Tune the hfo in 1 hz steps until the beat is slowest, then turn on the loop. In this chapter we will discuss ways of demodulating am, cw, fm, phase, and pulse modulation. You will model the pll, and recover the message from the fm signal. During the demodulation lesson, the modulated carrier is fed into a demodulator circuit. Then get rid of the dc signal, the audio signal will be recovered. To tune in a strong am station, first put the receiver in synchronousam mode with the pll turned off. Receiving am signals this tutorial is a guide to receiving am signals. To study and perform pulse width modulation and demodulation.
Note that this is on the very low end of the recommended voltage range. Frequency modulation fm is a process in which the carrier frequency is varied by the amplitude of the modulating signal i. The input modulated waveform, original audio waveform, demodulator output, and filtered output waveforms are displayed sequentially on the oscilloscope to allow the instructor to walk the students through the demodulation process. Double sideband modulation, amplitude modulation suppressed carrier single sideband vestigial sideband superhetrodyne am receiver amplitude modulation. Since the api 560 features proportional q, which intuitively widens the filter bandwidth at lower settings and narrows it at higher. To study and perform pulse amplitude modulation and demodulation. This is accomplished by a process called detection or demodulation. 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. Restoring or recovering the message signal from the received modulated waveform that is generally corrupted by noise types of am detectors. Fm demodulation is a key process in the reception of a frequency modulated signal. Pcs lab manual page 1 laboratory manual principles of communication system lab ee226f ivth semester prepared by. Vectors and modulation cse 466 interfacing 3 spose m and n are orthogonal unit vectors. This section facilitates the user to have his choice of external or internal clock feeding to the. Frequency division multiplexing, fdma amplitude modulation and demodulation.
Amplitude modulation is defined as the process in which the amplitude of the carrier wave ct is varied about a mean value, linearly with the baseband signal. Demodulation is extracting the original informationbearing signal from a carrier wave. There are different types of modulation and so are demodulators. Set the proper amplitude and frequency of the modulating signal to get a reasonable am waveform. The beat between the am carrier and the hfo will be audible in the speaker, and visible in the leds turning on and off alternately. The resulting amplitude modulation am waveform is then demodulated using an. Elenco electronics amfm108tk assembly and instruction manual. Double sideband suppressed carrierdsbsc mt message signal, m its spectrum, cosct carrier signal, c carrier. The singlesided spectrum of the modulated signal replicates the baseband. A dsbsc generation and demodulation instrument is described as side.
Doublesideband suppressedcarrier transmission dsbsc is transmission in which in the dsbsc modulation, unlike in am, the wave carrier is not transmitted. Ee4512 analog and digital communications chapter 6. Demodulation is defined as extracting the original informationcarrying signal from a modulated carrier wave. Frequency description, generation of vsb modulated wave, time domain description, envelope detection of a vsb wave pulse carrier, comparison of am techniques, applications of different am systems. Ee4512 analog and digital communications chapter 6 chapter 6 analog modulation and demodulation amplitude modulation pages 306309. 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. Demodulation of ssb waves, vestigial side band modulation.
Modulation is the process of altering the characteristics of the amplitude, frequency, or phase angle of the highfrequency signal in accordance with the instantaneous value of the modulating wave. If we can let mt be the envelope of the modulated signal, then a much simpler circuit, the envelope detector, can be used for demodulation noncoherent demodulation. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. Lab manual frequency modulation experiment 8 experiment 2 phase look loop. Discuss the requirements for recovery of intelligence from an am signal and describe the theory of operation of the following am demodulators. Other forms of modulation can avoid this sensitivity and are less. Describe fm demodulation circuit operation for the phaseshift and gatedbeam discriminators and the ratiodetector demodulator. Switch off the experimental kit during making connections. Remember to set up the vco module in 100 khz vco mode. Am modulation where the amplitude of the carrier does not depend on the value of the modulating signal. The block diagram of a phase locked loop pll is shown in figure 1. Demodulation of amplitude modulated signal submitted to. From dsbsc to dsbwc am carrier recovery circuits, which are required for the operation of coherent demodulation, are sophisticated and could be quite costly. A continuous wave goes on continuously without any intervals and it is the baseband message signal, which contains the information.
