ADAMA SCIENCE AND TECHNOLOGY UNIVERSITY
SCHOOL OF ELECTRICAL ENGINEERING AND COMPUTING
PROGRAM OF ELECTRONICS AND COMMUNICATION
ENGINEERING
Communication System II LABORATORY REPORT
[AM,FM MODULATION AND DEMODULATION]
COURSE CODE: -ECEg3202
LAB NO: -7&8
GROUP: -2
SUB GROUP: ---
GROUP MEMBERS:
1.WAKSHUMA DELESA ..............UGR/22539/13
2. EYOB GUGSA ..........................UGR/22982/13
SUBMITTED TO: -MR.ZENEBE.M
DATE OF EXPERIMENT: - MAY 30 2023
DATE OF SUBMISSION: -JUN 6 2023
Students Task: -
LAB 7
Students Tasks: - 1, Determine the cutoff frequency of the filter
On this task we give it cut of frequancy of 100 hz
2, Display the un modulated and modulated signal in the same
graph and identify their difference.
The observable difference between the unmodulated and modulated signals AM is
the amplitude variation in the modulated signal due to the modulation index. The
unmodulated signal is a pure sine wave with a constant amplitude, while the modulated
signal has a varying amplitude that is proportional to the amplitude of the message signal.
The amplitude variation in the modulated signal can be observed as a "envelope" that
follows the shape of the message signal. The depth of the amplitude variation is
determined by the modulation index, which is the ratio of the amplitude of the message
signal to the amplitude of the carrier signal. A higher modulation index will result in a
deeper amplitude variation in the modulated signal.
3. Write also a program for DSB_SC (Double Side Band Suppressed carrier) AM
modulated and Demodulated signal. Hint: - S(t)=m(t)*C(t) where m(t) is message signal
and c(t) is a carrier signal. To get the original signal just multiply the modulated signal
with the carrier.
LAB 8
1, Display both the base band message signal and the FM modulated
signal in the same graph.
Fig 1.2 display of both fm modulated and base band signal n
the same graph
Modify the message signal by adding a uniform white noise and control
it form front palette with numerical control or other mechanism. And
compare the resulting figure with all other noise type.
Fig 2.1 with uniform white noise noise
Fig2.2 with barinouli noise
Fig 2.3 with gamma noise
Fig2.3 with bionomial noise
Fig 2.5 With gassuian white noise
Fig 2.6 with periodic random noise
Fig 2.7 with passion noise
Fig 2.8 with mls sequance noise
Fig 2.9 with inverse f noise
3, From Help menu search MODULATION and select Function
Modulation with FM. Compare what you did previously with these
generated signals by changing different parameters
Here are some possible comparisons that could be made between the
previously done FM modulation and the generated signals from the
"Function Modulation with FM" function in LabVIEW:
1. Modulation index: The modulation index determines the amount of frequency
deviation in the FM signal. By changing the modulation index, we can observe how the
frequency deviation and the bandwidth of the FM signal change. Comparing the
previously done FM modulation with the generated signals from the "Function
Modulation with FM" function for different modulation indices can help us understand
the effect of modulation index on the FM signal.
2. Carrier frequency: The carrier frequency is the frequency of the sinusoidal carrier
wave used in the FM modulation. By changing the carrier frequency, we can observe how
the frequency spectrum of the FM signal changes. Comparing the previously done FM
modulation with the generated signals from the "Function Modulation with FM" function
for different carrier frequencies can help us understand the effect of carrier frequency on
the FM signal.
3. Message signal frequency: The message signal frequency is the frequency of
the modulating signal used in the FM modulation. By changing the message signal
frequency, we can observe how the frequency spectrum of the FM signal changes.
Comparing the previously done FM modulation with the generated signals from the
"Function Modulation with FM" function for different message signal frequencies can
help us understand the effect of message signal frequency on the FM signal.
4. Noise: The presence of noise in the FM signal can affect its quality and intelligibility.
By adding different types and levels of noise to the FM signal, we can observe how the
signal-to-noise ratio (SNR) and the quality of the FM signal change. Comparing the
previously done FM modulation with the generated signals from the "Function
Modulation with FM" function for different types and levels of noise can help us
understand the effect of noise on the FM signal.
TASK 9 : FM DEMODULATION
Procedures: - The rest procedure and the demodulator circuits are left
as an assignment for students which is also should be submitted.
SO THE QUASTION IS HOW FM DEMODULATOR OR ENVELOPE
DETECTOR IS WORK:-
A balanced slope detector is a type of circuit used in FM demodulation. It works
by first converting the FM signal to an AM signal, and then extracting the original
message signal from the AM signal. Here's how it works:
1. The FM signal is first passed through a limiter circuit, which clips the amplitude of the
signal to a fixed value. This ensures that the amplitude variations of the FM signal are
kept constant, and only the frequency variations remain.
2. The limiter output is then passed through a differentiator circuit, which produces an
output signal proportional to the rate of change of the input signal. This converts the
frequency variations of the FM signal into amplitude variations.
3. The differentiator output is then split into two equal parts, and each part is passed
through a RC circuit (resistor-capacitor circuit) with different time constants. This
produces two output signals which are 90 degrees out of phase with each other.
4. These two signals are then passed through a balanced modulator circuit, which
multiplies them together. This produces an output signal which is proportional to the
difference in phase between the two input signals.
5. Finally, the output of the balanced modulator is passed through a low-pass filter, which
removes the high frequency components and leaves only the original message signal.
The balanced slope detector offers several advantages over other FM demodulation
techniques, such as being less sensitive to noise and distortion
