The spectrum of an fm signal is quite complicated and is dependent on mf. In chapters 1 and 2 you studied how to apply intelligence modulation to an rf carrier wave. A carrier wave is purely made up of constant frequency, slightly similar to a sine wave. Frequency demodulation or detection can be obtained directly by using the pll circuit. Modulation is the process of influencing data information on the carrier, while demodulation is the recovery of original information at the distant end from the carrier. Double sideband suppressed carrier dsb sc modulation. Modulation and demodulation pdf on the various aspects of modulation and demodulation. Both modulation and demodulation schemes will be dis cussed binary fsk. Amplitude modulation am, demodulation and their circuit implementations. It does not carry much information that we can relate to data or speech. Theory, time domain, frequency domain chapter 4 radio frequency modulation pdf version.
One approach to reduce this interference, known as frequencydivision multiplexing, allocates. Typical modulation system the reverse process is called demodulation. Since frequency modulation is a nonlinear process, an exact description of the spectrum of an frequencymodulated signal for an arbitrary message signal is more complicated than linear process. Modulation can be defined as the process of impressing information from a modulating signal onto another signal called the carrier. Angle modulation is the process in which the frequency or the phase of the carrier varies according to the message signal. A simple pll fm demodulator circuit using ic xr2212 is shown here. However, it is much more complex to both modulate and demodulate a carrier wave with fm, and am predates it by several.
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. Radio frequency spectrum sound need for modulation radio broadcasting modulation methods of modulation amplitude modulation percent modulation upper and lower sidebands. The fm modulation and demodulation process is identical in stereo and monaural processes. Modulation and demodulation medium, it would be dif. The responses are compared against the theoretical. Fm demodulation is also called fm detection and sometimes the phrase fm discrimination is used, although this term tends to be used with older circuits and technology. In the doublesideband suppressedcarrier transmission dsb sc modulation, unlike am, the wave carrier is not transmitted.
Implementation of fsk modulation and demodulation using cd74hc4046a mahendra patel standard linear and logic abstract in telecommunications and signal processing, frequency modulation fm is encoding of information on a. The resulting signal is called the modulated signal in general, it is a bandpass signal. Amplitude modulation and demodulation objective amplitude modulation am is one of the simplest methods for modulating a sinusoidal carrier wave. The purpose of this lab is for you to gain familiarity with the concepts of amplitude. Ee4512 analog and digital communications chapter 6 the dsbsc am coherent receiver has a bandpass filter centered at f c and with a bandwidth of twice the bandwidth of st because of the lsb and usb. Yet, am continues to be used today in many communication applications. Frequency modulation fm is the encoding of information in a carrier wave by varying the. Multiple choice questions and answers on modulation and demodulation.
Phase modulation is similar to frequency modulation and is an important technique in digital communication systems. Frequency modulation is the process in which the frequency of the carrier signal is varied by the modulating signal while the amplitude remains constant. Demodulation is extracting the original informationbearing signal from a carrier wave. 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. 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. The frequency of a radiofrequency channel can be explained best as the frequency of a carrier wave. 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.
Frequency demodulation electronic circuits and diagrams. The goal of this experiment is to become familiar with fm modulation and demodulation. Key system features envelope analysis amplitude demodulation phase and frequency demodulation unlimited display layouts intuitive graphical user interface throughput to disk recording and. Frequency modulation fm frequency modulation is the process of varying the frequency of a carrier wave in proportion to the amplitude of a baseband signal. Frequencyshift keying fsk is the frequency modulation system in which digital information is transmitted through the discrete frequency change of a carrier wave. On amplitude and frequency demodulation using energy operators article pdf available in ieee transactions on signal processing 414. To study amplitude demodulation by linear diode detector 3. Modulation and demo dulation 66c h a p t e r learning objectives what is a carrier wave. Theory shows that in order to transmit a wave effectively, the length of the. Spectra have a typical trapezoidal shape in linear frequency and amplitude in decibels. Multiplexing generally refers to independent signals, those produced by different sources. When the centre frequency of the pll is selected or designed at the fm carrier frequency, the filtered or output voltage in the circuit shown in figure, is obviously the desired demodulated voltage, that varies in magnitude in proportion to the signal frequency. Modulation and demodulation in communication engineering.
