Using the circuit from part 3, connect the oscilloscope as shown in figure 4. Increase the modulated signal until an am waveform appears. A square law nchannel fet field effect transistor will pass a drainsource current. With the modulating voltage adjusted to zero amplitude, increase the carrier amplitude until v o has a value of 2 v pp. This chapter describes the essential principles behind. The am signal is taken from the transistor s collector. Then, the audio input is applied to the transistor s emitter through a transformer. In this code, it is considered the default value of ma equal to 1 for hundred percent modulation. Amplitude modulation circuit implementation for use in a. Amplitude modulation or am is a method to transmit signals via electromagnetic transmission.
I routed music audio to the collector, and the emitter was routed. Suppose the input is an analog voltage between 0 and 1 v. Generation of frequency modulation varactor diode modulator. Amplitude modulation am is the technique in which the amplitude peaktopeak voltage of the carrier wave is varied as a function of time in proportion to the strength of the data signal. Multiple choice questions and answers on amplitude modulation. It was developed in the first few decades of the twentieth century. Change the amplitude of fg1 to 2 v and capture the am signal and its spectrum, use a different file name. The amplitude modulation and demodulation technique involved in this project comprises of three stages. The chapter is designed to help teach and understand communication systems using a classroom. Explain the generation of am waves using square law. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Error rate probability for coded mqam with mrc diversity in the presence of cochannel interferers over nakagamifading channels,authors.
Collector amplitude modulation of the class e tuned power amplifier. The amplitude or the strength of a high frequency carrier wave is changed in accordance with the amplitude of message signal. The base band signal is referred to as the modulating signal and the output of the modulation process is called as the modulation signal. The fundamental goal of modulation is to produce an information bearing modulated signal with efficient utilization of the channel. The various parts of this lab unit will be used to explore and verify the operation of the two am modulation methods using four different am modulating circuits. Other versions of ask use differing nonzero amplitudes to represent 1 and 0.
When the modulation signal occurs, the ac voltage across the secondary of the modulation transformer will be added to and subtracted from the collector supply voltage. In pam the amplitude of the individual pulses are varied according to the. Amplitude modulation an overview sciencedirect topics. The demodulation is performed by an envelope detector. How to design a transistor circuit that controls lowpower devices. Envelopes the waveform of the amplitude variations of an amplitude modulated signal. University of north carolina at charlotte department of. An am wave may thus be dscribed, in the most general form, as a function of time as follows. Transistor is need to be operate as a switch hence choose saturation values from data sheet. When using it as a switch, is it possible to only output the collector signal.
The first of these, the am transmitter, generates such high powers that its prime requirement is efficiency, so quite complex means of. The original method of electronically encoding sound information on radio waves is called amplitude modulation, or am. In ook, either bursts of a carrier wave are transmitted or nothing is transmitted depending whether the input message signal is 1 or 0. Amplitude modulation circuit implementation electrical. In amplitude modulation am, we utilize the amplitude of the audio signal to modulate. What results is a new modulatedsignal, given by yt cftcos t. Quadrature amplitude modulation qam is the name of a family of digital modulation methods and a related family of analog modulation methods widely used in modern telecommunications to transmit information. If this voltage needs to be boosted from the dc source, it can be accomplished either before the ac stage by using a dcdc boost converter, or after the ac stage by using a boost transformer. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example.
The ad630 is a high precision balanced modulator demodulator. So we can say that we have a variable gain since the trans conductance of transistor. In ask, only the amplitude of the carrier signal is modified in modulation. Abstracta single tone sinusoidal signal is transmitted using amplitude modulation and is demodulated at the receivers end using an envelope detector and the attenuated signal is amplified using common source bjt amplifer. Electronics amplitude modulation am in ltspice xvii. The message signal is, for example, a function of the sound to be reproduced by a. Amplitude modulation with simple am radio transmitter duration. Making a carrier making a signal making a mixermodulator making an fft. The fm circuit using ic566 was designed and the modulation index for practical. Am is a relatively simple way to add audio information to a carrier wave so that sounds can be transmitted. Mc1496, mc1496b balanced modulators demodulators these devices were designed for use where the output voltage is a product of an input voltage signal and a switching function carrier. Collector modulation method is high level amplitude modulation c.
Modulated output is taken from the collector of the transistor. Aiaiai tma 1 studio engineered by young guru with mic. Generation of am waves using the switching modulator could be understood in a better way by observing the switching modulator diagram. Modulation is done at high power of carrier and modulating signal b. It conveys two analog message signals, or two digital bit streams, by changing modulating the amplitudes of two carrier waves, using the amplitude shift keying ask digital modulation. Pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. A pulse width modulation scheme uses a series of pulses to represent an analog value. There are two types of devices in which it may be necessary to the generation of amplitude modulation. Matlab code for amplitude modulation am file exchange. Amplitude modulation and demodulation electrical and computer. To study the amplitude modulation and demodulation and to calculate the modulation index.
