Amplitude modulation (ALIV - Bangladesh- [email protected])
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Transcript of Amplitude modulation (ALIV - Bangladesh- [email protected])
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. Jumpers6. 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
BackgroundModulating 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 Do1. 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
6. Using the results above and calculate and record the percentage modulation of output signal
7. 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= 1.3vEmin=1v
{(Emax - Emin)/ Emax }* 100
= 23%
200 mVp-p Emax= 130mvEmin=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
April 11, 2023 12
THANK YOU
April 11, 2023 13
• Amplitude modulation Presented by aliv. Bangladesh
• Email: [email protected]• Cell: +8801672462007