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Engineering

Published on April 26, 2014

Source: slideshare.net

## Description

Amplitude modulation Presented by aliv. Bangladesh
Cell: +8801672462007

Amplitude Modulation

Objective  Understanding the principle of amplitude modulation (AM)  Understanding the waveform and the frequency spectrum of AM signal  Calculating the percentage of modulation  Measuring and adjusting an amplitude modulator circuit

Equipment Required 1. Module KL-93002 2. Oscilloscope 3. Spectrum Analyzer 4. RF Generators 5. Jumpers 6. Connectors

Background • Modulation --Allow low frequency intelligence signal onto a high frequency carrier signal • AM -- A high frequency carrier signal is modulated by a low frequency modulating signal (usually an audio) • Carrier -- A sinusoidal of high frequency

• In AM modulation the amplitude of the carrier is modified in proportion to the baseband signal • The resulting band pass signal is the “Modulated” signal, which is a combination of the carrier and the original message Background

Background Modulating Signal V(t), at baseband(fB) Action on carrier’s amplitude, frequency or phase Modulated Signal carrying the information of V(t), bandpass (fC)

Task to Do 1. Locate AM modulator circuit on Module KL -93002. Insert connect plugs in J1 and J3 to set R8 =1k and R 9 =6.8k 2. Connect a 250mVp-p, 1 kHz sine wave to the audio input (I/P2) and a 250 mVp-p, 100 kHz sine wave to the carrier input (I/P1). 3. Connect the vertical input of the oscilloscope to the AM output (O/P) 4. Observe the output waveform and adjust the VR 1 for the modulation index of 50%

5. Using the spectrum analyzer, observe and record of the output signal spectrum 5. Using the results above and calculate and record the percentage modulation of output signal 5. Using the oscilloscope, observe the output signals for the audio amplitudes of 200 mVp-p and 150 mVp-p and record the results Task to Do

Audio Amplitude Output Waveform Percentage Modulation 250 mVp-p Emax= 1.3v Emin=1v {(Emax - Emin)/ Emax }* 100 = 23% 200 mVp-p Emax= 130mv Emin=70mv {(Emax - Emin)/ Emax }* 100 = 46% 150 mVp-p Emax= Emin= {(Emax - Emin)/ Emax }* 100 Records

 Entertainment - AM Radio (music, talk radio)  Business - CB Radio to relay shipment progress, conference calls with other branches via telephone or speakerphone  Government - Police officers keeping contact with the station, or relaying the information and location of a suspect  Personal - Cell phones or walkie-talkies for chatting with friends  Military - Using undetectable radio signals to communicate with other soldiers, or voice commands to control weapons Application of AM

Discussion  Amplitude Modulation is the simplest and earliest form of transmitters  AM applications include broadcasting in medium- and high frequency applications, CB radio and aircraft communications  AM is a nonlinear process  Sum and difference frequencies are created that carry the information

26 April 2014 12

• Amplitude modulation Presented by aliv. Bangladesh • Email: abujauad@gmail.com • Cell: +8801672462007 26 April 2014 13

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