Chapter 6modulation techniques shandong university. Amplitude modulation involves the transferring of information. Digital amplitude modulation involves varying the amplitude of a carrier wave in discrete sections according to binary data. By varying the amplitude of the pulses the carrier signal in proportion to the instantaneous values of. To study sampling and reconstruction of pulse amplitude modulation system. Message information can be transmitted in either the amplitude, frequency, or phase of the carrier, or. Control of functional electrical stimulation systems using. Amplitude modulation corresponds to multiplying the carrier by the shifted baseband signal. Am demodulation amplitude modulation refers to any method of modulating an electromagnetic carrier frequency by varying its amplitude in accordance with the message intelligence that is to be transmitted. The negative half cycles of the mixed frequency are rectified, as shown in view d. Consequently, the constellation points lie on the horizontal line.
We talked about only the time domain analysis of the amplitude modulation. The demodulation is performed by an envelope detector. Spectrum analysis amplitude and frequency modulation an 150. Pulse amplitude modulation pam, quadrature amplitude modulation qam 12. In analog modulation, the characteristics of the modulated sinusoid such as amplitude, frequency or phase can take a continuum of values depending on the source of the information. Pulse position modulation ppm is an analog modulation scheme in which, the amplitude and the width of the pulses are kept constant, while the position of each pulse, with reference to the position of a reference pulse varies according to the instantaneous sampled value of the message signal. Amplitude modulation am frequency modulation fm phase modulation pm click on the links given above to know more. The carrier frequency, fc, should be larger than the highest spectral component.
When the amplitude of a highfrequency carrier wave is changed in accordance with the intensity of the signal, it is called amplitude modulation. In this type of modulation, amplitude a c and angular frequency. It is analogous to pulse width modulation pwm, in which the magnitude of an analog signal is encoded in the duty cycle of a square wave. It is customary to arrange the points so that they are equally spaced and centered at zero. Another kind of pulse modulation is pulse duration modulation pdm, in which intelligence is represented by the length and order of regularly recurring pulses. The goal of this experiment is to become familiar with fm modulation and demodulation. This page on amplitude modulation vs frequency modulation vs phase modulation describes difference between amplitude modulation, frequency modulation and phase modulation. Pulsefrequency modulation has no significant practical applications and. This is accomplished by heterodyning the intelligence frequency with the carrier frequency. The pulse amplitude modulated signal, will follow the amplitude of the original signal, as the signal traces out the path of the whole wave. Pdf the perspectives of reinventing a pulseamplitudemodulated frequency converter for heating, ventilation and airconditioning applications are. A modulation technique in which the amplitude of the pulsed carrier signal is changed according to the amplitude of the message signal is known as pulse amplitude modulation pam. This is repeated every t seconds, such that the transmitted bit rate is bits per second. In the frequency domain, amplitude modulation corresponds to translating the baseband spectrum to a band.
Radio waves can carry audio, video, and digital information over great distances by using changes in a carrier waves amplitude, frequency, or phase to represent the information being transmitted. Feedback can be used to achieve an output that matches exactly the control signal. A simultaneous modulation of the stimulation intensity and frequency is proposed to improve the joint controllability and muscle endurance. Pradeep kshetrapal, tutorials point india private limited. In many cases, over some arbitrary interval of time, the situation is not of a collection of discrete components with explicit frequencies, but rather a. Frequency versus amplitude modulation l amplitude modulation am l changes the amplitude of the carrier signal according to the amplitude of the message signal. We saw here, how the waveform changes with time but here, we will discuss the frequency domain analysis of the amplitude modulation.
To study sampling and reconstruction of pulse amplitude modulation system 6. Pulse amplitude modulation pam is an analog modulating scheme in which the amplitude of the pulse carrier varies proportional to the instantaneous amplitude of the message signal. Overmodulated am signals and its requirement for coherent detection are also considered. Modulation is the process whereby some characteristic of one wave is v aried in accordance with some characteristic of another wave. Pulse amplitude modulation an overview sciencedirect topics.
