DESIGN AND CONSTRUCTION OF A 50W COLOUR TELEVISION TRANSMITTER

BY

AJINIHI EBENEZER OLUWADARE

MAT NO: 11/70960

DEPARTMENT OF ELECTRICAL ENGINEERING

(ELECTRONICS AND TELECOMMUNICATION OPTION)

SCHOOL OF ENGINEERING TECHNOLOGY

THE FEDERAL POLYTECHNIC

P.M.B. 55, BIDA

NIGER STATE.

OCTOBER, 2014.

1

TITLE PAGE

DESIGN AND CONSTRUCTION OF A 50W COLOUR TELEVISION TRANSMITTER

PRESENTED BY

AJINIHI EBENEZER OLUWADARE

MAT NO: 11/70960

SUBMITTED TO

THE DEPARTMENT OF ELECTRICAL ENGINEERING

THE FEDERAL POLYTECHNIC

P.M.B.55

BIDA

NIGER STATE.

IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE AWARD OF HIGHER

NATIONAL DIPLOMA (HND) IN ELECTRONICS AND TELECOMMUNICATION

ENGINEERING

OCTOBER, 2014

2

APPROVAL PAGE

This is to certify that this project was carried out by me, thoroughly examined, read and

approved as having met the partial requirement of the Department of Electrical Engineering for

the award of Higher National Diploma (HND) in Electronics and Telecommunication

Engineering.

------------------------------------------- ---------------------------

ENGR. JOHN C. IHEMELANDU DATE

(Project Supervisor)

------------------------------------------- ------------------------

ENGR.ABDULRAHEEM A.O DATE

(Project Coordinator)

------------------------------------------- ------------------------

External Moderator DATE

------------------------------------------- ---------------------------

ENGR.DR. SANI MANYAHAYA DATE

(Head of Department)

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DEDICATION

This project report is dedicated to God Almighty and also to my beloved parents Mr. and Mrs.

Samson O. Ajinihi.

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DECLARATION

Department of Electrical Engineering,

School of Engineering Technology,

The Federal Polytechnic,

P.M.B. 55,

Bida,

Niger state.

The Head of Department,

Department of Electrical Engineering,

The Federal Polytechnic,

Bida.

Sir,

LETTER OF TRANSMITTAL

I Ajinihi, Ebenezer Oluwadare of HND II (Electronics and Telecommunication) of the

Department of Electrical Engineering, School of Engineering, The Federal Polytechnic Bida

hereby submit this project (design and construction of 50w colour television transmitter) for your

kind consideration and in partial fulfilment of the requirements for the award of Higher National

Diploma in this institution.

I declare that this project was carried out by me.

Yours faithfully,

Ajinihi Ebenezer Oluwadare.

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ACKNOWLEDGEMENTS

To God be the glory for enabling me carry out this project work successfully.

The completion of this project would have been impossible without the support and

assistance of my Project Supervisor, Engr. John C. Ihemelandu who was extraordinarily helpful

in the course of carrying out the research. I pray that God Almighty will bless you immensely.

My profound gratitude goes to my able Project Coordinator, Mr. Abdulraheem. May God

the owner of the heaven and earth reward you abundantly.

I earnestly appreciate my HOD in person of Engr.Dr. Sani Man-Yahaya for his support

towards the success of this work. God bless you sir.

To my loved ones, Odunayo, Bro Shola, Bro Wale, Bro Seun, Sis Bunmi, Damilola; Eze,

the RCF family, my friends and course mates, I am humbled by your confidence, belief and

commitment to actualising this work. May all your labours not be in vain.

Finally I want to appreciate Mr Zacchaeus from Science and Laboratory Technology for his

support in this work. The Lord bless you real good.

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ABSTRACT

The design and construction of a low power (50w) colour television transmitter is aimed at transmitting audio – video signals at a frequency of 205MHz at a range of about 100m to be used to improve experiments within the Telecommunication laboratory. The laws employed during the course of this project were Ohm’s law, Lenz’s law and Faraday’s law of electromagnetic induction. A 220v / 12v step down transformer was used to supply the voltage to the circuit. The circuit consists of a frequency carrier stage that consists mainly of tuned circuit inductor L1 and variable capacitor 3 – 12 pF with transistor C1674. The transistor BC547 was used for amplifying the video signal. Another stage is the pre-amplifier stage consisting of transistor C1674 together with inductor L2. The other stages are the audio stage which consists of transistor C945, variable resistor R2, audio transformer to generate frequency in Voltage Controlled Oscillator (VCO) form; and the modulator / power amplifier stage consisting mainly of transistor C2570. At the end of the project work, the circuit was tested and was able to transmit at a distance of about 65m which covered the area of the Telecommunication laboratory with a transmitting frequency of 205MHz. The range was limited as a result of the short transmitting and receiving antennae used. Hence, the aim was achieved to a reasonable extent.

