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DESIGN AND CONSTRUCTION OF FM TRANMITTER

Technical Report · January 2023

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Pintu Chandra Paul Md Ashikul Islam

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 DESIGN AND CONSTRUCTION OF FM
TRANMITTER

Department of ICT

Comilla University
Prepared By:

NAME ID
MD Ashikul Iskam 12009015
Mohammad Abul Hashem 12009023
Mst Sunjida Afrin 12009006
Masaid Ahmed 12009032
Proma Sarkar 12009050
Md Mahmudur Rahman Sarkar 12009041

Supervised By:
Pintu Chandra Paul
Lecturer
Department of ICT
Comilla University
1
 Submission Date: 26 September,2022

DECLARATION

This declaration is made on the 26th September 2022.

Student’s declaration:

We , Md Ashikul Islam , Mohammad Abul Hashem , Mst Sungeda Afrin , Masaid Ahmed , Md
Mahmudur Rahman Sarkar , Proma Sarkar , hereby declare that the work entitled design of an fm
bugger circuit is our original work. We have not copied from any other sources except where due
reference or acknowledgment is made explicitly in the text, nor has any part been written for us
by another person.

Signature of Students:

.......................................................... .........................................................
Md Ashikul Islam Mohammad Abul Hashem

ID-12009015, Session-2019-20 ID-12009023, Session-2019-20

Dept of ICT, Comilla University Dept of ICT, Comilla University

.......................................................... .........................................................
Mst Sungeda Afrin Masaid Ahmed

ID-12009006, Session-2019-20 ID-12009032, Session-2019-20

Dept of ICT, Comilla University Dept of ICT, Comilla University

.......................................................... .........................................................
Proma Sarkar Md Mahmudur Rahman Sarkar

ID-12009050, Session-2019-20 ID-12009041, Session-2019-20

Dept of ICT, Comilla University Dept of ICT, Comilla University

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 APPROVAL
It is certified that the work contained in the project titled “DESIGN OF AN FM BUGGER
CIRCUIT” by Md Ashikul Islam , Mohammad Abul Hashem , Masaid Ahmed , Proma Sarkar ,
Sungeda Afrin , Md Mahmudul Hasan Sarkar has been carried out in under my supervision and
that this work has not been submitted elsewhere for a final year project.

………………………………
Supervisor’s Name: Pintu Chandra Paul
Lecturer
Dept. of ICT
Comilla University.

3
 ACKNOWLEDGEMENT

We would like to express our gratitude to Allah for His guidance , care and support He has
given us throughout the period of study .

Motivation, support, and proper guidance are essential for any initiative. It is impossible to
complete a project individually in perfection. We’d like to take this opportunity to express our
heartfelt gratitude and deepest respect to those who have supported and assisted us throughout
this project.

It is a pleasure to express thanks to our honorable supervisor , Pintu Chandra Pal, Lecturer,
Department of Information and Communication Technology , for the encouragement and
guidance throughout the course of this project. Without his guidance, completing this task would
have been nearly impossible. We are extremely happy to have him as a teacher and supervisor.
We will remember this enlightening experience for the rest of our lives.

For academic interactions and ideas, we cannot forget our friends in the Engineering faculty.

We thank our families, who gave us much care towards our life and base educational career. We
feel great pleasure to acknowledge all those involved in the process of our education and
research.

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 ABSTRACT

FM transmitter is a device which generates frequency modulated signal. It is one element of a

radio system which, with the aid of an antenna, propagates an electromagnetic signal. Standard
FM broadcasts are based in the 88 - 108 MHz range.

The signal (from the microphone) is fed into the audio frequency (AF) for amplification then to
the modulator which combines the modulating signal with the carrier wave transports the
modulated signal through (RF) for final amplification to the antenna.

Fm receivers can be operated in the very high frequency bands at which AM interference is
frequently severe, commercial FM radio stations are assigned frequencies between 88 and 108
MHz and is the intended frequency range of transmission.

