The student will learn the basic concepts of ssb modulation and using the theoretical knowledge of. Frequency modulation fm it is a process in which the frequency of the carrier is varied in accordance with the instantaneous value of modulating voltage. In the first model, you are provided a fm structure that is very similar to the theoretical background of this experiment. From experiment 3, we know that the amplitude modulation signal utilizes the amplitude of audio signal to modulate high frequency carrier signal. An outline of dsbscssbsc modulation and demodulation. This may be an advantage for cochannel allocations, but it is a. Frequency shift keying fsk modulation and demodulation. Frequency modulation definition, basics and waveform hd. Pcm is in binary form,so there will be only two possible states high and low 0 and 1. So, the fsk generation and detection can be done in this way. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. Frequency modulation and frequency demodulation experiment.
Monitor the waveforms at the output of following stages. The message signal is, for example, a function of the sound to be reproduced by a. Build simple envelope detector for fm demodulation. It does not carry much information that we can relate to data or speech. The message is recovered as the control input of the vco 4. A demodulator is an electronic circuit or computer program in a softwaredefined radio that is used to recover the information content from the modulated carrier wave. The frequency modulation and demodulation applet finds and displays the modulated wave spectrum modulated by the carrier wave and modulating signal using fast fourier transform, but if you compare this spectrum with a spectrum obtained with a bessel function of the first kind, you can see. Experiment 5 frequency modulation 1 objective to understand the principles of frequency modulation and demodulation. Frequency modulation fm is the standard technique for highfidelity. In the laboratory, you will use function generator as vco. Frequency modulation fm is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. The technology is used in communication systems such as amateur radio, caller id, and urgent situation broadcasts. Along with circuit components, introductions, an appendix section which. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave.
The different modules can be remotely connected with the help of ni switch 25292 wire 8 by 16 matrix. Experiment4 frequency demodulator preliminary work 1. So lower the frequency of signal greater will be its wave length as. The depth of modulation can be varied using the variable knob provided at a. To study and perform pulse width modulation and demodulation. First, since fm only changes the frequency and not the amplitude of the carrier w ave, fm receivers can be built to ignore amplitude voltage changes. Fm transmitting and receiving equipment tends to be more complex, particularly for modulation and demodulation. The message signal is multiplied by the modulation index, then it is added a dc carrier. The waveform, definition and basic concepts of frequency shift keying fsk are discussed here. From the purely theoretical point of view, the difference between fm and pm is quite simplethe modulation index is defined differently in each system.
Then, students will use labview to program an am demodulator and use it to explore and visualize the. Modulation allows us to transmit multiple signals in the same medium i. Information signal is usually of low frequency, so it cannot travel far. We can also get back our analog signal by demodulation.
Amplitude modulation theory frequency spectrum power. Amplitude modulation a1 49 you will see in this experiment, and in others to follow, that there is no problem in generating an am signal with a depth of modulation exceeding 100%, and without any rf distortion whatsoever. In analog applications, the carrier frequency is varied in direct proportion to changes in the amplitude of an input signal. C, so we will use the term excess frequency to refer to the frequency component contributed by the modulation procedure. This resulted in the translation of the message spectrum to the carrier frequency location. To design frequency modulator and demodulator using tms processor. Theory of frequency modulation and phase modulation. To study frequency modulation and determine its modulation factor. The goal of this experiment is to become familiar with fm modulation and demodulation.
Frequency modulation, or fm, is an important method of impressing information on a carrier. Frequency shift keying fsk 1 objective generation and demodulation of a frequency shift keyed fsk signal 2 preliminary discussion in fsk, the frequency of a carrier signal is modified in a discrete manner depending on the value of a modulating symbol. Vary the modulating frequency and amplitude and observe the effects on the modulated waveform. Modulation is a process of translating information signal from low band frequency to high band frequency that is suits the transmission medium. Frequency modulation and demodulation with spectrum analysis.
The demodulation of dsb am signal can be done either by using an envelope detector or by passing the amplitude modulated signal through a nonlinear device. 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. Random data for transmission is generated and it is tranmitted using bpsk modulation. Jan 30, 2017 basics of modulation and demodulation. In experiment 3, dsb signals were generated by the multiplication of a message signal with a carrier waveform. Sc modulation, and demodulation techniques for analog communication. This process can be known for the frequency shift keying modulation and demodulation experiment also. This term is slightly misleading, though, because excess implies a higher frequency, whereas modulation can result in a carrier frequency that is higher or lower than the nominal. A brief discussion about pulse code modulation and demodulation. Frequency modulation fm, as well as phase modulation pm, are types of angle exponential modulation. The very important conclusion to be made at this stage is that the bandwidth required for amplitude modulation theory is twice the frequency of the modulating signal. Delta modulation and demodulation techniques experiment. In the second model, you will observe the frequency variations with respect to the input signals waveform. Fsk frequency shift keying d1 61 conceptually, and in fact, the transmitter could consist of two oscillators on frequencies f1 and f2, with only one being connected to the output at any one time.
