frequecy modulation by mohammad afaneh and mohammad aldaour
1. Frequency Modulation (FM)
Researched By :-
1) YAZAN SAYEL ABUZAID (320200102144)
2) ABDALLAH WAEEL ALHAMEEDI (320200102105)
3) HUTHAIFA ABU KHARMA (320220114032)
Presented to :- Dr.Nashat Al-Bdoor
2. Introduction To
Frequency Modulation
What’s The Frequency Modulation ؟
►Frequency Modulation (FM) is a method of encoding information into a
carrier wave by varying its frequency in proportion to the amplitude of
the modulating signal, while the carrier wave's amplitude remains
constant.
►It is primarily used in radio broadcasting, telecommunications, and other
communication systems to provide higher sound quality and greater
resistance to noise and interference compared to other
modulation techniques like Amplitude Modulation (AM).
►Why does the carrier wave’s amplitude remains the same
because the modulation process focuses solely on altering the frequency of the
carrier wave, not its amplitude. This is a key characteristic that differentiates FM
from other modulation techniques like Amplitude Modulation (AM).
3. The Creation Of Frequency Modulation
Why did they create the (FM) from the start ?
► Frequency Modulation (FM) was created to address the limitations of earlier radio
transmission methods, particularly Amplitude Modulation (AM), and to improve the quality
and reliability of radio signals
►Improvements such as
1- Overcome Noise and Interference
AM radio signals are prone to noise and interference, while FM, invented by Edwin
Armstrong in 1933, varies the carrier's frequency, making it less susceptible to such
issues. This made FM ideal for clearer, high-fidelity audio transmission
2- Improve Audio Quality
AM radio signals have limited bandwidth, resulting in lower sound quality, while FM offers
a wider bandwidth for more detailed, high-quality sound. This made FM ideal for
music broadcasting, where sound fidelity is important
3- Support Better Signal Stability
AM signals suffer from amplitude fluctuations and interference, causing distortion, while
FM remains stable as it’s not affected by amplitude changes, ensuring consistent,
high-quality broadcasting.
4- Increase Transmission Range and Efficiency
AM signals degrade over long distances and in areas with obstructions, while FM signals
provide more stable quality, especially for line-of-sight transmissions. FM has a shorter
range than AM but performs better in urban environments with clear signal path
4. Frequency Modulation (FM) works by changing the frequency of a
constant amplitude carrier wave in response to the amplitude of the audio
signal being transmitted. When the audio signal has higher amplitude
(louder sound), the carrier frequency shifts more; when the audio signal has
lower amplitude (softer sound), the frequency shift is smaller. This process
allows FM to transmit higher-quality sound with greater resistance to
interference compared to Amplitude Modulation (AM), making it ideal for
clear, high-fidelity radio broadcasting and communication.
How Does It Work ?
5. Frequency Calculations
instantaneous frequency
The instantaneous frequency of an FM signal is given by:
f(t) = fc + kf * m(t)
where:
f(t): Instantaneous frequency (Hz) fc: Carrier frequency (Hz)
kf: Frequency sensitivity (Hz/V) m(t): Modulating signal (V)
This formula shows how the carrier frequency is continuously modified in proportion to the amplitude of the
modulating signal.
Instantaneous Frequency: The formula f(t) = fc + kf * m(t) describes how the carrier frequency is
instantaneously modified by the modulating signal. It's crucial to understand that this frequency change is
continuous and directly proportional to the amplitude of the modulating signal at any given moment.
Factors Influencing Frequency:
o Carrier Frequency (fc): This is the base frequency of the signal, which remains constant in the absence of
modulation. It's chosen based on the application (e.g., FM radio uses frequencies in the VHF band).
o Frequency Sensitivity (kf): This parameter, measured in Hz/V, determines how much the carrier frequency
changes for a given change in the modulating signal's voltage. A higher kf means a more sensitive system,
leading to larger frequency deviations.
o Modulating Signal (m(t)): This is the information-carrying signal, which can be an audio signal, sensor
data, or any other time-varying signal. Its amplitude and frequency directly influence the instantaneous
frequency of the FM wave.