This receiver filter will play a key role in filtering out the part of the noise that lies outside the frequency bands in which the signal information is concentrated. Frequency modulation is widely used on frequencies above 30 mhz, and it is particularly well known for its use for vhf fm broadcasting. The pulse amplitude modulated signal, will follow the amplitude of the original signal, as. It is primarily useful for optical communications systems, which tend to have little or no multipath interference. The following safety and common symbols may be used in this manual and on the equipment. It is a modulation system in which the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the signal at the instant of sampling. The modulation index can be used to make the carrier amplitude more or less sensitive to the variations in the value of the baseband signal. The standard equation of the angle modulated wave is in amplitude modulation, the. Analog communication angle modulation tutorialspoint. The useful links to difference between various terms are provided here. Simply put, the transmission of data takes place by the variation of the amplitude of pulse according to the modulating signal. Pulse amplitude modulation pam theory of and its applications. Can create various ways of transmitting information pulse amplitude modulation pulse width modulation pulse position modulation pulse code modulation.
A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Amplitude modulation, is a system, where the maximum amplitude of the carrier wave varies, according to the instantaneous value amplitude of the modulating message or baseband signal. Similarly, it can be frequency modulation and phase modulation also in other words modulation is the phenomenon of superimposition of modulating signal input signal into the carrier wave. To study and perform pulse position modulation and. Pulse width modulation traditional solenoid driver electronics rely on linear control, which is the application of a constant voltage across a resistance to produce an output current that is directly proportional to the voltage. Modulationtypesamplitude,frequency,phase modulation. The basic types of modulation are angular mo dulation including the special cases of phase and frequency modulation and amplitude modulation. Pulsefrequency modulation pfm is a modulation method for representing an analog signal using only two levels 1 and 0.
It is also possible to change the frequency of a signal to give frequency modulation or fm. Spectrum analysis amplitude and frequency modulation an. Amplitude modulation definition, types, solved examples. Here we will discuss in details, pulse modulation and pulse modulation techniques like pulse amplitude modulation pam, pulse width modulation pwm, pulse position modulation ppm and pulse code. The peaks of the positive half cycles follow the 1,000hertz beat frequency. However, it is the first step in another very popular conversion method called pulse code modulation. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Vary the modulating frequency and amplitude and observe the effects on the modulated waveform.
Its need, amplitude, frequency, and pulse modulation. With digital frequency modulation, the frequency of a carrier or a baseband signal is varied in discrete sections according to binary data. Nov 16, 2019 in amplitude modulation, angular frequency. Since bit values shift between 0s and 1s, digital modulation techniques that vary the carriers amplitude, frequency, and phase are referred to as shift keying. Pulse frequency modulation pfm is a modulation method for representing an analog signal using only two levels 1 and 0.
In case of frequency modulation fm or phase modulation pm, the frequency or phase respectively, of the carrier wave varies, according to the. Pulse amplitude modulation an overview sciencedirect. A 3phase, pulse amplitude modulated converter is developed and compared with a 3phase, pulse widthmodulated converter. Hence the information can be carried in the amplitude, frequency or phase, thus resulting in the following types of modulation schemes. By varying the amplitude of the pulses the carrier signal in proportion to the instantaneous values of the analog signal the message signal. To study and perform pulse position modulation and demodulation. The original waveform amplitude is quantized with a resulting loss of information.
Laboratory manual principles of communication system lab ee226f ivth semester prepared by. Bandwidth of amplitude modulation should be twice the frequency of modulating signal or message signal. The depth of modulation can be varied using the variable knob provided at a. Pulse amplitude modulation pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. Pulse width modulation axiomatic technologies corporation.
