FM Modulation
Project
Names & ID:
- Amr Ashraf Mohamed Gadalla 202101355
- Khaled Ashraf 202100751
- Eyad Hany 202101255
- Mohamed Mahmoud 202101352
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- Table of Contents
-Intro
- Results and discussions
- Conclusion
- References
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Intro
Modulation is widely used concept in communications where we
use another signal to aid us in transporting our main signal that
contains the info needed to be transported, The reason we use
Modulation is that the wireless transportation of different signals
is not practically applicable for all frequencies in which most
frequencies usually attenuate very quickly to be transported and
received.
Modulation has mainly two types:1.Amplitude Modulation
2.Angle Modulation
During this report we will demonstrate the differences between
these two types of modulations and the concepts beyond them
as well as practically implement them using Matlab code for a
multi-frequency signal.
However, Modulation is more commonly used at the present time
in most practical implications.
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Results and Discussions
Task (1,2,3):
We first generated a sinusoidal signal from 0 to 1 s with a time vector with sample rate
fs=1 kHz and the frequency of the sinusoidal signal fm= 5 Hz.
Then we generated the carrier signal from 0 to 1s with the same time vector with sample
rate fs=1 kHz. The frequency of the sine signal fc=100 Hz and its amplitude Ac=20 V.
Then we started to generate the FM modulated signal we first need to get the beta value
which is equal to (∇𝑓 / 𝑓𝑚 ) which is equal to (kf * Am / fm) then we plotted the three
signals using the subplot function in mat lap.
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Task (4):
Changing the modulation index (beta) in FM modulation will affect the bandwidth and power of the
FM signal in the frequency domain.
Bandwidth: As the modulation index increases, the bandwidth of the FM signal also increases. The
bandwidth is proportional to the maximum frequency deviation, which is equal to the modulation index
times the maximum frequency of the message signal. Therefore, a larger modulation index will lead to
a wider frequency range of the FM signal, resulting in a higher bandwidth.
Power: The total power of an FM signal is equal to the sum of the carrier power and the sideband
power. As the modulation index increases, the sideband power also increases, leading to an increase in
the total power of the FM signal. This is because the higher frequency components generated by the
modulation process have more power than the lower frequency components.
In summary, increasing the modulation index in FM modulation will increase the bandwidth and power
of the FM signal in the frequency domain.
In frequency modulation (FM), the bandwidth and power of the modulated signal depend on the
modulation index, which is related to the maximum frequency deviation and the frequency of the
modulating signal. As the modulation index increases, the bandwidth and power of the FM signal
increase.
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In frequency domain, the effect of increasing the modulation index is seen in the spread of the frequency
spectrum. As the modulation index increases, the spectrum of the FM signal spreads out over a wider
frequency range, resulting in an increase in the bandwidth. Additionally, the power of the signal increases
as the modulation index increases. This can be seen in the height of the peaks in the frequency spectrum,
which increase as the modulation index increases.
Task (4):
In FM modulation, the modulation index β represents the degree to which the frequency of the carrier
wave is modulated by the message signal. The modulation index β is defined as the ratio of the
maximum deviation frequency to the modulating frequency. When β=0, there is no frequency
deviation, so the carrier wave is not modulated by the message signal, resulting in a constant amplitude
carrier. When β is small, such as β=0.25, the frequency deviation is also small, so the carrier wave is
slightly modulated by the message signal. As β increases, such as β=1, the frequency deviation
becomes larger, so the carrier wave is more significantly modulated by the message signal. When β is
very large, such as β=9, the frequency deviation is very large, causing the carrier wave to be heavily
modulated by the message signal, resulting in a wideband signal with a large bandwidth.
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Task (5):
Task 5 was a critical part of our project as it involved demodulating the FM signal that
we had generated in Task 3. We approached this task with great care and attention to
detail to ensure that we could accurately recover the original message signal.
