All this does is produce a stronger rf field like a typical ham whos running a transmitter with about 100 watts output on cw, and then turning his 1kw amplifier. Frequency modulation is still in widespread use, both for broadcasting and for two way radio communications. When expressed as a percentage it is the same as the depth of modulation. Pdf response of a fabryperot optical cavity to phase. The sidebands carry the information transmitted by the radio signal.
As a result, a knowledge of the signal bandwidth and the way in which the sidebands are produced is useful for these systems. Phase modulation pm is used primarily in digital communication amplitude, frequency and phase modulation. A discussion of the fourier transform, how it captures phase information, and how the fourier transform of simple signals creates sidebands. This may cause serious interference to other users if not filtered. Quadrature modulation and single side band ssb duration. Analytical solution for modulation sidebands associated with. Such overmodulated wave causes interference, which cannot be eliminated. In radio communications, a sideband is a band of frequencies higher than or lower than the carrier frequency, that are the result of the modulation process. Even for the pure tone modulation, the fm spectrum consists of an infinite number of sidebands whose signs change from one sideband to the next one and. We introduce the symbol scriptxf in order to have useful terminology for the important concept of normalized am sideband power. Two signals are uncorrelated if their phase and amplitudes have different time distributions so that they do not cancel in a phase. Even for the pure tone modulation, the fm spectrum consists of an in nite number of sidebands whose signs change from one sideband to the next one and whose amplitudes are given by the horrible bessel functions. Frequency and phase, or angle, modulation systems on the other hand are nonlinear.
Amplitude modulation envelope maxima occur when the two sideband signals are in phase with one another and with the carrier envelope minima occur when the sidebands are in phase with one another, but 180 degrees out of phase with carrier envelope center occurs when sidebands are absent or are 180 degrees out of phase with one another. Fm frequency modulation pm phase modulation continued ee44510 22 narrowband fm only the j o and j 1 terms are significant same bandwidth as am using eulers identity, and. Phase modulation is one of the two principal forms of angle modulation, together with frequency modulation. The deviation ratio is the maximum frequency deviation divided by the maximum modulating frequency. The modulated signal has the information in the whole band except at the carrier frequency. Amplitude modulation can be thought of s mixing the audio signal and the carrier signal, resulting in 3 signals the carrier itself, the sum of the carrier and the audio, and the difference between the carrier and the audio. When the timevarying phase offset is, the modulation depth is 2 full modulation depth occurs when the modulation depth 1. A phase modulated beam has a carrier and sidebands spaced by frequency the. Pdf photonic rf phase shifter based on optical carrier and. If modulation causes changes in either pulse height or duty ratio, there is a corresponding modulation of the d. Osa photonic rf phase shifter based on optical carrier and. Angle modulation automatic frequency control modulation for a list of other modulation techniques. In radio communications, singlesideband modulation ssb or singlesideband suppressedcarrier modulation ssbsc is a type of modulation used to transmit information, such as an audio signal, by radio waves. Stronger signal, but if hes still using cw, there are no sidebands.
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. Phase modulation pm is a modulation pattern for conditioning communication signals for. Angle modulation is the process in which the frequency or the phase of the carrier varies according to the message signal. Amplitude modulation an overview sciencedirect topics.
The percent modulation can be varied simply by changing the amplitude of the 30 khz carrier signal. With digital signals the closest digital modulation format is pulse amplitude modulation pam. I and q are the in phase and quadrature components of a signal. Since the amount of phase shift is varying, the effect is. It encodes a message signal as variations in the instantaneous phase of a carrier wave. Here, the carrier amplitude is not constant, but when all sidebands are included, the carrier is. Pdf an optical single sideband ossb generation method using phase modulation in semiconductor optical amplifier soa is proposed to. In this experiment, you will examine the characteristics of amplitude modulation am. Pdf response of a fabry perot optical cavity to phase. Amplitude and frequencyphase modulation zurich instruments. An optical single sideband ossb generation method using phase modulation in semiconductor optical amplifier soa is proposed to overcome the dispersioninduced carrier suppression problem which. Mar 26, 2015 machinery fault diagnosis and signal processing by prof. The worldwide endeavor to build long baseline laser interferometers to detect and study gravitational radiation is well under way.
