FM (Frequency Modulation) transmitters are electronic devices that transmit audio signals over a radio frequency. These transmitters are commonly used in radio broadcasting, wireless microphones, and other communication systems. FM transmitters work by modulating the frequency of a carrier wave with the audio signal to produce a signal that can be transmitted over the airwaves.

1. Jimma University
Instituteof technology
FACULTYOF ELECTRICAL AND COMPUTER ENGINEERING
INTRODUCTIONTO COMMUNICATIONSYSTEMS
PROJECT NAME:- FMTRASMITTER
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FM TRANSMITTER 1

2. 1. Introduction to FM transmitters
1.1 OVERVIEW
 FM (Frequency Modulation) transmitters are
electronic devices that transmit audio signals
over a radio frequency. These transmitters are
commonly used in radio broadcasting, wireless
microphones, and other communication systems.
FM transmitters work by modulating the
frequency of a carrier wave with the audio signal
to produce a signal that can be transmitted over
the airwaves. 12/4/2023
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3. 1.2 HISTORICAL BACKGROUND
 The history of FM transmitters dates back to the early 20th
century when wireless communication was first invented. In
the 1930s, Edwin Armstrong, an American electrical engineer,
invented the FM radio system and the FM transmitter.
Armstrong's FM system was a significant improvement over
the existing AM radio system, which suffered from poor
sound quality and susceptibility to interference.
 The first FM broadcast was made in 1939 by Armstrong
himself, who transmitted a concert from the top of the Empire
State Building in New York City
1.3 PURPOSE OF THE PROJECT
• The purpose of an FM transmitter project could be to design,
build, and test a device that can transmit audio signals wirelessly
using FM radio waves. 12/4/2023
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4. Principles of frequency of modulation(FM)
2.1 Frequency modulation (FM) basics
• FM modulation is a technique used to transmit information, such
as audio signals, over radio waves by varying the frequency of
the carrier wave. In FM modulation, the amplitude of the carrier
wave remains constant, while its frequency is changed in
proportion to the modulating signal.
 The key characteristics of FM modulation include
1. Frequency deviation: This refers to the maximum amount by
which the carrier frequency is varied in response to the modulating
signal.
2. Modulation index: This is the ratio of the frequency deviation to
the maximum frequency of the modulating signal.
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5. 3.Noise immunity: FM modulation is less susceptible to noise
and interference than other modulation techniques such as
amplitude modulation (AM).
4.Bandwidth: FM modulation requires a wider bandwidth than
AM modulation due to the need to accommodate frequency
variations caused by the modulating signal.
5.Sound quality: FM modulation provides higher sound quality
than AM modulation due to its immunity to noise and distortion.
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7.  Frequency modulation (FM) is a method of encoding
information onto a carrier wave by varying its frequency. The
mathematical principles behind FM are based on the concept
of sinusoidal waves and their properties.
 A sinusoidal wave can be represented mathematically as:
y(t) = A sin(2πf t + Φ)
 where y(t) is the amplitude of the wave at time t, A is the
amplitude of the wave, f is the frequency of the wave, and Φ is
the phase of the wave.
 The frequency-modulated signal can be expressed
mathematically as:
s(t) = A sin[2π(f c + k fm(t))t + Φ]
 where s(t) is the frequency-modulated signal, f c is the carrier
frequency, and k fm(t) is the frequency deviation.
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8. 3.1 Transmitter Requirements and Specifications
 To discuss the desired specifications and features of
an FM transmitter, we need to consider various
aspects of its design and functionality. Here are some
key factors to consider
1. Frequency Range: The FM transmitter should be
capable of operating within the frequency range
allotted for FM broadcasting, typically 87.5 MHz to
108 MHz Ensure that it supports the desired
frequency band for your specific region.
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9. 2. Transmission Power: The transmitter's power output
determines the coverage range. Higher power output
generally results in a larger coverage area.
3.Audio Quality: The FM transmitter should provide
high-quality audio transmission.
4.Power Supply: Consider the power supply options for
the transmitter. It can be AC-powered or DC-powered,
depending on the application.
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10.  When designing an FM transmitter, various
components and circuitry are involved to generate and
transmit the FM signal. Here are some key transmitter
components and circuitry commonly used in FM
transmitter designs:
 Oscillator
 Modulation Circuit
 RF Amplifier
 Power Amplifier
 Low-Pass Filter
 Antenna etc..
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11.  Assembling an FM transmitter involves careful integration
of the components and ensuring proper connections. Here is
a step-by-step process that outlines the general procedure
for assembling an FM transmitter
 Gather the Components and Tools
 Mount and Connect the Components
 Establish Interconnections
 Perform Initial Testing
 Finalize the Assembly
 The specific assembly process may vary depending on the
FM transmitter design, complexity, and the availability of
detailed assembly instructions or documentation.
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13.  The main function of an FM Transmitter Circuit is to transmit
the sound using radio waves. So, at first, an FM Transmitter
Circuit converts the sound or audio into a radio wave then it
transmits wirelessly.
 You can see, in the block diagram of the FM Transmitter, the
first block is the Microphone. The microphone is a Transducer
that can convert the sound energy into an audio signal in the
form of electrical energy. So microphone is a source of an
audio signal. In this block diagram, the microphone is used as
the source of the audio signal but it may be another audio
source also.
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14.  The next block is Audio Pre-amplifier. The audio pre-
amplifier is used to amplify the audio signal coming
from the microphone.
 The next one is the Modulator. The modulator circuit is
the main part of an FM transmitter circuit. It converts
the audio signal into a radio signal which is to be
transmitted. The modulator circuit takes two signals as
input one is the audio signal coming from the audio
pre-amplifier and another is the carrier signal.
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• The RF amplifier circuit amplifies the modulated RF signal
coming from the modulator.
• In general FM transmitter works by modulating the frequency of
a carrier wave with an audio signal, and transmitting is as radio
waves.