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TABLE OF CONTENT

Cover page i

Title page ii

Approval page iii

Dedication iv

Declaration v

Acknowledgement vi

Abstract vii

Table of content viii

Chapter One

Introduction ……………………………………………………………………....... 1

1.1 Aim and Objectives …………………………………………………………… 2

1.2 Motivation …………………………………………………………………….. 2

1.3 Statement of Problems ………………………………………………………... 3

1.4 Scope of the Project …………………………………………………………… 3

1.5 Project Outline …………………………………………………………………. 3

Chapter Two

Literature Review ………………………………………………………………….. 4

2.1 Previous Studies Relevant to the Project ……………….................................... 5

2.1.1 Overnight TV – first vision, then sound ……………………………………. 5

2.1.2 The inevitable format war ………………………………………………….. 6

2.2 Theoretical background ………………………………………………………. 9

8

Chapter Three

Design Methodology……………………………………………………………… 10

3.1 Design Parameters of Power Supply Unit………………………………… 11

3.1.1 Determination of step down transformer…………………………………. 11

3.1.2 Determination of bridge rectifier……………………..……………………. 12

3.2 Design Calculation for the Audio Stage …………………............................ 12

3.3 Design Calculation for the Oscillator Stage……………………………….. 15

3.4 Design Calculation for the Pre-amplifier Stage…………………………… 17

3.5 Design Calculation for the Video Stage …………………........................... 18

3.6 Design for the power amplifier / modulator stage……………………….. 19

3.7 Determination of the Antenna Parameters and Range of the Transmitter.. 20

3.8 Project Construction and Assembly……………………………………… 22

3.9 Circuit Analysis and Operation ……………………………………….... 24

Chapter Four

Project Testing, Results And Discussion……………………………………… 28

4.1 Testing Approach Consideration……………………………………….. 28

4.2 Result …………………………………………………………………… 29

4.3 Discussion ………………………………………………………………. 30

4.4 Project Bill of Engineering Measurement and Estimation……………. 30

Chapter Five

Conclusion, Limitation and Recommendation ………............................................ 32

5.1 Conclusion ……………………………………………………………….. 32

5.2 Limitation ………………………………………………………………… 32

5.3 Recommendation ……………………………………................................. 32

REFERENCES

APPENDICES

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LIST OF FIGURES

FIG. NO TITLE PAGE NO.

2.1 Micro television transmitter 8

2.1(a) External section of the transmitter 8

2.1(b) Internal section of the transmitter 8

3.1 Block diagram of 50w colour television transmitter 10

3.2 Circuit diagram of power supply to the transmitter 11

3.3 Circuit diagram of the audio stage of the 50w colour tv transmitter 12

3.4 Circuit diagram of the oscillator stage of the 50w colour tv transmitter 15

3.5 Circuit diagram of the oscillator stage of the 50w colour tv transmitter 17

3.6 Circuit diagram of the video stage of the 50w colour tv transmitter 18

3.7 Circuit diagram of the power amplifier/modulator stage of the 50w

colour tv transmitter 19

3.8 Circuit diagram of the 50w colour tv transmitter 23

4.1 Pictorial diagram of the testing with multimeter for power supply output 29

A1 Pictorial view of the internal circuitry of the 50w TV transmitter 34

A2 Pictorial view of the etched board of the 50w TV transmitter 34

B2 Pictorial view of the casing and antenna of the 50w TV transmitter 35

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LIST OF TABLES

3.1 Parts list for the television transmitter 25

4.1 Result of the project 29

4.2 Project bill of engineering measurement and estimation 30

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CHAPTER ONE

INTRODUCTION

Television is a device for delivering images and sound. A television transmitter also

known as audio and video sender circuit employs frequency modulation in the audio stage and

amplitude modulation in the video stage. The signal is conveyed either through cables or

microwave link to a transmitting station where it modulates a carrier. The resultant carrier wave

is passed on to the transmitting antenna to be radiated. At the same time the sound signal

associated with the scene is picked up by the microphone and converted into electronic signal.

This is also conveyed to the transmitting station where the sound modulates a carrier and the

resultant routed to the combining unit. Within a certain distance from the transmitting antenna, a

receiving antenna picks the combined vision and sound modulated wave and passes that to a

television receiver. The receiver amplifies the weak signals, separates vision from sound in a

demodulation process. Sound is heard from a loudspeaker connected while a CRT or LCD helps

to display the vision. The video though amplitude modulated employs a negative Phase

Alternating Line PAL modulation. Unlike the video, the audio is processed to produce a desired

audio quality as the bass and treble and the intensity by the use of a volume control knob. For the

video, it is amplified, mixed with the crystal oscillator signal at the video R.F mixer. The entire

television transmitter is advanced at the combining unit, which in the ancient time consists of a

balance wheatstone bridge. In recent times, the combining of the audio and video is done by a

simple heterodyne transistor in a simple circuitry.

The transmitter in general is used to transfer signals from one source to another with the

aid of a modulator which is usually used to modulate the signals from the transmitting board,

filter and amplify in the intermediate frequency filter board such as in simplified communication

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equipment also known as a transceiver which comprises of both transmitter and receiver, and

hence it is used for point to point communication such as in mobile radio telephone system,

outside broadcast, microwave link between studio and transmitter and also in data transmission.

(Adedibu, 2003)

1.1 AIM AND OBJECTIVES

AIM

The aim of this project work is to design and construct an audio and video sender circuit

of 50w to cover a range of 100m transmitting at a frequency of 205MHz.

OBJECTIVES

- To integrate the knowledge and skills acquired from major courses taken so far.

- To develop a low power television transmitter to be used in specialized applications for local area

learning purposes e.g in telecommunication laboratory.

- To provide a reference for further study in a similar stream having ambition to deal with low power TV

transmitter design.

