Each radio station is assigned 200 khz, to transmit a stereo audio. The wave form of am modulation is shown in figure 3. Am is widely used for the transmission of data in everything from short range wireless links such as wifi to cellular telecommunications and much more. 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. Watch theory lectures to improve your physics and remove your confusions. Carrier modulation allows the transmission of modulating frequencies without the use of transmission wire as a medium. Angle modulation changes the phase of a signal as well as its amplitude, where amplitude modulation leaves the phase unchanged. Mixer s and amplitude modulation the underlying theme of this lab is amplitude modulation. Both the dac and dds operate with an spi interface.
Amplitude modulation ang man shun october 30, 2012 reference hwei p. Signal modulation this worksheet and all related files are. Remember, the purpose of this board is to demonstrate the concept of modulation, consequently the circuit is designed to reliably produce a modulated waveform for. Here is the circuit used for modulation and its simulation. The main advantage of using am modulation is that it has a very simple circuit implementation especially for reception, creating widespread adoption quickly. Now we will observe the demodulation of an am signal with the circuit shown in figure 87. Amplitude modulation a1 49 you will see in this experiment, and in others to follow, that there is no problem in generating an am signal with a depth of modulation exceeding 100%, and without.
Set the scope vertical scale to 1 volt and the horizontal scale to 200 us. Am an amplitude modulated signal that contains the carrier signal and. 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. 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. These form some of the main uses of amplitude modulation. Then as the audio signal amplitude is changed to 150 mvpp, the percentage modulation dropped to around 30%. A simple modulator can be constructed using a multiplier as shown in figure 7. Thus the amplitude modulation and demodulation circuit were designed and the modulation index for various modulating voltage were calculated. The original method of electronically encoding sound information on radio waves is called amplitude modulation, or am.
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. University of north carolina at charlotte department of. The continuous wave modulation techniques are further divided into amplitude modulation and angle modulation. Using amplitude modulation to shift the baseband signal fm radio 88mhz108 mhz. Frequency modulation is a type of angle modulation. The circuit s carrier generator, modulator and demodulator are provided with the. The same signal was used to modulate both configurations. Power amplifiers are used to boost the carrier and modulating signals before modulation d. Adjust the carrier and modulated signals for a modulation index of 0. Equivalent circuit of a piezoelectric transformer pt loaded by ro. To define modulation and demodulation on must know about modulation of angle and demodulation of angle.
Varying amounts of distortion become evident as the modulation level goes beyond 100%. To involve data information or speech information, another wave has to be imposed known as input signal above the carrier wave. Collector modulation method is high level amplitude modulation c. Explain briefly in your report how amplitude modulation is accomplished by this circuit. Ppt amplitude modulation powerpoint presentation free. 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. When expressed as a percentage it is the same as the depth of modulation. The general form of a sinusoidal signal can be written as ft. I tried to explain the circuit connections that is needed for the experiment. Multiple choice questions and answers on amplitude modulation.
The math you have used assumes the transistor circuit is operating in the linear region i. The demodulation is performed by an envelope detector. The two signals are mixed and amplified by the transistor and an amplitude modulated signal appears at the collector of the bc548. Dutton ee3 winter 2004 1 ee3 lab 1 amplitude modulation and demodulation 1 lab notes a word about power. The amplitude modulation and demodulation technique involved in this project comprises of three stages.
The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier. Phase modulation is another type of angle modulation very similar to frequency modulation. It is still in use today in a variety of systems, including, of course, am broadcast radio. This experiment examines the characteristics of the amplitude modulation am. The modulating signal contains the intended message or information sometimes consisting of audio data, as in am radio. The singlesided spectrum of the modulated signal replicates the baseband. Amplitude modulation receiver circuit eeweb community. 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. An am wave may thus be dscribed, in the most general form, as a function of time. What is amplitude modulation, am electronics notes. Wave fundamentals and modulation demonstration board purpose. Effectively it is formed by having two carriers 90 out of phase. In the next chapter demodulation of amplitude in which lateral band and carrier are described using circuits. The r set modification circuit, figure 2, uses q1 as a variable resistor and r2 as a fixed current.
