Apr 26, 2015 frequency discrimination slope detector major limitations. In analog frequency modulation, such as radio broadcasting, of an audio signal representing voice or music, the instantaneous frequency deviation, i. Frequency modulation is a technique or a process of encoding information on a particular signal analogue or digital by varying the carrier wave frequency in accordance with the frequency of the modulating signal. Theory of lock in modulation and demodulation 1 general scheme of lock in ring the synchronous moddemod is also called lock in modulation fig. Learn the definition of frequency modulation, and get answers to faqs. Frequency modulation definition, applications, advantages. However, despite the fact that a carrier is not radiated, the need for such a signal at the transmitter where the modulated signal is generated, and also at the receiver, remains fundamental to the modulation and demodulation. Recall that our goal is to transmit data over a commu nication link, which we achieve by mapping the.
It is relatively difficult to tune, as tuned circuit must be tuned to different frequency than carrier frequency. Amplitude modulation is defined as a process in which the amplitude of the carrier wave c t is varied linearly with the instantaneous amplitude of the. To understand the principles of frequency modulation and demodulation. In the laboratory, you will use function generator as vco. This application report discusses logiclevel implementation of binary fsk bfsk modulator and demodulator using a. It is a modulation on a different frequency from the original signal, to transfer out of f 1 noise fig. Recovery of a modulating signal with the coincidence demodulator integrated on the module. Build simple fm demodulator by using frequency discriminator 2. In the first model, you are provided a fm structure that is very similar to the theoretical background of this experiment. One of the minor disadvantages of frequency modulation is that the demodulator is a little more complicated, and hence slightly more expensive than the very simple diode detectors used for am. Part i experiments involving linear modulation and demodulation. Apr 11, 2012 of demodulation, to recover the original baseband signal from the received version. A synchronous detector could be utilized when a signal is modulated with a linear modulation technique. The technology is used in telecommunications, radio broadcasting, signal processing, and computing.
The changes in the carrier signal are chosen from a finite number of m alternative symbols the modulation alphabet. In analog frequency modulation, the data signal can be modulated through a continuously changing sine carrier signal. These are covered in chapter 5 of 2, or chapter 3 of 1. It depends on the actual modulation type whether or not the spectra become similar with respect to shapes, symmetries, and bandwidths. Build simple envelope detector for fm demodulation. The technology is used in telecommunications, radio broadcasting, signal processing, and computing in analog frequency modulation, such as radio broadcasting, of an audio signal representing voice or music, the instantaneous frequency deviation, i. Fsk modulation fsk technique is to modulate the data signal to. Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave. Build simple fm demodulator by using frequency discriminator.
Teach the basics of frequency modulation and demodulation. Random binary signal generation has been done by using matlabs function. At the receiver, the data signal will be recovered based on the different frequencies of the received signal. Therefore, when we receive the amplitude modulation signal, we need to restore the audio signal. Modulation is the process of impressing a low frequency information signal. Demodulation refers to baseband waveform recovery dr. In theory, an fm wave contains an infinite number of sidefrequencies. Note, when a modulator is set up, v dc is fixed at a particular value. This application report discusses logiclevel implementation of binary fsk bfsk modulator and demodulator using a phaselocked loop pll. Frequency modulation and demodulation last modified. 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. Use modulation to transfer information to a higher frequency.
Demodulation is defined as the process of extracting this information. Carsons rule and woodwards theorem use a 250 hz sine wave, square wave, and triangle wave to frequency modulate the hp3314a. The carrier frequency, fc, should be larger than the highest spectral component. Vary the modulating frequency and amplitude and observe the effects on the modulated waveform. Choose the amplitude of the message such that the maximum frequency deviation is 30 khz. It is included to create a positive envelope which allows demodulation by a simple inexpensive envelope detector. 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. Although there could be more than two frequencies involved in an fsk. In any radio that is designed to receive frequency modulated signals there is some form of fm demodulator or detector. Fm modulation and demodulation will be presented and you will implement two types of demodulators, the frequency. Amplitude modulation am frequency modulation fm bandwidth occupancy in am and fm amplitude shift keying ask frequency shift keying fsk phase shift keying psk nary coding and mary modulation bandwidth occupancy in ask, fsk, and psk this text has been primarily designed for electrical engineering.
