Matlab code for amplitude modulation am file exchange. Double sideband dsb is one of the easiest modulation techniques to understand, so it is a good starting point for the study of modulation. It is still in use today in a variety of systems, including, of course, am broadcast radio. Pulsecode modulation pcm is a method used to digitally represent sampled analog signals. Experiment 10 amplitude modulation and demodulation introduction in this experiment we generate and display. Set g so that the sinewave peaks just fall to zero.
Dec 05, 2014 types of modulation sine wave carrier described by 3 parameters. Apr 28, 20 i assume the decreasing amplitude is an artifact of the low sampling rate. Frequency of the input carrier is fixed at constant amplitude of 1. In your lab write up compare this with what is expected for a modulation depth of m 1. In amplitude modulation, the amplitude of the carrier wave is made to vary in accordance with the message signal.
Therefore, both fm and pm are often referred to as angle modulation. Notice that the sine wave will move up and down as the dc is varied, its mean value equalling the dc value. Bandwidths limit is also big advantage for amplitude modulation, which doesnt have in frequency modulation. Transmitter and receiver are simple in amplitude modulation. Amplitude modulation a1 53 experiment aligning the model the low frequency term at to generate a voltage defined by eqn. Because, atmospheric propagation is good for amplitude modulated signals. Dsb modulation, the transmitted carrier is created from. Amplitude modulation and demodulation electrical and computer.
Frequency modulation fm the process of combining the message signal with the carrier signal that causes the message signal to vary the frequency of the carrier signal. To generate and demodulate an amplitude shift keyed ask signal and a binary fsk signal. When i increase the sampling rate 10 times more and decrease the time to account for memory shortage, i got what i wanted. Phase modulation pm is a different form of frequency modulation and the carrier is similar in appearance to a frequencymodulated carrier. In amplitude modulation, the amplitude signal strength of the carrier wave. In the next part, we looked at envelope detection and demodulation. In a pcm stream, the amplitude of the analog signal is sampled regularly at uniform intervals, and each sample is quantized to. A type of dsb, called binary phaseshift keying, is used for digital telemetry. Modulation is a process by which characteristics of a highfrequency carrier signal are altered to convey information contained in a lowerfrequency message. Then as the audio signal amplitude is changed to 150 mvpp, the percentage modulation dropped to around 30%.
The fmmodulated signal has its instantaneous frequency that varies linearly with the amplitude of the message signal. The percentage modulation can be calculated using the formula. This lab gives you the opportunity to actually work on amplitude modulation and reinforce the theory taught in class. With the modulating voltage adjusted to zero amplitude, increase the carrier amplitude until v o has a value of 2 v pp. Amplitude modulation fundamentals modulation detector. In this lab, students investigate two methods to recover an amplitude modulation am signal in order to develop an understanding of the demodulation process in the time and frequency domain. For an introduction to the basics of matlab, see appendix a. Amplitude modulation am is a modulation technique used in electronic communication, most commonly for transmitting information via a radio carrier wave. Chao wang eee203 signals and systems i page 1 of 2 lab.
Once you execute the mscript file, you have to press any key after you have one figure in order to see the subsequent figures. As before, this may require a manual adjustment of the voltsdiv and. Calculate the modulation index based on frequency domain representation of the signal. On your scope, look simultaneously at the srspragmatic still in the am mode and the audio out signal from the demodulator. From an information theory point of view, the power in the carrier. The frequency of the modulation signal determines the rate of the frequency change from the center frequency. To study frequency modulation and determine its modulation factor 4.
Build the simulink model of am modulator and demodulator figure7 explained in this manual. The amplitude of the modulation signal determines the amount of the frequency change from the center frequency. You can publish your book online for free in a few minutes. Increase the modulated signal until an am waveform appears. The lab sheets for the 12 experiments are collected in one booklet. Note that this is on the very low end of the recommended voltage range.
Amplitude modulation matlab tutorial amplitude modulation. Hapter modulation and demodulation mit opencourseware. The amplitude of the high frequency carrier of the signal is controlled by the low. Using matlab m file and simulink to implement fm modulation and demodulation. Build simple fm demodulator by using frequency discriminator 2. Attend the lecture or watch the video on amplitude modulation 1. Intro to generation of ask amplitude shift keying ask in the context of digital communications is a modulation process, which imparts to a sinusoid two or more discrete amplitude levels.
The instantaneous amplitude overall signal power varies depending on the instantaneous amplitude of the modulating data. Modulation by the serial data stream of a ct waveform that can be transmitted. Analog communications lab manual pdf ac lab manual pdf. Considerable upfront effort will be placed on the exploration of circuits that perform signal multiplication. Amplitude modulationand coherent detection standard am contains a sinusoidal component at the carrier frequency which does not convey any message information. Vary the modulating frequency and amplitude and observe the effects on the modulated waveform. Data loss is also more in amplitude modulation due to noise addition. In the lab report, explain the patterns of the line spectra. The original waveform amplitude is quantized with a resulting loss of information. Compare doublesideband and singlesideband amplitude modulation. The first is to gain experience in actually programming the usrp to act as a transmitter or a receiver. Sep 29, 2016 matlab tutorial amplitude modulation how to generate amplitude modulation am using matlab. Amplitude modulation am is a method of impressing data onto an alternatingcurrent ac carrier waveform.