The project enhances one’s practical skill and it involves both the electronics and
telecommunication engineering fields. Theoretical knowledge such as circuit theory, electronic
circuit and principles of telecommunication learned through several courses offered by the
electrical and telecommunication program is applied in the project

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 TABLE OF CONTENTS
DECLARATION……………………………………………………….........................................2
APPROVAL……………………….……………………………………………………...............3
ACKNOWLEDGEMENT………………………………………………………………...............4
ABSTRACT……………………………………………………………………………….............5
TABLE OF CONTEXT…..……………………………………………………………………….6
LIST OF ABBREVIATIONS……………………………………………………………………..8
LIST OF FIGURES……………………………………………………………………….............9

CHAPTER 1: INTRODUCTION 10
1.1 BACKGROUND OF THE STUDY 10
1.2 FM TRANSMISSION SYSTEM 10
i) Microphone
ii) Audio Amplifier
iii) RF Oscillator
iv) Modulator
1.3 OBJECTIVES 12

CHAPTER 2: LITERATURE REVIEW 12

2.1 THEORETICAL BACKGROUND 12
2.2 FREQUENCY MODULATION (FM) TRANSMITTER 13
2.3 REVIEW OF PROJECT WORKS ON FM TRANSMITTERS 13

6
 i) MULTICHANNEL FM TRANSMITTER BY F.
MC_SWIGGAN. [12]
ii) SINGLE TRANSISTOR FM TRANSMITTER BY
D. MOHANKUMAR [13]
iii) 2 WATT FM TRANSMITTER BY SINNER. [14]
CHAPTER 3: METHODOLOGY & MODELING 15
3.1 METHODOLOGY 15
3.2 COMPONANTS 16
3.3 CIRCUIT DIAGRAM 18
3.4 WORKING METHOD 19
3.5 SCOPE 19
CHAPTER 4: TEST AND RESULTS 20
4.1 INTRODUCTION 20
4.3 TEST RESULT 21
CHAPTER 5: CONCLUSION 23
5.1 CONCLUSION 23
5.2 LIMITATIONS 23
REFERENCES 24

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LIST OF ABBREVIATIONS

FM - Frequency Modulation
RF - Radio Frequency

8
 LIST OF FIGURES
No. Name of Figures Page
Fig-1.1 BASIC BLOCK OF A FM TRANSMITTER 11
Fig-2.1 PORTABLE MULTICHANNEL FM 14
TRANSMITTER BY F. Mc SWIGGAN
TRANSMITTER
Fig-2.2 SINGLE TRANSISTOR FM TRANSMITTER BY D. 15
MOHANKUMAR
Fig-3.1 CIRCUIT DIAGRAM 19

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 CHAPTER - 1
INTRODUCTION

1.1: BACKGROUND OF THE STUDY

The world has developed to an era of information when electronics communication systems
influence most of human activities. These electronics communication systems consists of three
major aspects; the receiver, the channel and the source, which is the transmitter. A transmitter is
an electronics device, which, with the aid of an antenna, propagates an electromagnetic signal
such as radio, television or other telecommunications. In the previous years, signal energy was
generated in transmitting plants using arcs or mechanical alternators. Presently, a transmitter
usually has a power supply, an oscillator, a modulator and amplifiers for audio frequency (AF),
intermediate frequency (IF) and radio frequency (RF). Transmitters are sometimes classified
according to the signal information they process and radiate. Television transmitter’s processes
sounds and picture signal while radio transmitter processes only sound The research dealt with
the production of an FM transmitter of appreciable range for practical application. This system
will incorporate, at the output stage, the very high frequency (VHF) power transistor (NTE343)
which has produced excellent results in other circuits

1.2: FM TRANSMISSION SYSTEM

A FM transmission system, primarily comprises 4 basic sub-sections:

a) Microphone
b) Audio Amplifier

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 c) Modulator
d) RF Oscillator

Fig 1.1 BASIC BLOCK OF A FM TRANSMITTER

a) Microphone: A microphone is an input device that was developed by Emile Berliner in 1877.
It is used to convert sound waves into electric waves or input the audio into computers. It
captures audio by converting sound waves into an electrical signal, which may be a digital or
analog signal. This process can be implemented by a computer or other digital audio devices.
The first electronic microphone was based on a liquid mechanism, which used a diaphragm that
was connected to a current- charged needle in a diluted sulfuric acid solution. It was not able to
reproduce the intelligible speech.

b) Audio Amplifier: Audio amplifiers are the basic power amplifiers that can be of various types
like it is designed in various versions. There are various parameters technically and even the
parameters related to infrastructure also affect the audio amplification. The audio amplifiers are
designed in the form of chips and various sizes.

c) RF Oscillator: The function of the RF oscillator is to produce a high frequency signal in the
FM range (88 – 108MHz), called a carrier wave. The carrier wave is a sinusoidal signal with
constant amplitude and constant frequency. The frequency at which the FM transmitter operates,
is referred to as the carrier wave frequency.