- To further explore research in signal wave transmission from mini project (FM transmitter) to main

project (TV transmitter).

1.2 MOTIVATION

The inadequate number of television transmitter units in the Telecommunication laboratory

coupled with the time spent trying to use the few ones available motivated me into carrying out

this project. Also, the success of the mini project (design and construction of low power FM

transmitter) gave me a drive to explore yet further in research in transmitting audio and video

signals together.

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1.3 STATEMENT OF PROBLEMS

At present, there are very few functional television transmitters for laboratory experiments in the

Telecommunication laboratory. As a result, a lot of time is spent in sharing these transmitters

during practical sessions, which is likely to deny students of the practical knowledge they are

expected to acquire. Thus this project proffers solution to the problem.

1.4 SCOPE OF THE PROJECT

The low power television transmitter is to operate within the range of VHF (54 – 210MHz). This

project is meant to be able to transmit within the Telecommunication laboratory at a frequency of

205MHz to cover a range of about 100m.

1.5 PROJECT OUTLINE

This section describes the introduction part of our project. It introduces basic concepts of television transmitter

which translates information using higher rate with a higher performance using a minimum amount of

transmitted power and bandwidth. The second chapter explains the literature review. It includes back ground

history of television transmission, previous studies and the laws and theories used to guide during our project.

The third chapter discusses the design, construction and analysis of the body of the project. It explains block

diagrams, calculation of component values, schematic diagrams and results. The fourth chapter explains the

various test carried out, the results in tabular format and the discussions from the result. Finally the project also

includes conclusion, limitations, recommendation, references and appendices.

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CHAPTER TWO

LITERATURE REVIEW

A television transmitter is a device which broadcasts electromagnetic signals to a television

receiver within Very High Frequency (VHF) and Ultra High Frequency (UHF). Television

transmitters may be analogue or digital. The prinicipals of primarily analog systems are

summarized as they are typically more complex than digital transmitters due to the multiplexing

of VSB and FM modulation stages. (Adedibu, 2003)

For short-range transmission of TV signals (50–200 feet), a power level of around 1–10

milliwatts (mW) RF output is adequate. This chapter describes a low-power transmitter suitable

for this purpose. This unit operates at the lower VHF frequencies and can be used as an

educational project for experimenting with TV transmitters in general; however, note that

currently, the act of broadcasting any signals on VHF TV channels under current NCC rules.

You may cause interference with licensed commercial TV stations and/or interfere with TV

reception in your neighborhood if you do not or cannot confine the signal to your own property.

Therefore, an antenna should not be used if you cannot guarantee this provision. The circuit will

radiate enough RF by itself to be detectable on a close by TV receiver within the

telecommunication laboratory. The TV system just about to breathe its last is a long way from

those early broadcasts: in the intervening years we've gone from Baird's first electromechanical

system, using ever-larger scanning discs with near-lethal capabilities, to the current HD format;

from short-wave to VHF to UHF; from five lines to 40 to 240, on to 405 then 625 and 1080i;

from five frames a second to 50 or 60, and from fuzzy black and white to crisp colour and even

3D. (Adedibu, 2003)

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2.1 PREVIOUS STUDIES RELEVANT TO THIS PROJECT.

The first mechanical television systems were developed by John Logie Baird in England and by

Charles Jenkins in the USA in the 1920’s. An end was put to the history of analogue television

transmission developed by the early rivals Baird and Marconi-EMI systems back in the 1920s.

There has also been a transition from PAL TV, Ceefax text services and Nicam stereo sound to

HD digital system. Of course, the TV system just about to breathe its last is a long way from

those early broadcasts: in the intervening years we've gone from Baird's first electromechanical

system, using ever-larger scanning discs with near-lethal capabilities, to the current HD format;

from short-wave to VHF to UHF; from five lines to 40 to 240, on to 405 then 625 and 1080;

from five frames a second to 50 or 60, and from fuzzy black and white to crisp colour and even

3D. By early 1925 Baird was able to give public demonstrations of the technology in Selfridges

department store in London's Oxford Street, using just five lines to create 'shadowgraphs' –

silhouettes of what was being shot – and leading Baird to realise at least 30 lines would be

needed to create shades of grey and thus recognisable images. He achieved this in October 1925,

and just three months later was able to give the world's first demonstrations of television. Within

three years he had also developed the beginnings of colour TV, 3D TV, infrared TV and even a

TV recording system, which he called Phonovison, storing TV pictures on discs.(Whathifi, 2010)

2.1.1 Overnight TV – first vision, then sound

Originally the service ran during the closedown period of the radio transmissions from 2LO,

which ended around 11pm and didn't start up again until mid-morning – no late-night radio

or Today programmes in those days. Since there was just the one transmitter, the broadcasts ran

as two minutes of pictures, then two minutes of sound, but by early 1930 the BBC had two

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transmitters, so sound and vision could be sent together, and in June the first TV play was

transmitted, using a fixed camera in front of which the different characters appeared.

The BBC took over the transmissions in 1932, using a TV studio in the basement of

Broadcasting House, and watched by a few thousand buyers of early Baird 'Televisors', sales of

which funded the Baird transmissions. The service shut down in 1935, and was replaced in 1936

by the BBC's 'high definition' service.(Whathifi, 2010)

2.1.2 The inevitable format war

There was a rival system developed by a team at EMI in Hayes, west London. They came up

with a version of the Icomoscope electronic camera tube invented by Russian exile Vladimir

Zworykin at RCA in the States – he had also come up with the Kinescope receiver tube – and

this EMI, Emitron technology became the mainstay of BBC TV cameras for over 20 years.

