Amplitude modulationwhich of course is the origin of the term am radiovaries the amplitude of the carrier according to the instantaneous value of the baseband signal. The original waveform amplitude is quantized with a resulting loss of information. This is a laboratory manual for analog communication experiments. Amplitude modulation circuit implementation for use in. 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. The original method of electronically encoding sound information on radio waves is called amplitude modulation, or am. This section contains questions regarding the results obtained. The modulating signal contains the intended message or information sometimes consisting of audio data, as in am radio. Then, the audio input is applied to the transistors emitter through a transformer. The resulting plate current flows in pulses, the amplitude of each pulse being proportional to the instantaneous bias and therefore to the instantaneous modulating voltage. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that. Diagram from 1922 showing the circuit of a crystal radio. Tuned circuits filter out the modulating signal and carrier harmonics, leaving only carrier and sidebands.
To study frequency modulation and determine its modulation factor 4. One of the easiest ways to implement qam with hardware is to generate and mix two sine waves that are 90 degrees out of phase with one another. Amplitude modulation is mostly used in the form of electronic communication. The binary signal when ask modulated, gives a zero value for low input while it gives the carrier output for high input. The carrier frequency, fc, should be larger than the highest spectral component. Other methods of demodulating an am signal use synchronous techniques and provide much lower levels of distortion and improved reception where. Amplitude modulation can be carried out by linearly combining the carrier and intelligence signals then applying the result to a nonlinear component or circuit. 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. The following algorithm is commonly used to represent amplitude modulation.
Analog communication lab manual, prepared by nakka. The depth of modulation, defined below, can be adjusted with the adder gain control g. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Mar 05, 2019 quadrature amplitude modulation qam requires changing the phase and amplitude of a carrier sine wave. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. A demodulator is an electronic circuit that is mainly used to recover the information content from the modulated carrier wave. Am is a relatively simple way to add audio information to a carrier wave so that sounds can be transmitted.
Analysis, design and modelling of analog and mixedsignal circuits and systems. A carrier wave, after being modulated, if the modulated level is calculated, then such an attempt is called as modulation index or modulation depth. As in figure 34, the application of these pulses to the tuned tank circuit will yield generation of amplitude modulation. The simplest method for representing this kind of modulation is fresnels vectorial representation with. Frenzeljr, in handbook of serial communications interfaces, 2016.
The two most common forms of amplitude modulation use either a complex carrier or a single sinusoidal carrier. We can treat the theoretical concept of am in a much better way using. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. Use fg1 as the message signal and fg2 as the carrier signal. Amplitude modulation and demodulation electrical and computer. Pdf this paper presents a lowfrequency amplitude modulator and demodulator. It is possible to look at the theory of the generation of an amplitude modulated signal in four steps. Dec 21, 2017 amplitude modulation is one of the earliest radio modulation techniques. The resulting plate flows in pulses, the amplitude of each pulse being proportional to the instantaneous bias and therefore to the instantaneous modulating voltage. Remember, for analysis purposes keep the modulation index and frequency the same as part 2, step 3. We give the theory and the experimental results of the modified switching modulator. The pulse may take any real voltage value that is proportional to the value of the original waveform. It states the level of modulation that a carrier wave undergoes.
The method of ordinary differential equations has been demonstrated as a simple yet powerful tool in dealing with the complex circuit phenomena of either amplitude, phase or frequency modulation. There are different types of modulation and so are demodulators. Demodulation is defined as extracting the original informationcarrying signal from a modulated carrier wave. The am generator, or exciter, as such a low power source of modulated signal is often called, is now set up. Amplitude modulation am, demodulation and their circuit.
In this circuit, the carrierwave generated by an oscillator that isnt shown in the circuit is applied to the base of a transistor. It was developed in the first few decades of the twentieth century. Generation of amplitude modulation basic requirements. When expressed as a percentage it is the same as the depth of modulation. This experiment examines the characteristics of the amplitude modulation am process. Source called v1 generates the message to be transmitted.
The percent modulation can be varied simply by changing the amplitude of the 30 khz carrier signal. Oct 09, 2018 the resulting plate current flows in pulses, the amplitude of each pulse being proportional to the instantaneous bias and therefore to the instantaneous modulating voltage. Modulation allows us to transmit multiple signals in the same medium i. To generate and demodulate an amplitude shift keyed ask signal and a binary fsk signal. The second is to investigate classical analog amplitude modulation and the envelope detector. It can be achieved in a number of ways, but the simplest uses a single diode rectifier circuit.
Phase modulation is similar to frequency modulation and is an important technique in digital communication systems. Amplitude modulation, am, is one of the most straightforward ways of modulating a radio signal or carrier. Amplitude modulation a1 53 experiment aligning the model the low frequency term at to generate a voltage defined by eqn. The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier. There are no amplitude scales shown, but you should be able to deduce the depth of modulation 1 by inspection. The math the mathematical relationship for amplitude modulation is simple and intuitive. Frequency modulation is a type of angle modulation.
The basic theory and equations behind amplitude modulation are relatively straightforward and can be handled using straightforward trigonometric calculations and manipulation. The pam modulator and demodulator circuits simple compared to other kind of modulation and. Lowers amplifier gain when strong signal amplitude is present to keep transducer output constant avoids having to adjust the volume control for weak vs strong signals needed because signal strength can vary due to many factors such as. In this video, i have explained amplitude modulation by following outlines. Gathering like terms and simplifying the equation leaves. Theory, time domain, frequency domain chapter 4 radio frequency modulation pdf version. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. Learn about the most straightforward way of encoding information in a carrier waveform. What is amplitude modulation, am electronics notes. Mc1496d 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. Set channel b to be a 29khz sine wave, amplitude 1v, phase 90deg, destination out1 set channel c to be a 31khz sine wave, amplitude 1v, phase 270deg, destination out1 at this point, you should have a 100 % amplitude modulated signal.