One way to realize the 9 requirement, is to use discriminators devices which distinguish one frequency from another, by converting frequency variations into amplitude variations. Experiment 1 amplitude modulation and demodulation 1 amplitude modulation and demodulation preliminary discussion in an a mplitude m odulation am communications system, speech and music are converted into an electrical signal using a device such as a microphone. Frequency modulation is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. Second, an fm demodulator based on a phase locked loop pll will be designed and simulated, using the previous modulator as the signal source. Ask, fsk and psk are sometimes described as binary. In the following illustrations we will have a fixed message, v m cos m t and vary v dc to obtain different types of double sideband modulation.
For am, the frequency of the carrier wave may be chosen to be around a few hundred khz from the mf band of the radio spectrum the demodulator extracts the original baseband signal from the received modulated signal to summarize. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. The frequency modulator and demodulator structures are as explained below. However this is much less of an issue these days because many radio integrated circuits incorporate a built in. You are free to choose the frequency and magnitude of the carrier and message signals. On the other hand, the theory may be applied to the demodulation or filtering of rather arbitrary types of stationary signal and noise processes. Orthogonal frequency division multiplex ofdm tutorial 1 intuitive guide to principles of communications orthogonal frequency division multiplexing ofdm modulation a mapping of the information on changes in the carrier phase, frequency or. Modulation is the process of transforming a baseband message to a form suitable for fig. In contrast, a frequency modulation demodulator or a phase modulation demodulator can be utilized for a signal attuned with a unintended one. In this discussion, dt is a binary or 2 level signal representing 1s and 0s the types of modulation produced, i. Pm and digital modulation s p where 2 is the pkpk phase change in one symbol duration, t for digital signals the modulation index. This article provides a general tutorial on fsk in its many forms.
This chapter describes the essential principles behind. Chapter 6 doublesideband suppressedcarrier amplitude. Frequency shift keying moduation and demodulation implementation in matlab for digital communications course at new york institute of technology. Radio transmission voice microphone electric signal, 20 hz 20 khz transmitter antenna. The output of a fsk modulated wave is high in frequency for a binary high input and is low in frequency for a binary low input. In this experiment, we will use a famous chip, the lm 566c to generate the fm signal. We consider binary modulation schemes and multilevel modulation schemes here. A carrier, frequency modulated by a 1,000 hz sinusoid. Orthogonal frequency division multiplex ofdm tutorial 1 intuitive guide to principles of communications orthogonal frequency division multiplexing ofdm modulation a mapping of the information on changes in the carrier phase, frequency or amplitude or combination. Chapter 14 modulation school of computing and information. Angle modulation is the process in which the frequency or the phase of the carrier varies according to the message signal. Use the signal generator to generate an fm signal with the message signal being sine signal. Advantages and disadvantages of frequency modulation.
Digital modulation methods can be considered as digitaltoanalog conversion and the corresponding demodulation or detection as analogtodigital conversion. If the baseband signal is bandlimited, then there is a finite maximum frequency of the corresponding sinusoids. Theory it is a type of modulation in which the frequency of the high frequency carrier. Frequency modulation fm is the encoding of information in a carrier wave by. The percentage modulation can be calculated using the formula. Both modulation and demodulation schemes will be discussed binary fsk. We discuss discrete changes in the characteristics of the carrier digital modulation in 14. In this experiment pll based frequency demodulation technique is used and the circuit is shown in fig 2. Chapter 8 frequency modulation fm contents umd ece.
Fm to obtain a frequency modulated signal we fix the amplitude and let the time derivative of the phase, d. The modulation index has been adjusted to around 2. A simple yet effective fm demodulator is one which takes a time average of the zero crossings of. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating. Frequency modulation equations mainly consist of a sinusoidal expression with the integral of the baseband signal that can be either a sine or cosine function. Example commercial fm signals use a peak frequency deviation of. The chapter concludes with the characterization of the spectrum of bfsk for various modulation indices. A smarter approach for reducing the amount of data without loosing essential information is to apply a complex baseband modulation technique with bandwidth reduction known as iq demodulation.
