Design And Construction Of A Digital FM Transmitter

A digital FM transmitter with the aid of an antenna, LC circuit and microcontroller produces radio waves. The transmitter itself generates a radio frequency alternating current, which is applied to the antenna. When excited by this alternating current, the antenna radiates radio waves.

A digital FM transmitter is basically a VHF colipits oscillator capable of transmitting sound or music to any standard FM receiver. The circuit works on a D.C source which makes it for a pure rectification. FM transmitter also has a capacitor microphone which picks up very weak sound signals.

TABLE OF CONTENTS

TABLE OF CONTENT

TITLE PAGE

APPROVAL PAGE

DEDICATION

ACKNOWLEDGEMENT

ABSTRACT

TABLE OF CONTENT

CHAPTER ONE

• INTRODUCTION

1.1      BACKGROUND OF THE STUDY

1.2      PROBLEM STATEMENT

1.3      OBJECTIVE OF THE PROJECT

1.4      PURPOSE OF THE PROJECT

1.5      LIMITATIONS OF THE PROJECT

1.6      SCOPE OF THE PROJECT

1.5      APPLICATION OF THE PROJECT

1.7      DEFINITION OF TERMS

1.8      PROJECT ORGANISATION

CHAPTER TWO

2.0 LITERATURE REVIEW

2.1 HISTORITICAL BACKGROUND OF THE PROJECT

2.2 REVIEW OF PARTS OF RADIO TRANSMITTER

2.3 REVIEW OF FM BROADCAST BANDS

2.4 MODULATION AND DEMODULATION

2.5 PRE-EMPHASIS AND DE-EMPHASIS

2.6 REVIEW OF MODULATION CHARACTERISTICS

CHAPTER THREE

3.0      METHODOLOGY

3.1      SYSTEM BLOCK DIAGRAM

3.2      SYSTEM DESCRIPTION

3.3      SYSTEM CIRCUIT DIAGRAM

3.4      CIRCUIT DESCRIPTION

3.5      INTERFACING PIC16F870 WITH 7-SEGMENT DISPLAY CIRCUIT

3.6      PLL AND MICROCONTROLLER

3.7      DIGITAL FM TRANSMITTER CIRCUIT OUTPUT POWER

CHAPTER FOUR

4.0      RESULT ANALYSIS

4.1      CONSTRUCTION PROCEDURE AND TESTING

4.2      CASING AND PACKAGING

4.3      ASSEMBLING OF SECTIONS

4.4      TESTING OF SYSTEM OPERATION

4.5       INSTALLATION OF THE COMPLETED DESIGN

4.6      SYSTEM TROUBLESHOOTING METHOD

4.7      COST ANALYSIS

CHAPTER FIVE

5.0      CONCLUSION

5.1      RECOMMENDATION

5.2      BIBLIOGRAPHY

CHAPTER ONE

1.0                                                        INTRODUCTION

1.1                            BACKGROUND OF THE STUDY

In the telecommunication, the frequency modulation (FM) transfers the information by varying the frequency of carrier wave according to the message signal. Generally, the FM transmitter uses VHF radio frequencies of 87.5 to 108.0 MHz to transmit & receive the FM signal. This transmitter accomplishes the most excellent range with less power. The performance and working of a transmitter circuit is depends on the induction coil & variable capacitor.

The FM transmitter is a low power transmitter and it uses FM waves for transmitting the sound, this transmitter transmits the audio signals through the carrier wave by the difference of frequency. The carrier wave frequency is equivalent to the audio signal of the amplitude and the FM transmitter produce VHF band of 88 to 108MHZ.

To generate the radio frequency carrier waves the FM transmitter circuit requires an oscillator. The tank circuit is derived from the LC circuit to store the energy for oscillations. The input audio signal from the mic penetrated to the base of the transistor, which modulates the LC tank circuit carrier frequency in FM format. The variable capacitor is used to change the resonant frequency for fine modification to the FM frequency band. The modulated signal from the antenna is radiated as radio waves at the FM frequency band and the antenna is nothing but copper wire of 20cm long and 24 gauge. In this circuit the length of the antenna should be significant and here you can use the 25-27 inches long copper wire of the antenna.

This work will explain about the design and construction of a digital fm transmitter, the working of the working of digital FM transmitter circuit with its applications.