After passing the modulated signal over a band limited channel the data is demodulated using either a squaring loop or b using a costas loop. Since reception is limited to line of sight, the area of reception for fm is much smaller than for am. The process of recovery of modulating signal is called demodulation. The frequency of a radiofrequency channel can be explained best as the frequency of a carrier wave. To study and perform amplitude modulation and demodulation. The percentage modulation can be calculated using the formula. Fm modulation and demodulation frequency modulation. In this experiment, another widely used modulation technique will be introduced. It would be advantageous to have completed some of the part 1 experiments involving linear modulation and demodulation. The carrier frequency f c is much greater than the highest frequency component. Fm concepts explained what is frequency modulation. To understand the theoretical foundations for angle modulation as well as.
Therefore, when we receive the amplitude modulation signal, we need to restore the audio signal. In amplitude modulation theory, the amplitude of a carrier signal is varied by the modulating voltage, whose frequency is invariably lower than that of the carrier. The simplicity of the modulation process contrasted with the strict requirement for a synchronous local carrier at the receiver. The phase of the carrier wave is also kept constant. Once the signal has been received, filtered and amplified, it is necessary to recover the original modulation from the carrier. Amplitude modulation or am is a method to transmit signals via electromagnetic transmission. Frequency modulation and phase modulation are the two complementary principal methods of angle modulation. Build simple fm demodulator by using frequency discriminator. There are many types of modulation so there are many types of demodulators.
Therefore, this technique is valid only for a small frequency deviation from the center frequency e. If a high pass filter is used, the demodulation process is much more linear since the. In this chapter the basic theory of fm modulation and demodulation will be presented and you will implement two types of demodulators, the frequency discriminator and the phaselocked loop. Essentially an amplitude modulated wave consists of a radio frequency carrier a sine wave at one frequency, typically in the radio frequency portion of the spectrum. Binary fsk is the most common form of fsk where a pair of discrete. Connections are made for the am modulator and demodulator as shown in the circuit. Each techbook is provided with detailed multimedia learning material which covers basic theory, step by step procedure to conduct the experiment and other useful information. While amplitude modulation is achieved by varying e p, frequency modulation is realized by varying. Recall that we can write an equation for a sine wave as follows. To study and perform pulse amplitude modulation and demodulation. Fm is considered an analog form of modulation because the baseband signal is typically an analog waveform without discrete, digital values. This circuit takes in frequency modulated rf signals and takes the modulation from the signal to output only the modulation that had been applied at the transmitter.
Frequency modulation fm is an important modulation scheme both because of its widespread commercial use, and because of its simplicity. Evaluate the modulated carrier when the modulation index is varied and demodulate the signal and recover the original modulating waveform using two methods for demodulation. The amount of change in frequency is determined by. In your report you will compare the properties of the fm signal you created experimentally with those suggested by theory. This lab introduces students to communications theory with amplitude modulation and demodulation. Frequency modulation and phase modulation is a system in which the amplitude of the modulated carrier is kept constant, while its frequency and rate of change are varied by the modulating signal. It needs a carrier signal of higher frequency for long distance destination. The fm input signal is first subjected to a limiter in order to eliminate any amplitude modulation noise present in the signal. The term and technology us used in both telecommunications and signal processing in analog frequency modulation, such as fm radio broadcasting of an audio signal representing voice or music, the instantaneous frequency deviation, the difference between the frequency.
Frequency modulation is a form of modulation, which represents information as variations in the instantaneous frequency of a carrier wave. Bpsk modulation and demodulationsimulation experiment. Modulation is defined as the process by which some characteristics of a carrier signal is varied in accordance with a modulating. T he classic definition of fm is that the instantaneous output frequency of a transmitter is varied in accordance with the modulating signal. To study and perform pulse position modulation and demodulation. A phaselocked loop can be used as an fm demodulator. Pulse code modulation is a method that is used to convert an analog signal into a digital signal, so that modified analog signal can be transmitted through the digital communication network. Demodulation is extracting the original informationbearing signal from a carrier wave. Scientech 2155 delta modulation and demodulation techniques techbook. To study and perform frequency modulation and demodulation.
