DESIGN AND CONSTRUCTION OF A DIGITAL FM TRANSMITTER
In a digital FM transmitter, with the aid of an antenna, 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.
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.
The FM transmitter was designed using transistors and other component such resistor, inductor and capacitors. 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. The distant of transmission is limited to 100m and fixed frequency of transmission, away from all other radio station. This gives best range and least interference. This work was built around a PIC16F870 microcontroller and 16x2 LCD. The heart of this unit is a PIC processor called PIC16F870, a 2 x 16 char display and four buttons
TABLE OF CONTENTS
TABLE OF CONTENT
TITLE PAGE
APPROVAL PAGE
DEDICATION
ACKNOWLEDGEMENT
ABSTRACT
TABLE OF CONTENT
CHAPTER ONE
1.0 INTRODUCTION
1.1 PURPOSE OF THE PROJECT
1.2 OBJECTIVE OF THE PROJECT
1.3 LIMITATIONS OF THE PROJECT
1.4 SCOPE OF THE PROJECT
1.5 ADVANTAGES OF THE PROJECT
1.6 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 CONSTRUCTION
3.1 BASICS OF FM TRANSMITTER
3.2 BLOCK DIAGRAM OF AN FM TRANSMITTER
3.3 FUNCTION OF FM TRANSMITTER BLOCK
3.4 CIRCUIT DIAGRAM OF THE SYSTEM
3.5 CIRCUIT PARTS
3.6 CIRCUIT OPERATION
3.7 DESCRIPTION OF COMPONENTS USED
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
The digital FM transmitter is a low power transmitter and it uses FM waves for transmitting the sound using microcontroller, 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
A transmitter can be a separate piece of electronic equipment, or an electrical circuit within another electronic device. A transmitter and receiver combined in one unit is called a transceiver. The term transmitter is often abbreviated "XMTR" or "TX" in technical documents. The purpose of most transmitters is radio communication of information over a distance. The information is provided to the transmitter in the form of an electronic signal, such as an audio (sound) signal from a microphone. The transmitter combines the information signal to be carried with the radio frequency signal which generates the radio waves, which is often called the carrier. This process is called modulation. The information can be added to the carrier in several different ways, in different types of transmitter.
In a frequency modulation (FM) transmitter, it is added by varying the radio signal's frequency slightly. Many other types of modulation are used.
The antenna may be enclosed inside the case or attached to the outside of the transmitter, as in portable devices such as cell phones, walkie-talkies, and garage door openers. In more powerful transmitters, the antenna may be located on top of a building or on a separate tower, and connected to the transmitter by a feed line, that is a transmission line.
1.1 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.
The FM transmitter plugs into the audio output of audio devices and converts the audio output into an FM radio signal, which can then be picked up by appliances such as car or portable radios.
1.2 OBJECTIVE OF THE PROJECT
The objective of this work is to construct a digital FM transmitter using microcontroller 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 and picked up by the receiver.
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 transmitters 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 ports other than the headphone jack have no means of controlling the volume, 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.
- In the digital FM transmitter the huge wider channel is required.
- The digital FM transmitter and receiver will tend to be more complex.
- Due to some interference there is poor quality in the received signals
- Requires more complicated demodulator: One of the minor limitation of frequency modulation is that the demodulator is a little more complicated, and hence slightly more expensive than the very simple diode detectors used for AM. Also requiring a tuned circuit adds cost. However this is only an issue for the very low cost broadcast receiver market.
- Some other modes have higher data spectral efficiency: Some phase modulation and quadrature amplitude modulation formats have a higher spectral efficiency for data transmission that frequency shift keying, a form of frequency modulation. As a result, most data transmission system use PSK and QAM.
- Sidebands extend to infinity either side: The sidebands for an FM transmission theoretically extend out to infinity. To limit the bandwidth of the transmission, filters are used, and these introduce some distortion of the signal.
1.4 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. Digital 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.
1.5 APPLICATION OF THE PROJECT
- Digital FM transmitters used in many different environments. Some of the more popular uses are churches, sporting events, fitness centers, homes, cars, correctional facilities and holiday light shows.
- The Digital FM transmitters are used in the homes like sound systems in halls to fill the sound with the audio source.
- These are also used in the cars and fitness centers.
- The correctional facilities have used in the Digital FM transmitters to reduce the prison noise in common areas.
1.6 ADVANTAGES OF THE PROJECT
- The FM transmitters are easy to use and the price is low
- The efficiency of the transmitter is very high
- It has a large operating range
- This transmitter will reject the noise signal from an amplitude variation.
- it is less affected by buildings and can received indoors.
- Waves at higher frequencies can carry more data than the waves at low frequency. Smaller geographical interference between neighboring station
1.7 SIGNIFICANCE OF THE STUDY
The project signifies a lot in the digital 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. One of the most interested aspect of the work is that the frequency is displayed on the LCD, meaning that there is no need of imagining the frequency it operates on.
1.8 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
1.9 PROJECT WORK ORGANISATION
The various stages involved in the development of this project have been properly put into five chapters to enhance comprehensive and concise reading. In this project thesis, the project is organized sequentially as follows:
Chapter one of this work is on the introduction to a digital fm transmitter. In this chapter, the background, significance, objective limitation and problem of a digital fm transmitter were discussed.
Chapter two is on literature review of a digital fm transmitter. In this chapter, all the literature pertaining to this work was reviewed.
Chapter three is on design methodology. In this chapter all the method involved during the design and construction were discussed.
Chapter four is on testing analysis. All testing that result accurate functionality was analyzed.
Chapter five is on conclusion, recommendation and references.
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