Ata5790ek1 immobilizer base station immobilizer chip remote keyless entry for car ata5279 atmega168 application touch screen avr immobilizer antenna car key ata2270ek2. Amplitude modulation early radio ee 442 spring semester. As an example, the following figure shows the amplitude modulation with. Sidebands the frequency bands on each side of the carrier frequency that are formed during modulation. Carrier modulation allows the transmission of modulating frequencies without the use of transmission wire as a medium. The simple pulse modulation technique called pulse amplitude modulation pam proved to be more power efficient than the pwm and consumes constant power for individual pulses like ppm. Design and implementation of amplitude modulator and demodulator introduction communication is the most important needs from the very beginning of civilization. Alternatively look into the early effect because this can also be used to create amplitude modulation. The modulating signal contains the intended message or information sometimes consisting of audio data, as in am radio. The ad630 is a high precision balanced modulatordemodulator. The pulse width modulation pwm varies the width of individual pulses according to the amplitude of.
These might be operating with the transistor in the saturation region i. Chapter 7 amplitude modulation techniques generation and detection chapter outline 7. I put together a 555 astable with a frequency of a few kilohertz and outputted it to a 2n3904s base. It is a modulation system in which the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the signal at the instant of sampling. Sc am signal can still be successfully demodulated. In the frequency domain, amplitude modulation produces a signal with power. What we do in am, very roughly,is to throw away the frequency content of. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. Overmodulated am signals and its requirement for coherent detection are also considered. We find that the expression for v o t of equation 3 represents an am wave with m 2ba hence, the square law modulator produces an am wave. Abstractthis project explores the robust design of amplitude modulation and demodulation using bjt amplifier and diode detector. Analog communication laboratory manual santhosh thottingal.
Amplitude modulation am, demodulation and their circuit. Amplitude modulation am transmission and reception bent 31. Amplitude modulation am is a modulation technique used in electronic communication, most. The code for amplitude modulation am with control of modulation index ma has been developed using matlab according to conventional theory. Frequency modulation fm the process of combining the message signal with the carrier signal that causes the message signal to vary the frequency of the carrier signal. Power amplifiers are used to boost the carrier and modulating signals before modulation d. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. Hapter modulation and demodulation mit opencourseware. Showing you how to multiply two signals and show the frequency spectrum of the signals fft. If you are new to matlab, please go through our tutorials. It is defined as the process in which one of the characeteristic of carrier signal is varied in accordance with the instantaneous values of message signal amplitude of the message signal. The focus of this lab is to familiarize the student with the modulation and demodulation of an am signal.
There are different kinds of modulation technique based on varying the properties of a pulse train. Typical applications include suppressed carrier and amplitude modulation, synchronous detection, fm detection, phase detection, and chopper applications. Real and complex modulation tipl 4708 presented by matt guibord prepared by matt guibord 1. The focus of this lab is to familiarize the student with the modulation and.
By deleting the sine wave block and revising the mdlslx file, the received dsb. I ntroduction an amplitude modulated signal is composed of both low frequency and high frequency components. The pulse frequency is constant, but the width of each pulse varies according to the value of the input. An amplitude modulated signal is composed of both low frequency and high.
Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave. Chapter 7 amplitude modulation techniquesgeneration and. The inverted signal itself is composed of a pulsewidthmodulated pwm signal which encodes a sine wave. 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. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave.
Naturally, the amplitude of the current pulses through transistor q1 will vary. Can anyone explain the pulse width modulation circuit. To understand the theoretical foundations of analog communications as well as of doublesideband amplitude modulation and demodulation dsbam to design the simulink model of the dsbam to analyze each signal in time and frequency domains using time scope and spectrum analyzer. It may be necessary to adjust the level and frequency of both v c and v m to achieve a suitable waveform and index of modulation. Set the amplitude of the carrier signal generator output voltage to 2 vpp, and the frequency to 100 khz, and set the amplitude of the em generator to 6 vpp. The spectrum of the modulated signal yt can be found by using the modulation property of the fourier transform. Amplitude modulation am is a modulation technique where the. What results is a new modulated signal, given by yt cftcos t. The ad633 can be used as a linear amplitude modulator with no external components. Modulation is defined as the process by which some characteristics of a carrier signal isvaried in accordance with a modulating signal. Am modulators base, collector, grid and plate modulators.
Amplitude modulation am is a one of the conventional modulation technique to transmit signals using a carrier wave. Am an amplitude modulated signal that contains the carrier signal and. This varying supply voltage is applied to the class c amplifier. When expressed as a percentage it is the same as the depth of modulation. Adj products mega flat tri pak bright tri colored led lighting system. Generation of amplitude modulation basic requirements. The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier. In this circuit, the carrierwave generated by an oscillator that isnt shown in the circuit is applied to the base of a transistor.
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