The size of the antenna depends inversely on the frequencies present in the message. This lab will explore basic linear modulation and demodulation using the envelope detector. The ad633 can be used as a linear amplitude modulator with no external components. As we mentioned before, well use dsbc modulation because of its ease in demodulation. Amplitude modulation definition, types, solved examples.
Source called v1 generates the message to be transmitted. Am modulator and demodulator with integrated ad633 youspice. Amplitude modulation am 9 t15 use speech or music from trunks as the message, and show that this also generates a trapezoid, and that setting the message amplitude so that the depth of modulation reaches unity on peaks a triangle is especially easy to do, using. Amplitude modulation a continuouswave goes on continuously without any intervals and it is the baseband message signal, which contains the information. The symbol for amplitude modulation is a multiplier, but actual circuits use the nonlinearity of transistors or diodes, or switching operations. Ad633 is a functionally complete, fourquadrant, analog multiplier. It is often called as am and is commonly used in transmitting a piece of information through a radio carrier wave. The output from the summer and the demodulated signal. Pdf communication engineering analog and digital laboratory. Amplitude modulator circuit with ad633 the ad633 can be used as a linear amplitude modulator with no external components. Show that if the demodulator output is to follow the envelope of vt it is.
Am an amplitude modulated signal that contains the carrier signal and the two sidebands. Amplitude modulation definition and its applications. Amplitude modulation am communication systems arose from the need to send an acoustic signal, the message, over the airwaves using a reasonably sized antenna to radiate it. This gives us something to modulate and carry the information pattern from. A simple example of generating am modulated rf with an ad633 analog multiplier chip. Amplitude modulation an overview sciencedirect topics. As a crucial bandwidthlimiting component in the zaxis feedback loop of an. Amplitude modulation differentiation using a phase shifter. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. The schematic is in the examples section of the ad633 datasheet. Pulse amplitude modulation is a technique in which the amplitude of each pulse is controlled by the instantaneous amplitude of the modulation signal.
The carrier and modulation inputs to the ad633 are multiplied to produce a double sideband signal. The ad633 is a complete fourquadrant multiplier offered in low cost 8lead plastic packages. Hence, we can calculate the value of modulation index by using the above formula, when the amplitudes of the. What we do in am, very roughly,is to throw away the frequency content of. Amplitude modulation circuit implementation for use in a.
Amplitude modulation can be produced in various ways. Demodulation channel decoding is the corresponding process at the receiver of converting the received waveform into a. Amplitude modulation am, demodulation and their circuit. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Analog communication laboratory manual santhosh thottingal. It includes high impedance, differential x and y inputs, and a high impedance. Amplitude modulation am, still widely used in commercial radio today, is one of the simplest ways that a message signal can modulate a sinusoidal carrier wave. Lab 5 amplitude modulation and demodulation prelab 5. Dsbfc and dsbsc am modulation with the ic ad633 youspice. T1 first patch up according to figure 6, but omit the input x and y connections to the multiplier.
The idea is simple, though the notion that it can be used to modulate signals. Here well use the example of a square law fet as illustrated in figure 9. Amplitude modulation of a sine or cosine carrier results in a variation of the carrier amplitude that. Note down frequency and amplitude of the demodulated output waveform. Dsb modulation, the transmitted carrier is created from. To understand the theoretical foundations of analog communications as well as of doublesideband amplitude modulation and demodulation dsbam to design the simulink model of the dsbam to analyze each signal in time and frequency domains using time scope and spectrum analyzer. In fact, all radio channels in the am band use this type of modulation. As a first step, i played around with the ad633 analog multiplier, and tried out amplitude modulation using only the tools available on board. The modulated carrier signal is sent to the receiver where demodulation of the. Types of amplitude modulation am double sideband with carrier we will call it am. In this experiment, the properties and characteristics of amplitude modulated am signals and their frequency spectra are examined. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Here is the circuit used for modulation and its simulation.
Yet, am continues to be used today in many communication applications. Analog modulation and demodulation amplitude modulation pages 306309. Ee4512 analog and digital communications chapter 6 the analytical signal for double sideband, large carrier amplitude modulation dsblc am is. Both processes aim to achieve transfer information with the minimum distortion, minimum loss and. The process of demodulation for signals using amplitude modulation can be achieved in a number of different. Lab1 am modulation demod handout free download as pdf file. Its still used in radio systems to transmit audio signals although it has lesser in popularity compared to fm due to its lower signal to noise ratio. It is a modulation system in which the signal is sampled at regular intervals and each sample is made proportional to the amplitude of the signal at the instant of sampling. Amplitude modulation is mostly used in the form of electronic communication. Ad633s z input where it is summed with the doublesideband signal to produce a double. Amplitude modulation and demodulation objective amplitude modulation am is one of the simplest methods for modulating a sinusoidal carrier wave. Actual dsbscssbsc modulation and demodulation modulation we explained the theory of amplitude modulation above, but what sort of circuit is actually used. Connect to the two oscilloscope channels using the scope selector, as shown. Many more components of the rf board will be utilized in this lab as well.
Demodulation is the process by which the original information bearing signal, i. An interactive demo which enables you to both see and hear the result of multiplying a sine wave with a cosine amplitude envelope. The message signal is, for example, a function of the sound to be reproduced by a. An am modulator is constructed using the analog devices ad534 four quadrant multiplier, and the properties of the resulting. A similar approach is then taken for developing models for multiple phase shift keying mpsk, minimum shift keying msk, and frequency shift. Amplitude modulation demodulation using matlab simulink model. Demo of amplitude modulation using a mydaq and ad633. Modulation is the process of influencing data information on the carrier, while demodulation is the recovery of original information at the distant end from the carrier. Pspice simulation of a cascade of ad633 in modulator configuration and the same integrated ad633 in demodulator configuration. This is the same as the am modulation above but without the carrier.
Amplitude modulation is a process by which the wave signal is transmitted by modulating the amplitude of the signal. This is the most widely used type of am modulation. There is now a center section of the ece 4670 home page title rf board details dedicated to the board and the components on the board. The discussion then moves to binary phase shift keying bpsk and shows how this simpler format is modeled using the generic quadrature modulation models. The purpose of this lab is for you to gain familiarity with the concepts of amplitude modulation and demodulation. A modem is an equipment that performs both modulation and demodulation. Amplitude modulation or am is a method to transmit signals via electromagnetic transmission.
Restoring or recovering the message signal from the received. 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. It travels in the air like waves, read more about amplitude modulation and its applications at. Lab1 am modulation demod handout detector radio modulation. The ad633 is available in 8lead pdip and soic packages. Analog communication laboratory manual kavya manohar. Two analog devices ad633 multipliers provide the modulation and. This video demonstrates the principles of double sideband amplitude modulation dsbam using carriers in the audio frequency range. The amplitude modulation and demodulation technique involved in this project comprises of three stages. Universal voltage rate sensor interface tennessee research and. The ad633 is a complete fourquadrant multiplier offered in low cost 8pin plastic packages. Amplitude modulation is a simple method to transmit a signal for example sound, from one end to other. An outline of dsbscssbsc modulation and demodulation. 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.