To begin this task, we plotted the original message signal that we had generated in Task
1 to serve as a reference for comparison. We then proceeded to demodulate the FM
signal using the mathematical formula z(t) = Ac[2πfc + 2πkf m(t)].
Using this formula, we were able to recover the original message signal with great
accuracy. We plotted the demodulated signal in the time domain and compared it to the
original message signal, and we were pleased to see that they were nearly identical.
To further validate our demodulation process, we also used the MATLAB function
'fmdemod' to demodulate the FM signal. We plotted this demodulated signal alongside
our manual demodulated signal and once again saw a very close match.
Overall, we are confident that our demodulation process was successful and that we were
able to accurately recover the original message signal from the FM signal that we had
generated. This task required a great deal of precision and attention to detail, and we are
proud of the hard work and dedication that we put into it.
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Difference between FM and AM:
FM modulation (Frequency Modulation) and AM modulation (Amplitude Modulation)
are both techniques used to transmit information over a carrier wave, but they differ in
how the information is encoded onto the carrier wave.
In AM modulation, the amplitude of the carrier wave is varied in proportion to the
amplitude of the modulating signal. This variation in amplitude is used to carry the
information. The frequency and phase of the carrier wave remain constant.
In FM modulation, the frequency of the carrier wave is varied in proportion to the
amplitude of the modulating signal. This variation in frequency is used to carry the
information. The amplitude and phase of the carrier wave remain constant.
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The main advantage of FM modulation over AM modulation is that it is less sensitive to
noise . In AM modulation, changes in amplitude due to noise can result in the loss of the
information being transmitted. In FM modulation, changes in frequency due to noise or
interference have less of an effect on the information being transmitted.
Task (bonus):
Amplitude modulation comes with different types and various techniques and was the
only modulation used before the FM
We will demonstrate two different kinds of this type of modulation:1.Low carrier Modulation & High-carrier Modulation
2.single side-band Modulation(upper and Lower)
Both types uses the carriers signal amplitude to transmit the info as a varying amplitude
modulated signal received by transmitter with a slight advantage in the single side-band
technique
The SSB filters the lower or upper side-band as well as the carrier frequency, this
technique highly reduces the band-width used (by half) without actually neglecting any
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of the information since the two side-bands contains exactly the same info, However a
filter is demanded after modulating to pass only one side band to be received
Conclusion
The results of both types of modulations and the plots for the modulated signals in both
domains spot the light on the main differences across them and make it more perceivable
why FM is more common at the present.
Although AM has less bandwidth it comes with a tradeoff with the quality but actually
this is not the main reason, AM uses the amplitude to transmit the info which make the
modulated far highly sensitive to the noise compared to the FM also the amplitude varying
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consumes even more power on the other hand, FM uses the frequency its self to deliver
the modulating signal which offer more protection against noise, the amplitude is also
proportional to the modulating signal’s and usually constant makes FM more powerefficient.
These two advantages makes the FM very beneficial in modern communications systems
especially that the demodulation works for both modulations almost with same precision
and accuracy(regardless the noise) making the FM highly preferable by experts and
engineers to transmit their info’s across the world.
References
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Ashish. (2022, July 8). What’s The Difference Between AM And FM Radio Waves?
Science
ABC.
https://www.scienceabc.com/innovation/what-differencefrequency-amplitude-modulation-radio-waves.html
Notes, E. (n.d.). What is FM, Frequency Modulation » Electronics Notes.
https://www.electronics-notes.com/articles/radio/modulation/frequencymodulation-fm.php
Vedantu. (n.d.). Difference between AM, FM and PM. VEDANTU.
https://www.vedantu.com/physics/difference-between-am-and-fm
Yoder, J. H. M. R. W. S. M. A. (n.d.). DSP First. McClellan, Schafer, and Yoder, DSP
First, ISBN 0-13-065562-7. Prentice Hall, Upper Saddle River, NJ 07458. © 2012
Pearson Education, Inc. https://dspfirst.gatech.edu/
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