Amplitude modulation in machine vibration signatures. Pdf 4amplitude modulator and demodulator circuits appi t. 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. Theory the reason why you get sidebands when you multiply by a sinusoidal carrier is the trig identity math\displaystylecosxcosy. Understanding the cause of sidebands in amplitude modulation. In radio communications, singlesideband modulation ssb or singlesideband suppressedcarrier. Frenzel selftest in amplitude modulation and singlesideband. In amplitude modulation, it is the voltage level of the signal to be transmitted. Amplitude modulation is done by a circuit called modulator. Then, amplitude modulate the signal using a sine with the same carrier frequency. The basic types of modulation are angular mo dulation including the special cases of phase and frequency modulation and amplitude modulation. Amplitude modulation and singlesideband modulation from the book communications electronics by louis e.
As the value of the modulation index increases, the carrier experiences a 180 o phase reversal, which causes additional sidebands and hence, the wave gets distorted. Now it is obvious that during am modulation process sidebands are generated. Single sideband modulation is normally used for voice transmission, but technically it can be used for many other applications where two way radio communication using analogue signals is required. Advantages and disadvantages of standard amplitude modulation. This is sometimes called double sideband amplitude modulation dsbam. Spectrum analysis amplitude and frequency modulation an 1501. A refinement of amplitude modulation, it uses transmitter power and bandwidth more efficiently. Practical circuitry is more likely to use a modulator, rather than the more idealised multiplier. Mar 26, 2015 machinery fault diagnosis and signal processing by prof.
Nov, 20 the amplitude of the carrier wave will vary in accordance with a modulator wave. Jul 22, 2019 we report on the method of the sideband amplitude modulation sam to achieve highsensitivity spectroscopy with a fiber electrooptic modulator fibereom. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. 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. Each of the two sidebands is equal in bandwidth to that of the modulating signal and is a mirror image of the other. 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. Many machines produce vibration signatures which contain amplitude modulation, and as we have seen in the introduction to vibration section, amplitude modulation causes sidebands to occur in the vibration spectrum. Single sideband amplitude modulation pdf in singlesideband ssb modulation only the upper sideband. The demodulation is performed by an envelope detector. Mohanty,department of mechanical engineering,iit kharagpur.
Phase shift of carrier transforms phase modulation into amplitude modulation. Ssb amplitude modulation reduces the bandwidth of the signal by half. 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. 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. The equations defining the amplitude of sidebands resulting from either frequency modulation or phase modulation by either squarewave, sinewave, sawtooth.
A theoretical study on the amplitude symmetry of sidebands in. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. 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. The message signal is, for example, a function of the sound to be reproduced by a. Process by which a property or a parameter of a signal is varied in proportion to a second signal. 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. To carry out ssb amplitude modulation, you must first compute the hilbert transform of the signal. Amplitude modulation of a carrier signal normally results in two mirrorimage sidebands. In the process of modulating a carrier, you are adding audio voice, if youre a ham. An imaginary line joining the peaks of the modulated carrier waveform, called the. Nov 16, 2019 when the amplitude of a highfrequency carrier wave is changed in accordance with the intensity of the signal, it is called amplitude modulation. Basics of amplitude and distortion measurements on a.
For amplitude modulated signals, the way in which these sidebands are created and their bandwidth and amplitude are quite straightforward. One signal carrier varies according to the changes in another signal modulator. 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. A sideband is a band of frequencies, containing power, which are the lower and higher frequencies of the carrier frequency.
Amplitude, frequency and phase modulation can be applied directly by software to the generated signals, which gives great flexibility where complicated and precise waveforms are required. What is sideband single sideband, dsbsc, and vestigial 2020. 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. Ive read it many places that amplitude modulation produces sidebands in the frequency domain. The signal components above the carrier frequency constitute the upper sideband usb, and those below the carrier frequency constitute the lower sideband lsb. Machinery fault diagnosis and signal processing by prof.
In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. The modulation of any carrier in any way produces sidebands. Modulation modulation is the process whereby some characteristic of one wave is v aried in accordance with some characteristic of another wave. Dec 01, 2012 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. The sidebands comprise all the spectral components of the modulated signal. If the modulated beam impinges on a square law detector, each of the sidebands beats with the carrier to produce a signal at the modulation frequency.
Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. Amplitude modulation, modulators, and demodulators ese 488. Aug 11, 2019 amplitude modulation equation with sidebands. 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.
Carriersideband picture negative phase shift no phase shift positive phase shift. The situation for frequency modulated signals is rather different. The amplitude of the two sidebands increases in proportion to the amount of modulation, but never exceeds half the level of the carrier. Abstracta new modulation scheme single sideband quadrature amplitude modulation ssb qam is proposed. Share your notes in amplitude modulation and singlesideband modulation. Three frequencies result, the carrier, and two sidebands. Vsb signals are generated using standard am or dsbsc modulation, then passing modulated signal through a. What is an intuitive way of explaining frequency sidebands in. Amplitude modulation generates a pair of sidebands for every sinusoidal component in the carrier and the modulator. From the start of the 20 century until now the main emphasis concerning amplitude. Subjects include modulation methods, modulation degree and sideband amplitude, zero span and markers, the fast fourier transform, special forms of amplitude. I dont know whether this is intuitive or not, but it can be followed without using any fourier stuff. Such overmodulated wave causes interference, which cannot be eliminated. It is strongly suggested that you examine your text book for other methods.
Single sideband modulation or ssb is derived from amplitude modulation am and ssb modulation overcomes a number of the disadvantages of am. As the value of modulation index increases, the carrier experiences a 180 phase reversal, which causes additional sidebands and hence, the wave gets distorted. Amplitude modulation, modulators, and demodulators ese 488 double sideband amplitude modulation am t figure 1 sinusoidal signal with a dc component in double sideband modulation the usual am a dc component is added to the signal voltage before the signal is multiplied by a carrier. Reviewer in amplitude modulation and singlesideband. In the process of amplitude modulation or phase modulation, the modulated wave consists of the carrier wave and two sidebands.
Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. The carrier amplitude is unchanged, but the sideband amplitude is directly proportional to the modulation. The sidebands carry the information transmitted by the radio 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. Aug 30, 20 technical explanation of amplitude and doublesideband modulation using an ocilloscope and spectrum analyzer.
A type of single sideband amplitude modulation that uses techniques such as compression and expansion to enhance signal transmission and reception in. Pdf photonic rf phase shifter based on optical carrier and. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Pdf sideband amplitude modulation absorption spectroscopy. In its basic form, amplitude modulation produces a signal with power concentrated at the carrier frequency and in two adjacent sidebands.
Frenzeljr, in handbook of serial communications interfaces, 2016. Once a signal has been modulated, information is retrieved through a demodulation process. Amplitude modulation, am frequency modulation, fm double and single sideband, dsb and ssb digital modulation phase shift keying. If the value of the modulation index is greater than 1, i. In amplitude modulation, the amplitude of the carrier is varied in accordance with the information signal. Nov 30, 2015 advantages and disadvantages of standard amplitude modulation.
342 1183 1594 122 341 247 1471 526 608 571 1205 39 400 756 1359 1565 585 1486 1269 352 893 320 443 1151 1030 653 929 754 944 983 124 670 435 1234 190 585 949