From an information theory point of view, the power in the carrier component is wasted. Its amplitude a, which leads us to the class of systems designated as amplitude modulating am systems. First, a frequency modulation system will be created and simulated using simulink. The type of modulation is determined by the modulation depth, which for a fixed mt depends on the dc offset, v dc. Modulation fm, amplitude shift keying ask, phase shift keying psk, etc. Modulation shifts the spectrum of a baseband signal to some high frequency. Information signal is usually of low frequency, so it cannot travel far. Frequency modulation fm is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. Theory, analysis, design, simulation, testing, and. Modulation and demodulation technology innovation and. Its amplitude a, which leads us to the class of systems designated as amplitude. Fm signals have the same peak frequency deviation, then when mt is a sinusoidal signal set such that the pm and note. This is further divided into frequency and phase modulation. However, despite the fact that a carrier is not radiated, the need for such a signal at the transmitter where the modulated signal is generated, and also at the receiver, remains fundamental to the modulation and demodulation process respectively.
Analog communications lab manual bapatla engineering. Frequency modulation is the process of varying the frequency of the carrier signal linearly with the message signal. A frequency demodulation with using frequency discriminator in this section we are going to build a simple fm demodulator. Schaums outlines of theory and problems of signals and systems, pp. If the message dt controls frequency gives frequency shift keying fsk.
Using matlab mfile and simulink to implement fm modulation and demodulation. Guide students to gain a working understanding of theories such as demodulation, bandwidth, and carsons rule. The modulation property for fourier transforms applies directly to amplitude modulation, that is, the interpretation in the frequency domain of the result of multiplying a carrier signal by a modulating signal. Frequency modulation fm, as well as phase modulation pm, are types of angle exponential modulation.
Frequency modulation 1 objective to understand the principles of frequency modulation and demodulation. Amplitude modulation is defined as a process in which the amplitude of the carrier. It needs a carrier signal of higher frequency for long distance destination. In the second model, you will observe the frequency variations with respect to the input signals waveform.
Frequency modulation and demodulation aim to verify frequency modulation and demodulation to measure frequency deviation and modulation index of fm. It is inefficient, as it is linear in very limited frequency range. The depth of modulation can be varied using the variable knob provided at a. In theory, an ideal frequency modulation fm detector is a device that produces an output that is proportional to the instantaneous frequency of the input. In addition to commercial radio, it is used as a component of television signals, for satellite and microwave communications, and for digital data transmission.
Modulation is defined as the process of transmission of information such as images or videos on an electrical signal. The carrier frequency 400hz, message signal frequency 10hz, and frequency deviation 100hz. Amplitude modulation is defined as a process in which the amplitude of the carrier wave ct is. In particular, we discuss amplitude and frequency modulation. From the modulation property we know that for amplitude modulation the spectrum of the.
Third, an fm demodulator will be implemented on a tms320c6711 dsp platform. What is fm, frequency modulation electronics notes. Frequency shift keying fsk is the digital modulation technique in which the frequency of the carrier signal varies according to the digital signal changes. Upon completion of the experiment, the student will. If you have the time, take a look at the theory behind phaselocked loops pll, as in pp. Preparation generation as its name suggests, a frequency shift keyed transmitter has its frequency shifted by the message. Frequency shift keying fsk is a frequency modulation scheme in which digital information is transmitted through discrete frequency changes of a carrier wave. Fm demodulator circuits are found in any receiver that uses fm. Implementation of fsk modulation and demodulation using. Modulation is a process of translating information signal from low band frequency to high band frequency that is suits the transmission medium.
To understand the measurement and adjustment of am demodulator. Signals and demodulation frequency shift keying fsk is the most common form of digital modulation in the high frequency radio spectrum, and has important applications in telephone circuits. In digital modulation, an analog carrier signal is modulated by a discrete signal. Fsk modulation fsk technique is to modulate the data signal to different frequencies to achieve effective transmission. If the message dt controls phase gives phase shift keying psk. It reacts to all amplitude changes needs a limiter. Carrier modulation allows the transmission of modulating frequencies without the use of transmission wire as a medium. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude.
From experiment 3, we know that the amplitude modulation signal utilizes the amplitude of audio signal to modulate high frequency carrier signal. Digital communications with emphasis on data modems. This is the process of influencing data information on the carrier. In this case, you will use the modulator and demodulator blocks provided by simulink.
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