Going into the mid-1930s, the two TV systems – Baird's 40-line electromechanical system and

the infant EMI electronic one – were both proposed for tests at the BBC's London station.

The Government wanted 'High Definition television – while Baird strove to increase the

definition of his system to 240 lines, and his company started building its transmitters, the team

at EMI went for broke and aimed for 405 lines, also bringing in radio pioneer Marconi to design

its transmission system. The Government plan was to run a six-month trial, the two systems

broadcasting for alternate weeks.(Whathifi, 2010)

The two rival companies broadcast on alternate days, and each had its own studio and control

room, and the TV service started for real on November 2nd, 1936 with an opening ceremony

broadcast twice – once on each system. You see, the idea of repeats started early on the BBC!

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By the end of January 1937 the Baird system was ditched and – apart from a break during World

War II – the 405-line service would run on the BBC until it was finally turned off in 1985, 16

years after the first 625-line UHF services had started in the UK. When the service shut down for

the war, on September 1st 1939, there were only around 20,000 sets in use, all in London and the

surrounding counties, but as early as 1943, with TV still dark, a Government committee was

planning the resumption of services. Published in 1945, and inspired by the arrival of the higher-

definition NTSC system in the USA, offering 525 lines in place of the UK's 405, their report

called for a 1000-line service, hoped for colour and stereoscopic effects, and required wider

geographical availability. In the end, although EMI would come up with a prototype 1001-line

TV system some three years later, it was decided to stick with 405 lines, add extra transmitters to

spread the service – the second one was at Sutton Coldfield in 1949 – , and relaunch the service

on June 7th, 1946. TV was becoming a part of our lives, and by 1954 there were 3.2m licences

held, ITV was on the way, and the BBC was planning to move from its base in the converted

film studios in Shepherd's Bush to a purpose-built Television Centre. Colour, stereo sound and

Ceefax – the text service destined to become the precursor of the mass of information we now

have on the internet – were yet to come. (Whathifi, 2010)

Spinak (1999) designed and constructed an audio and video wireless sender circuit that could

cover a very short range of about 100 metres. His limited distance was to avoid interference with

other legally permitted television broadcast stations. He made use of a whip antenna for home

use and recommended an external antenna for more range.

Kogawa (1997) made use of television technology to produce what was referred to as a micro

television which comprised of a VCR. He used a RF module that was installed in every VCR and

TV game machine at the time. Using an "antenna booster" or a hand-made booster circuit, the

18

very weak output signals (images and sound) of a RF module were led to an antenna. But there

was a significant loss in the cable connection between the VCR and the booster. He took out the

module from the VCR and soldered it to the booster circuit and obtained RF module units both

for VHF and UHF. His Micro TV project in Shimokitazawa, Tokyo in 1987 covered a range of 2

kilometres frequency bandwidth between 55 – 70 MHz. People of Radio Home Run tried to

watch the program that was broadcast at the square of the Shimokitazawa train station. The

broadcasting was not so successful because there were too many snowy images and noises.In the

late 80s, Kogawa mastered the boosting method to use RF module and tested a mobile version of

the UHF transmitter outside. It worked very well.

Retrieved from (www.poptronix.com, 1997)

Some students of the Federal Polytechnic have also jointly embarked on this project.

Kolawole , Samuel, Husseini, Enemuo and Abdulkarim (2006), embarked on a design and

construction of a 50 watt coloured television transmitter covering an average radius of 200

metres. Their work was limited to short distance and private broadcast.

2.2 THEORETICAL BACKGROUND

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Fig 2.1 Micro television transmitter

(b) Internal section of the transmitter

(a) External section of the transmitter

The scientific methods favoured in this project are: Ohm’s law, Faraday’s law of electromagnetic

induction and lenz’s law.

Ohms law: Is used to determine the resistance, current and voltage in the battery and the power

supply unit and its application as relevant in the other units.

This law states that the current flowing through a metallic conductor is directly proportional to

the applied voltage, provided the temperature and other external factors remain constant.

Mathematically; V α I

V = IR ------------------------------------------ (2.1)

Where

R = constant of proportionality (resistance of the metallic conductor). The SI unit is Ohms (Ω)

I = current flowing through the metal. SI unit is Ampere (A).

V = Voltage and the S.I unit is Voltage (V).

Faraday’s Law of Electromagnetic Induction Is used to determine the ratio of turns and the

the current flowing through the transformer in the power supply section.

The law states that the induced electromotive force e.m.f in a circuit is directly proportional to

the rate of change of magnetic flux linking the coil.

Lenz’s law also supporting states that the induced current flows in such direction as to oppose

the change producing it.

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CHAPTER THREE

DESIGN METHODOLOGY

The design methodology employed in this project work is divided into stages:

1. Design parameters for the power supply unit.

2. Design and construction of the audio stage.

3. Design and construction of the oscillator stage.

4. Design and construction of the radio frequency pre-amplifier stage.

5. Design and construction of the video stage.

6. Design and construction of the power amplifier / modulator stage.

Fig 3.1 Block diagram of the 50w colour television transmitter

The block diagram of the low power (50w) television transmitter is explained as follows:

1. A carrier frequency generator which consists of the tank circuit L1 and C4, and transistor

Q1, acts as to produce the carrier signal of the television signal and is the main frequency of this

project.

