Modulation translates the signal from one region of frequency domain to. It is in the field of telecommunications and signal processing, that this kind of technique is mostly used. The subject is new and all of its ramifications and prob lems are not known as yet, hence this volume of compara tively few pages is not intended as a complete exposition of the subject. Fm modulated signal st is a nonlinear function of the modulating signal mt, thus it is known as nonlinear modulation process. Frequency modulation is a form of modulation, which represents information as variations in the instantaneous frequency of a carrier wave. Wide band fm first lets know about the frequency modulation 3. Or modulation is defined as the precess by which some characteristics, usually amplitude, frequency or phase, of a carrier is varied in accordance with instantaneous value of some other voltage. This is important because most external noise is in the form of voltage.
Principles of communication systemsi class central. If we do phase modulation it is nothing but a frequency modulation. Phase modulation pm is a different form of frequency modulation and the carrier is similar in appearance to a frequency modulated carrier. The carrier amplitude is constant and the phase variation of the signal contains the information. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note. In frequency modulation fm, unlike am, the amplitude of the carrier is kept constant, but its frequency is altered in accordance with variations in the audio signal being sent. The first frequency modulation was invented by edwin howard armstrong in december181890 4. The advantage of fm over am is the greater suppression of noise at the expense of bandwidth in fm. Pulse modulation timedivision multiplex tdm continued advantages of tdm the circuitry required is digital, thus affording high reliability and efficient operation. Next month, well take a closer look at some practical aspects of frequency modulation, and introduce the idea of operators a common. Frequency modulation is the process in which the frequency of the carrier signal is varied by the modulating signal while the amplitude remains constant.
A number of signals were combined to send through a single cable. In frequency modulation, the instantaneous frequency of the carrier wave is modified in order to transmit information. Frequency modulation objectives upon completion of this chapter, the student should be able to. Lecture 35 noise in am and angle modulation systems. There are two common forms of angle modulation, namely, phase modulation and frequency modulation. An important feature of angle modulation is that it. Angle modulation, description of phase modulation pm and frequency modulation fm lecture 29 frequency modulation fm with sinusoidal modulation. The classic definition of fm is that the instantaneous output frequency of a transmitter is varied in accordance with the modulating signal. Discuss the differences between am and angle modulation.
Interpreting vibration spectrum and twf patterns understanding motion through pattern recognition. Nov 11, 2016 frequency modulation is widely used for radio transmission due to the fact that the signaltonoise ratio snr is large in this method of modulation and hence radio frequency interference is minimized. Indian institute of technology kanpur and nptel via swayam. Study on intrawave frequency modulation phenomenon in detection of rubimpact fault article pdf available in mechanical systems and signal processing 122. I mean, i am not playing wav file, and i cannot just speed up its playback. It is analogous to pulsewidth modulation pwm, in which the magnitude of an analog signal is encoded in the duty cycle of a square wave. The frequency components present in the am wave are represented by vertical lines approximately located along the frequency axis. Calculate modulation index, signal bandwidth, sideband frequencies and.
The full audio spectrum ranges form 20 to 20,000 hz, but fm radio limits the upper modulating frequency to 15 khz cf. The frequency band for fm radio is about 88 to 108 mhz. In amplitude modulation, the amplitude of the carrier wave is modified in order to transmit information. From the above information, finally, we can conclude that, in frequency modulation, both efficiencies as well as bandwidth depends on the maximum the modulation index and modulating frequency. Audio signals transmitted by fm radio communications are the most common. Types of modulation 6 flynnkatz 7810 analog modulation amplitude modulation, am frequency modulation, fm double and single sideband, dsb and ssb digital modulation phase shift keying. Frequency modulation fm is an important modulation scheme both because of its widespread commercial use, and because of its simplicity.