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. Bpsk, qpsk, msk frequency shift keying, fsk quadrature amplitude modulation, qam. Types of modulation sine wave carrier described by 3 parameters. Amplitude modulation is used for broadcasting because a. The focus of this lab is to familiarize the student with the modulation and demodulation. The various parts of this lab unit will be used to explore and verify the operation of the two am modulation methods using four different am modulating circuits. The amplitude of the fm signal is constant at all times and is independent of the modulation signal. Build simple envelope detector for fm demodulation. The main difference in generating balanced amplitude modulation to standard amplitude modulation is the missing offset of the 1 offset in the modulating signal. 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. This experiment examines the characteristics of the amplitude modulation am process. Teach online lab this is an online, interactive lab that contains instructions, multimedia, and assessments where students can learn at their own pace. Am is a method of transmitting signals, such as sound or digital information, in which the amplitude.
Matlab program for pulse code modulation m file matlab. Lab 3 mixer s and amplitude modulation the underlying theme of this lab is amplitude modulation. In amplitude modulation, the amplitude signal strength of the carrier wave is varied in proportion to that of the message signal being transmitted. Connections are made for the am modulator and demodulator as shown in the circuit diagrams. University of north carolina at charlotte department of. No information is lost, but the energy is redistributed in the frequency domain. Amplitude modulation part 1 in class you have studied the theory of amplitude modulation. If you are new to matlab, please go through our tutorials.
Amplitude modulation am is similar to dsb but has the advantage of permitting a simpler demodulator, the envelope detector. The second is to investigate classical analog amplitude modulation and the envelope detector. Matlab, simulink, and a communications example 1 introduction. The pulse may take any real voltage value that is proportional to the value of the original waveform. The demod ulation is performed by an envelope detector. Basic concept of modulation the information source typically a low frequency signal referred to as the baseband signal carrier a higher frequency sinusoid example. It may be necessary to adjust the level and frequency of both v c and v m to achieve a suitable waveform and index of modulation. The amplitude or the strength of a high frequency carrier wave is changed in accordance with the amplitude of message signal. So can have amplitude modulation am frequency modulation fm phase modulation pm frequency and phase combined are known as angle modulation 8. The receivers used to listen to amdsbc are perhaps the simplest receivers of any radio modulation technique. The code for amplitude modulation am with control of modulation index ma has been developed using matlab according to conventional theory.
Chapter 6 doublesideband suppressedcarrier amplitude. It is included to create a positive envelope which allows demodulation by a simple inexpensive envelope detector. You must determine the analog filters passband edge frequency. The amplitude modulation receiver will be wider when compared to the fm receiver. Each part may be of any convenient amplitude at the input to an adder.
Signal multiplication of baseband signals and radio frequency rf signals is quite challenging. An additional goal is to provide you with applications of trigonometric identities in matlab. Introduction in this lab, we used the datex board along with ni elvismx programs to simulate and analyze amplitude modulation. To study amplitude demodulation by linear diode detector 3. Adding of noise for amplitude modulated signal will be more when compared to frequency modulated signals. It is the standard form of digital audio in computers, compact discs, digital telephony and other digital audio applications. To create in matlab a software radio that will implement an am modulator and demodulator. Amplitude modulation is one of the earliest radio modulation techniques. T12 measure the peaktopeak amplitude of the am signal, with m 1, and confirm that this magnitude is as predicted, knowing the signal levels into the multiplier, and its k factor. An interactive demo which enables you to both see and hear the result of multiplying a sine wave with a cosine amplitude envelope. When the simulation is run you can view a time domain plot and export the data to a. The message signal is, for example, a function of the sound to be. In this experiment, you will examine the characteristics of amplitude modulation am. Amplitude modulation am the process of combining the message signal with the carrier signal and the two sidebands.
Amplitude modulation fundamentals free download as powerpoint presentation. The depth of modulation can be varied using the variable knob provided at a. Dutton ee3 winter 2004 1 ee3 lab 1 amplitude modulation and demodulation 1 lab notes a word about power. The highest frequency of the modulating data is normally less than 10 percent of the carrier frequency. Try to match the audio with the envelope of the am signal.
The 9410 am dsb ssb generator controls and connectors carrier level changes the level of the carrier when using am. Amplitude modulation matlab code file exchange matlab. Lab assignment 2 amplitude modulation 1 introduction this lab assignment is concerned with practical issues associated with the implementation of modulators and demodulators for doublesideband suppressed carrier dsbsc and doublesideband large carrier dsblc modulation. In this code, it is considered the default value of ma equal to 1 for hundred percent modulation. We also see how to use a balanced mixer to modulate a signal. Oct 14, 20 amplitude modulation am is a one of the conventional modulation technique to transmit signals using a carrier wave. Hence balanced amplitude modulation can be described as. First, students will generate an am signal using data from a file, and then they will use the envelope detector method to recover the original message by connecting the am signal to. 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.