Amplitude and phase can be modulated simultaneously and separately. Phase modulation pm amount of phase change on angle of carrier is proportional to intelligence amplitude frequency modulation fm frequency change on angle. If modulating signal ft has a bandwidth of 6 bw, then f6, the spectrum of ft, will. In this video, i have explained frequency modulation fm by following outlines. Berrou c, glavieux a, thitimajshima p 2010 near shannon limit errorcorrecting pdf. What is frequency deviation, what is bandwidth of fm wave, carsons rule related videos 1. The two common forms of analog modulation are amplitude modulation am and frequency modulation fm which is speci. Invented in 1933 by american engineer edwin armstrong, wideband fm is used worldwide to provide highfidelity sound over broadcast radio. Slide 3 discretetime fm modulator slide 4 single tone fm modulation slide 5 single tone fm cont. For small values of the modulation index, the spectrum of the fm wave is effectively limited to one pair of sidefrequencies at so that the bandwidth approaches. We will get the percentage of modulation, just by multiplying the modulation index value with 100. Anglemodulation,ii lecturetopics fmbandwidthandcarson.
Nbfm has power 1 2a 2, which does not depend directly on mt. When noise occurs naturally in radio systems, frequency modulation with sufficient bandwidth provides an advantage in cancelling the noise. 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. Modulation bandwidth an overview sciencedirect topics.
For amplitude modulation the bandwidth occupied by a signal is twice the highest audio frequency in the modulation. Once a signal has been modulated, information is retrieved through a demodulation process. An fm signal with a modulation index 9 is applied to a frequency tripler. The major advantage of this approach is that it allows the tradeoff between bandwidth and noise performance. These notes define the angle modulated signal, of which pm and fm are special cases. The bandwidth of an fm signal depends on the modulation index mf, and is approximated by the wellknown. But phase modulation seems to be in a different categorypm radio is by no means a common term. The subsystem that takes the information signal and processes it prior to transmission.
Principles of communication modulation a signal can be anything like a sound wave which comes out when you shout. The modulation bandwidth of the rsoa is typically in the range of ghz. 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. Fm modulation with modulating frequency 1, carrier frequency 10 and modulation index 2. Angle modulation changes the phase of a signal as well as its amplitude, where amplitude modulation leaves the phase unchanged. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Fmdirectdigitalsynthesis currently, it is very common to synthesize the fm waveform digitally either at an intermediate frequency fi and then mix it up to the desired carrier, or. What is fm, frequency modulation electronics notes. This shout can be heard only up to a certain distance. 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. In radio transmission, an advantage of frequency modulation is that it. In general the determination of the frequency content of an fm waveform is complicated, but when. Frequency and phase modulation have a variety of desirable features but may not provide the required bandwidth efficiency, especially for higher bit rates.
Amplitude distortion of narrowband fm ideally, fm wave has a constant envelope but, the modulated wave produced by the narrowband fm differ from this ideal condition in two fundamental respects. Some phase modulation and quadrature amplitude modulation formats have a higher spectral efficiency for data transmission than frequency shift keying, a form of frequency modulation. Amplitude modulation in the form of single sideband is still used for hf radio links. Phase modulation, and frequency modulation are both the modulation techniques analyzed in angle modulation. To limit the bandwidth of the transmission, filters are often used. This is different from the amplitude modulation am in which the amplitude of the carrier wave is varied while its frequency remains constant. Am works by modulating varying the amplitude of the signal or carrier transmitted according to the information being sent, while the frequency remains constant. However, it usually becomes smaller than this maximum value due to the electrical parasitics associated with the packaging. Narrowband frequency modulation narrowband fm means that the fm modulated wave has narrow bandwidth. From this it can be seen that the narrower the filter bandwidth the greater the frequency resolution. For wideband fm, the frequency deviation contributes to fm bandwidth. An important feature of angle modulation is that it can provide better.
Frequency modulation fm is the method of conveying informations over a carrier wave by varying its frequency. This type of modulation is commonly used for broadcasting music and speech, magnetic tape recording systems, two way radio systems and video transmission systems. Figure 511 magnitude spectra for fm or pm with sinusoidal modulation for various modulation indexes. Frequency modulation is widely used for fm radio broadcasting. Angle modulation, ii lecture topics fm bandwidth and carsons rule. Here is 1mhz carrier signal signwave with an amplitude of 2v peak to peak pp or 1v peak. They are normally significant for wideband frequency modulation transmissions, although small for narrow band fm. Frequency modulation an overview sciencedirect topics. Frequency modulation is widely used on frequencies above 30 mhz, and it is particularly well known for its use for vhf fm broadcasting. This assumes no distortion in the modulation process which would cause a larger bandwidth to be occupied. Frequency modulation consists of encoding information onto a carrier signal by varying the frequency of the carrier.