2. A pre-amplifier that consists mainly transistor Q2, amplifies the r.f signal coming from

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Video Amplifier

Audio Source Voltage Controlled

Oscillator VCO

Video Source Power Amplifier

& Modulator

FM Modulating

Amplifier

Radio Frequency

Amplifier

Carrier Frequency

Generator

Transmiting

Antenna

the frequency generator circuit enough to a level that can drive the power amplifier circuit.

3. A frequency generator in voltage controlled oscillator (VCO) form consisting of the

audio transformer and capacitor C21 will produce a center frequency of 5.5 MHz which will

change by an input signal and contribute to the FM signal by a television signal system.

4. There is also the video section consisting of video source and preamplifier.

The various stages have been broken down in details below:

5. This power amplifier which is the last stage before broadcast also acts as a modulator for

the video signal and audio. The FM modulation mixes with the carrier signal frequency of the

video signal in the AM as well.

3.1 DESIGN PARAMETERS FOR POWER SUPPLY UNIT

Fig 3.2 Circuit diagram of power supply to the transmitter

3.1.1 DETERMINATION OF STEP DOWN TRANSFORMER

Input voltage = 220V

Output voltage = 18V

Frequency = 50Hz

Current rating = 350mA

The reasons for selecting the transformer are: the load current of the transformer is 300mA, thus

a value greater than 300mA, was needed that is why a 350mA current rating transformer was

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N2N1

18:1

C3C2C1

Input Voltage

7812CTBRIDGE

Voltage regulator

chosen and another reason is to prevent low voltage. Also it is selected since the load required is

12V D.C for its efficient operation. Therefore the transformer maximum secondary voltage is

18V.

3.1.2 DETERMINATION OF BRIDGE RECTIFIER

A diode consists of a PN junction which converts A.C to D.C. The main characteristic of a diode

is the voltage and the secondary characteristics are the ampere or wattage which determines its

durability / stability.

The maximum voltage rating of the bridge rectifier = 100V

The maximum current rating of the bridge rectifier = 5A

The input voltage of the bridge rectifier = 18V

The output voltage of the bridge rectifier = 15V

3.2 DESIGN CALCULATION FOR THE AUDIO STAGE

Fig 3.3 Circuit diagram of the audio stage of the 50w colour TV transmitter

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To modulator

To oscillator

Voltage across audio input = 300mV

Current rating of audio input, I = 4mA

Resistance across audio input Rm = ?

From Ohm’s law V = I x R

Rm = V / I

Rm = 300mV / 4mA = 75Ω

Reference voltage Vref = Vin x R4

= 9 x 10 6 = 8.9V

Capacitive reactance of C17, Xc17 = 1 / 2πfc17

= 1 / 2 x π x 50 x 22 x 109

= 144.7K Ω

Hence C17 is useful in the circuit and cannot be taken as a short circuit.

But, the input resistance Rin in transistor Q3 = Xc17

Thus, Xc17 = 144.7K Ω

The gain,Av of the transistor Q1 without feedback

Av1 = hfe x Rfe / Rm

= 22 x 103 x 20 / 144.7 x 103

= 3.04

As specified by the manufacturer, transistor Q3 (C945) has:

Collector current Ic = 10mA

Base current Ib = 0.5mA

24

Rin x R4

R4

75 + 106

Transition frequency = 100KHz – 50MHz

Calculating gain hfe,

Hfe = Ic / Ib

= 10mA / 0.5mA

= 20

In order to increase the gain of Av1,

a 1MΩ resistor R15 is fed back into the input.

Avf = R15 / Xc12 = 1 x 106 / 144.7 x 103

= 6.9

The output frequency for Q3

F = 1 / 2Πr12C19

= 1 / 2π x 22 x 103 x 1 x 10-6 = 720KHz

An audio transformer to generate the carrier frequency of 5.5MHz for the modulation of the FM

is selected.

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3.3 DESIGN CALCULATION FOR THE OSCILLATOR STAGE

Fig 3.4 Circuit diagram of the oscillator stage of the 50w colour TV transmitter

The tank circuit produces the radio frequency carrier signal consisting of C4 // L1. The frequency

of oscillation will be set somewhere in the VHF band width (54 – 210) MHz.

Frequency variation is achieved by increasing or reducing the turns of the inductor coil. The

inductor is an 8 turns of enameled coil measuring inductance using the RLC gives about 50pH.

Frequency of oscillation, F chosen is 205MHz, this frequency is in the VHF bandwidth and has

no interference with the nearest standard frequency- that is, that of NTA Bida which is 229MHz.

