Amplitude modulation electronic engineering mcq questions. Power amplifiers are used to boost the carrier and modulating signals before modulation d. Transistor modulator transistor modulation consists of a resistive mixing network, a transistor, and an lc tuned circuit. The left and right channels each limited to 15khz are multiplexed into a single baseband signal using amplitude modulation using frequency modulation to shift the baseband. In pam the amplitude of the individual pulses are varied according to the. Amplitude modulation can be accomplished by multiplying the carrier sine wave by a gain or attenuation factor that varies in accordance with the intelligence signal 2. To code an analog signal in pulse form one can use the height of the pulse, the width or duration, or the position of the pulse relative to standard position. Connect to the two oscilloscope channels using the scope selector, as shown. In this modulation scheme, however, many pulses are transmitted in every time slot, and the number of pulses present in the slot represents the number being transmitted. Pdf origin of 1f am and pm noise in bipolar junction. With an input signal of 5v and a supply voltage of 15v, the output is going to be clipping pretty much all the time. Theres a general overview under am receiver which covers the basic blocks in an amplitude modulated am system.
Intro to generation of ask amplitude shift keying ask in the context of digital communications is a modulation process, which imparts to a sinusoid two or more discrete amplitude levels. To achieve ssb amplitude modulation, we will utilize the following three blocks on the module. Amplitude modulation with simple am radio transmitter duration. Feb 23, 2017 how do i make a circuit of amplitude modulation using transistor. However only the definition of amplitude modulation addresses this side of an am system. Naturally, the amplitude of the current pulses through transistor q1 will vary. In this system we have a fixed amplitude and starting time of each pulse. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. The gain from the modulating signal input port to the. Generation of amplitude modulation basic requirements. Amplitude modulation am involves changing the amplitude of a carrier signal using the output of another modulator signal. Amplitude modulation free download as powerpoint presentation. Then, the audio input is applied to the transistors emitter through a transformer. Amplitude modulator and demodulator circuits unimap portal.
It was developed in the first few decades of the twentieth century. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. The am diode detector is an envelope detector it provides an output of the envelope of the signal. As a result, the amplitude of the carrier sine wave varies in accordance with the modulated signal. This can also be extended to frequency modulation fm and frequencyshift keying fsk, for these can be regarded as a special case of phase modulation. This is the audio frequency sine wave which will be our modulating signal whose frequency range is 300hz3. Pdf digital demodulator of the quadrature amplitude.
With an input signal of 5v and a supply voltage of 15v, the. I routed music audio to the collector, and the emitter was routed. Chapter 7 amplitude modulation techniquesgeneration and. T1 first patch up according to figure 6, but omit the input x and y connections to the multiplier. Please point me to resources that can help me decide what values of components to use. How to make a circuit of amplitude modulation using. Amplitude modulation can be carried out by linearly combining the carrier and intelligence signals then applying the result to a nonlinear component or circuit. Thus the larger the modulation index, the better the transmission efficiency. Ee3 prelab 2 using oscillators to generate fm signals. Amplitude modulation am, demodulation and their circuit implementations. Demodulation the process of recovering or detecting the message signal from the modulated. But the width of each pulse is made properly proportional to the amplitude of the signal at that instant.
Origin of 1f am and pm noise in bipolar junction transistor amplifiers article pdf available in ieee transactions on ultrasonics ferroelectrics and frequency control 442. 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. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Amplitude modulation am the process of combining the message signal with the carrier signal and the two sidebands.
The emitterbase junction of the transistor serves as a diode and nonlinear device. This varying supply voltage is applied to the class c amplifier. Amplitude modulation am transmission and reception bent 31. The term keying is the legacy term from the times of telegraphy, when an operator would manually push keys to make short and long tones. Collector modulation method is high level amplitude modulation c. Modulation is defined as the process by which some characteristics of a carrier signal isvaried in accordance with a modulating signal. The fact that rapidly modulating the amplitude of one wave results in a waveform identical to playing two notes of different frequencies is quite remarkable and for more information on such wave interference, please see our wave interference and beat frequency demo. 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. Its application to the vacuum environment is very difficult because of the long scanning times imposed by the high quality factor q of the cantilevers in vacuum, which present. 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. The feedback you provide will help us show you more relevant content in the future. Name of the specificationsrange quantity componentequipment transistor bc 107 bc107 1 diode0a79 max current 35ma 1. Implementing modulation functions in microwave frequency.