Amplitude modulation early radio ee 442 spring semester. The am signal is taken from the transistors collector. 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. The general form of a sinusoidal signal can be written as ft. To study sampling and reconstruction of pulse amplitude modulation system 6. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. Channeltochannel variance on signal strength changes on weather and ionosphere conditions. Amplitude modulation am the process of combining the message. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation.
Carrier modulation allows the transmission of modulating frequencies without the use of transmission wire as a medium. Peter wilson, in the circuit designers companion fourth edition, 2017. Enough about modulation theory, lets get a more practical view of what pwm really is. Am modulators base, collector, grid and plate modulators. For creating the fpaa circuits, amplitude modulation and synchronous. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. Here, the carrier signal can be varied by using the r1, r2 and c. Communication systemsamplitude modulation wikibooks, open. Pdf realization of lowfrequency amplitude modulator and.
Quadrature amplitude modulation qam national instruments. Index terms amplitude modulation, analog circuit, analog modulator. Connect the carrier signal at carrier ip of the modulator circuit. In amplitude modulation, it is the voltage level of the signal to be transmitted. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. Angle modulation changes the phase of a signal as well as its amplitude, where amplitude modulation leaves the phase unchanged. In this modulation, the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the modulating signal. Amplitude shift keying ask is a type of amplitude modulation which represents the binary data in the form of variations in the amplitude of a signal. The circuit s carrier generator, modulator and demodulator are provided with the. 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. Therefore, when we receive the amplitude modulation signal, we need to restore the audio signal. Explain briefly in your report how amplitude modulation is accomplished by this circuit. 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. It requires that the amplitude of the dc a part of at is equal to the amplitude of the ac part a.
Each part may be of any convenient amplitude at the input to an adder. Jun 17, 2018 in this video, i have explained amplitude modulation by following outlines. R in the circuitary, so that the capacitor may discharge through it. Pulse amplitude modulation is the basic form of pulse modulation. Before we study in detail about pam lets know the concepts of modulation. The application of these pulses to the tuned tank circuit will give amplitude modulation. Amplitude modulation definition, types, solved examples. The binary signal when ask modulated, gives a zero value for low input while it. The carrier frequency can be instantly calculated by the formulae as 0.
Connect channel 1 probe of the oscilloscope to the output of the modulator at pin 7. The maximum and minimum values of the envelope of the modulated wave are represented by a max and a min respectively. Amplitude modulation am broadcastband transmitter power levels tend to be around 100500 kw, but the transmitters are usually located away from centers of population. As before, this may require a manual adjustment of the voltsdiv and.
It is still in use today in a variety of systems, including, of course, am broadcast radio. Use the spectrum analyzer to compare this modulator to the one in part 2. It requires that the amplitude of the dc a part of a t is equal to the amplitude of the ac part a. Prepare the second channel of the signal generator for a v m of 500 hz, and adjust the amplitude to something. Amplitude modulation we will start our study of communications systems by first analyzing the am method of communicating signals. In pam the amplitude of the individual pulses are varied according to the amplitude of the modulating signals. This principle is at the heart of amplitude modulation. Amplitude, frequency and phase modulation can be applied directly by software to the generated signals, which gives great flexibility where complicated and precise waveforms are required. No information is lost, but the energy is redistributed in the frequency domain.
Quadrature amplitude modulation qam requires changing the phase and amplitude of a carrier sine wave. Phase modulation is another type of angle modulation very similar to frequency modulation. In amplitude modulation or am, the carrier signal has its amplitude. Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave.
An am wave may thus be dscribed, in the most general form, as a function of time. 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. Field strength levels in the 110 vm range may be experienced occasionally, but at medium frequencies coupling to circuit. Pulse amplitude modulation pam theory of and its applications. In modulation, one characteristic of a signal generally a sinusoidal wave known as the carrier is changed based on the information signal that we wish to transmit modulating signal. Amplitude modulation am is defined as a process in which the amplitude. That could be the amplitude, phase, or frequency, which result in amplitude modulation am, phase modulation pm, or frequency modulation fm. Frequency modulation keeps constant the amplitude of the highfrequency oscillation that is used as a signal and to vary the instantaneous frequency for presenting the information. To study amplitude demodulation by linear diode detector 3. Here is the circuit used for modulation and its simulation. But phase modulation seems to be in a different categorypm radio is by no means a common term.
Frequency division multiplexing, fdma amplitude modulation and demodulation. Amplitude modulation an overview sciencedirect topics. Keywords analogue circuits, amplitude modulation, synch. The carrier frequency, fc, should be larger than the highest spectral component in mt. The circuit for generating an am modulated waveform must produce the product of the carrier. From experiment 3, we know that the amplitude modulation signal utilizes the amplitude of audio signal to modulate high frequency carrier signal. We have seen that rf modulation is simply the intentional modification of the amplitude, frequency, or phase of a sinusoidal carrier signal. Notice that the pulses are wider where the amplitude of the sine wave is higher and narrower where the amplitude is lower. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. With the modulating voltage adjusted to zero amplitude, increase the carrier amplitude until v o has a value of 2 v pp. As we mentioned before, well use dsbc modulation because of its ease in demodulation. Amplitude shift keying modulation circuit can be designed with 555timer ic as an astable mode. Typical applications include suppressed carrier and amplitude modulation, synchronous detection, fm detection, phase detection, and chopper. Amplitude modulation am is a modulation technique where the.
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