6. Frequency Calculations
Example:
imagine a simple FM signal where the carrier frequency (fc) is 100 MHz. This signal is
modulated by a sinusoidal wave (like a single tone) with a frequency (fm) of 1 kHz. The
frequency sensitivity (kf) of the modulator is 10 kHz/V. Let's say at a particular moment
in time, the amplitude (Am) of the modulating signal is 0.5V.
fi = fc + kf * m(t)
Where m(t) represents the instantaneous value of the modulating signal. In this case,
m(t) = 0.5V. Therefore:
fi = 100 MHz + (10 kHz/V * 0.5 V)
fi = 100 MHz + 5 kHz
fi = 100.005 MHz
7. Frequency Deviation (Δf)
Frequency deviation (Δf) is the maximum change in instantaneous frequency from the carrier frequency.
It's directly proportional to the amplitude of the modulating signal.
In the previous example, the frequency deviation is 50 kHz. This means the carrier
frequency swings 50 kHz above and below its center frequency.
· Formula: Δf = kf * Am
kf is the frequency sensitivity of the modulator (Hz/V)
Am is the peak amplitude of the modulating signal (V)
Frequency Calculations
8. Example: Let's say you have an FM transmitter with kf = 5 kHz/V. If your modulating
signal (e.g., an audio signal) has a peak amplitude of 2V:
Δf = 5 kHz/V * 2 V = 10 kHz
This means the carrier frequency will deviate by a maximum of 10 kHz above and below its
center frequency. A higher Δf generally leads to:
Wider bandwidth: More frequency variation requires more space in the spectrum.
Better signal-to-noise ratio (SNR): FM is inherently more resistant to amplitude-based noise,
and a larger Δf further enhances this.
Higher audio fidelity (in FM broadcasting): A wider range of audio frequencies and dynamics
can be transmitted.
Frequency Calculations
9. Frequency Modulation Index (β)
The modulation index (β) is a dimensionless quantity that represents the ratio of the frequency deviation
to the modulating frequency:
β = Δf / fm
where: Δf: Frequency deviation (Hz)
fm: Modulating frequency (Hz)
β determines the bandwidth and fidelity of the FM signal.
FM signals are often categorized as wideband (β 1) and
≥ narrowband (β < 1)
Narrowband FM (NBFM)
Characteristics:
o Small Modulation Index: β << 1 (typically less than 0.2)
o Limited Frequency Deviation: The frequency deviation is small compared to the
modulating frequency.
Spectrum: The spectrum primarily consists of the carrier and two significant sidebands,
similar to AM but with different phase relationships
Frequency Calculations
10. Example: A two-way radio communication system uses NBFM with Δf = 2 kHz and fm =
5 kHz:
β = 2 kHz / 5 kHz = 0.4
This falls within the range of NBFM.
Applications:
o Two-way Radio: Police, fire departments, and amateur radio often use NBFM due
to its bandwidth efficiency.
o Mobile Communications: Some mobile communication systems employ NBFM for
voice transmission.
o Telemetry: NBFM can be used to transmit sensor data in applications where
bandwidth is limited.
Advantages:
o Bandwidth Efficiency: NBFM requires less bandwidth than WBFM, making it
suitable for crowded frequency bands.
o Simple Circuitry: NBFM transmitters and receivers are generally simpler and less
expensive to implement.
Disadvantages:
o Limited Fidelity: Due to the small frequency deviation, NBFM is not well-suited for
high-fidelity audio transmission.
o Susceptibility to Noise: Although FM is generally more noise-resistant than AM,
NBFM can be more susceptible to noise than WBFM.
Frequency Calculations
11. Wideband FM (WBFM)
Characteristics:
o Large Modulation Index: β > 1 (can range from a few to hundreds)
o Significant Frequency Deviation: The frequency deviation is larger, often significantly
exceeding the modulating frequency.
o Spectrum: The spectrum contains multiple sidebands spread over a wider frequency range. The
number of significant sidebands increases with the modulation index.
Frequency Calculations
12. Example: FM radio broadcasting uses WBFM. A typical FM radio station might have Δf = 75 kHz
and a maximum fm of 15 kHz (representing the highest audio frequency):
β = 75 kHz / 15 kHz = 5
Applications:
o FM Broadcasting: WBFM is used for high-fidelity audio broadcasting due to its ability to
reproduce a wide range of frequencies and dynamics.
o High-Quality Audio Transmission: Professional audio applications and some wireless
microphones use WBFM for its superior sound quality.
o Satellite Communications: WBFM is employed in some satellite communication systems for its
robustness and noise immunity.