An inductor L1 of 50pH was also selected to give the set frequency – since inductors of varying

26

To 12 D.C. supply

To modulator

From Audio Stage

values are not always readily available. The value of capacitor C4 to be used can be calculated

from the expression below:

F = 1

2π√L1 x C4

205MHz = _______1________

2π√50x10-12 x C4

C4 = 12 x 10-12pF

To determine the input impedance to transistor Q1, c1674

C1 = 56pF; Xc1 = 1 / 2πfC1 = 56MΩ

R2 = 1.2KΩ; Xc1 // R2 = 1.2KΩ

R1 = 5.6KΩ;

Input impedance to Q1 Rin1 = R1 // (Xc1//R2) = 988Ω

C3 = 22pF; Xc3 = 1 / 2πfc2 = 144.8MΩ

R3 = 1KΩ; R3 // Xc3 = 126MΩ

Manufacturer specification for Transistor Q1, C1674

Ic = 20mA

Ib = 0.5mA

Hfe = 40

Frequency Bandwidth = 200MHz - 400MHz

C2 = 3pF; Xc2 = 1 / 2πfc2 = 1016KΩ

Rf = C2 // (Xc3 // R3) = 144.5KΩ

Rin1 = 988Ω

Gain of transistor Q1, Av = (hfe x Rf) / Rin

Av = 40 x 144.5K = 0.046

988Ω

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3.4 DESIGN CALCULATION FOR THE PRE-AMPLIFIER STAGE

Fig 3.5 Circuit diagram of the pre-amplifier stage of the 50w colour TV transmitter

Capacitor C5 is required to serve as a coupling capacitor to the input of transistor Q2 C1674 from

the oscillator stage. R4 and R5 are chosen in parallel to form a voltage divider to bias transistor Q2

C1674. Capacitor C6 is chosen to help prevent power loss at R6.

Manufacturer’s specification for transistor Q2 is same for Q1 as stated under section 3.4 (design

calculation for the oscillator stage).

C5 = 3pF; R4 = 10k; R5 = 2.2k; R6 = 560ohms; C6 = 33pF

XC5 = 1 / 2πfC5; where frequency f = 50Hz,

XC5 = 1 / 2 x π x 50 x 3 x 10-12 = 20

Input impedance to transistor, Rin2 Q2, c1674

Rin2 = XC5 + (R4 // R5)

R4 // R5= 10K // 2.2K = 1.8k

XC5 + (R4 // R5) = 1016MΩ

28

From Oscillator Stagedd

C5

From Power supply

To power amplifier stage

3.5 DESIGN CALCULATION FOR THE VIDEO STAGE

Fig 3.6 Circuit diagram of the video stage of the 50w colour TV transmitter

Capacitive reactance of C13, Xc13 = 1 / 2πfc15

= 1 / 2 x π x 50 x 22 x 109

= 144.7K Ω

Hence C13 is useful in the circuit and cannot be taken as a short circuit.

But, the input resistance Rin in transistor Q5 = Xc15

Thus, Xc13 = 144.7K Ω

The gain, Av of the transistor Q1 without feedback

Av1 = hfe x Rfe / Rm

= 22 x 103 x 20 / 144.7 x 103

= 3.04

As specified by the manufacturer, transistor Q5 (BC547) has:

Collector current Ic = 10mA

Base current Ib = 0.5mA

Transition frequency = 100KHz – 50MHz

Calculating gain hfe,

Hfe = Ic / Ib

= 10mA / 0.5mA

= 20

In order to increase the gain Av1,

a 1MΩ resistor R10 is fed back into the input.

Avf = R10 / Xc15 = 1 x 106 / 144.7 x 103

= 6.9

29

To modulator

The output frequency F for Q1

F = 1 / 2πR15C15

= 1 / 2π x 220 x 1 x 10-9 = 723.431 KHz

3.6 DESIGN FOR THE POWER AMPLIFIER / MODULATOR STAGE

Fig 3.7 Circuit diagram of the power amplifier/modulator unit of the 50w color TV transmitter

A power amplifier is required to boost the signal from the video section and the audio section to

a sufficient value that can be radiated through the antenna. This stage will also help to modulate

the signal from the video and audio stages. The main component to be selected is transistor Q4

(C2570) because of its high transition frequency, low noise figure and high power gain.

Manufacturer specification of transistor C2570:

Transition frequency = 100 – 1000MHz

Low noise figure = 1.5 – 7.5

VCE (Collector to emitter voltage) = 10v

IB (Base current) = 5mA

IC (Collector current) = 40mA

Gain bandwidth = 4.5 – 50

30

To antenna

From Audio stage

From Pre-amp

3.7 DETERMINATION OF THE ANTENNA PARAMETERS AND RANGE OF THE

TRANSMITTER

An antenna is a multidimensional reflector and receptor used to radiate and receive radio

frequency signal. It is an isotropic radiator with the following parameters:

1. Power density P.d: = (w / m2)

Where P is the radiating power

Π is 3.142

r is the distance covered by the transmitter

P = 50w; r = 100m

P.d =

= 3.97 x 10-4w/m2

2. Gain of the Antenna, Aant = 4πAeff

λ2

Where Aeff is the effective aperture and λ is the wavelength.

If V = f λ; the frequency of transmission f is 205MHz and the Velocity of light

electromagnetic wave V is 3 x 108m/s in free space.

1/ λ = 205MHz

3 x 108m/s

Aant =

31

P

4πr2

4 x 3.142 x 1002

50

= 0.68m

4 x 3.142 x 12594

0.682

= 2322560

3. Power Radiated = Radiation Resistance x Current

Where Radiation resistance = 4.5ohms(measured)

Radiation voltage = 13v (measured)

From Ohm’s law; Current = 15v / 4.5ohms

= 3.3Amps

Power radiated = 3.3 x 15 = 49.99w

Bandwidth = 204 – 208MHz

Frequency of transmission = 204.25MHz

4. Length of the Antenna - for effective radiation = 1/ λ

λ = V / F

λ = 3 x 108 / 205MHz

= 1.46m

Antenna length = 1.46/4 = 0.365m

The frequency of transmission is 205MHz as selected above to cover a range of 100m with a

transmitted power of 50w.