1.2                                                  PROBLEM STATEMENT

The invention of digital fm transmitter is to overcome the problem of tuning and frequency selection found from the analogue type of transmitter.

1.3                                              PURPOSE OF THE PROJECT

The main purpose of this work is to construct a device that will allow music or other audio content from a portable media player, CD player or other portable audio system to be played through a nearby FM radio. It can either be a capability built into a portable media player, or a portable appliance that plugs into the headphone jack or proprietary output port of a portable media player or video device. The sound is then broadcast through the transmitter on an FM broadcast band frequency and picked up by the receiver. The purpose is generally to allow portable audio devices to make use of the better sound quality of a home audio system or car stereo without requiring a wired connection between them.

1.4                                       AIM / OBJECTIVE OF THE PROJECT

The main aim of this work is to design and construct a digital FM transmitter which transmits a frequency modulated signal to an fm radio. That is, to construct a device that can broadcast signals on an FM broadcast band which can be picked up by an fm receiver.

At the end of this work the student involved shall achieve the following objectives:

1. The device shall be constructed, tested and package for academic purposes.
2. The way fm signal was generated shall also be observed

• Antenna used for the transmission shall be studied

1.5                                       LIMITATIONS OF THE PROJECT

1. In the digital FM transmitter the huge wider channel is required.
2. Digital FM transmitter will tend to be more complex.

• Due to some interference there is poor quality in the received signals

1. Digital transmitter is more cost effective than the analogue.
2. High output power supply should not be used in this transmitter. The transistor used is a small one and tends to get hot.
3. The antenna I used I a 1/4 wave whip antenna (wire) about 75cm long. This type of antenna is smaller but not so good performance as a dipole. With a dipole you will be able to transmitter much longer distance.
   • SCOPE OF THE PROJET

Digital FM transmitter is basically a VHF colipits oscillator capable of transmitting sound or music to any standard FM receiver. The circuit works on a D.C source which makes it for a pure rectification. FM transmitter also has a capacitor microphone which picks up very weak sound signals, and discrete components such as: Transistor, Diode, Resistor, Capacitor and Inductor.

This project transmits frequency on 100MHz± 5%. The transmitting distance is l00metres. It is powered with 5volt – 15volts D.C battery using suitable F.M receiver tuned to the transmitting frequency of this project. F.M Transmitter can be used as cordless microphones, mobile phone and for public address purposes.

1.7                                          APPLICATION OF THE PROJECT

1. FM transmitters used in many different environments. Some of the more popular uses are churches, sporting events, fitness centers, homes, cars, correctional.
2. The correctional facilities have used in the FM transmitters to reduce the prison noise in common areas.

1.8                                           SIGNIFICANCE OF THE STUDY

1. The project signifies a lot in the electronic communication system which telecommunication is the vital aspect which is usually demonstrated through radio communication system the frequency modulation transmitter is applied in a lot of instance frequency modulation is used in FM radio stations scattered all over the country whose advantage is paramount compared to its counterpart AM modulation frequency modulation transmitted is equally used in a miniaturized from as wireless morpheme.
2. Components used in this construction are popular and inexpensive.

iii. The FM transmitter is easy to use

1. The efficiency of the transmitter is very high
2. It has a large operating range
3. This transmitter will reject the noise signal from an amplitude variation.

1.9                                                  DEFINITION OF TERMS

FM    –                  Frequency Modulation

VHF  –                  Very High Frequency (30MHz to 300MHz)

UHF  –                  Ultra High Frequency (300MHz to 3GHz)

VFO  –                  Variable Frequency Oscillator

VCO –                  Voltage Controlled Oscillator

PLL  –                  Phase Locked Loop

Oscillator –                    device that generates a frequency

1.10                                                    METHODOLOGY

This research work was carried out using many passive and active electronic components. The design of this project includes the placing of components on Vero boards, soldering and connection of components, test for continuity of components and devices, programming of microcontroller, circuit testing and troubleshooting and result analysis.

1.11                                                      PROJECT ORGANISATION

The work is organized as follows: chapter one discuses the introductory part of the work, chapter two presents the literature review of the study, chapter three describes the methods applied, chapter four discusses the results of the work, chapter five summarizes the research outcomes and the recommendations.