Transmitter radio receiver between transmitter and radio receiver. Phase modulation pm is a modulation pattern for conditioning communication signals for transmission. The spectrum and bandwidth of a amplitude modulated signal are determined by the sidebands that are generated when amplitude modulation is applied to the carrier. Understanding the cause of sidebands in amplitude modulation. The information signal frequency also deviates the carrier frequency in pm. Aug 21, 2015 amplitude modulation can be thought of s mixing the audio signal and the carrier signal, resulting in 3 signals the carrier itself, the sum of the carrier and the audio, and the difference between the carrier and the audio. The other type of modulation in continuouswave modulation is the angle modulation. A second, and perhaps more correct, definition of compatible single sideband cssb refers to a form of amplitude and phase modulation in which the carrier is transmitted along with a series of sidebands that are predominantly above or below the carrier term. Transmission in which only one sideband is transmitted is called singlesideband modulation or ssb. These notes define the angle modulated signal, of which pm and fm are special cases.
With am, ie carrier with two sidebands, the carrier of the transmitted signal mixes with the sidebands on the receivers detector to get back to baseband. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note. Three frequencies result, the carrier, and two sidebands. With ssb, ie a single sideband with no carrier, the carrier has to be inserted at the receiver end, so the sideband can be mixed down to baseband. 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. In these sequences the rotor period is split up by a series of pulses. Set channel b to be a 29khz sine wave, amplitude 1v, phase 90deg, destination out1 set channel c to be a 31khz sine wave, amplitude 1v, phase 270deg, destination out1 at this point, you should have a 100 % amplitude modulated signal. This will absolutely beneficial to those aspiring to become professional engineers by taking the board exam and eventually to become successful in their chosen field. Heinzel advanced optical techniques for laserinterferometric. Understanding the phasing method of single sideband. Pdf photonic rf phase shifter based on optical carrier.
If the value of the modulation index is greater than 1, i. 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. Optical single sideband signal generation using phase modulation of semiconductor optical amplifier article pdf available in ieee photonics technology letters 165. It is based on controlling the amplitude and phase of the optical carrier and the two rf modulation sidebands via the dc bias voltages to a dualparallel machzehnder modulator dpmzm. Two signals are uncorrelated if their phase and amplitudes have different time distributions so that they do not cancel in a phase detector. Analytical solution for modulation sidebands associated.
The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. Since the amplitude of each sideband varies according to the strength of the modulation, as expressed by the modulation index, the sum of the contributions of each sideband becomes. The modulation depth is an expression of the extinction ratio of the phase offset function. Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index. The basis of measurement is that when noise modulation indices are small, correlation noise can be neglected.
Modulation sphere polar modulation electrooptic modulator for pockels effect phase modulation for applying sidebands to a. By way of illustration let us consider the nbfm signal s. Another important point about the modulation index. Therefore, both fm and pm are often referred to as angle modulation. Phase modulation, like all other signal modulation, generates sidebands in the frequency spectrum. The sidebands consist of all the spectral components of the modulated signal except the carrier. Frequency and phase or angle modulation systems on the other hand are nonlinear. The spectrum of the modulated signal y t does not contain the spectrum of the original. Then the phase shift is used to cancel one of the sidebands it can be either the upper sideband or the lower sideband. In my internet searching, i found the ssb information available on the net to be either badly.
Since the sidebands are mirror images, which sideband is used is a matter of convention. Phase angle is not absolute, but relates to some arbitrary reference. The carrier amplitude is unchanged, but the sideband amplitude is directly proportional to the modulation. Thus in pure pm which must stay on the unit circle meaning no am, we will see additional sidebands appear as the angles increase which serve the purpose of keeping the net sum of all the phasors involved. Photonic rf phase shifter based on optical carrier and rf modulation sidebands amplitude and phase control article pdf available in journal of lightwave technology 3023. Response of a fabryperot optical cavity to phase modulation sidebands for use in electrooptic control systems. Response of a fabry perot optical cavity to phase modulation. The amplitude modulation am modulation index can be defined as the ratio of the peak value of the message signal to the amplitude. Lecture 2829 fm frequency modulation pm phase modulation. Single sideband modulation ssb standard am and dsbsc techniques are wasteful of bandwidth because they both require transmission bandwidth of 2b hz, where b is the bandwidth of the baseband modulating signal mt. Dec 01, 2012 photonic rf phase shifter based on optical carrier and rf modulation sidebands amplitude and phase control article pdf available in journal of lightwave technology 3023. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. The number of signicant spectral components is a function of argument see table1. As seen in the animation, the higher order sidebands are necessary to keep the amplitude of the resultant phasor in red constant and thus produce pure phase modulation.
