Apr 12, 2015 modulation and demodulation in communication engineering 1. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Pcm demodulator quantizing levels xt nts q0 q1 q2 q3 q4 q6 q5 qnts. Frequencyshift keying fsk is the frequency modulation system in which digital information is transmitted through the discrete frequency change of a carrier wave. Modulation involves multiplying the input signal xt by a cosine with a frequency f2. Digital modulation schemes are possible because the transmitterreceiver pair has prior knowledge of how data is encoded and represented in the communications system. Nov, 2018 a modem or broadband modem is a hardware device that connects a computer or router to a broadband network. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i.
Multiplexing generally refers to independent signals, those produced by different sources. 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. Terms like diode detector, synchronous detector and product detector are widely used. But the term demodulation tends to be used more widely when referring to the process of extracting the modulation from the signal. In most media for communication, only a fixed range of frequencies is available for transmission. The fmmodulated signal has its instantaneous frequency that varies linearly with the amplitude of the message signal.
The term detection is the older term dating back to the early days of radio. The amplitude of the carrier remains constant phase modulation pm another form of analog modulation technique which we will not discuss. Dhanalakshmi college of engineering is committed to provide highly disciplined, conscientious and. Pcm is in binary form,so there will be only two possible states high and low0 and 1. Hapter modulation and demodulation mit opencourseware. One way to communicate a message signal whose frequency spectrum does not fall within that fixed frequency range, or one that is otherwise unsuitable for the channel, is to alter a transmittable signal according to the information in your message signal. There are many types of modulation so there are many types of demodulators. Berrou c, glavieux a, thitimajshima p 2010 near shannon limit errorcorrecting pdf. What is amplitude modulation, am electronics notes. 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. To understand the methods of measuring and adjusting the pcm demodulation circuit. Analog communication vsbsc modulation tutorialspoint.
The principle of fsk modulation is to send binary data with two different frequencies and the resultant modulated signal is regarded as amplitude modulation am of different carrier frequencies. The pulse code modulator technique samples the input signal xt at a sampling frequency. Multiplexing method of sharing a bandwidth with other independent data channels. In pulse code modulation, the message signal is represented by a sequence of coded pulses. To improve the quality of reception to increase the range of communication need of demodulation the wireless signal consists of radio frequency high frequency carrier wave modulated by audio frequency low frequency. This chapter describes the essential principles behind. Modulation a mapping of the information on changes in the carrier phase, frequency or amplitude or combination. Carrier modulation allows the transmission of modulating frequencies. Figure 1 shows the block diagram of the top level integration of ofdm modulation and demodulation. Pcm is even used in the database management systems. Laboratory manual principles of communication system lab ee226f ivth semester prepared by. Mar 16, 2019 multiple choice questions and answers on modulation and demodulation.
Instead of a pulse train, pcm produces a series of numbers or digits, and hence this process is called as digital. A signal is pulse code modulated to convert its analog information into a binary sequence, i. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Pulse code modulation is used in compressing the data that is why it is used in storing data in optical disks like dvd, cds etc. There are many modulation techniques, which are classified according to the type of modulation employed. The instructor would begin the demodulation demonstration by providing some background material on the concept of demodulation. Of them all, the digital modulation technique used is pulse code modulation pcm. Modulation types of modulation definition applications. Implementation of fsk modulation and demodulation using. Today, a modem is most often used to describe a broadband modem. A modem is an equipment that performs both modulation and demodulation. Single bit pcm output at different line speed clock. In chapters 1 and 2 you studied how to apply intelligence modulation to an rf carrier wave.
Amplitude modulation or am as it is often called, is a form of modulation used for radio transmissions for broadcasting and two way radio communication applications. Sn of the pll demodulated signal with a sn of 20db at the input fm signal. To implement the simulink models for fm including a basic sinusoid and a multimedia file music to analyze each signal in time and frequency domains using time scope and spectrum analyzer. To understand the theory of pcm demodulation circuit. There are many types of modulation so there are many. In addition to reading the questions and answers on my site, i would suggest you to check the following, on amazon, as well. Analog communication vsbsc modulation in the previous chapters, we have discussed ssbsc modulation and demodulation. For example, a cable modem and dsl modem are two examples of these types of modems. Parallel to serial conversion by varying the line speed clock. Amplitude modulation can be produced in various ways.
