University of Dhaka
Department of Computer Science and Engineering
Project Name:
Construction of an Amplitude Modulation Circuit
Course Title: Data and Telecommunication Lab
Course Code: CSE-2213
Submitted To :
Dr. Shabbir Ahmed
Dr. Md. Rezaul Karim
Submitted By :
Sabbir Ahmed
Roll: 89
Sourove Hossen
Roll:90
Theory:
Amplitude Modulation (AM) stands as a foundational method in analog
signal processing and communication systems. It encompasses altering the
amplitude of a carrier signal based on the instantaneous amplitude of a
modulating signal, often an audio signal in the context of broadcast radio.
This modulation procedure facilitates the transmission of information via the
carrier wave, establishing its significance in analog communication.
Elements of Amplitude Modulation:
Carrier Signal (C(t)): The carrier signal is a high-frequency sinusoidal
waveform designed for effective long-distance transmission. Its frequency
typically exceeds that of the modulating signal. In AM, the carrier signal
conveys information through fluctuations in its amplitude.
Modulating Signal (M(t)): This signal represents the information intended
for transmission. Commonly, it is a low-frequency audio signal, particularly
in applications like radio broadcasting. The modulating signal dictates the
changes in the carrier signal's amplitude.
Product (Modulated) Signal (S(t)): Resulting from the combination of the
carrier and modulating signals, the modulated signal carries the information
encoded by the modulating signal. This output signal is observable in the
context of this project.
Circuit Overview:
Diode (D): The diode plays a vital role in the circuit by facilitating
rectification. It permits current to flow in a single direction, ensuring the
modulation signal undergoes rectification prior to subsequent processing.
Inductor (L): Collaborating with the diode, the 3mH inductor serves as an
essential component in creating a fundamental envelope detector. Its
function involves smoothing the rectified signal, allowing for the extraction
of the modulating signal from the carrier. Operating as a high impedance
for high-frequency components and a low impedance for low-frequency
components enhances its performance.
Capacitor (C): Connected in parallel with the inductor, the 0.1 microfarad
capacitor forms a filter network. This network improves the separation of
the modulating signal from the carrier signal.
Resistors (R): Two 1K resistors are linked to a common point, establishing
a junction for the carrier and message signals. This common point is pivotal
in amalgamating the signals before modulation.
Steps for the Experiment:
Amplitude Modulation (AM):
1.Modulation:
● Establish a connection between the audio source and the amplitude
modulator.
● Adjust the modulating signal and carrier frequency as necessary.
● Utilize the modulation index formula to determine and set the
modulation depth.
2. Observation:
● Connect the modulator's output to an oscilloscope.
● Carefully observe the characteristics of the modulated waveform.
3.Transmission (Optional):
● Connect the output of the modulator to an antenna (if allowed by
regulations).
● Transmit the modulated signal.
Materials:
● 1 kΩ Resistors
● Jumper wires
● Signal Generator
● Oscilloscope
● Probe
● 3 mH inductor
● 0.1 μF conductor
● Diode
Procedure:
Initially, we parallelly linked two 1k-ohm resistors and attached a diode at
the junction where the two resistors terminated. Subsequently, we
introduced a capacitor and an inductor, connecting them in parallel, with
the other end linked to the ground. For the message signal, one resistor was
connected to a signal generator, while another signal generator was
employed to provide the carrier signal through the second resistor.
Following this setup, a segment was taken from the diode, and another
segment from the ground, both of which were connected to an oscillator to
observe the resulting output.
Image :
This image provides a distinct depiction of the combined addition of the
message signal and carrier signal, resulting in the generation of a
modulated signal.
Observation with Oscilloscope:
Here the circuit of Amplitude Modulation.
Discussion:
This laboratory experiment involves exploring amplitude modulation. The
modulation circuit is supplied with two signals, yielding a modulated signal
as the output. Signal generators are employed to produce both message
signals and carrier signals in this experimental setup. An oscillator is
utilized to capture the output of the modulated amplitude signal.
To minimize noise, we opted to eliminate connection jumpers and directly
connected wires to the primary components. However, during the
experiment, we encountered challenges with the oscillator, as it failed to
produce the anticipated result. In response, we systematically examined our
circuit with various oscillators until achieving the desired outcome.