In theory the total integrated noise approaches zero as the filter. There are many types of modulation so there are many. The slope detection method revolves around a differentiation operation that exploits the instantaneous frequency of the fm signal. This chapter describes the essential principles behind. The big advantage of frequency modulation is its noise reduction ability, because most of noise is appeared as additional amplitude and in fm the amplitude of signal is hold fixed. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i. This principle is at the heart of amplitude modulation. 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 modem is an equipment that performs both modulation and demodulation. Once the signal has been received, filtered and amplified, it is necessary to recover the. The fm input signal is first subjected to a limiter in order to eliminate any amplitude modulation noise present in the signal. Multiple choice questions and answers on modulation and.
Pulse width modulation with frequency changing emo. Here well use the example of a square law fet as illustrated in figure 9. This book discusses the development in the application of frequency modulation. This is further divided into frequency and phase modulation. The fmmodulated signal has its instantaneous frequency that varies linearly with the amplitude of the message signal. Xr2212 is a highly stable, monolithic pll phase locked loop ic specifically designed for communication and control system applications. Frequency shift keying fsk is the digital modulation technique in which the frequency of the carrier signal varies according to the digital signal changes. Amplitude modulation am, demodulation and their circuit. The simulation involves, generating random message bits, modulating them using qpsk modulation, addition of awgn channel noise corresponding to the given signaltonoise ratio and demodulating the noisy signal using a coherent qpsk receiver.
Carrier modulation allows the transmission of modulating frequencies. In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors. Frequency modulation and demodulation file exchange. To study frequency modulation and determine its modulation factor. Fm demodulation is a key process in the reception of a frequency modulated signal. Modulation and demodulation in communication engineering 1. Most radio systems in the 20th century used frequency modulation fm or amplitude modulation am for radio broadcast.
Implementation of fsk modulation and demodulation using. However if st is sinusoidal, then the instantaneous frequency deviation of the anglemodulated signal is sinusoidal. Both processes aim to achieve transfer information with the minimum distortion, minimum loss and. Analog communication pulse modulation tutorialspoint. This chapter describes the essential principles behind modulation and demodulation, which we introduced briefly in chapter.
Modulation a mapping of the information on changes in the carrier phase, frequency or amplitude or combination. Hapter modulation and demodulation mit opencourseware. The complete waveform simulation for the aforementioned qpsk modulation and demodulation is given next. 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. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. The circuit for fast demodulation of pwmf signal is also described and measuring results are. Amplitude modulation can be produced in various ways. Ofdm is a combination of modulation and multiplexing. Each channel sharing scheme a set of basis vectors. Amplitude modulation or am is a method to transmit signals via electromagnetic transmission. Application to microwave links provides information pertinent to the fundamental aspects of microwave beam techniques. Pdf on amplitude and frequency demodulation using energy. Frequency domain view digital iq modulation phase shift keying constellations lecture 9 analog and digital iq modulation.
Multiplexing method of sharing a bandwidth with other independent data channels. The concepts of amplitude modulation, modulation and demodulation, along with their. Signals and demodulation frequency shift keying fsk is the most common form of digital modula tion in the high frequency radio spec trum, and has important applications in telephone circuits. But such system needs fast demodulator separately for pwm and fm. This gives us something to modulate and carry the information pattern from place to place. In addition to reading the questions and answers on my site, i would suggest you to check the following, on amazon, as well. The amplitude of the carrier remains constant phase modulation pm another form. This article pro vides a general tutorial on fsk in its many forms. The demodulator is composed of a lowpass filter, whose cutoff frequency is slightly higher than fm. Frequency modulation is the process of varying the frequency of the carrier signal linearly with the message signal. If the received carrier phase is assumed to be constant, each of the seven reference values will have to be shifted only once at the beginning of the simulation. 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.
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