Demodulation is extracting the original informationbearing signal from a carrier wave. Ssbsc modulated signal has only one sideband frequency. 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. This application report discusses logic level implementation of binary fsk bfsk modulator and demodulator using a phaselocked loop pll device.
To understand the theoretical foundations for angle modulation as well as frequency modulation fm and demodulation. Tcom 370 notes 995 modulation and demodulation modems for. The bandwidth of each is dependent on the message bit rate. In this article, we are going to briefly talk about what modulation is and the need for it. The goal of this experiment is to become familiar with fm modulation and demodulation.
The demodulation demonstration is set up by configuring the board for 100% modulation and connecting one channel of the scope to the audio waveform at tp1 and the other channel the output. The signal output from a demodulator may represent sound an analog audio signal. Storage oscilloscope is desired for satisfactory observation of pcm wave forms 4. Frequency shift keying fsk modulation and demodulation. In early days, the communication system is mostly using the analog signal to transmit signals. This demodulator is more complex than most asynchronous demodulators. 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. This gives us something to modulate and carry the information pattern from place to place. Recall that our goal is to transmit data over a commu nication link, which we achieve by mapping the. Introduction it is a process in which the frequency of the carrier is varied in accordance with the instantaneous value of modulating voltage. In addition to a variable bandpass filter, one auto notch and one manual notch filter can be utilized to eliminate interfering signals. The technology is used in communication systems such as amateur radio, caller id, and urgent situation broadcasts. Demodulation involves multiplying the modulated signal again by a.
Figure 2 lists the io ports of the modulation and demodulation modules. Observation simulation of signal constellations of bpsk, qp sk and qam 8. We can also get back our analog signal by demodulation. To study and perform pulse code modulation and demodulation. Modulation techniques pwm and pulse code modulation. To study and perform amplitude shift keying modulation and demodulation. Review pulse train bandwidth s ingle pulse of duration. Both processes aim to achieve transfer information with the minimum distortion, minimum loss and. Multiple choice questions and answers on modulation and.
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. Radio frequency spectrum sound need for modulation radio broadcasting modulation methods of modulation amplitude modulation percent modulation upper and lower sidebands mathematical analysis of a modulated carrier wave power relation in an am. This book presents a comprehensive overview of the various modulation tech niques mentioned. Communication systems has used a very clever technique called modulation to increase the reach of the signals. Wave fundamentals and modulation demonstration board. Modulation and demo dulation 66c h a p t e r learning objectives what is a carrier wave.
However, can also be used to describe what was initially considered a modem described. Modulation and demodulation in communication engineering. In all digital communication systems, both the modulator at the transmitter and the demodulator at the receiver are structured so that they perform inverse operations. There will be a minimum frequency separation required of the two tones. Each one of these digits, though in binary code, represent the approximate amplitude of the signal sample at that instant. A read is counted each time someone views a publication summary such as the title, abstract, and list of authors, clicks on a figure, or views or downloads the fulltext.
This principle is at the heart of amplitude modulation. Modulation and demodulation summary figure 19 is a block diagram that summarizes the steps involved in modulating and demodulating a signal by a frequency f2. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. Digital phase modulation and demodulation request pdf. In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors. Fsk frequency shift keying d1 63 fsk in f 1 f 2 decision out figure 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. Although one of the earliest used forms of modulation it is still used today, mainly for long, medium and short wave broadcasting and for some aeronautical point to point. Ee4512 analog and digital communications chapter 6 chapter 6 analog modulation and demodulation amplitude modulation pages 306309. The fft core is clocked faster than the baseband data so that it can be shared, for instance, for fdd operation or by multiple antennas in mimo systems.
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