Feb 09, 20 this is a short presentation video of my self made amplitude modulator. Analog communication laboratory manual santhosh thottingal. Considerable upfront effort will be placed on the exploration of circuits that perform signal multiplication. The purpose of this board is to give the instructor a ready instructional resource to support lesson presentations in wave fundamentals and modulation. Amplitude modulation circuit and block diagram youtube. Why modulation is used suitable for signal transmission distanceetc. Note that this is on the very low end of the recommended voltage range. In this video i tried to explain the experiment amplitude modulation and demodulation. This is in contrast to pcm encodings where quantization levels vary as a function of amplitude as with the alaw algorithm or the. The concepts of amplitude modulation, modulation and demodulation, along with their differences is explained below. The process of amplitude modulation consists of the amplitude of the carrier wave being varied in sympathy with a modulating signal. It requires that the amplitude of the dc a part of a t is equal to the amplitude of the ac part a.
Connect the circuit as per the given circuit diagram. Among the types of modulation techniques, the main classification is continuouswave modulation and pulse modulation. If you want to experiment with other sounds, try the following files. With no modulation, the am carrier is transmitted by itself. There is no over modulation means that modulation index is less than or equal to 1. Remember, for analysis purposes keep the modulation index and frequency the same as part 2, step 3. Frequency versus amplitude modulation l amplitude modulation am l changes the amplitude of the carrier signal according to the amplitude of the message signal. Diagram from 1922 showing the circuit of a crystal radio. Showing you how to multiply two signals and show the frequency spectrum of the signals fft. A page 2 of 3 the circuit operates on a 3 v to 5 v single supply. Pulse position modulation using 555 timer circuit pulse position modulator 555 circuit schematic diagram output signal plot in the above timing chart, and compare it with our previous pulse width modulation.
A method for finding frequencymodulated and amplitude. Though pcm is a more general term, it is often used to describe data encoded as lpcm. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. A pam is generated from a pure sine wave modulating the signal and a square wave generator which produces the carrier pulse and a pam modulator circuit. The circuit was designed to be able to obtain signals via amplitude modulation where the sensitivity and selectivity is fairly good. In this experiment, a carrier signal and an audio modulating signal are applied to the modulator ic mc 1496 and the produced modulated waveform is observed. Amplitude modulation circuit and how am works youtube. This conforms to the expectation as the maximum and minimum peak of the modulated signal waveform varies proportional to the amplitude of the modulating signal. Oct 30, 2012 amplitude modulation carrier lowersideband lsb uppersideband usb amplitude modulation 01 public. Quadrature amplitude modulation qam national instruments. Am is a relatively simple way to add audio information to a carrier wave so that sounds can be transmitted. Feb 12, 2018 millions of thanks from depths of my heart to every subscriber and visitor. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted.
Two signal generators are used in this circuit, one representing a high frequency 200khz rf carrier, vg2, the other signal generator is used to inject a 1khz audio signal. Use your project files from the previous fir laboratory. It was developed in the first few decades of the twentieth century. Some phase modulation and quadrature amplitude modulation formats have a higher spectral efficiency for data transmission than frequency shift keying, a form of frequency modulation. The following algorithm is commonly used to represent amplitude modulation. Use fg1 as the message signal and fg2 as the carrier signal. 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 am is a modulation technique where the.
Amplitude modulation of the ad9850 direct digital synthesizer. A free powerpoint ppt presentation displayed as a flash slide show on id. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. Repeat the steps 3 and 4 by changing the applied input signal frequency to 100khz and 500 khz. The message signal is, for example, a function of the sound to be reproduced by a. As we mentioned before, well use dsbc modulation because of its ease in demodulation. The analog communications circuit board contains the following circuit blocks. Amplitude modulation am, demodulation and their circuit.
Source called v1 generates the message to be transmitted. Here the student can see the amplitude of the audio wave increase and at beyond a certain point 100% modulation, the carrier waveform becomes distorted flat topping and no. As given is the problem the modulation is sinusoidal this is also called tone modulation. Senior member, ieee, robert callan student member, ieee, and christopher wang abstractthis paper presents an algorithm for.