Oct 09, 2014 frequency modulation and its application 1. Frequency modulation, phase modulation, and fm spectra. Therefore, both fm and pm are often referred to as angle modulation. Fm signals are used in technology such as radars, telemeters, eeg, radio broadcasting, satellite communication and magnetic tape recording systems. Pdf gearbox vibration signal amplitude and frequency modulation. As we have seen in this document, frequency modulation can be simplified to angle modulation with a simple integrator. An important feature of angle modulation is that it can provide better. Frequency modulation, or fm, is an important method of impressing information on a carrier. To generate a frequency modulated signal, the frequency of the radio carrier is changed in line with the amplitude of the incoming audio signal. A ring modulator is an electronic device for ring modulation. Using amplitude modulation to shift the baseband signal fm radio 88mhz108 mhz. Dey, department of electrical engineering,iit bombay.
The main features are high fidelity transmission and a modulation system that avoids some of the interference. We also mentioned that frequency modulation fm and phase modulation pm can also be used. While this is the simplest technique available, it is nonlinear since a first order lowpass filter response falls as. Besides, it is simpler than the modulators and demodulators required in frequency division multiplexing fdm. Frequency modulation is a form of analog angle modulation in which the baseband informationcarrying signal, typically called the message or information signal mt, varies the frequency of a carrier wave. If the problem frequency is 1 x rpm, the answer to. When the audio signal is modulated onto the radio frequency carrier, the new radio frequency signal moves up and down in frequency. Frequency modulation keeps constant the amplitude of the high frequency oscillation that is used as a signal and to vary the instantaneous frequency for presenting the information. In telecommunications and signal processing, frequency modulation fm is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave in analog frequency modulation, such as fm radio broadcasting of an audio signal representing voice or music, the instantaneous frequency deviation, the difference between the frequency of the carrier and its center. Lecture 12 digital modulation techniques part 1 youtube. Lecture 36 noise in phase and frequency modulation systems. Pulse frequency modulation pfm is a modulation method for representing an analog signal using only two levels 1 and 0. This is further divided into frequency and phase modulation.
In analog applications, the carrier frequency is varied in direct proportion to changes in the amplitude of an input signal. Fm does not touch the amplitude of the carrier and. Lecture 36 noise in phase and frequency modulation systems duration. Different types of modulation techniques in communication systems. Frequency modulation fm varies the frequency of the carrier in proportion to the message or data signal while maintaining other parameters constant. Though less intuitive than amplitude modulation, frequency modulation is still a fairly straightforward method of wireless data transmission. Gearbox vibration signal amplitude and frequency modulation article pdf available in shock and vibration 194. Surendra prasad, department of electrical engineering,iit delhi. The left and right channels each limited to 15khz are multiplexed into a single baseband signal using amplitude modulation using frequency modulation to shift the baseband. Frequency modulation fm one frequency carrier is speeding up and slowing down. Amamplitude modulation fm frequency modulation pmphase modulation in phase modulation, modulation index is directly proportional to modulating voltage only while in frequency modulation, modulation index is also inversely proportional to modulat. Explain the advantages and disadvantages of the different analog modulation techniques. The simplest method for representing this kind of modulation is fresnels vectorial representation with. This form of modulation was developed by the american electrical engineer edwin h.
In an earlier section we saw how amplitude modulation am can be used to convey information. Sep 15, 20 lecture series on communication engineering by prof. The big advantage of frequency modulation is its noise reduction ability, because most of noise is appeared as additional amplitude and in fm the amplitude of signal is hold fixed. First, since fm only changes the frequency and not the amplitude of the carrier w ave, fm receivers can be built to ignore amplitude voltage changes. The process of modulation can be defined as varying the rf carrier wave in accordance with the intelligence or information in a low frequency signal. The process of multiplexing divides a communication channel into several number of logical. The possibilities expand still further when we consider what happens when you use one audio frequency signal to modulate the frequency of another. Angle modulation is the process in which the frequency or the phase of the carrier varies according to the message signal. What is the difference between phase modulation and frequency. Amplitude modulation frequency spectrum frequency spectrum of am wave. Frequency modulation and its application slideshare. Learn for free, pay a small fee for exam and get a certificate.
