Modulator vs demodulatordifference between modulator. The modulation index of the am signal is defined as. Modulate using doublesideband amplitude modulation. Am modulators free download as powerpoint presentation. An am modulator is constructed usingthe analog devices ad534 four quadrant multiplier, and the properties of the resultingsignal are examined using labview. Acoustooptic modulator 41145 an acoustooptic modulator aom, also called a. The modulator is a downloadable, interactive pdf that gives you a page of six modulations for each major key change. Plot v3 vcc 1 0 30 vg2 2 0 dc 0 ac 1 0 sin 0 10m 200k 0 0.
In this case, since the source is a multimedia file rather than a pure sine wave, we need the dsp process, which is the resampling and filtering. Am is defined as a modulation technique in which the amplitude of the carrier is. The idea is simple, though the notion that it can be used to modulate signals for transmission was hardly obvious before its discovery. Amplitude modulation the envelope of the modulated carrier has the same shape as the message signal. Experiments with a 6ar8 amssb modulator qrz forums. The combined signal is transmitted over a frequency. This stores two files, one with the random bit sequence of nbit bits and the other file contains the active group being processed. Typically the modulation depth is the amplitude modulation index expressed as a percentage. In this code, it is considered the default value of ma equal to 1 for hundred percent modulation. Dec 21, 2017 the output stage is an ordinary am modulator however. Lab 5 amplitude modulation and demodulation pages 1 7.
Of demodulation, to recover the original baseband signal from the received version. The result is then a amplitudemodulated sine, as intended. Modulation indices are described for various forms of modulation. Thus, a narrowband fm signal requires essentially the same transmission band width. A modulating output signal is coupled through a modulation transformer to a class c amplifier. Transmitters that transmit amplitude modulated signals require an am modulator circuit to produce the required signal. This page on modulator vs demodulator covers basics of modulator and demodulator and also mention difference between modulator and demodulator as we know in telecommunication, in order to send information to longer distance and to take care of high bit rate requirement of the system different modulation techniques. There will be zero modulation voltage across the secondary of t1. The amplitude of the message signal is varied to produce different values of the modulation index.
In this modulator the amplitude of a carrier is varied in accordance with instantaneous value of message signal. Building simulink model of the music transmission using dsb am modulator and demodulator baseband here, we will implement the dsb am baseband modulator and demodulator using a music file as a source. Measuring the modulation index of an am signal using an. The measurement and definition of amplitude modulations. Modulation index, m, is used to describe the ratio of maximum voltage to minimum voltage in the modulated signal. The modulation index or modulation depth of a modulation scheme describes by how much the modulated variable of the carrier signal varies around its unmodulated level. The code for amplitude modulation am with control of modulation index ma has been developed using matlab according to conventional theory. Print the modulations you need, or view them on your ipad or tablet device. The purpose of this bulletin is to issue updated handbook pages that include the. The signal can travel long distances, and appear in faraway places, because of the earths ionosphere. Practical circuitry is more likely to use a modulator, rather than the more idealised multiplier. The following schematic is a class c am modulator without use of any transformers ive just changed the parameters in spice to get a correct modulation.
Three modelling approaches to sound design, by e r miranda pdf file. In this case the transmitter needs to transmit much larger power. This filters out all the components of the messy cutsine signal except those close to the carrier frequency. What is the modulation index in amplitude modulation. The modulation index m defines the power efficiency but m must be less than 1. Note that this kind of primitive am modulator is not all that linear. A carrier wave is modulated changed by adding audio. The output stage is an ordinary am modulator however. Heres a circuit that i came up with that works nicely as a dsb or am modulator depending on the bias on the deflector plates.
There are several methods by which the modulation index can be measured. Ee4512 analog and digital communications chapter 6 the analytical signal for double sideband, large carrier amplitude modulation dsblc am is. In class c modulators using transformers modulation index is proportional to the ratio of vm to vcc. A balanced modulator is a device that modifies a signal, usually in the form of an amplitude modulated am radio signal. Am modulator is one which is used for superimposing a low frequency signal on a high frequency carrier signal. The amplified audio signal and carrier wave are fed to the modulator. View online or download blonder tongue am45550 reference manual. Amplitude modulation simple english wikipedia, the free. In this amplitude modulation circuit, what is the purpose of. It is strongly suggested that you examine your text book for other methods. Too much and the signal will create interference well beyond the channel on which it is operating. The carrier frequency, fc, should be larger than the highest spectral component.
Chapter 6 analog modulation and demodulation astro temple. What is modulation index modulation index in am and fm. Chapter 3 amplitude modulation fundamentals topics covered 31. Ee4512 analog and digital communications chapter 6 chapter 6 analog modulation and demodulation amplitude modulation pages 306309. Modulator vs demodulatordifference between modulator,demodulator. Amplitude modulation, usually shortened to am, is a simple way to send a radio signal. Am signals can be received by a crystalpowered radio set, that. Amplitude and frequency modulation hp memory project. The modulation index is ratio of modulating signal voltagevm to the carrier voltagevc. Collector modulator the collector modulator is a linear power amplifier that takes the lowlevel modulating signals and amplifies them to a highpower level. In reality the terms am modulation index and the am modulation depth are often used interchangeably, so there are often no hard and fast rules regarding their use.