Advantages:
o High Fidelity: WBFM provides excellent audio fidelity, making it ideal for music and high-
quality speech transmission.
o Noise Immunity: WBFM is highly resistant to noise and interference, resulting in clearer
reception.
Disadvantages:
o Increased Bandwidth: WBFM requires a significantly larger bandwidth than NBFM, which can
be a limiting factor in spectrum-constrained environments.
o More Complex Circuitry: WBFM transmitters and receivers are more complex and typically
more expensive than NBFM equipment.
Frequency Calculations
13. Carson's Rule and Bandwidth
Carson's rule provides an approximation of the bandwidth required for an FM signal:
BW ≈ 2(Δf + fm)
where:
BW: Bandwidth (Hz)
Δf: Frequency deviation (Hz)
fm: Highest modulating frequency (Hz)
• Example:
For an FM signal with Δf = 75 kHz and fm = 15 kHz, the approximate bandwidth
using Carson's rule would be:
BW ≈ 2 (75 kHz + 15 kHz) = 180 kHz
This rule is a useful guideline, but the actual bandwidth can vary depending on the
modulation index and desired signal quality.
Frequency Calculations
14. Power Calculations
In Frequency Modulation
Power in Frequency Modulation (FM):
►In FM, the total power depends primarily on:
The Carrier Wave Only: Total power remains constant, regardless of the modulation index.
It is distributed among the carrier and infinite sidebands.
Formula for Power in FM:
Power Distribution:
Power distribution depends on the frequency modulation index :
where:
o : Frequency deviation.
o : Frequency of the modulating signal.
15. Examples for Power Calculation in AM and FM:
Given:
You have a carrier wave with the following parameters:
•Carrier amplitude Ac =10 V.
•Antenna resistance R=50 Ω.
Modulation parameters:
•Frequency deviation Δf=5 KHz.
•Modulating signal frequency fm=1 KHz.
Calculate:
1.Total power PF.
2.Frequency modulation index β.
Solution:
1.
Total Power (F):
.
2.
Frequency Modulation Index (β):
Power Calculations
In Frequency Modulation
16. Applications of FM Modulation
Main Applications of FM Modulation
1. FM Radio:
►Widely used in broadcasting radio signals, providing high-quality audio with minimal noise.
2. Aviation Communication Systems:
►Ensures clear and stable communication between pilots and air traffic control by reducing interference.
3. Radar Systems:
►Enhances signal accuracy and minimizes interference with other systems.
4. Wireless Data Transmission:
►Used in modern communication systems like mobile phones and Wi-Fi to ensure stable and high-quality
data transfer.
5. Electronic Musical Instruments:
►FM synthesis is used in synthesizers to create a wide range of musical tones.
17. Comparison Between FM and AM Modulation
Aspect FM Modulation AM Modulation
Definition
Varies the frequency of the carrier Varies the amplitude of the carrier
Audio Quality Higher audio quality Medium audio quality
Interference Resistance
Less prone to interference More prone to interference
Bandwidth
Requirements
Requires a wider bandwidth
Requires a narrower bandwidth
Equipment More complex and expensive Simpler and more affordable
Applications FM radio and aviation systems broadcasting AM radio and analog TV
18. Advantages, Disadvantages, and Conclusion
Pros and Cons of FM Modulation
• Advantages of FM Modulation:
o High audio quality: Less affected by noise and interference
compared to AM.
o Signal stability: Remains strong even in varying environmental
conditions.
o Noise resistance: Well-suited for environments with high
interference.
• Disadvantages of FM Modulation:
o High bandwidth requirement: Needs a larger frequency range,
limiting the number of available channels. o Complex equipment:
Requires more expensive and intricate transmission and reception
devices.
19. Conclusion:
frequency Modulation (FM) : is a widely used and effective method of signal transmission
that offers significant advantages in terms of sound quality and resistance to interference. Its
ability to maintain a constant amplitude while varying frequency makes it ideal for
applications such as radio broadcasting and communication systems. FM continues to play a
vital role in modern communication technologies, demonstrating the lasting impact of its
innovative design Despite its higher costs and complexity, its applications in radio, aviation,
and radar systems highlight its importance in both daily life and critical operations.
