Generation of various forms of amplitude modulation am, continues to find place. Amplitude modulation can be produced in various ways. Am is defined as a process in which the amplitude of the carrier t i i d b t l li l ith b b dct a cc cos 2. Failure to accurately recover this intelligence will result in distortion and degradation of the demodulated signal and intelligence will be lost.
Modulation index vs sideband amplitude c0 c 1 coc1 c 2 c3 c 4 dr dr nn or n dr 0. Design and development of an amplitude modulator using. Explain the generation of am waves using square law. In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. Figure 1 shows the graphical settings of a function generator modulated by sine wave with am depth of 100% and am frequency of 100 hz. Based on these results, it is easy to conclude that an amplitude modulated carrier has all of the. Communication systemsamplitude modulation wikibooks. This paper discusses a simple, reliable and cheap way of achieving amplitude modulation am using a square law method. Message power in st slide 6 powers in single tone case cont.
Amplitude modulation by a carrier sine wave is by far the most common in terms of usage. Design and development of an amplitude modulator using square. Most radio systems in the 20th century used frequency modulation fm or amplitude modulation am for radio broadcast a modulator is a device that performs modulation. The block diagram of square law demodulator is shown in fig 2. The only difference is that in the square law modulator, the diode is operated in a nonlinear mode, whereas, in the switching modulator, the diode has to operate as an ideal switch. The probability density function pdf for v is the rectangle.
Low modulation frequency produces low frequency effect in targeted tissue. Continuous wave modulation the message signal mt is bandlimited to the interval c. The disadvantages of amplitude modulation include the following. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. In frequency modulation fm, unlike am, the amplitude of the carrier is kept constant, but its frequency is altered in accordance with variations in the audio signal being sent. Amplitude modulation early radio ee 442 spring semester. The switching modulator using a diode has been shown in fig 3 a. A carrier wave of frequency 1 mhz is modulated 50 per cent by a sinusoidal. Modulation allows for the designated frequency bands with the carrier frequency at the center of the band to be utilized for communication and allows for signal multiplexing. A square law modulator has three features shown in figure. Communication is a process of conveying information at a distance. The carrier frequency, fc, should be larger than the. What is am modulation amplitude modulation need of.
This process of detection is exactly opposite to that of modulation. The efficiency of this modulation is very low because it uses a lot of power. The modulating signal contains the intended message or information sometimes consisting of audio data, as in am radio. In effect, modulation converts ft to a bandpass form, in the neighborhood of the center frequency f c. Frequency modulation vs amplitude modulation frequency modulation. Am signal after squarelaw demodulation in time domain and frequency domain. 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. Carrier phase ft modulates ct in either amplitude, frequency or phase. You can publish your book online for free in a few minutes. Let the modulating and carrier signals be denoted as m. This modulation uses amplitude frequency several times to modulate the signal by a carrier signal. When expressed as a percentage it is the same as the depth of modulation. Fig 3 a fig 3 b this diode is assumed to be operating as a switch. T1 first patch up according to figure 6, but omit the input x and y connections to the multiplier.
Message signal mt, which is also known as modulating signal or modulating wave. When the percent modulation is 0% m 0, the total side frequency power psf is zero because there are no side frequencies in an unmodulated carrier. In a simple sentence, they are used to generate and filter the am signal, respectively from the carrier signal and message signal taken separately. Multiple choice questions and answers on amplitude modulation its amplitude, frequency or phase are varied in proportion to message signal. The carier frequency is much greater than the highest frequency in baseband signal amplitude modulation am. Describe the behaviour of square law device like diode. Also it is worthwhile to note that, in general, square law modulators are low.
Electrotherapy made simple how to perform safe and effective. The fourier transform of am signal is given by 22 cac cc c c aka. The distortion may be in amplitude, frequency, or phase, depending on the nature of the demodulator. Amplitude modulation and frequency modulation are used to transmit data using the method of modifying a carrier signal. One of the principal techniques used in electronic communication is the modulation.