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d) Modulator: The modulator provides the means by which the electrical signal representation
of the sound wave is embedded within the carrier wave. In frequency modulation (FM), this is
achieved by varying the frequency of the carrier wave in relation with amplitude changes in the
modulating signal (i.e. audio signal). The resultant is a modulated wave of high frequency that
contains the audio signal. This is a very important part of a FM transmission system, because it
allows the advantages of high frequency signal transmission to be exploited such as: I. Practical
antenna length: The Length of the antenna is directly related to the wavelength of the wave; and
the higher the frequency, the shorter the wavelength. Hence the smaller the antenna required .
Higher Energy Transmission: The energy carried by a wave depends upon its frequency. The
higher the frequency of the wave, the greater the energy possessed by it. As the audio signal
frequencies are small, they cannot be transmitted over large distances if radiated directly into
space.

1.3: OBJECTIVES
The objective of this project is:

1. To review some modern digital technologies that has been developed for effective FM signal

generation.

2. To show the design and components of a FM transmitter

3. To show the construction process of an electronically operated system known as FM

transmitter capable of transmitting a frequency modulated signal.

Chapter - Two

LITERATURE REVIEW

2.1: THEORETICAL BACKGROUND

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German physicist Heinrich Hertz developed the first crude radio transmitters (also known as
spark gap transmitters) in 1887 while conducting ground-breaking research on radio waves. A
high voltage spark between two conductors produced the radio waves. These transmitters were
used by Guglielmo Marconi to create the first effective radio communication systems starting in
1895, and radio started to be used commercially around 1900. The operator tapped a telegraph
key to turn on and off the transmitter, which produced radio wave pulses that represented text
messages in Morse code since audio (sound) could not be transmitted by spark transmitters.
Instead, information was transmitted by radiotelegraphy. These pulses were audible in the
receiver's loudspeaker as "beeps" and were converted back to text by an operator who understood
Morse code. The wireless telegraphy or "spark" era, also known as the first three decades of
radio (1887–1917), saw the use of these spark-gap transmitters. Spark transmitters were
electrically "noisy" because they produced damped waves. They produced radio noise that
interfered with other transmitters because they dispersed their energy over a wide range of
frequencies. In 1934, damped wave emissions were made illegal by international law.
Practical Frequency Modulation (FM) transmission was invented by Edwin Armstrong in 1933, who
showed that it was less vulnerable to noise and static than AM. The first FM radio station was
licensed in 1937.

2.2 FREQUENCY MODULATION (FM) TRANSMITTER

FM signals can be produced by either directly varying the frequency of the carrier oscillator, or
by converting phase modulation to frequency modulation (indirect method). Depending on the
method employed, FM transmitters are classified into 2 types: Direct and Indirect frequency
modulation transmitter.

2.3: REVIEW OF PROJECT WORKS ON FM TRANSMITTERS

A quick review of some of the past works done in this field will be evaluated. The results
obtained and the method used will be described.
a) MULTICHANNEL FM TRANSMITTER BY F. MC_SWIGGAN.

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The circuit design of the Portable Miniaturised, Multichannel FM transmitter employed the
direct frequency modulation technique and implemented it using a 2 stage transistor circuit. The
first stage of the circuit was used as a pre-audio amplifier while the 2nd transistor stage acts as an
oscillator and modulator circuit. The circuit works based on the transistor reactance modulator
concept. The reactance modulator is an amplifier designed so that its output impedance has a
reactance that varies as a function of the amplitude of the applied input voltage. The circuit was
able to provide an effective tuning range of 6 MHz and an effective range of 80 feet. The range
achieved by this circuit is quite small and would limit its applications.

