This principle is at the heart of amplitude modulation. Modulation and demodulation hold dominant positions in communication. In am modulation the carrier signal changes almost linearly according to the. To study and perform phase shift keying 10 modulation and. Pulse amplitude demodulation peak detection is used to detect pam. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. 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. The original waveform amplitude is quantized with a resulting loss of information. Source called v1 generates the message to be transmitted.
Amplitude modulation am is a modulation technique used in electronic communication, most. The original amplitude modulation is a family of modulation schemes, in which the amplitude of a. In particular, all telephone modems faster than 300 bits use quadrature amplitude modulation qam. Cr1 is the input diode which allows capacitor c1 to charge to the peak value of the pam input pulse. If the beam is modulated at rf and pushpull audio applied to the plates, an amplitude modulated signal will appear in both plates. Sampling theorem and pulse amplitude modulation pam. Sampling theorem determines the necessary conditions which allow us to change an analog signal to a discrete one. Modulation allows us to transmit multiple signals in the same medium i.
There are different types of modulation and so are demodulators. Analog communication pulse modulation tutorialspoint. Amplitude modulation and demodulation objective amplitude modulation am is one of the simplest methods for modulating a sinusoidal carrier wave. 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. Modulation is the process of altering the characteristics of the amplitude, frequency, or phase angle of the highfrequency signal in accordance with the instantaneous value of the modulating wave. Pulse position modulation ppm is an analog modulation scheme in which, the amplitude and the width of the pulses are kept constant, while the position of each pulse, with reference to the position of a reference pulse varies according to the instantaneous sampled value of the message signal. No information is lost, but the energy is redistributed in the frequency domain.
Application note of pampulse amplitude modulation signal. It requires that the amplitude of the dc a part of a t is equal to the amplitude of the ac part a. The pulse may take any real voltage value that is proportional to the value of the original waveform. Here is the circuit used for modulation and its simulation. Amplitude modulated am signal and four demodulation methods for fre. The percentage modulation can be calculated using the formula. Ee4512 analog and digital communications chapter 6 chapter 6 analog modulation and demodulation amplitude modulation pages 306309. Amplitude demodulation matlab amdemod mathworks india. Aly elosery october 25, 2010 this lab is divided into two parts. Double sideband large carrier dsblc modultion for general message signal mt. A demodulator is an electronic circuit that is mainly used to recover the information content from the modulated carrier wave. Amplitude modulation and demodulation of harmonic signal. Each channel sharing scheme a set of basis vectors.
Frequency division multiplexing, fdma amplitude modulation and demodulation. Amplitude modulation am works by varying the amplitude strength of a carrier signal, in proportion to amplitude of a modulation signal that is to be transmitted to one or more receivers. The disadvantages of standard amplitude modulation or dsbfc double sideband full carrier system are as follows. Pulse amplitude modulation pam, quadrature amplitude modulation qam 12. This gives us something to modulate and carry the information pattern from. Eee2009eee2009 communicationscommunications contents introduction to communication systems analogue modulation am, dsbsc, vsb, ssb, fm, pm, narrow band fm, pll demodulators, and fll loops sampling systems time and frequency division multiplexing systems, nyquist principle, pam, ppm, and pwm. Process by which a property or a parameter of a signal is varied in proportion to a second signal. In singlechannel efield sensing, the carrier we transmit is m, the sensed value is a, and the noise is n vectors.
Introduction modulation in the modulation process, some characteristic of a highfrequency carrier signal bandpass, is changed according to the instantaneous amplitude of. Vary the modulating frequency and amplitude and observe the effects on the modulated waveform. Nov 30, 2015 disadvantages of standard amplitude modulation. As we mentioned before, well use dsbc modulation because of its ease in demodulation. Modulation fm, amplitude shift keying ask, phase shift keying psk, etc.
Oct 30, 2017 amplitude modulation and demodulation. In this modulation, the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the modulating signal. Apr 15, 2017 amplitude modulation and demodulation by. However its presence provides a simple means of demodulation using envelope. Demodulation is defined as extracting the original informationcarrying signal from a modulated carrier wave. Adaptation of the information signal to the transmission channel. Sampling theorem and pulse amplitude modulation pam reference stremler, communication systems, chapter 3. Pulse amplitude modulation pam theory of and its applications. Amplitude modulation can be produced in various ways. For a perfect modulation, the value of modulation index should be 1, which implies the percentage of modulation should be 100%. Jun 17, 2014 introduction to modulation and demodulation 1.
Amplitude modulation refers to any method of modulating an electromagnetic carrier frequency by varying its amplitude in accordance. Students will explore the mathematical theory behind amplitude modulation and use the analog discovery 2 to visualize the effects of amplitude modulation in the time and frequency domains. Demodulation is the process by which the original information bearing signal, i. Bikram modak departmentcomputer science and engineering semester4th roll no. Message signal embed into the amplitude of carrier simple am is also called. It can be demodulated using a circuit consisting of very few. The demonstration centers around a number of signals displayed in both the time domain and the frequency domain using a signal generator, an oscilloscope to view the signal. Figure 321 includes a simplified circuit view a for this demodulator and its waveforms views b and c. Amplitude modulation am is a modulation technique where the. Amplitude modulation an interactive demo which enables you to both see and hear the result of multiplying a sine wave with a cosine amplitude envelope. Before we study in detail about pam lets know the concepts of modulation. Demodulation is a key process in the reception of any amplitude modulated signals whether used for broadcast or two way radio communication systems. If only the middle portion of the deflection characteristic is used, the modulation distortion is very low.
Yet, am continues to be used today in many communication applications. 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. Amplitude modulation am, demodulation and their circuit. Then as the audio signal amplitude is changed to 150 mvpp, the percentage modulation dropped to around 30%. Pulse amplitude modulation is the basic form of pulse modulation. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Here well use the example of a square law fet as illustrated in figure 9. Pulse amplitude modulation is widely used in modulating signal transmission of digital data, with nonbaseband applications having been largely replaced by pulse code modulation, and, more recently, by pulse position modulation. Unicamp university of campinas, state of sao paulo pdf. The depth of modulation can be varied using the variable knob provided at a. Advantages and disadvantages of standard amplitude modulation. In addition to a variable bandpass filter, one auto notch and one manual notch filter can be utilized to eliminate interfering signals. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave.
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