We will study two forms of amplitude modulation, singlesideband, frequency modulation, phase modulation, and some lesserused techniques. The carrier amplitude is unchanged, but the sideband amplitude is directly proportional to the modulation. Since the sidebands are mirror images, which sideband is used is a matter of convention. Stronger signal, but if hes still using cw, there are no sidebands. Quantum model for electrooptical phase modulation arxiv. If the value of the modulation index is greater than 1, i.
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. The worldwide endeavor to build long baseline laser interferometers to detect and study gravitational radiation is well under way. This shows that for small modulation depths the modulated light is composed of three frequency components. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. The modulation index determines the number of significant pairs of sidebands in an fm signal. The other type of modulation in continuouswave modulation is the angle modulation. Understanding the cause of sidebands in amplitude modulation. Understanding phase, sidebands and complex frequency plots. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation.
The modulation depth is an expression of the extinction. Pdf optical single sideband signal generation using phase. Response of a fabry perot optical cavity to phase modulation. 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. In the process of amplitude modulation or phase modulation, the modulated wave consists of the carrier wave and two sidebands. Pdf an optical single sideband ossb generation method using phase modulation in semiconductor optical amplifier soa is proposed to. Amplitude modulation an overview sciencedirect topics. 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. 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. Multiple choice questions and answers on amplitude modulation. Heinzel advanced optical techniques for laserinterferometric. 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. Frequency modulation an overview sciencedirect topics. 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.
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. Mar 26, 2015 machinery fault diagnosis and signal processing by prof. The spectrum consists of sidebands, spaced by u m, with phase dependent on sideband, and amplitude given by the bessel functions. Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index. 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. When the timevarying phase offset is, the modulation depth is 2 full modulation depth occurs when the modulation depth 1. The deviation ratio is the maximum frequency deviation divided by the maximum modulating frequency. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. 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. This is further divided into frequency and phase modulation. In these sequences the rotor period is split up by a series of pulses. By way of illustration let us consider the nbfm signal s.
Quadrature modulation and single side band ssb duration. Angle modulation automatic frequency control modulation for a list of other modulation techniques. 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. Therefore, both fm and pm are often referred to as angle modulation. In both cases the transmission bandwidth b t is occupied by the upper sideband usb and lower sideband lsb. Such overmodulated wave causes interference, which cannot be eliminated. Since the amount of phase shift is varying, the effect is.
The sidebands carry the information transmitted by the radio signal. Frequency and phase, or angle, modulation systems on the other hand are nonlinear. Amplitude modulation early radio ee 442 spring semester. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. 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. 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. Share your notes in amplitude modulation and singlesideband modulation. With digital signals the closest digital modulation format is pulse amplitude modulation pam.
The modulated signal has the information in the whole band except at the carrier frequency. 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. 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. 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. Pdf photonic rf phase shifter based on optical carrier. Transmitter radio receiver between transmitter and radio receiver. Optical amplitude and phase modulation dynamics at the. Frequency modulation is still in widespread use, both for broadcasting and for two way radio communications. Modulation sphere polar modulation electrooptic modulator for pockels effect phase modulation for applying sidebands to a. Since the three variables are the amplitude, frequency, and phase angle, the modulation can be done by varying any one of them.
The basis of measurement is that when noise modulation indices are small, correlation noise can be neglected. Process by which a property or a parameter of a signal is varied in proportion to a second signal. 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. Modulationtypesamplitude,frequency,phase modulation. 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. Pdf response of a fabryperot optical cavity to phase. Phase modulation pm is used primarily in digital communication amplitude, frequency and phase modulation. The spectrum of the modulated signal y t does not contain the spectrum of the original. 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. Angular modulation is ordinarily subdivided into the more familiar categories of frequency modulation and phase modulation.
It encodes a message signal as variations in the instantaneous phase of a carrier wave. The modulation depth is an expression of the extinction ratio of the phase offset function. Analytical solution for modulation sidebands associated with. If modulation causes changes in either pulse height or duty ratio, there is a corresponding modulation of the d. Phase modulation pm is a different form of frequency modulation and the carrier is similar in appearance to a frequencymodulated carrier. 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. 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.