3.8 PROJECT CONSTRUCTION AND ASSEMBLY

32

After the design of each stage has shown above, construction was carried out on the bases of the

parameters of the design on a printed circuit board. The construction involves mounting of the

components on the printed circuit board (PCB). The board was designed and etched with the help

of echants. Each component was examined with the leads identified. The mounting was done in

stages in order to easily identify units especially during troubleshooting.

The project assembly involves the enclosure of all the mounted components on the

constructed board inside the casing – which is plastic.

33

BRIDGE 7812CT

230V/12v

50Hz

18:1

1000uf

3.9 CIRCUIT ANALYSIS AND OPERATION

34

Fig. 3.8

0.1uf0.1uf

N2

C1 C2 C3

N1

From the circuit diagram shown in figure 3.7 above, the analysis and mode of operation of the

50w colour television transmitter is explained as follows:

The main frequency generator circuit in form of LC is in a ground-base configure type consisting

of L1 and trimmer C4(3-12pF) together to form a tuning circuit at the output. The video signal

carrier frequency can be tuned as needed within the VHF range of 54MHz-210MHz. The R1, R2,

R3 are bias circuits to Q1(C1674). Capacitor C1 cuts a high frequency at pin base. Both

capacitors C2 and C3 are connected as divider circuits to determine the rate of signals that

feedback from collector to emitter. C3 is not a bypass signal capacitor as in general case. This

frequency signal is sent to be amplified through coupling capacitor C5 by transistor Q2(C1674)

that is the signal amplifier circuit. The resistors R4,R5,R6 are set to the bias circuit to Q2, a

capacitor C6 is capacitor bypass frequency to the ground, to protect the loss of power at R6. The

inductor L2 sends the DC voltage to Q2 and at the same time acts as a RF choke to prevent

visual signal carrier frequency, output to supply it. Since we want to have frequency stability

over power, we make regulate the power supply circuit a with zener diode ZD1 with R9 to limit

the current and filter smoothly with two capacitors C8 and C9. The signal is amplified through

the link on the capacitor C7 to Q4 that is power amplifier circuit and AM modulation circuit at

the same time. The input will be reduced by the resistor R8 to the appropriate size for the audio

signal to pass through the base pin of Q4. The same R7 and R8 are the bias resistors to Q4 . The

inductor L3 acts same as L2 to feed current to the transistor. Capacitors C10,C11 and C23 are to

filter current for the signal that is modulated with the video carrier wave, ready with the sound

signal in AM form that will be coupling and adjust the amplitude of signal suitably with

C13,C14,C15 and R10, by has the VR1 is used to adjust percentage of modulation. The audio

signal will be coupled through C14 and C17 to Q3 and to VR2 adjust the range of frequency

35

deviation. Both R11,R12 are the bias resistors. The C18 is to cut off high frequency on pin base.

C19 and C20 are the divider capacitors as same C2,C3, that is set at the generator circuit on LC

ground, base and configure same with Q1. But the circuit is determined as VCO (voltage

controlled oscillator) to modulate the audio signal into the FM input, by a center frequency of

5.5MHz, which is the frequency difference between the Signal carrier frequency video signals

with audio carrier signal. The set of values to determine this are T1 and C21. The audio signals

through the FM modulation are coupled to the base of Q4. The power supply that enters into this

section will be regulated to 5 volts by zener diode ZD2. R3 is current limiter and output is

filtered by C22. The television signal is in its complete at the output of Q4 which will be spread

through the broadcast antenna. The capacitors C24 and C25 act as matching circuits. The status

of the device is indicated by LED1 with current limiter R14.

Table 3.1 Parts List for the 50w Colour Television Transmitter

SYMBOL NAME OF COMPONENT

Q1 – - C1674 transistor

Q2 - C1674 transistor

Q3 - C945 transistor

Q4 - C2470 transistor

LED1 - diode

ZD1 - 11V zener diode

R1 - 5.6K

R2 - 1.2K

R3 - 1K

R12 - 1K

36

R4 - 10K

R5, R8 - 2.2K

R6 - 560Ω

R7,R13,R14 - 1.5K

R9 - 47Ω

R10 - 100Ω

R11 - 220K

VR1 - 1K

VR2 – 10K C1 – 56pF

C2, C5, C7, C22, C23 - 3pF

C3 – 22pF

C4 – 3-12pF (Variable)

C6,C21 - 33pF

C9,C11,C18,C24 - 0.001uF

C12 – 10pF

C13 – 15pF

C14 – 470Pf

C15 – 10uF, 25V (electrolytic)

C16,C17 - 4.7uF, 50V (electrolytic)

C19 – 100pF

C20 – 180pF

L1,L2 – 8 turns

37

L3 – 6 turns

T1 – Audio transformer

CHAPTER FOUR

TESTING, RESULTS AND DISCUSSION

38

4.1 TESTING APPROACH CONSIDERATIONS

The methods for testing and the criteria for acceptance will be discussed here. Testing is another

consideration that should not be overlooked. This project will be tested by the following means:

At the end of the project work, the following were tested:

- The output voltage of the power supply using a multimeter.