Upon completion of the experiment, the student will. Oct 12, 2018 frequency modulation and phase modulation. 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. If you have the time, take a look at the theory behind phaselocked loops pll, as in pp. Frequency modulation is used in many fields including transceivers and fm radio broadcasting. But we are getting ahead of ourselves, as we have not yet even defined what am is. The frequency modulator and demodulator structures are as explained below. In addition to commercial radio, it is used as a component of television signals, for satellite and microwave communications, and for digital data transmission. Students will explore the mathematical theory behind amplitude modulation and use the analog discovery 2 to visualize the effects of amplitude modulation in the time and frequency domains. Fm demodulation principle in order to be able to demodulate fm it is necessary for the radio receiver to convert the frequency variations into voltage variations it is a frequency to voltage converter.
Its amplitude a, which leads us to the class of systems designated as amplitude modulating am systems. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. In this fsk experiment, fsk can be generated by the 555 timer ic and detection can be possible by 565ic which is known as a phaselocked loop pll. In practice, the carrier may be high frequency hf while the modulation is audio. To understand the principles of frequency modulation and demodulation. The signal output from a demodulator may represent sound an. The theory of dsbscssbsc modulation and demodulation double sideband suppressed carrier modulation at the beginning of the explanation of amplitude modulation, we explained the am radio system, but the term for amplitude in the theoretical expression was complex. Carrier modulation allows the transmission of modulating frequencies without the use of transmission wire as a medium.
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. As it is clearly seen that the am model is exactly based upon the mathematical foundation provided in the theoretical section. If a range of frequencies is used to modulate the carrier, the maximum modulating frequency and its corresponding modulation index are used. Fm modulation introduction in this lab, you will investigate frequency modulation fm and its properties. Dec 15, 2017 frequency modulation and demodulation with spectrum analysis. Understanding the principle of frequency modulation fm and demodulation understanding the waveforms of modulated and demodulated signals designing frequency modulator and demodulator using simulink theory phase modulation pm and frequency modulation fm are special cases of anglemodulated signaling. Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave. It is this process that is called demodulation or detection. In this case, you will use the modulator and demodulator blocks provided by simulink. Scientech techbook 2203 frequency modulation and demodulation techniques is a comprehensive learning solution specifically designed to study basic operation as well as to provide conceptual and step by step understanding of frequency modulation and demodulation techniques through observation of waveforms at various test points. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i. Amplitude modulation am, demodulation and their circuit.
The slope detection method revolves around a differentiation operation that exploits the instantaneous frequency of the fm signal. In this experiment, we shall consider demodulation using envelope detector. This is shown in block diagram form in figure 2 below. Parameter fm is the frequency of the modulating signal. Frequency modulation fm is a form of modulation in which changes in the carrier wave frequency correspond directly to changes in the baseband signal. Frequency shift keying fsk is the frequency modulation system in which digital information is transmitted through the discrete frequency change of a carrier wave. In frequency modulation, the amplitude of the carrier wave is kept constant but its frequency is varied in accordance with the amplitude of the audio frequency signal. In order to observe the spectrum analyzer, please increase the simulation time to 1 or 2 seconds. However, this is not nearly as obvious as the difference between am and fm, and it must be developed further. Generation and demodulation of a binary fsk signal. Frequency modulation frequency modulation fm is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. What we do in am, very roughly,is to throw away the frequency content of. The concepts of amplitude modulation, modulation and demodulation, along with their. A carrier wave is purely made up of constant frequency, slightly similar to a sine wave.
Another pitfall of this technique is that it does not have any rejection of unwanted am signals noise. Eed314 analog communication 20 spring experiment 4 distortion level. As we have seen in this document, frequency modulation can be simplified to angle modulation with a simple integrator. Modulation and demodulation using pll 51 10 mixer circuit using bjt 57 a quick reference. Its still used in radio systems to transmit audio signals although it has lesser in popularity compared to fm due to its lower signal to noise ratio. Fm demodulation is a key process in the reception of a frequency modulated signal. 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. Frequency shift keying modulationfsk modulation digital. The theory of frequency modulation and demodulation. In the simulation experiment section2, we used the vco to demodulate the information signal to make life easier. Oct 09, 2018 the two additional terms produced are the two sidebands outlined. Designing and analyzing frequency modulator and demodulator. Frequency division multiplexing, fdma amplitude modulation and demodulation. These methods contrast with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency and phase remain constant.
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