Connect to the two oscilloscope channels using the scope selector, as shown. Slide 8 demodulating by envelope detection slide 9 square law. The idea is simple, though the notion that it can be used to modulate signals for transmission was hardly obvious before its discovery. An am signal is detected using an envelope detector. Detailed explanation of am modulation amplitude modulation, its working principle, and basic need of modulation. Assume the diodes act as perfect switches either on or off and are controlled by the rf. The message signal is, for example, a function of the sound to be reproduced by a. Since modulation signal is symmetrical square wave it will contain only odd harmonics i. Modulation is a process by which some characteristics of the carrier signal like its amplitude, frequency or phase are varied in proportion to message signal. The pulse may take any real voltage value that is proportional to the value of the original waveform.
Frequency division multiplexing, fdma amplitude modulation and demodulation. The heterodyne principle is the basic idea governing several different modulation schemes. We talked about only the time domain analysis of the amplitude modulation. Amplitude modulation is a technique used in electronic communication most commonly for transmitting information via a. The original waveform amplitude is quantized with a resulting loss of information. The sideband amplitude is never zero for any value of modulation greater than zero. Lecture notes on analogue communication techniques 1. The main difference between both modulations is that in frequency modulation, the frequency of the carrier wave is modified as per the transmit data, while in amplitude modulation, the carrier wave is modified according to the data. Armstrong during the early 1930s in an effort to overcome interference and noise.
Reduce the frequency of e c to 1 khz, observe and draw the waveform as e m is adjusted from 0 to 100% modulation. Amplitude modulation am is an analog and linear modulation process as opposed to frequency modulation fm and phase modulation pm. This form of modulation was developed by the american electrical engineer edwin h. It is the process of changing the amplitude of high frequency carrier signal in accordance with. What is the function of a square law device and band pass. The amplitude modulation am modulation index can be defined as a measure of the amplitude variation upon a carrier. 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 is a modulation technique where the.
The receivers used to listen to amdsbc are perhaps the simplest receivers of any radio modulation technique. Amplitude modulation is one of the earliest radio modulation techniques. Here well use the example of a square law fet as illustrated in figure 9. Amplitude modulation refers to the process in which amplitude of the carrier wave is varied. This gives us something to modulate and carry the information pattern from. Timedomain description, frequency domain description, generation of am wave. Difference between amplitude modulation and frequency modulation 8. The bandwidth of an am signal is twice the highest modulating frequency. An appropriate value for the time constant of the envelope detector is a 500 sec b 20 sec c 0. Amplitude modulated medium frequency current 2,000 5,000 hz uses two channels of differing carrier frequencies to. Where ma emec where ma is the modulation index or depth of modulation. Frequency modulation vs amplitude modulation advantage. Modulation index for some common functions using frequency and phase modulation abstract the equations defining the amplitude of sidebands resulting from either frequency modulation or phase modulation by either square wave, sinewave, sawtooth or triangular modulating functions are presented. This circuit uses the same principles as the diode square law modulator.
This is achieved by varying the strength of the carrier signal in relation to the information being sent. Modulation allows us to transmit multiple signals in the same medium i. It is the process in which characteristics of one wave form is varies in accordance with instantaneous value of another wave formlike message single. Switching modulator is similar to the square law modulator.
A method of frequency translation, recovery of base band signal, amplitude modulation, spectrum of am signal, the balanced modulator, the square law demodulator, dsbsc, ssbsc and vsb, their methods of generation and demodulation, carrier acquisition, phaselocked loop pll, frequency division multiplexing. There are two types of am detectors or demodulators such as. A method of frequency translation, recovery of base band signal, amplitude modulation, spectrum of am signal, the balanced modulator, the square law demodulator, dsbsc, ssbsc and vsb, their methods of generation and demodulation, carrier. Introduction to communication system introduction, orientation introduction to communication system, need for modulation, amplitude modulation, time domain and frequency domain description, power relations in am wave, square law modulator, switching. The carrier frequency and modulation signal frequency are 1 mhz and 2 khz respectively. Characteristies parameter of amplitude, frequency of.
For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Am wave in its most general formam wave, in its most general. Double sideband suppressed carrier modulation dsbsc. If the distance is involved is beyond direct communication, electronic communication comes into the picture. The switchingmodulator or the squarelaw modulator can be used. Hence, the square law modulator produces an am wave. Amplitude modulation vs frequency modulation am vs fm modulation hd. The process of recovering the message signal from the received modulated signal is known as demodulation.