Its good enough to be useful for voice, for example, but quality am transmitters use more sophisticated mixers. The standard form of an amplitude modulated am signal is given by. Since carrier is suppressed, so am 0, and thus m am. On 100% positive audio peaks waveform, as seen on an oscilloscope, doubles in voltage. In this amplitude modulation circuit, what is the purpose.
So remember, if a modulation index is used, the signal must be shifted based on the maximum amplitude of mx bb, not x bb. There are many ways in which amplitude modulation can be generated and a variety of circuits that can be used. Now lets look at the effect of the modulation index. Therefore, the limiter output is really a phasemodulated signal. The amplitude modulation, am, modulation index can be defined as the measure of extent of amplitude variation about an unmodulated carrier.
Here was the final plot baseband in red, am waveform in blue. Plot v3 vcc 1 0 30 vg2 2 0 dc 0 ac 1 0 sin 0 10m 200k 0 0 90 vg1 4 0 dc 0 ac 1 0 sin 0 5 1k 0 0 90. Use the spectrum analyzer to compare this modulator to the one in part 2. Design and implementation of amplitude modulator and demodulator introduction communication is the most important needs from the very beginning of civilization. The modulator online offers a new and improved version of the modulator software that has been purchased by thousands of churches. Jan 24, 2018 modulation indices are described for various forms of modulation. Incoming light scatters see brillouin scattering off the resulting periodic index. Multiplying the am waveform by the carrier shifts the baseband spectrum down to 0 hz, but it also shifts it up to 2f c in this case 200 mhz, because as stated above multiplication moves the existing spectrum up by f c and down by f c. The percentage that the carriers amplitude varies above and below its unmodulated. Note that the modulation index modulator and p1db amplifier parameters are set to be tunable. You can print just what they need and place it in their binder alongside the current music selections, or they can prop up a mobile device and view transitions on a whim. Adjust these values and look at the change in waveforms. Typical applications include suppressed carrier and amplitude modulation, synchronous detection, fm detection, phase detection, and chopper.
The signal can travel long distances, and appear in faraway places, because of the earths ionosphere amplitude is the height of a wave. Modulate using doublesideband suppressedcarrier amplitude modulation. 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. View attachment 585749 you can read about all of the gory details of my experiments here. Additive synthesis, amplitude modulation and frequency.
The modulating output signal is coupled through modulation transformer t1 to the class c amplifier. The result is then a amplitude modulated sine, as intended. This article includes a list of related items that share the same name or. It is defined differently in each modulation scheme. Section ii angiotensin modulator combinations medical assistance handbook prior authorization of pharmaceutical services. Modulation index is basically the ratio of amplitude of the massage signal the message we want to transmit to the amplitude of carrier signal. Am modulators base, collector, grid and plate modulators. Remember, for analysis purposes keep the modulation index and frequency the same as part 2, step 3. Its good enough to be useful for voice, for example, but quality am transmitters use more sophisticated. In part i you will learn how to design an amplitude modulator am and in part ii you will be able to demodulate an am signal.
Amplitude modulation fundamentals unimap portal pages 1. The modulation index is equal to the peak phase deviation of the carrier. This same technique is used at the amplifier output to compare the envelope with the modulated carrier. Carrier signal is the higher frequency wave with higher energy to carry the message signal to long dis. The secondary winding of the modulation transformer is connected in series with the collector supply voltage vcc of the class c amplifier. Building simulink model of the music transmission using dsbam modulator and demodulator baseband here, we will implement the dsbam baseband modulator and demodulator using a music file as a source. In this experiment, the properties and characteristics of amplitude modulated amsignals and their frequency spectra are examined. Communication systemsamplitude modulation wikibooks, open. Modulator demodulator pdf this principle is at the heart of amplitude modulation. Process by which a property or a parameter of a signal is varied in proportion to a second signal. We looked at am timedomain waveforms in the previous page.
In early am transmitters the amplitude modulator circuit was a key element of the transmitter. Amplitude modulation uses the instantaneous amplitude of a modulating signal voice, music, data, etc. Communication systemsamplitude modulation wikibooks. Sep 09, 2019 and the 6ar8 and 7360 and others balanced modulator and decided to run a 6ar8 through its paces. It takes the original signal that has both sidebands and a carrier signal, and then modulates it so that only the sideband signals come through the output modulator. Aly elosery october 25, 2010 this lab is divided into two parts. A periodic signal consists of the exponentially decreasing waveform eat, 0.
May 12, 2020 a balanced modulator is a device that modifies a signal, usually in the form of an amplitude modulated am radio signal. The modulation index m is simply the percentage of modulation divided by one hundred. With the modulator, your accompanists wont need to carry an extra book of transitions to shuffle around between songs. Now apply the modulating waveform to the y input of the oscilloscope and the modulating signal to the x input. Explain briefly in your report how amplitude modulation is accomplished by this circuit. Let us understand modulation index in am amplitude modulation. Matlab code for amplitude modulation am file exchange.