As for the mechanism, when amplitude modulation is used there is a variation in the amplitude of the carrier. In the case of amplitude modulation am, the modulated oscillation vector is always in phase with the carrier field while its length oscillates with the modulation frequency. The time dependence of its projection onto the real axis gives the signal strength as drawn to the right of the corresponding phasor diagram. In the particular case when the message signal is a sinusoid of frequency fx. Vary the modulating frequency and amplitude and observe the effects on the modulated waveform. Overmodulation distorts the information and causes excessive bandwidth to be used by the transmitter.
The percent modulation can be varied simply by changing the amplitude of the 30 khz carrier signal. Overmodulated am signals and its requirement for coherent detection are also considered. This modulation uses amplitude frequency several times to modulate the signal by a carrier signal. In experiment 3, dsb signals were generated by the. The demodulation is performed by an envelope detector. The second and third figures show the actual spectra that would be found in the major lobe and in the pattern minimum, respectively. With amplitude modulation, the carrier signal is alternately driven above and below its resting unmodulated value. Assuming that m 0 for the msample delay no delay, plot the coef. Modulation is defined as a process in which the amplitude of the carrier wave ct is varied linearly with the instantaneous amplitude of the message signal mt. At 100% modulation, the peaks will be driven to twice the resting power, and the valleys will reach zero. In the above question, what is the power in sidebands. The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier.
The message signal is, for example, a function of the sound to be. The mathematical relationship for amplitude modulation is simple and intuitive. Effectively it is formed by having two carriers 90 out of phase. In this experiment, you will examine the characteristics of amplitude modulation am. 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. The instantaneous carrier phase changes with the modulating waveform. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. What is amplitude modulation, am electronics notes. Pdf the effect of amplitude modulation index and frequency. Message power in st slide 6 powers in single tone case cont. Multiple choice questions and answers on modulation and. In the diagram, the modulation frequency, km, is 500. Here the student can see the amplitude of the audio wave increase and at beyond a certain. Message signal embed into the amplitude of carrier.
Varying amounts of distortion become evident as the modulation level goes beyond 100%. Amplitude modulation am the process of combining the message signal with the carrier. It is a kind of modulation where the amplitude of the carrier signal is changed in proportion to the message signal while the phase and frequency are kept constant. Both dsb and ssb techniques are widely used in communication.
It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. This is a relatively constant oscillation usually but not necessarily in the radio frequency band that gets modulated altered by the signal. Amplitude modulation am is a modulation technique where the. The modulating signal contains the intended message or information sometimes consisting of audio data, as in am radio.
In addition to reading the questions and answers on my site, i would suggest you to check the following, on amazon, as well. Therefore, both fm and pm are often referred to as angle modulation. Recommendations for the am broadcast industry harrison j. This is the modulation where the phase of the carrier signal is altered according to the low frequency of the message signal is called phase.
Amplitude modulation fundamentals ies romero vargas. When you transmit a signal, you do so over whats called a carrier frequency. Amplitude modulation am is similar to dsb but has the advantage of permitting a simpler demodulator, the envelope detector. Ee and ece important mcq pdfmodulation and demodulation 1. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. The overmodulation range is divided into two modes depending on the modulation index mi. Example 33 what percentage of modulation corresponds to a modulation index m of 0. Amplitude modulation contents slide 1 amplitude modulation slide 2 the envelope and no overmodulation slide 3 example for single tone modulation slide 4 measuring the modulation index slide 5 transmitted vs.
The idea is simple, though the notion that it can be used to modulate signals for transmission was hardly obvious before its discovery. Overmodulated am signals and its requirement for coherent. Overmodulation overmodulation is a condition that occurs when an excessive intelligence signal overdrives an am modulator making %m 100% because e i e c modulated carrier amplitude reach value greater than double of unmodulated value it produces a distortion known as sideband splatter, which results on transmission at frequencies outside. Overmodulation results in spurious emissions by the. For a perfect modulation, the value of modulation index should be 1, which means the modulation depth should be 100%.
The depth of modulation can be varied using the variable knob provided at a. 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. There are no amplitude scales shown, but you should be able to deduce the depth of modulation 1 by inspection. Define overmodulation and explain how to alleviate its effects. A 50 kw carrier is to be amplitude modulated to a level of 85%. Amplitude modulation this experiment examines the characteristics of the amplitude modulation am process. The disadvantages of amplitude modulation include the following. If the audio v a sinw at modulates the carrier v c sinw ct, then the modulation index, m, is.
Since m0 means 0% modulation and m1 means 100% modulation, we get. In the sense of this definition, it is almost always considered a fault condition. Dec 05, 2014 amplitude modulation modulated signal. Multiple choice questions and answers on modulation and demodulation. Maximum modulation that can be retrieved with an envelope detector without distortion. There is no over modulation means that modulation index is less than or equal to 1.
Amplitude modulation definition, types, solved examples. A type of dsb, called binary phaseshift keying, is used for digital telemetry. In laymans terms, the signal is going off the scale. In general, amplitude modulation definition is given as a type of modulation where the amplitude of the carrier wave is varied in some proportion with respect to the modulating data or the signal. Amplitude modulation is mostly used in the form of electronic communication. Double sideband dsb is one of the easiest modulation techniques to understand, so it is a good starting point for the study of modulation. Overmodulation is the condition that prevails in telecommunication when the instantaneous level of the modulating signal exceeds the value necessary to. The efficiency of this modulation is very low because it uses a lot of power. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. Pdf overmodulation strategies of inverterfed ac drives. Phase modulation pm is a different form of frequency modulation and the carrier is similar in appearance to a frequencymodulated carrier. In such case the formula for modulation index is given by. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. A 100 v carrier is made to vary between 160 v and 40 v by the signal.
Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. If the modulation level is increased beyond this value, the valleys will attempt to go below zero. These form some of the main uses of amplitude modulation. As given is the problem the modulation is sinusoidal this is also called tone modulation. Overmodulation is the condition that prevails in telecommunication when the instantaneous level of the modulating signal exceeds the value necessary to produce 100% modulation of the carrier.
Modulation is done in transmitter radio receiver between transmitter and radio receiver none of the above answer. When expressed as a percentage it is the same as the depth of modulation. The percentage modulation can be calculated using the formula. In mode i, the reference angles are derived from the fourier series expansion of the reference voltage. The standard form of an amplitude modulated am wave is defined by. 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.
The effect of amplitude modulation index and frequency modulation index on total harmonic distortion in 1phase inverter to cite this article. 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 instructor can next demonstrate the concept of over modulation by increasing the audio wave amplitude beyond the 100% modulation level. Amplitude modulation early radio ee 442 spring semester. Overmodulation overmodulation is a condition that occurs when an excessive intelligence signal overdrives an am modulator making %m 100% because e i e c modulated carrier amplitude reach value greater than double of unmodulated value it produces a distortion known as sideband splatter, which results on transmission at frequencies. Modulation, overmodulation, and occupied bandwidth 3890 am. Modulation, overrnodulation, and occupied bandwidth. Restoring or recovering the message signal from the received modulated waveform that is generally corrupted by noise types of am detectors. Mar 16, 2019 multiple choice questions and answers on modulation and demodulation in addition to reading the questions and answers on my site, i would suggest you to check the following, on amazon, as well.
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