Modulationtypesamplitude,frequency,phase modulation. Frequency and phase modulation sharlene katz james flynn overview history why fm. The aim of the exercise is to demonstrate the process of frequency modulation on the basis of the available test circuit, illustrating in detail the attributes, which are. In this experiment, you will examine the characteristics of amplitude modulation am. Lecture 2829 fm frequency modulation pm phase modulation. Narrowband frequency modulation narrowband fm means that the fm modulated wave has narrow bandwidth. Frequency modulation fm is the encoding of the information in a carrier wave by varying the instantaneous frequency of the wave. In effect, modulation converts ft to a bandpass form, in the neighborhood of the center frequency f c. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. What is fm, frequency modulation electronics notes. Recall that we can write an equation for a sine wave as follows. Frequency modulation fm modulation fm wave equation modulation index of fm frequency deviation duration. The other type of modulation in continuouswave modulation is the angle modulation.
As explained last month, audio frequency modulation of the amplitude of a signal can be a powerful synthesis tool. Chapter 2 concerns all the general problems of frequency modulation, while chapter 3 deals with the propagation distortion, which is apparent in a variablevelocity guided transmission channel, and, which appears on an echoing path either in free space, or over a badly matched feeder. Questions from video lectures of nptel sl no questions video number time in minutes 1 give some examples for the communication systems which use space as the channel. Frequency modulation download ebook pdf, epub, tuebl, mobi. Frequency modulation is a powerful method of synthesis that is as relevant to analogue synthesizers as it is to digital ones, and which is capable of generating sounds unobtainable by any other method. A ring modulator may be used in music synthesizers. The sound quality offered by am radio stations is poorer, having low. The guard bands are provided to prevent the interference between adjacent channels in fm signals.
However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is. The information signal is music and voice which falls in the audio spectrum. Lecture 35 noise in am and angle modulation systems youtube. Frequency modulation uses the information signal, v m t to vary the carrier frequency within some small range about its original value. Each radio station is assigned 200 khz, to transmit a stereo audio. The height of each vertical line is drawn in proportion to its. This section sets out the basic properties of fmpm signals and how we can produce them. As we know from amplitude modulation, we need two sine or cosine waves for modulation. Difference between amplitude modulation and frequency. This site is like a library, use search box in the widget to get ebook that you want. Fm is in contrast with amplitude modulation where amplitude of the carrier waves is modulated with frequency remaining unchanged and constant.
Multiplexing is the process of combining multiple signals into one signal, over a shared medium. In electronics, ring modulation is a signal processing function, an implementation of frequency mixing, performed by creating multiple frequencies from those of the two signals, where one is typically a sine wave or another simple waveform and the other is the signal to be modulated. We are all at least vaguely familiar with frequency modulationits the origin of the term fm radio. Frequency modulation frequency modulation is the process by which frequency of the carrier signal ct changes with respect to the modulating signal mt. The spectrum of an fm signal is quite complicated and is dependent on mf. Example commercial fm signals use a peak frequency deviation of.
With at being maybe nonperiodic, its maybe frequency modulation. Click download or read online button to get frequency modulation book now. Angle modulation modulation where the angle of a sinewave carrier is varied as a function of the intelligence amplitude. Principles of communication multiplexing tutorialspoint. Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index.
Lecture series on communication engineering by prof. Frequency modulation is a new development in the art of radio, and short cuts should be used only when the features that frequency modula tion stands for are not violated. Nptel, online courses and certification, learn for free. When we do frequency modulation, we are differentiating the particular modulating signal which then automatically depicts it as phase modulation. Phase modulation pm amount of phase change on angle of carrier is proportional to intelligence amplitude frequency modulation fm frequency change on angle.
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