The ratio of the frequency of the tone modulator fm. Process by which a property or a parameter of a signal is varied in proportion to a second signal. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. The second disadvantage is that almost twothirds of the power is used by th. The amplitude modulation of one sinusoidal carrier by another sinusoid. Mathematically the bandwidth of the angle modulated signal of eqn. Figure 28 shows how the modulation index is defined and measured. Tone modulation is a modulation in which the modulation is carried out by a single frequency tone signal. This can be seen by first writing the fm output signal in terms of nth order bessel functions of the first kind 2, 3. Derive an expression for single tone amplitude modulated. A comparison of singletone and twotone techniques article pdf available in applied optics 2617. Slide 3 discretetime fm modulator slide 4 single tone fm modulation slide 5 single tone fm cont. The unmodulated carrier is represented by the expression.
Double sideband dsb and single sidebandssb sharlene katz. Amplitude modulation is the simplest of the three to understand. The single side frequency spectrum of tone amplitude modulation is in figure 1. You will get here what is single tone modulation and the derivation of equation of am wave. The message signal is, for example, a function of the sound to be reproduced by a. Amplitude modulation a continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. There is no over modulation means that modulation index is less than or equal to 1. Q5 an am signal, depth of modulation 100% from a single tone message, has a peaktopeak amplitude of 4 volts. Amplitudecompanded singlesideband modulation amplitudecompanded single sideband is a narrowband modulation method using a single sideband with a pilot tone, allowing an expander in the receiver to restore the amplitude that was severely compressed by the transmitter. 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. Frequency modulation spectroscopy with leadsalt diode lasers. In singletone modulation modulating signal consists of only one. Amplitudemodulation,ii single sideband modulation ssb.
As given is the problem the modulation is sinusoidal this is also called tone 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. Slide 6 narrow band fm slide 7 bandwidth of an fm signal. We propose two simple cases for the spectral analysis of an fm signal. This is a very convenient type of signal for initial settingup, as it results in easytorecognise oscilloscope pictures, although not very interesting as a program. Note also that the sidebands are separated from the carrier by a frequency equal to that of the tone.
Define effect of modulation index on amplitude modulated signal. One tone causes a modulation index of m 1 and the other tone causes a. The envelope contains a residual amplitude modulation that varies with time. Am modulation where the amplitude of the carrier does not depend on the value of the modulating signal. Let us consider a single tone modulating signal as. Re exp 2 sin2 we need to expand the exponential into a fourier series so that. Amplitude modulation am is a modulation technique where the amplitude of. A cornucopia of algebraic curves is then derived assuming a single tone or a double tone modulation signal. Amplitude modulation early radio ee 442 spring semester. Am wave frequency spectrumam wave equation derivation. It offers improved effective range over standard ssb modulation while.
Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. To understand the theoretical foundations of analog communications as well as of doublesideband amplitude modulation and demodulation dsbam to design the simulink model of the dsbam to analyze each signal in time and frequency domains using time scope and spectrum analyzer. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. For wideband fm we have a nonlinear process, with single tone modulation. Quadrature amplitude modulation uses the 2b transmitter bandwidth to. The information is considered as the modulating signal and it is superimposed on the carrier wave by applying both of them to the. Am modulation index is measured using a singletone sine wave as the message signal. The equations for the simple example of the a single tone used for modulation can be expanded to show how the signal will appear of a typical sound consisting of many frequencies is used to modulated the carrier. The envelope contains a residual amplitude modulation that varies with time the angle contains harmonic distortion in the form of third. In this method of modulation the amplitude of the carrier wave is maintained constant. As discussed earlier conventional am and dsbsc is wasteful from the band width point of view and requires a bandwidth equal to twice the message signal bandwidth.
This type of amplitude modulation is known as single tone amplitude modulation. Vsb modulation with envelope detection is used to modulate image in analog tv signals. 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. Complete derivation of am wave equation and frequency spectrum of amplitude modulated wave is given here. Single tone amplitude modulation rktcsu1e10 youtube. In this section we shall discuss amplitude modulation in which the modulating or baseband signal consists of only one single frequency i. Farshad lahouti january 20, 2003 winter 2003 uw, ece 318 lecture notes 2 information source signal modulator propagation channel signal demodulator information destination analog communication system analog signals may be transmitted directly via carrier modulat ion over. A single tone modulation that produces wideband fm signal. Consider a modulating wave mt that consists of a single tone or single frequency component. It can be seen that for a case where there is 100% modulation, i.
Consequently, unlike amplitude modulation, the spectrum of an fm signal is not related in a simple manner to that of a modulating signal its analysing is much more different than that of an am signal. Properties of single tone fm for arbitrary modulation index j nj n, for n even j nj. This is usually expressed as a ratio of the maximum information signal to the amplitude of the carrier. Pdf frequency modulation spectroscopy with leadsalt. Amplitude spectrum amplitude spectrum amplitude spectrum amplitude spectrum amplitude spectrum the amplitude spectrum relative to f. The amplitude modulation am modulation index can be defined as the ratio of the peak. The toned single frequency modulating signal consists of only one frequency component and this signal is modulated with a carrier signal.
Compare doublesideband and singlesideband amplitude modulation. Carrier is modulated by varying amplitude linearly proportional to intelligence baseband signal amplitude. Introduction, orientation introduction to communication system, need for modulation, amplitude modulation, time domain and frequency domain description, power relations in am wave, square law modulator, switching. As we have already discussed that the phase angle of the carrier signal is changed in accordance with the amplitude of the message signal. Sidebands on an amplitude modulated carrier when modulated with a single tone. The expression for conventional am is now if the message signal is a singletone where is called as modulation index this equation can be further simplified as follows that is by taking the fourier transform from the above expression the amplitude spectrum can be drawn as follows from the spectrum single.
Message power in st slide 6 powers in single tone case cont. That is m t a f t cos2 m s m, where a m is the amplitude and f m. Amplitude modulation am 3 this model uses a single sine wave a tone as the message or program to be transmitted. Pdf analog communication system pdf notes ac notes sw. The amount of modulation depends on the amplitude of the information signal. Their zero crossings are not uniform, so the functions are not. The bandwidth required for am system is twice the maximum frequency component of the modulating signal, which is an analogue signal. In both cases the transmission bandwidth b t is occupied by the upper sideband usb and lower sideband lsb. The method of varying amplitude of a highfrequency carrier wave in accordance with the information to be transmitted, keeping the frequency and phase of the carrier wave unchanged is called amplitude modulation. Suppose the voltage of the carrier signal is given as. Amplitude modulation contents slide 1 amplitude modulation slide 2 the envelope and no overmodulation slide 3 example for single tone modulation slide 4 measuring the modulation index slide 5 transmitted vs.
683 311 1331 291 1283 1340 1348 1033 886 1249 1144 550 9 636 1333 1244 1364 668 367 553 1470 1241 26 465 1581 441 272 595 1218 785 903 1673 1646 22 1460 1384 1302 1090 1283 91 178 819 1448 580 1403