This shows that for small modulation depths the modulated light is composed of three frequency components. Amplitude modulation am frequency modulation fm phase modulation pm click on the links given above to know more. Pdf optical single sideband signal generation using phase. For larger angles, the phase modulation is the same but an incidental am will be introduced if we are limited to having only two sidebands. Ssb is the predominant voice mode on shortwave radio other than shortwave broadcasting. A sideband is a band of frequencies, containing power, which are the lower and higher frequencies of the carrier.
Mohanty,department of mechanical engineering,iit kharagpur. Multiple choice questions and answers on amplitude modulation. Understanding phase, sidebands and complex frequency plots. Aug 30, 20 technical explanation of amplitude and doublesideband modulation using an ocilloscope and spectrum analyzer. But as best as i can imagine it, modulating the amplitude of a fixedfrequency carrier wave just makes that louder or quieter, not higherfrequency or lowerfrequency. Amplitude modulation is said to be linear modulation, because as a system it behaves like a linear system. Amplitude and frequency phase modulation i always had di culties in understanding frequency modulation fm and its frequency spectrum. We will study two forms of amplitude modulation, singlesideband, frequency modulation, phase modulation, and some lesserused techniques. Aug 11, 2019 amplitude modulation equation with sidebands. A phase modulated beam has a carrier and sidebands spaced by frequency the modulation frequency f m, as long as f m. What this means acoustically is that the amplitudes of the two sidebands will add together, influenced as well by the phase inversion of the reflected sideband. Optical amplitude and phase modulation dynamics at the. Modulationtypesamplitude,frequency,phase modulation. Amplitude modulation early radio ee 442 spring semester.
Parallel phase modulation scheme for interferometric. Since the three variables are the amplitude, frequency, and phase angle, the modulation can be done by varying any one of them. The amplitude modulation, am bandwidth is important when designing filters to receive the signals, determining the channel spacing, and for a number of other reasons. Phase modulation on the other hand would instead move the phasor on a circle red line, with no changes to its radius. In both cases the transmission bandwidth b t is occupied by the upper sideband usb and lower sideband lsb. Share your notes in amplitude modulation and singlesideband modulation. Ive read it many places that amplitude modulation produces sidebands in the frequency domain. Due to this phase reversals, there is a rise in additional sidebands resulting from the phase reversals phase modulation that extend out, to infinity theoretically. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. As the value of modulation index increases, the carrier experiences a 180 phase reversal, which causes additional sidebands and hence, the wave gets distorted. Interest in angle modulation is due to the decreasing effect of noise or interferences when compared with am, although at the cost of a much wider bandwidth and complexity in implementation. The phase shift method uses two balanced and identical to eliminate the carrier. Phase modulation pm is a different form of frequency modulation and the carrier is similar in appearance to a frequencymodulated carrier.
Two basic properties available for modulation are the amplitude characteristics and angular characteristics of the carrier. Quantum model for electrooptical phase modulation arxiv. In the german british geo600 project, it is proposed to pass the sidebands induced on the light by an electrooptic. Now it is obvious that during am modulation process sidebands are generated. This is further divided into frequency and phase modulation. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. The modulation depth is an expression of the extinction.
Process by which a property or a parameter of a signal is varied in proportion to a second signal. The modulation index determines the number of significant pairs of sidebands in an fm signal. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. The spectrum consists of sidebands, spaced by u m, with phase dependent on sideband, and amplitude given by the bessel functions. But ssb demodulation information at that web site was terribly sparse. The spectrum of unmodulated narrowband laser light consists of a single peak at the laser carrier frequency. I and q components in communications signals and single sideband. Phase modulation amplitude modulation frequency modulation. You can see how each pair of higher order sidebands is needed to correct the deviation from a circular arc introduced by the lower order sidebands. Frequency modulation an overview sciencedirect topics. Angular modulation is ordinarily subdivided into the more familiar categories of frequency modulation and phase modulation. Modulation transfers energy from the laser carrier to sidebands. In the process of amplitude modulation or phase modulation, the modulated wave consists of the carrier wave and two sidebands. The modulation index m of an fm signal is the ratio of the frequency deviation fd to the modulating frequency fm m fd fm.