Waves greg wells voicecentric user guide 4 the ingredients of the voicecentric plugin are all the elements of my favorite waves plugins, reacting how and when i want them to. The term demodulator is used because the demodulation process is considered to be the opposite of modulation. The envelope demodulator is a simple and very efficient device which is suitable for the detection of a narrowband am signal. Suppose there is a nonmodulated carrier at the input.
Introduction frequency modulation is a form of modulation, which represents information as variations in the instantaneous frequency of a carrier wave. The signal output from a demodulator may represent sound an. It is a system of modulation in which the amplitude of the carrier signal is made proportional to the instantaneous amplitude of the modulating message signal. First, the amplitude modulated if signal is applied to a diode in such a way as to leave only the negative portion of that signal see figure 12. Modulation allows us to transmit multiple signals in the same medium i. Dutton ee3 winter 2004 1 ee3 lab 1 amplitude modulation and demodulation 1 lab notes a word about power. The circuit in which restoration is achieved is called the detector or demodulator both of these terms are used in neets. To extend the range of sound, we need to transmit it through a medium other than air, such as a phone line or radio. Digital modulation and demodulation fsk,psk,bpsk,qpsk techniques. Note down frequency and amplitude of the demodulated output waveform.
Pdf on amplitude and frequency demodulation using energy. Demodulation is a key process in the reception of any amplitude modulated signals whether used for broadcast or two way radio communication systems. Feed the am wave to the demodulator circuit and observe the output. On amplitude and frequency demodulation using energy operators article pdf available in ieee transactions on signal processing 414. Demodulation is the process by which the original information bearing signal, i. If you have a usrp available you could also use that as your input and receive live signals. A demodulator is an electronic circuit that is mainly used to recover the information content from the modulated carrier wave. The envelope detector is a half wave rectifier and provides a dc bias c to the processed dsblc am. Pdf analog communication system pdf notes ac notes sw. This is why am radio tends to suffer from buzzes, crackles, whistles, etc. Then inner products dot products are 1 1 0 can interpret inner product as projection of vector 1 v1 onto vector 2 v2in other words, inner product of v1 and v2 tells us how much of vector 1 is there in the direction of vector 2.
Page 16 am detector and agc stage the purpose of the detector is to change the amplitude modulated if signal back to an audio signal. To understand the theory of amplitude demodulation. The bandwidth is set wide enough to pass the transmitted signal provides adjacent channel rejection. Cme312 lab manual frequency modulation experiment 8. The circuits carrier generator, modulator and demodulator are provided with the. It rectifies the modulated am signal and obtains a positive half wave signal.
There are no amplitude scales shown, but you should be able to deduce the depth of modulation 1 by inspection. There are many types of modulation so there are many types of demodulators. After that, the signal will pass through a lowpass filter and obtain an envelop detection. Circuit used suitable for envelope detector noncoherent diode with an rc. The goal of this experiment is to become familiar with fm modulation and demodulation. A narrowband am wave is the one in which the carrier frequency f c is much higher as compared to the bandwidth of the modulating signal. The main intensity knob is deceptively simple to use. At the end of this experiment, the students are expected to. The theory behind multichannel am radio for k 1k, let x kt be a continuoustime signal with fourier transform x kj. Among the types of modulation techniques, the main classification is continuous wave modulation and pulse modulation. The am demodulator essentially measures the power or amplitude of the signals presented to it. To verify amplitude modulation and demodulation and to calculate the. It uses a data file that contains several seconds of recorded signals from the am broadcast band. Basic concepts of modulation three kinds of modulations modulation is the process of facilitating the transfer of information over a medium.
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