Portable FM Transmitter

ABSTRACT

A portable fm transmitter which is also known as miniature FM transmitter is an electronic device which, with the aid of an antenna, produces radio waves and which it’s transmissions can be picked up on any standard FM radio. It has a range of up to 1/4-mile (400 meters) or more, depending on the line-of-sight, obstructions by large buildings. 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.

This 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.

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

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

In electronics and telecommunications a portable transmitter or radio transmitter is an electronic device which, 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. In addition to their use in broadcasting, transmitters are necessary component parts of many electronic devices that communicate by radio, such as cell phones, wireless computer networks, Bluetooth enabled devices, garage door openers, two-way radios in aircraft, ships, and spacecraft, radar sets, and navigational beacons. The term transmitter is usually limited to equipment that generates radio waves for communication purposes; or radiolocation, such as radar and navigational transmitters. Generators of radio waves for heating or industrial purposes, such as microwave ovens or diathermy equipment, are not usually called transmitters even though they often have similar circuits.

The term is popularly used more specifically to refer to a broadcast transmitter, a transmitter used in broadcasting, as in FM radio transmitter. This usage usually includes the transmitter proper, the antenna, and often the building it is housed in.

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 portable 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 design and construct portable 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 and picked up by the receiver.

1.3                                      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.^[1] 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.