There are two types of devices in which it may be necessary to the generation of amplitude modulation. The amplitude modulation is called amplitude shift keying ask, when the data signal is a digital signal. Department of electronics and communication engineering. Transistor is need to be operate as a switch hence choose saturation values from data sheet. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. To generate and demodulate an amplitude shift keyed ask signal and a binary fsk signal. The dictionary links provide many of the definitions relating to the topic. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%.
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. 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. As such the diode detector or demodulator is able to provide an output proportional to the amplitude of the envelope of the amplitude modulated signal. Jul 09, 2018 amplitude modulation is defined as a process in which the amplitude of the carrier wave ct is varied linearly with the instantaneous amplitude of the messa. Amplitude modulation is a powerful tool that allows you to create and play new sounds that you cannot obtain using conventional oscillators alone. Amplitude modulation an overview sciencedirect topics. Am demodulation amplitude modulation refers to any method of modulating an electromagnetic carrier frequency by varying its amplitude in accordance with the message intelligence that is to be transmitted. Pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal. 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.
One of the simplest electronic methods of modulation is amplitude modulation, or am. In the specific am case of ring modulation discussed in tutorial 8 the two signals are simply multiplied. How does one select the values of components used in amplitude modulation circuit using a transistor common emitter amplifier circuit. Amplitude modulation financial definition of amplitude modulation. Types of modulation 6 flynnkatz 7810 analog modulation amplitude modulation, am frequency modulation, fm double and single sideband, dsb and ssb digital modulation phase shift keying. Theory pulse width modulation is also referred as pulse duration modulation or less often pulse length modulation.
To demodulate the modulated wave using envelope detector. T he main function of a frequency synthesizer is to deliver a stable and clean signal. In this circuit, the carrierwave generated by an oscillator that isnt shown in the circuit is applied to the base of a transistor. When the height is used, it is called pulse amplitude modulation pam. Multiple choice questions and answers on amplitude modulation. The first of these, the am transmitter, generates such high powers that its prime requirement is efficiency, so quite complex means of.
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. Using high level modulation was the only viable option in the early days of radio aka wireless, because it wasnt easy to make a large amplifier to start with, but making it essentially distortion free or linear wasnt feasible at the time. Essentially an amplitude modulated wave consists of a radio frequency carrier a sine wave at one frequency, typically in the radio frequency portion of the spectrum. What is amplitude modulation, am electronics notes. However, there is very little energy wasted when using a fastswitching transistor to control electrical power, unlike when a. Amplitude modulation a continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. What three functions does the transistor in a regenerative detector serve. Useful for engineering students a topic from edlceccf. Other versions of ask use differing nonzero amplitudes to represent 1 and 0. Sep 10, 2017 transistor collector am modulator hsjyothi elelearning. From equation 32, we know that the double sideband signals are proportional to the modulation index.
Multisim simulation of amplitude modulation youtube. I ntroduction an amplitude modulated signal is composed of both low frequency and high frequency components. Amplitude modulation is mostly used in the form of electronic communication. 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. Am modulators base, collector, grid and plate modulators. The circuit that i designed ends up giving a weird waveform but i am pretty sure my professor gave us the same circuit. The demodulation is performed by an envelope detector. 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. 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. Phase modulation analog pm and phaseshift keying digital psk can be regarded as a special case of qam, where the amplitude of the transmitted signal is a constant, but its phase varies.
The am signal is taken from the transistors collector. Am is a relatively simple way to add audio information to a carrier wave so that sounds can be transmitted. There are different kinds of modulation technique based on varying the properties of a pulse train. A ppt explaining amplitude modulation in simple language. How do i make a circuit of amplitude modulation using transistor. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. Using amplitude modulation to shift the baseband signal fm radio 88mhz108 mhz. Implementing modulation functions in microwave frequency synthesizers by alexander chenakin phase matrix, inc. For example, when the modulating signal goes positive, it adds to the collector supply voltage, thereby increasing its value and causing higher current pulses and a higher amplitude carrier.