16.  During FM transmitter operation, several common problems
can arise. Here are some examples:
 Interference: Interference from other nearby electronic devices,
such as mobile phones, Wi-Fi routers, or other radio
transmitters, can cause distortion or disruption in the
transmitted FM signal.
 Signal Weakness: If the FM transmitter does not have sufficient
power or is located too far from the receiver, the transmitted
signal may become weak.
 Frequency Drift: FM transmitters rely on stable carrier wave
frequencies to maintain accurate modulation.
 Noise and Distortion: Poor audio quality, noise, or distortion
can occur if there are issues with the audio source,
amplification, or modulation process.
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17.  Improper Antenna Placement or Design: The antenna
plays a crucial role in transmitting the FM signal
effectively.
 Power Supply Issues: Inadequate or unstable power
supply to the FM transmitter can lead to performance
issues.
 Licensing and Legal Compliance: It's important to
ensure that the FM transmitter operates within the legal
frequency bands and power limits defined by
regulatory authorities.
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18.  Some troubleshooting techniques to diagnose and
resolve common issues that may arise during FM
transmitter operation:
 Interference
 Signal Weakness
 Frequency Drift
 Noise and Distortion
 Improper Antenna Placement or Design
 Power Supply Issues
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19.  In conclusion, the FM transmitter is a vital component in
wireless communication systems. Through the project, we
have gained a deeper understanding of the principles of
frequency modulation (FM) and the practical aspects of
designing, constructing, and evaluating an FM
transmitter. An FM transmitter is a device that uses
frequency modulation to transmit sound signals
wirelessly through a carrier wave. It can be used for
various applications such as broadcasting,
communication, and entertainment. The FM transmitter
circuit consists of a microphone, an audio pre-amplifier, a
modulator, an oscillator, an RF amplifier, and an antenna.
The microphone converts the sound signals into electrical
signals, which are then amplified by the audio pre-
amplifier. 12/4/2023
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