DESIGN AND CONSTRUCTION OF FM TRANSMITTER

1.1 Introduction

A frequency modulated (fm) transmitter is an electronic circuit designed to modulate, amplify, filter and possibly encode incoming information signal to make it suitable for transmission over a channel. A message arriving from the information source must be in electrical nature before it will be suitable for immediate transmission. Even then, a lot of work must be done to make such message suitable.

The crowding in the AM broadcasting band and the inability of standard AM receivers to eliminate noise has made the total fidelity of standard stations purposely limited. Fm does not have these drawbacks and therefore can be used to transmit music, reproducing the original performance with a degree of fidelity that cannot be reached on AM bands. Fm stereophonic broadcasting has drawn increasing numbers of listeners to popular as well as classical music, so that commercial fm stations draw higher audience rating than AM stations.

As a prelude to other parts of this study, this chapter will discuss the background upon which this study was initiated, the statement of problems that led to this study, the Aim and Objectives of the study. Others are Significance of the study, Scope of work, Limitations of the Study and Definition of technical terms.

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1.2 Background of 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.

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.

Therefore, in Nigeria where the research was carried out, the activities that was conducted is to design and construct an FM Transmitter.

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1.3 Statement of Problems

Investigation reveals that FM transmitters are however a complex equipment demanding high power supply, high voltage system design, critical maintenance and exorbitant price. These problems of the transmitter constitute major impediments to institutions and individuals that may wish to adopt radio broadcast as means of electronic media.

Farlex (2005) stated that transmitters of large powers require large current flow with high voltage up to 20kiv and transmitting plants are exposed to increased over voltage risk due to the usually exposed tower.

These problems of the transmitter constitute major impediments to individual and institution that may wish to adopt radio broadcast as means of electronic media. The private individual and organizations lack resources to purchase and maintain complex transmitting plant whose price is exorbitant and requires critical maintenance.

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1.4 Aim and Objectives of Study

The aim of the study is to Design and Construct of Frequency Modulator (FM) Transmitter. In achieving this aim, the following specific objectives were laid out as follows:

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.

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1.5 Significance of 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.

This study will be of immense benefit to researchers who intend to know more on this study and can also be used by non-researchers to build more on their research work. This study contributes to knowledge and could serve as a guide for other study.

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1.6 Scope of Study

The study focuses on the Design and Construction of Frequency Modulator (FM) Transmitter.

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1.7 Limitations of the Study

During the course of this study, many things militated against its completion, some of which are:

1. Time Constraint: The time frame given to accomplish this project was very short due to school academic calendar and it was carried out under pressure which made the researcher not to implement some necessary features.
2. Research material: availability of research material is a major setback to the scope of the study.
3. Frequent power failure: This made the researcher append more money on fuel to ensure sustainable power.
4. Financial Constraint: Insufficient fund tends to impede the efficiency of the researcher in sourcing for the relevant materials, literature or information and in the process of data collection (internet).

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1.8 Technical Terms Definition

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