Amplitude Modulation
Amplitude
Modulation
Experiment No:
Experiment Name: Study of
Amplitude Modulation
Objective:
To study and understand
the process of amplitude modulation by observing the changes in the carrier
wave’s amplitude in accordance with the message signal’s variations.
Theory:
Amplitude Modulation (AM)
is a technique used in electronic communication, most commonly for transmitting
information via a radio carrier wave. In AM, the amplitude (signal strength) of
the carrier wave is varied in proportion to that of the message signal being
transmitted. This contrasts with frequency modulation (FM) and phase modulation
(PM).
AM involves modulating a high-frequency carrier signal with
a lower-frequency message signal. The modulated signal’s envelope changes
proportionally to the voltage of the message signal. The AM signal can be
expressed mathematically as:
s(t)=(1+m⋅cos(2πfmt))⋅cos(2πfct)
where:
(s(t)) is the modulated signal.
(m) is the modulation index
(represents the strength of modulation).
(fm) is the message
signal frequency.
(fc) is the carrier
frequency.
Demodulation:
Demodulation is the
process of extracting the original information-bearing signal from a modulated
carrier wave. The most common method for AM demodulation is envelope detection,
which uses a diode to rectify the AM signal and a low-pass filter to remove the
high-frequency components.
Apparatus:
1.Signal generator.
2.Function generator.
3.Amplitude Modulator
circuit.
4.Oscilloscope.
5.Connecting wires.
6.Breadboard or a
modulation trainer kit.
Circuit Diagram:
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Procedure:
Setup: Connect the signal
generator and function generator to the amplitude modulator circuit as per the
circuit diagram.
Carrier Signal: Set the
signal generator to produce a sine wave with a frequency of around 1 MHz (carrier
wave).
Message Signal: Set the
function generator to produce a lower frequency sine wave (1 kHz), which will
serve as the message signal.
Observation: Use the
oscilloscope to observe the carrier wave, the message signal, and the modulated
signal.
Connect one channel of
the oscilloscope to the carrier wave to ensure it’s correctly set.
Connect another channel
to the message signal to verify its frequency and amplitude.
Connect the output of the
modulator to the oscilloscope to observe the amplitude-modulated signal.
Adjustments: Adjust the
amplitude of the message signal and observe how it affects the modulated
output. Notice the changes in the envelope of the carrier wave as the message
signal’s amplitude varies.
Recording Data: Capture
screenshots or drawings of the waveforms displayed on the oscilloscope for
analysis.
Construct the AM
Demodulator:
Connect the AM signal to
the input of the demodulator circuit.
Use a diode (D1) for
rectification and an RC filter (R3, C2) to smooth the signal.
Observe the Demodulated
Signal:
Use the oscilloscope to
observe the output of the demodulator.
Compare the demodulated
signal with the original modulating signal.
Conclusion:
Through this experiment,
the principles of amplitude modulation were successfully demonstrated. By
varying the amplitude of the message signal, we could see corresponding changes
in the amplitude of the carrier wave, thereby confirming the theoretical
concepts of amplitude modulation. The use of an oscilloscope was crucial in visualizing
these changes, allowing for a clear understanding of the modulation process.
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