is another way of modulating a, sinusoidal carrier wave, namely, angle modulation in which the angle of the carrier wave is varied according to the baseband signal. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note. Modulation index is proportional to modulating signal mt.
Slide 3 discretetime fm modulator slide 4 single tone fm modulation slide 5 single tone fm cont. Am has only two sidebands usb and lsb and the bandwidth was found. In frequency modulation, the instantaneous frequency of the carrier wave is modified in order to transmit information. In amplitude modulation, the amplitude of the carrier wave is modified in order to transmit information. The fm wave is effectively composed of a carrier and a single pair of sidefrequencies at. Angle modulation changes the phase of a signal as well as its amplitude, where amplitude modulation leaves the phase unchanged. Modulation index is basically the ratio of amplitude of the massage signal the message we want to transmit to the amplitude of carrier signal. Modulation index for some common functions using frequency and phase modulation abstract the equations defining the amplitude of sidebands resulting from either frequency modulation or phase modulation by either squarewave, sinewave, sawtooth or triangular modulating functions are presented. Calculation of modulation index in fm signal babur 011919 i think answer given is wrong by mistake and fol is probably the right soulution. Frequency modulation or commonly referred to as fm is a common term that we hear in our daily lives. Know the relationship of carrier frequency, modulation frequency and modulation index to efficiency and bandwidth compare fm systems to am systems with regard to efficiency, bandwidth and noise. Angle modulation provides the improved noise performance. In this second experiment, we will examine the most common modulation scheme in daily life, namely, the frequency modulation, or fm. The fm modulation index is equal to the ratio of the frequency deviation to the.
Before we start discussing fm modulation we take a look at some important terms. Calculate modulation index, signal bandwidth, sideband frequencies and. Let us understand modulation index in fm frequency modulation. This can be seen by first writing the fm output signal in terms of nth order bessel functions of the first kind 2, 3. The process by virtue of which some characteristic, normally amplitutude, frequency, phase of a voltage signal is varied in accordance to the instantaneous value of some other voltage signal called carrier. The article will help especially the student to understand theory of fm modulation and related fm concepts in a much better way.
Understanding frequency modulation fm, frequency shift keying fsk, sundes fsk and msk and some more the process of modulation consists of mapping the information on to an electromagnetic medium a carrier. The spectrum of an fm signal is quite complicated and is dependent on mf. For small values of m f, the values of the j coefficients are as under. Slide 6 narrow band fm slide 7 bandwidth of an fm signal slide 8 demod.
It can be seen in figure 8 that phase and frequency modulation are closely related. The modulation index determines the number of significant pairs of sidebands in an fm signal. Pdf on jan 1, 2010, geng peng and others published modulation index estimation of frequency and phase modulated signals find, read. It is defined differently in each modulation scheme. Difference between amplitude modulation and frequency. In fm, modulation index is the ratio of frequency deviationfd to the modulating frequency fm. Phase modulation pm amount of phase change on angle of carrier is proportional to intelligence amplitude frequency modulation fm frequency change on angle. But phase modulation seems to be in a different categorypm radio is by no means a common term.
Today, fm is used widely in radio communication and broadcasting. The average power of an fm wave may also be determined from. We know that the modulation index of nbfm wave is less than one. Frequency modulation fm is used extensively in audio communication and data transfer. Armstrong, a radio pioneer who invented first the regenerative and then the superheterodyne receiver in the 1910s, worked on the principles of frequency and phase modulation starting in. Principles of communication modulation a signal can be anything like a sound wave which comes out when you shout.
Mar 05, 2019 the modulation index affects the modulated sinusoid in that the larger the modulation index, the greater the instantaneous frequency can be from the carrier. Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index. Performance of pulse code modulation phase modulation. The amplitude of the carrier component of an fm wave is dependent on the modulation index.
Subjects include modulation methods, modulation degree and sideband amplitude, zero span and markers, the fast fourier transform, special forms of amplitude modulation, angular modulation, bandwidth of fm signals, fm measurements with the spectrum analyzer, and am plus fm incidental fm. It is also possible to change the frequency of a signal to give frequency modulation or fm. These notes define the angle modulated signal, of which pm and fm are special cases. Fm modulation with modulating frequency 1, carrier frequency 10 and modulation index 2. The frequency modulation index is the equivalent of the modulation index for am, but obviously related to fm. Fm concepts explained what is frequency modulation. Recall, the bandwidth of a complex signal like fm is the difference between its highest and lowest frequency components, and is expressed in hertz hz.
A simple method to achieve fm is to vary the capacitance of a resonant lc circuit in a transmitter. Principles of communication modulation tutorialspoint. This 26page application note provides information on amplitude and frequency modulation. To answer this, we must turn to the second attribute of the modulator its gain, a 2 and introduce a new concept called the modulation index, or simply. In radio transmission, an advantage of frequency modulation is that it. Frequency modulation objectives upon completion of this chapter, the student should be able to. Frequency modulation an overview sciencedirect topics. It is also used in telemetry, radar, seismic prospecting, and monitoring newborns for seizures via eeg, twoway radio systems, music synthesis, magnetic taperecording systems and some videotransmission systems.
Frequency modulation is widely used on frequencies above 30 mhz, and it is particularly well known for its use for vhf fm broadcasting. When modulation index is multiplied by 100, the degree of modulation is expressed as a percentage. Apr 23, 2016 frequency modulation fm modulation fm wave equation modulation index of fm frequency deviation duration. Amplitude modulation a1 49 you will see in this experiment, and in others to follow, that there is no problem in generating an am signal with a depth of modulation exceeding 100%, and without any rf distortion whatsoever. Spectra have a typical trapezoidal shape in linear frequency and amplitude in decibels. For both phase and frequency modulation, the modulating signal causes the carrier to increase and decrease. Angle modulation modulation where the angle of a sinewave carrier is varied as a function of the intelligence amplitude.
As in other modulation systems, the modulation index indicates by how much the modulated variable. Difference between amplitude modulation and frequency modulation type of modulation. Depending to this modulation index fm can ne classified into two types narrowband fm. Explain the advantages and disadvantages of the different analog modulation techniques.
Frequency modulation fm in frequency modulation, the frequency rather than the amplitude of the carrier wave is made to vary in proportion to the varying amplitude of the modulating signal, as shown in fig. The index of modulation of an fm signal of the form. In frequency modulation, the amplitude and phase of the. Analysis of the fm spectruspectrummm introduction introduction to understand the next few experiments it is necessary to have a basic understanding of the nature of phase modulated pm and frequency modulated fm signals. Carrier signal is the higher frequency wave with higher energy to carry the message signal to long dis. When the frequency of carrier wave is changed in accordance with the intensity of the signal, the process is called frequency modulation. The modulation index affects the modulated sinusoid in that the larger the modulation index, the greater the instantaneous frequency can be from the carrier. In view of the differences between the two forms of modulation, the fm modulation index is measured in a different way. Lecture 2829 fm frequency modulation pm phase modulation. Frequency modulation is widely used for fm radio broadcasting. Spectrum analysis amplitude and frequency modulation an. Modulation fm, amplitude shift keying ask, phase shift keying psk, etc. The history and evolution of angle modulation basically revolves around one man, major edwin armstrong. Hence, in order to get the required modulation index greater than one of fm wave, choose the frequency multiplier value properly.
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