To understand the theoretical foundations of analog communications as well as of doublesideband amplitude modulation and demodulation dsbam. Modulation fm, amplitude shift keying ask, phase shift keying psk, etc. No information is lost, but the energy is redistributed in the frequency domain. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. The pulse may take any real voltage value that is proportional to the value of the original waveform. Pulse code modulation is a method that is used to convert an analog signal into a digital signal so that a modified analog signal can be transmitted through the digital communication network. Frequency modulation 1 objective to understand the principles of frequency modulation and demodulation. The modulated signal y has zero initial phase and zero carrier amplitude, resulting from a suppressedcarrier modulation.
Amplitude modulation am, demodulation and their circuit. The implementation of the pcm demodulator is similar to experiment 3, which is ic cw6694 from conwise. Cr1 is the input diode which allows capacitor c1 to charge to the peak value of the pam input pulse. Pulse amplitude demodulation peak detection is used to detect pam. This principle is at the heart of amplitude modulation. However its presence provides a simple means of demodulation using envelope. The amplitude of a carrier wave is modified by a modulating signal. The fmmodulated signal has its instantaneous frequency that varies linearly with the amplitude of the message signal. To study and perform pulse amplitude modulation and demodulation. The responses are compared against the theoretical. Process by which a property or a parameter of a signal is varied in proportion to a second signal. Double sideband suppressed carrier dsb sc modulation. 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. 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.
Am modulation and demodulation with circuit and output 1. 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. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Content introduction what is modulation types of modulation amplitude modulation modulation index amplitude demodulation circuit diagram about project conclusion 3. The message signal is, for example, a function of the sound to be reproduced by a. Figure 321 includes a simplified circuit view a for this demodulator and its waveforms views b and c. In a classical linear fm process, the instantaneous frequency of the output signal undergoes a time variation. Hapter modulation and demodulation mit opencourseware. Unicamp university of campinas, state of sao paulo pdf. Since the carrier component is part of the received am.
Mcnames portland state university ece 223 communications. This is an increase compared to normal am transmission dsb, which has a maximum efficiency of 33. Overview of communication topics sinusoidal amplitude modulation amplitude demodulation synchronous and asynchronous double and singlesideband am modulation pulse amplitude modulation pulse code modulation frequencydivision multiplexing timedivision multiplexing narrowband frequency modulation j. Berrou c, glavieux a, thitimajshima p 2010 near shannon limit errorcorrecting pdf. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. Modulation allows us to transmit multiple signals in the same medium i.
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. Then, students will use labview to program an am demodulator and use it to explore and visualize the. Demodulation is a key process in the reception of any amplitude modulated signals whether used for broadcast or two way radio communication systems. To study and perform pulse width modulation and demodulation. To study and perform 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. Sampling theorem and pulse amplitude modulation pam reference stremler, communication systems, chapter 3. To study and perform frequency modulation and demodulation. Discover the key aspects about the demodulation detection of amplitude modulated signals. Source called v1 generates the message to be transmitted. Frequency division multiplexing, fdma amplitude modulation and demodulation. As we mentioned before, well use dsbc modulation because of its ease in demodulation.
Here is the circuit used for modulation and its simulation. We can also get back our analog signal by demodulation. Quadrature amplitude modulation or qam pronounced kwam is a digital. Pulse amplitude modulation is the basic form of pulse modulation. Spectra associated with demodulation of an amplitude modulated signal with a sinusoidal carrier. Application note of pampulse amplitude modulation signal. Am modulation and demodulation with circuit and output. To study and perform pulse position modulation and demodulation. Before we study in detail about pam lets know the concepts of modulation. Amplitude modulation refers to any method of modulating an electromagnetic carrier frequency by varying its amplitude in accordance. Vectors and modulation cse 466 interfacing 3 spose m and n are orthogonal unit vectors. Yet, am continues to be used today in many communication applications. Its amplitude a, which leads us to the class of systems designated as amplitude. 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.
Each part may be of any convenient amplitude at the input to an adder. Amplitude modulation a1 53 experiment aligning the model the low frequency term at to generate a voltage defined by eqn. Demodulation is the process by which the original information bearing signal, i. The focus of this lab is to familiarize the student with the modulation and demodulation of an. The spectral efficiency of the transmitted ask waveform is also a consideration and the mary quadrature amplitude modulation qam waveform has a distinct advantage as m increases.
Sampling theorem determines the necessary conditions which allow us to change an analog signal to a discrete one. Amplitude modulation can be produced in various ways. The computational expense of this approach depends upon the particular modulation format and demodulation algorithm being implemented. The original waveform amplitude is quantized with a resulting loss of information. 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. We only need a few components to achieve the pcm demodulator. Then inner products dot products are 1 1 0 can interpret inner product as projection of vector 1 v1 onto vector 2 v2in other words, inner product of v1 and v2 tells us how much of vector 1 is there in the direction of vector 2. This gives us something to modulate and carry the information pattern from. Amplitude modulation am is a modulation technique used in electronic communication, most. A demodulator is an electronic circuit that is mainly used to recover the information content from the modulated carrier wave.
Then as the audio signal amplitude is changed to 150 mvpp, the percentage modulation dropped to around 30%. Pass the recovered carrier phase into the demodulator model where it can be used directly as the reference phase. It is specifically designed to stir the interest of junior or senior level electronics minded electrical. However, a simpler demodulator for am signals is the envelope detector.
Communications i amplitude modulations and demodulations. Here well use the example of a square law fet as illustrated in figure 9. This is basically an amplitude modulation wave without the carrier therefore reducing power wastage, giving it a 100% efficiency rate. An am wave may thus be dscribed, in the most general form, as a function of time as follows. 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. Sinusoidal amplitude modulation amplitude demodulation. Amplitude modulation and demodulation electrical and computer.
Amplitude modulation and demodulation objective amplitude modulation am is one of the simplest methods for modulating a sinusoidal carrier wave. Sampling theorem and pulse amplitude modulation pam. Amplitude modulation circuit implementation for use in. The carrier signal and y have sampling frequency fs. Pcm is in binary form, so there will be only two possible states high and low0 and 1. There are different types of modulation and so are demodulators. This lab introduces students to communications theory with amplitude modulation and demodulation. Aly elosery october 25, 2010 this lab is divided into two parts. Demodulation is defined as extracting the original informationcarrying signal from a modulated carrier wave. Finally, the significance of an adequate demodulator bandwidth is highlighted during highspeed tapping. Quadrature phase shift keying qpsk the generation and demodulation. In amplitude modulation or am, the carrier signal has its amplitude.
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