The base band signal is referred to as the modulating signal and the output of the modulation process is called as the modulation signal. Naansc member wsnet announced that it now offers its network of multiple dwelling unit mdu service providers digital video via quadrature amplitude modulation qam, one of the most costeffective methods of providing 200 channels of digital satellite television to apartment complexes, condominiums, townhomes, retirement communities, nursing homes, marinas, rv parks, university dormitories. Special circuits are required in the receiver to reduce the effects of communication channel and demodulate the modulated signal to receive the message signal. Amplitude modulation article about amplitude modulation by. Pdf in this paper, the digital algorithm and the device for the demodulation of the quadrature amplitude modulation signals are considered. Dutton winter 2004 1 ee3 prelab 2 using oscillators to generate fm signals 1 introduction now that we have a. Each radio station is assigned 200 khz, to transmit a stereo audio. Therefore one performs modulation of signals where a characteristic of a high frequency signal called carrier is modified w. The wave form of am modulation is shown in figure 3.
In ask, only the amplitude of the carrier signal is modified in modulation. The pulse width modulation pwm varies the width of individual pulses according to the amplitude of. In addition, a simple form of am detection and a novel use of the oscilloscope for percent modulation measurements, will. Chapter 7 amplitude modulation techniques generation and detection chapter outline 7.
The basic theory and equations behind amplitude modulation are relatively straightforward and can be handled using straightforward trigonometric calculations and manipulation. University of north carolina at charlotte department of. Introduction to analog communication modulation the process of combining the message signal with the car rier signal that causes the message signal to vary a characteristic of the carrier signal. Modulation for analog new york university tandon school. Modulation is done at high power of carrier and modulating signal b. Amplitude modulation or am is a method to transmit signals via electromagnetic transmission.
When using it as a switch, is it possible to only output the collector signal. Hence, we can calculate the value of modulation index by using the above formula, when the amplitudes of the. T2 use the frequency counter to set the audio oscillator to about 1 khz. Why isnt the frequency of the modulated signal retained when the message. Amplitude modulation with simple am radio transmitter. So this form of amplitude modulation offers a way to create complex nonharmonic timbres that change pitch normally as you play up and down the keyboard. Typical applications include suppressed carrier and amplitude modulation, synchronous detection, fm detection, phase detection, and chopper applications. If greater than 1, we call it over modulation as shown in figure 34. The focus of this lab is to familiarize the student with the modulation and demodulation of an am signal. An am wave may thus be dscribed, in the most general form, as a function of time as follows. Pulse number modulation pnm related to ppm in the sense that we are using pulses with fixed amplitude and width.
In direct modulation, the amplitude modulation of the backscatter approach is the only modulation used. 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. An amplitude modulation circuit according to claim 1 wherein said means for applying a modulating signal includes an audio frequency transformer having a primary winding for receiving an input modulating signal and having a secondary winding resistively coupled between the base and emitter electrodes of said current control transistor. Amplitude modulation am refers to the modulation technique where the carriers amplitude is varied in accordance to the instantaneous value of the modulating or baseband signals amplitude. In amplitude modulation, the message signal mt is impressed on the amplitude of the carrier signal ct a c cos2 f c t there are several different ways of amplitude modulating the carrier signal by mt each results in different spectral characteristics for the transmitted signal we will describe these methods, which are. In amplitude modulation am, we utilize the amplitude of the audio signal to modulate the amplitude of carrier signal, which means that the amplitude of carrier signal will be varied with the amplitude of the audio signal. Data modulation although all the data is transferred to the host by amplitude modulating the carrier backscatter modulation, the actual modulation of 1s and 0s is accomplished with three additional modulation methods. Amplitude modulation definition, types, solved examples. Amplitude modulation am, demodulation and their circuit. I put together a 555 astable with a frequency of a few kilohertz and outputted it to a 2n3904s base. In ook, either bursts of a carrier wave are transmitted or nothing is transmitted depending whether the input message signal is 1 or 0.
How to design a transistor circuit that controls lowpower devices. 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. Feb 17, 2018 free propagation of signals requires it to posses considerable power. Amplitude modulation afm amafm and in particular its large amplitude version, commonly known as tapping mode, is the most extended dafm mode, but it has limitations. However, many applications require not only a fixed frequency signal but also various modulation functions ranging from simple pulse, amplitude, fre. To generate amplitude modulated wave and determine the percentage modulation.
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