The voltage at the r set pin is part of the feedback loop of the internal control amplifier and must not be externally altered. Amplitude modulation is a technique which uses a low frequency signal to control the amplitude of a highfrequency signal. This site uses cookies to offer you a better browsing experience. 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. The board would be used in conjunction with a projection capable oscilloscope and an. Amplitude modulation circuit implementation electrical. 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. What is modulation 2 modulation in the modulation process, some characteristic of a highfrequency carrier signal bandpass, is changed according to the instantaneous amplitude of the information baseband signal. Introduction in chapters 1 and 2 you studied how to apply intelligence modulation to an rfcarrier wave.
Amplitude modulation am is an analog modulation scheme where the amplitude a of. Amplitude modulation an overview sciencedirect topics. Connect channel 1 probe of the oscilloscope to the output of the modulator at pin 7. Measure the output signal frequency and amplitude by connecting the output to cro.
Linear pulsecode modulation lpcm is a specific type of pcm where the quantization levels are linearly uniform. Note that the rms circuit outputs the wellknown result of 0. The circuit therefore behaves as an amplitude modulator. A method for finding frequencymodulated and amplitudemodulated electromagnetic emanations in computer systems milos prvulovic senior member, ieee, alenka zajic. Dsb modulation, the transmitted carrier is created from. The second is to investigate classical analog amplitude modulation and the envelope detector. Modulation is done at high power of carrier and modulating signal b. Overmodulated am signals and its requirement for coherent detection are also considered.
Apply a 5 khz signal to both rf and af inputs of 0. The carrier frequency, fc, should be larger than the highest spectral component. Fm modulation and demodulation circuit multisim live. Amplitude modulation a continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. When the modulating information signal a sine wave is applied, the carrier amplitude.
The output can be used to simulate the response of lc and tank circuits. 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. Amplitude modulation can be carried out by linearly combining the carrier and intelligence signals then applying the result to a nonlinear component or circuit. For creating the fpaa circuits, amplitude modulation and synchronous demodulation methods known from designing analogue rf transmission systems have. Amplitude modulation am is a method of impressing data onto an alternatingcurrent ac carrier waveform. Now we will observe the demodulation of an am signal with the circuit. To heterodyne means to mix to frequencies together so as. Figure 6 shows a probe plot of the input, and the outputs from each circuit. The reference current to the dac is a function of the internal. A continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information.
You can publish your book online for free in a few minutes. Wave fundamentals and modulation demonstration board. The resulting amplitude modulation am waveform is then demodulated using an. Recall that in double sideband dsb modulation, the transmitted carrier is created from message signal via where is the carrier amplitude and is the carrier frequency in hz. Amplitude modulation am a method of emphasizing data on an alternating current waveform or radio wave wherein the carried transmitted signal varies with reference to the amplitude. As before, this may require a manual adjustment of the voltsdiv and secdiv to obtain a suitable waveform. Use the spectrum analyzer to compare this modulator to the one in part 2. In amplitude modulation, it is the voltage level of the signal to be transmitted that changes the amplitude of the carrier in proportion, see figure 63. Amplitude modulation circuit implementation for use in a communication. Linear modulation signal multiplication is fundamental to the generation of linear modulation. The onchip dac for many dds devices provides a complementary current output, iout and ioutb, for the ad9834.
Amplitude modulation early radio ee 442 spring semester. In modulation, the message signal changes the amplitude, frequency, or phase of the. Describe phase demodulation circuit operation for the peak, lowpass filter, and conversion detectors. Am modulator this circuit uses two signal generators to simulate an amplitude modulated rf carrier wave. Public circuits tagged amplitudemodulation circuitlab. 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. Gathering like terms and simplifying the equation leaves. Electronics amplitude modulation am in ltspice xvii. This process of imposing an input signal on a carrier wave is known as modulation. For the special case of a sinusoidal message, we have that. Quadrature amplitude modulation qam requires changing the phase and amplitude of a carrier sine wave.