Fig 2.1 PORTABLE MULTICHANNEL FM TRANSMITTER BY F. Mc SWIGGAN

b) SINGLE TRANSISTOR FM TRANSMITTER BY D. MOHANKUMAR

The single transistor FM transmitter is based on the transistor reactance modulator model. The
circuit is simplified by excluding a pre-amplifier stage, while the modulator and carrier oscillator
stage are implemented on a single 2N3904 or BC547 general purpose transistors. The
modulating effect is achieved by the specific arrangement of the input resistor R1 = 4k7 and C1
= 1nF capacitor. The single transistor FM Transmitter had a very poor range of about 9 - 15
meters, and also the stability of the circuit was a bit poor, as the frequency often drifted off.

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 Fig 2.2 SINGLE TRANSISTOR FM TRANSMITTER BY D. MOHANKUMAR

Chapter-Three

METHODOLOGY & MODELING

3.1: METHODOLOGY

The FM transmitter will be based on direct frequency modulation technique using a BC457 NPN
transistor and some capacitors and resistors . The Transistor does the main work of creating
modulated frequency of electric signal which is gained from electric mic as an analog signal .
With the help of DC voltage source of high amount , it creates a signal of high frequency . In
accordance of help , there are used of several pf and uf capacitors and resistors . The capacitors
help to store the voltage for a several amount of time and resistors create hindrance according to
necessary of the project . Here 6 to 12 voltage of power source can be used for power of high
frequency which will work as a carry frequency . The hope is to have a perfect FM transmitter of
a range of 10m with a clear sound transmission . Here sound frequency should be in the range of
89 to 90 Hz . Our expected frequency is 89.7. An antenna will be used for higher output on
emitter or collector in any side . And a coil is necessary for the project which would be
connected with the emitter side of the NPN transistor .

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3.2: Components :
The necessary components are :
1. BC547 NPN Transistor : The BC547 transistor is an NPN transistor. A transistor is
nothing but the transfer of resistance which is used for amplifying the current. A small
current of the base terminal of this transistor will control the large current of emitter and
base terminals. The main function of this transistor is to amplify as well as switching
purposes. The maximum gain current of this transistor is 800A.
BC547 Transistor Pin Configuration

The BC547 transistor includes three pins which include the following.

 Pin1 (Collector): This pin is denoted with symbol ‘C’ and the flow of current will be through
the collector terminal.
 Pin2 (Base): This pin controls the transistor biasing.
 Pin3 (Emitter): The current supplies out through emitter terminal

Features

The features of the BC547 transistor include the following.

 The gain of DC current (hFE) = 800 A

 Continuous Ic (collector current) = 100mA
 VBE (emitter-base voltage) = 6V
 IB (base current) = 5mA
 The polarity of the transistor is NPN
 The transition frequency is 300MHz
 It is obtainable in semiconductor package like-92
 Power dissipation is 625mW

2. Resistors and Capacitor :

 12k one piece

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 27k one piece

 (104) .1µF two piece

 10k one piece

 .o1 uF (103) one piece

 470 ohm one piece

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 10 pF one piece

3. Coil :

0.8 mm wire 3-4 turn

4. Power Suply : 9 V DC

5. Electret Mic :

3.3 Circuit Diagram :

Fig-3.1: Circuit Diagram

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 3.4 Working Method :

First of all we need a NPN Transistor BC547 . Then we add a 10 pF capacitor with the
emitter and collector pin of the transistor . Now we add one side of a 27k resistor with the
base pin of transistor and a 10k resistor with the 27k resistor. Now 470 ohm resistor will be
connected with collector and 10k resistor. 103 pf capacitor will be connected on two sides of
10k resistor. 104 capacitor will be connected with base pin on one side and on other side with
another 10k resistor. And the other side of this 10k resistor will be connected with 27k
resistor . Mic will be connected with the join of 104 and 10k and other side with the join of
103 and 10k . Now the coil will be connected with emitter pin and positive reel . And a
antenna can be connected with emitter or collector point . Now the power supply will be
connected as the positive side on the emitter part and negative side on the collector part .

3.5 SCOPE OF THE PROJECT

This project report consists of five chapters. The chapter one contains Introduction of the
project, chapter two: Literature Review and theoretical background of the project, chapter
three: system design and calculation, chapter four: construction, testing and packaging, and
finally, chapter five: conclusion and recommendation.