Using a lower bandwidth and providing more effective. The subsystem that takes the information signal and processes it. Is a nonlinear function of the modulating signal mt, which makes frequency modulation a nonlinear modulation process. For amplitude modulated wave, the bandwidth is given by. In fm, the amplitude of the modulating carrier is kept constant while its frequency is varied by the modulating message signal. Frequency modulation the fm signal st defined by equation 2. Modulation fm, amplitude shift keying ask, phase shift keying psk, etc. The bandwidth is the difference between lowest and highest frequencies of the signal. For large values of the modulation index, the bandwidth approaches, and is only slightly greater than the total frequency excursion. Jul 30, 2019 this type of modulation is commonly used for broadcasting music and speech, magnetic tape recording systems, two way radio systems and video transmission systems.
Ee4512 analog and digital communications chapter 6 the dsbsc am coherent receiver has a bandpass filter centered at f c and with a bandwidth of twice the bandwidth. Frequency modulation and phase modulation are closely related. The modulation index in the output signal will be a 0 b 3 c 9 d 27 gate 1996. The sidebands for an fm transmission theoretically extend out to infinity. This bandwidth is in principle determined by the carrier lifetime 204. Angle modulation modulation where the angle of a sinewave carrier is varied as a function of the intelligence amplitude. Carsons rule, calculating fm modulation bandwidth fm systems. Armstrong, known as one of the founding fathers of radio technology, invented the superheterodyne radio receiver in 1918 and frequency modulation fm in 1933 1. Phase modulation is another type of angle modulation very similar to frequency modulation. Dec 26, 2018 this ezed video explains frequency modulation. The modulation takes place by varying the three parameters of the sinusoid carrier. Phase modulation is similar to frequency modulation and is an important technique in digital communication systems. Frequency modulation frequency deviation bandwidth of fm. Anglemodulation,ii lecturetopics fmbandwidthandcarsonsrule.
Consequently, unlike amplitude modulation, the spectrum of an fm signal is not related. Understand the bandwidth requirement channel bandwidth signal bandwidth understand the principle of amplitude modulation know how to modulate a signal to a certain frequency know how to demodulate a signal back to the baseband can write the equation and draw block diagram for both modulation and demodulation. Angle modulation provides the improved noise performance. While changing the amplitude of a radio signal is the most obvious method to modulate it, it is by no means the only way. The modulation index or modulation depth is often denoted in percentage called as percentage of modulation. Both transmit the information in the form of electromagnetic waves. Principles of communication modulation tutorialspoint. This approach is called angle modulation, and includes frequency modulation fm and phase modulation pm. 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. With an fm transmission bandwidth of 200 khz and a message signal bandwidth of 15 khz 5. Slide 6 narrow band fm slide 7 bandwidth of an fm signal slide 8 demod. There are two common forms of angle modulation, namely, phase modulation and frequency modulation.
Signals and spectrum lets first discuss sinewave signals using the diagram below of a 1mhz carrier signal. What is the difference between bandwidth and modulation. Similarly, the narrowband approximation for phase modulation is. Fm radio the bandwidth of an audio signal speech and music in is almost 15 khz. 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. 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. Frequency modulation is that from of angle modulation in which the instantaneous frequency if. The envelope contains a residual amplitude modulation that varies with time the angle contains harmonic distortion in the form of third. The amplitude of the carrier is maintained constant. Am has only two sidebands usb and lsb and the bandwidth was found. In this second experiment, we will examine the most common modulation scheme in daily life, namely, the frequency modulation, or fm. Carsons rule is a formula that is used to determine the rf bandwidth or occupancy for an fm signal. Am or amplitude modulation and fm or frequency modulation are ways of broadcasting radio signals. Since frequency modulation is a nonlinear process, an exact description of the. Digital modulation in communications systems an introduction. Early investigators thought that narrowband fm could have arbitrar ily narrow bandwidth, allowing more channels than am.
518 619 415 1250 177 1323 859 179 816 1338 45 378 323 1273 623 82 1017 724 623 1088 1244 1548 1261 416 178 1274 783 497 412 562 659 560 898