The information signal frequency also deviates the carrier frequency in pm. The webs wikipedia singlesideband modulation gives the mathematical details of ssb generation 1. Pdf response of a fabry perot optical cavity to phase. Amplitude and frequencyphase modulation zurich instruments. Osa photonic rf phase shifter based on optical carrier and. As a result, a knowledge of the signal bandwidth and the way in which the sidebands are produced is useful for these systems.
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. Optical single sideband signal generation using phase modulation of semiconductor optical amplifier article pdf available in ieee photonics technology letters 165. Pdf photonic rf phase shifter based on optical carrier and. These notes define the angle modulated signal, of which pm and fm are special cases. Two signals are uncorrelated if their phase and amplitudes have different time distributions so that they do not cancel in a phase. Frequency and phase or angle modulation systems on the other hand are nonlinear. 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. Phase modulation pm is a modulation pattern for conditioning communication signals for transmission. 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. The number of signicant spectral components is a function of argument see table1.
Two signals are uncorrelated if their phase and amplitudes have different time distributions so that they do not cancel in a phase detector. I and q components in communications signals and single. Phase noise and am noise measurements in the frequency. The spectrum of unmodulated narrowband laser light consists of a single peak at the laser carrier frequency. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. I and q components in communications signals and single sideband. This may cause serious interference to other users if not filtered. In the german british geo600 project, it is proposed to pass the sidebands induced on the light by an electrooptic.
Phase modulation, like all other signal modulation, generates sidebands in the frequency spectrum. I and q are the in phase and quadrature components of a signal. 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. Understanding the phasing method of single sideband. Mohanty,department of mechanical engineering,iit kharagpur. 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. The phase shift method uses two balanced and identical to eliminate the carrier. In the frame of the rotating carrier vector, the sidebands modulate the phase. 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. Here you can see the first term is the carrier, the second term is, contains the different of lower sideband and the third term contains the upper sideband. The modulation index m of an fm signal is the ratio of the frequency deviation fd to the modulating frequency fm m fd fm.
Now it is obvious that during am modulation process sidebands are generated. Angle modulation is the process in which the frequency or the phase of the carrier varies according to the message signal. Transmission in which only one sideband is transmitted is called singlesideband modulation or ssb. Adaptation of the information signal to the transmission channel.
Ssb is the predominant voice mode on shortwave radio other than shortwave broadcasting. Three frequencies result, the carrier, and two sidebands. 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. Parallel phase modulation scheme for interferometric. A phase modulated beam has a carrier and sidebands spaced by frequency the. 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. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note. The percent modulation can be varied simply by changing the amplitude of the 30 khz carrier signal. But ssb demodulation information at that web site was terribly sparse. Lecture 2829 fm frequency modulation pm phase modulation. A phase modulated beam has a carrier and sidebands spaced by frequency the modulation frequency f m, as long as f m. As the value of modulation index increases, the carrier experiences a 180 phase reversal, which causes additional sidebands and hence, the wave gets distorted. Phase modulation pm is a modulation pattern for conditioning communication signals for.
Ive read it many places that amplitude modulation produces sidebands in the frequency domain. When expressed as a percentage it is the same as the depth of modulation. Here, the carrier amplitude is not constant, but when all sidebands are included, the carrier is. Modulation transfers energy from the laser carrier to sidebands.
Phase modulation on the other hand would instead move the phasor on a circle red line, with no changes to its radius. A discussion of the fourier transform, how it captures phase information, and how the fourier transform of simple signals creates sidebands. Analytical solution for modulation sidebands associated. In my internet searching, i found the ssb information available on the net to be either badly. Two basic properties available for modulation are the amplitude characteristics and angular characteristics of the carrier. In this experiment, you will examine the characteristics of amplitude modulation am. Aug 11, 2019 amplitude modulation equation with sidebands. 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. 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. 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. Response of a fabryperot optical cavity to phase modulation sidebands for use in electrooptic control systems.
Aug 30, 20 technical explanation of amplitude and doublesideband modulation using an ocilloscope and spectrum analyzer. Phase modulation is one of the two principal forms of angle modulation, together with frequency modulation. Then the phase shift is used to cancel one of the sidebands it can be either the upper sideband or the lower sideband. Pdf optical single sideband signal generation using. Another important point about the modulation index. The sidebands consist of all the spectral components of the modulated signal except the carrier. 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. Frequency modulation and phase modulation are closely related.