Chapter-Four

TEST AND RESULTS

4.1 INTRODUCTION

This section will discuss tests carried out on the final circuit and the results obtained. Measured
waveforms from the oscilloscope will be used to illustrate the performance at each stage of the
circuit and the method used to evaluate the obtained result will be described. 4.2 TEST
EQUIPMENT At various stages of the circuit different test were required to confirm the
performance of the stages. The following test tools were used:
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 a) Digital Multimeter:

This is an electronic device used to measure continuity, voltage and current. The multimeter
was particularly useful for measuring the base-emitter voltage of each transistor in order to
verify if it was within the voltage range (i.e 0.6V to 0.7V) of the transistor active region.

b) Oscilloscope:

This is a type of electronic test instrument that allows observation of constantly varying
signal voltages with respect to time. It allows the observation of signal amplitude and the
period of the signal. The oscilloscope was used to check if the oscillator part of the circuit
was oscillating as desired. Also the performance of the audio amplifier and the output of the
electret microphone was evaluated with the oscilloscope.

c) Analogue FM Radio Receiver:

An analog FM receiver was required to tune to the transmitting frequency of the transmitter.
The FM receiver will intercept the transmitted FM signal and demodulate it to reproduce the
original sound input. With the FM radio receiver it was possible to determine the range of the
FM transmitter and also its sound quality.

4.2 RESULT

Our transmitter is working very well . It works in a range of 10m well . It works at the frequency
of 89.7 Hz.

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21
 Pic : Our Transmitter Project

Chapter – Five

CONCLUSION

5.1: CONCLUSION
A direct FM transmitter with a range up to 10 meters can be built using this BC547 Transistor
and some pf and uf capacitors with some resistors . While doing the designation of FM
transmitter circuit, we have faced a problem with the electronic component such the transistor
and the capacitor referred with the serial number and the value to be use. In this part of problem
we were required to solve it and some alternative and creativity are needed to apply.

While doing the construction process we found that several components is hard to do the
soldering..

22
we have to care about the value of the components related where the values of the components
will affect the output of the FM transmitter circuit. After do the adjustment of the component’s
value we have to do the simulation where the simulation result is performed by waveforms.

We have been analyzing the waveforms and do comparisons with the theory due to checked and
identified for any error related with.

5.2: LIMITATIONS OF THE PROJECT

The relatively low power output of FM transmitters sometimes makes it unsuitable for use in
some large urban areas because of the number of other radio signals. This is compounded by the
fact that strong FM signals can bleed over into neighboring frequencies making the frequencies
unusable with the transmitter. Removing a car`s radio antenna has been found to significantly
improve transmitter reception. Some frequencies below 88.1 have even been supported as
reception frequencies on some car stereos, and some indegeneous FM transmitter even take
advantage of those unused frequencies which are generally more reliable as no frequency below
88.1 is used for mainstream broadcasters in the US.

. Some models which connect via connect via ports other than the headphone jack have no
means of controlling the voluome,which can force the sound to transmit out from the device
harshly (causing over modulation, audio distortion and possible radio interference), or too low.
In theory a device could use an automatic level control or audio limiter circuit to overcome this
problem although there are few ( if any ) devices with such a facility available out on the market
yet.

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 REFERENCES
[1] Transmitter Revolution. [Online]. Available: https://en.wikipedia.org (accessed Aug 14, 2022)

[2] How To Build An FM transmitter Circuit Its Working and Applications. [Online]. Available:
https://www.elprocus.com (accessed Aug 14, 2022)

[3] A.P Godse and U.A. Bakshi, Analog Communications. Technical Publications Pune, 2009.

[4] V.K Mehta, Rohit Mehta, Principles of Electronics. S. CHAND & COMPANY, 2008.

[5] Miniaturised FM transmitter.” [Online]. Available: http://pe2bz.philpem.me.uk/Comm/-

%20Transmitters/-%20FMx/FMx-902-PortableMiniSterio/Index. [Accessed: 18-Aug-2022].

[6] Single Transistor FM Transmitter Design | electronics hobby.” [Online]. Available:

https://dmohankumar.wordpress.com/2011/04/23/single-transistor-fm-transmitter-design/.
[Accessed: 18-Aug-2022].

[7] Paul McLane, “Radio World: FM Signal Count Grew 38% in Ten Years.” [Online].
Available: http://www.radioworld.com/article/fm-signal-count-grew--in-ten-years/277873.
[Accessed: 18-Aug-2022].

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