If the negative symbol is transmitted, the pdf for z will be as sketched below. If the modulating signal frequency is 10 khz then the amplitude modulation frequency. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. To convert an audio signal 020khz to digital form, the minimum sampling frequency is 40khz. Pulse position modulation ppm is a form of signal modulation in which m message bits are encoded by transmitting a single pulse in one of possible required time shifts. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. The modulation processisprobablyeasier tounderstand whenviewed fromthe perspective of amplitude modulation. Sampling theorem and pulse amplitude modulation pam.
If we vary the amplitude of the carrier wave in accordance with the modulating signal input signal it is known as amplitude modulation. While this is the simplest technique available, it is nonlinear since a first order lowpass filter response falls as. In pulse amplitude modulation pam, the a m are purely real, that is im a m 0 for m 1, 2, m. To study and perform pulse width modulation and demodulation. Sampling as modulation page 7 the spectrum of an amplitude modulation signal in this article we will be very concerned with the matter of the different frequency components of various waveforms. While changing the amplitude of a radio signal is the most obvious method to modulate it, it is by no means the only way. To study and perform frequency modulation and demodulation. In this experiment, a carrier signal and an audio modulating signal are applied to the modulator ic mc 1496 and the produced modulated waveform is observed. The transmitter can choose one of m frequencies for the sinusoidal carrier signal. Pulse amplitude modulation has some applications, but it is not used by itself in data communication.
We use modulation technique to alter signals in time and frequency to accomplish desired objectives. Message information can be transmitted in either the amplitude, frequency, or phase of the carrier, or a combination thereof, in either analog or digital format. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. Subjects include modulation methods, modulation degree and sideband amplitude, zero span and markers, the fast fourier transform, special forms of amplitude modulation, angular modulation, bandwidth of fm signals, fm measurements with the spectrum analyzer, and am plus fm incidental fm. The two common forms of analog modulation are amplitude modulation am and frequency modulation fm which is speci. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. Envelope intelligence amplitude varies at the beat difference frequency of 1,000 hertz 501,000. To study and perform amplitude modulation and demodulation. For the example above, the carrier signal is p es cos2. Angle modulation is the process in which the frequency or the phase of the carrier signal varies according to the message signal.
Pdf pulseamplitudemodulated frequency converter for hvac. The pulse may take any real voltage value that is proportional to the value of the original waveform. The presented control method determines pulse width pw, amplitude, and frequency of the electrical stimulation signal, synchronously. The percentage modulation can be calculated using the formula. To study and perform pulse amplitude modulation and demodulation. Chapter 4 digital modulation and power spectrum modulation is the process whereby message information is embedded into the radio frequency carrier. In practice, sampling frequency for encoding music into cd is 44. A carrier signal is a steady waveform with constant amplitude and frequency. Pulse amplitude modulation pulse code modulation sampling rate. When the amplitude of a high frequency carrier wave is changed in accordance with the intensity of the signal, it is called amplitude modulation. Connect this signal to the oscilloscope and the low frequency spectrum analyzer and check that you have.
Difference between pam, pwm, and ppm comparison of pwm and pam. Note that the frequency modulation and phase modulation of a carrier wave is collectively called the angle modulation. There are m possible signal amplitudes, which represent log 2 m bits. Nov 17, 2017 modulation is a process by which some characteristic amplitude frequency or phase of a high frequency carrier wave is varied in accordance with the instantaneous value of the message signal.
No information is lost, but the energy is redistributed in the frequency domain. Since the three variables are the amplitude, frequency, and phase angle, the modulation can be done by varying any one of them. A familiar example of pdm is the international morse code, used in shiptoshore communications, amateur radio, and certain other forms of radiotelegraphy. Pulse amplitude modulation pulse code modulation sampling. The most straightforward approach to digital amplitude modulation is onoff keying. To study frequency modulation and determine its modulation factor 4. What is fm, frequency modulation electronics notes. This 26page application note provides information on amplitude and frequency modulation. Emc, losses, acoustic noise, line and shaft performance and cost are compared. Pdf pulseamplitudemodulated frequency converter for. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i. Pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that. The other type of modulation in continuouswave modulation is angle modulation.
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