Design And Construction Of A 2Km Transmitter For Yagi Antenna Part Two

ABSTRACT

An FM 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.

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.

CHAPTER ONE

1.0                                                        INTRODUCTION

In electronics and telecommunications a 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.

This device was built using Yagi antenna. A Yagi antenna is a directional antenna consisting of a driven element such as dipole or folded dipole and additional parasitic elements, typically a reflector and one or more directors.  A Yagi antenna is used for communications in a long range of three to five miles between two points. It can also be used as a bridge antenna to connect clients to an access point.

1.1                                           BACKGROUND OF THE STUDY

Information transmission is very vital to human life just as the early men used sticks to produce sound which indicates the location of each other as they wander about also down to the middle era when town crises come into play for the same information propagation to be transmitted from one point to another with the aid of radio communication which necessities the application of radio transmitter and receiver.

Frequency modulation (FM) is a technique for wireless transmission of information where the frequency of a high frequency carrier is changed in proportion to message signal which contains the information (Chen, 2002). FM was invented and developed by Edwin Armstrong in the 1920’s and 30’s. Frequency modulation was demonstrated to the Federal Communications Commission (FCC) for the first time in 1940, and the first commercial FM radio station began broadcasting in 1945 (Mohn, 2007).

A radio transmitter is device whose major function is to send information (intelligence) from one point to another in most cases the information to be transmitted are voice music and code signals. However the transmission of radio signal is done with the aid of electrical resonance this is when the frequency of the receiver is equal to the incoming one from the transmitter resonance is observed which is the totality of radio communication, frequency modulation (FM) transmitter is less distorted than other wave bands like amplitude modulation and short wave band. The frequency on the tuning dial ranges from 88MHZ to 108MHZ (Louis, 2008).

In telecommunications and signal processing, frequency modulation (FM) is the encoding of information in a carrier wave by varying the instantaneous frequency of the wave. This contrasts with amplitude modulation, in which the amplitude of the carrier wave varies, while the frequency remains constant. In analog frequency modulation, such as FM radio broadcasting of an audio signal representing voice or music, the instantaneous frequency deviation, the difference between the frequency of the carrier and its center frequency, is proportional to the modulating signal. In radio transmission, an advantage of frequency modulation is that it has a larger signal-to-noise ratio and therefore rejects radio frequency interference better than an equal power amplitude modulation (AM) signal. For this reason, most music is broadcast over FM radio. However, the concept of FM is essential to a wide gamut of radio frequency wireless devices and is therefore worth studying (“The Future of Radio”, 2008).

1.2                                              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.

1.3                                             OBJECTIVE OF THE PROJECT

• The main aim of this project is to develop a long-range FM transmitter circuit to transmit the audible signals in the range of 2 Km using Yagi antenna connected to the circuit.

At the end of this work, the student involved will be able:

• To show the design and components of a FM transmitter
• To show the construction process of an electronically operated system known as FM transmitter capable of transmitting a frequency modulated signal.
• To design yagi antenna.

1.4                                          LIMITATIONS OF THE PROJECT

88. 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.

1. Another problem of this work is that yagi antenna radiates in only one direction which can cause reception to be strong in one direction and faint in another direction.

iii. Also,  the Yagi design is large size, especially for the range achieved.

1.5                                          APPLICATION OF THE PROJECT

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. Other applications include

• Non-commercial broadcasting.
• Commercial broadcasting.
• Television audio.
• Public Service communications.
• Radio Service Communications.

Finally, This concept can be extended and implemented in colleges or in university, wherein the latest happenings in a college can be known to the students by tuning to the frequency using an FM receiver.

1.6                                           SIGNIFICANCE OF THE STUDY

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.

The benefits of the Yagi antenna in this work include good range and ease of aiming the antenna compared to other directional dishes and designs.

1.7                                                 SCOPE OF THE PROJECT

The proposed system mainly uses these three components: a variable frequency oscillator (VFO), voltage control oscillator (VCO), power amplifier and a battery for power supply.  The variable frequency oscillator is used for generating the frequencies.

The frequency is followed by the tuning circuit.  The voltage control oscillator is used to generate the respective signals at a given frequency with minimal attenuation. The power amplifier is used to increase the power of the week input audio signal.

If anyone starts speaking the audible message via a microphone connected to this system, then others can listen to this audio by a mobile phone using FM radio in the  range of 2 Km with the help of the Yagi antenna.

 1.8                                                  DEFINITION OF TERMS

FM    –                  Frequency Modulation

ANTENNA    -           An antenna is a specialized transducer that converts radio-frequency (RF) fields into alternating current (AC) or vice-versa.

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