- The frequency of transmission by tuning the channel of the television receiver to VHF.

- The coverage (range) of the transmitter through the use of a television receiver and a tape

rule for distance measurement.

- Short circuit and continuity tests.

The instruments used for testing were probes, multimeter for short circuit and continuity test,

and tape rule for measuring distance.

39

Fig 4.1 Pictorial diagram of testing with multimeter for power supply output

4.2 RESULTS

During the test, the following observations were made:

Table 4.1 Results obtained from testing the project

PARAMETERS RESULTS OBTAINED

Power supply output 12.8V D.C

Range of coverage 65 metres

Frequency of transmission 205MHz

Short circuit test OK

Continuity test OK

4.3 DISCUSSION

The aim of this project as stated earlier is to obtain a working television transmitter with a

frequency of transmission of 205MHz and a range of 100 metres. In the course of this project

design and construction, I discovered that the range of coverage is dependent on the radiating

power of the antenna, its length and the length of the receiving antenna. However, the receiving

antenna used was an indoor antenna and as such, determined the distance of coverage. The

distance of coverage of the Telecommunication laboratory from measurement is about 45m. The

transmitter was able to cover beyond the laboratory at a range of 65m making the aim achieved

to a reasonable point.

4.4 PROJECT BILL OF ENGINEERING MEASUREMENT AND ESTIMATION

The table below shows the description of materials used, quantity, the unit and total price.

Table 4.2 Project Bill of Engineering Measurement and Estimation

S/NO MATERIALS DESCRIPTION QTY UNIT PRICE(₦) TOTAL(₦)

1. C 1674 2 150 300

40

2. C 945 1 200 200

3. C 2570 1 150 150

4. 11V Zener diode 1 200 200

5. 5V Zener diode 1 200 200

6. 5.6K Resistor 1 30 30

7. 1K Resistor 3 30 90

8. 1.2K Resistor 1 50 50

9. 1.5K Resistor 4 50 200

10. 2.2K Resistor 3 60 180

11. 10K Resistor 2 70 140

12. 47K Resistor 3 60 180

13. 220K Resistor 1 60 60

14. 1K Variable Resistor 1 100 100

15. 10K Variable Resistor 1 150 150

16. 56pF Capacitor 1 50 50

17. 33pF Capacitor 2 50 100

18. 22pF Capacitor 2 50 100

19. 3pF Capacitor 3 60 180

20. 0.001uF Capacitor 4 70 280

21. 220uF Capacitor 1 50 50

22. 10pF 3 100 300

23. 100pF Capacitor 2 50 100

24. 10 uF 25V Capacitor 4 100 400

25. 4.7 uF 50V elect. Capacitor 4 100 400

26. 1nF Capacitor 1 100 100

27. 470pF Capacitor 2 100 200

28. Audio transformer 1 700 700

29. Soldering lead 6m 30 300

30. 12V d.c transformer 1 500 500

31. LED 1 50 50

32. IN4001 5 50 250

33. Aluminium antenna - - 400

34. Flexible cable 1.2m 30 60

35. Control knob - - 50

41

36. PCB production - - 3000

37. Casing - - 2000

38. Power cable 1 100 100

39. Surfing and Printing - - 4000

40. Transport - - 5000

41. Miscellaneous - - 5000

Total 22 000

CHAPTER FIVE

CONCLUSION, LIMITATIONS AND RECOMMENDATION

In this chapter conclusion has been reached based on the experience gathered during the course

of this project work. Some limitations were also faced from which recommendations for further

study are made.

5.1 CONCLUSION

The aim of this project was to design and construct a 50w colour television transmitter to cover a

range of 100m and to be used within the Telecommunication laboratory at a transmitting

frequency of 205MHz. At the end of this project, the television transmitter was able to broadcast

at a frequency of 205MHz at a range of 65m, covering more than electronics and

telecommunication laboratory. The aim was not fully achieved because of the length of the

antenna used for transmission and reception of the signal. However this project has not only

enhanced my practical knowledge and skills, but has also helped me to appreciate even better

electronics and telecommunication engineering.

5.2 LIMITATIONS

During the course of the project, the following limitations were encountered:

42

- The range was limited to the antenna used for transmission and reception. The

constructed antenna was made of aluminum instead of copper which was not readily

available and also lacked a booster.

- The carrier frequency of the video was not stable.

5.3 RECOMMENDATIONS

To increase the range of transmission, a helix or yagi antenna can be used for transmission.

An antenna booster can also be incorporated with the one used for this project to increase its

radiating power and hence the range. However, that will depend on registering with the Nigerian

Communication Commission to avoid violations. Also the carrier frequency section of the circuit

can be modified with a crystal oscillator to generate a more steady carrier signal.

REFERENCES

Adedibu, J .S. (2003). Approach to Telecommunication Studies. 1st Edition. Ibadan.: Akan Communications.

Adesina, A.I. (2002). Basic Electronics. Lagos: Kenia Publishers.

Breeding, J. (1989). Design Fundamental. New Jersey City: Prentice Hall Inc.

Charles, A.S. (1991). Electronics Principles and Application, Fifth Edition. Columbus: Glencore Mc Graw-Hill.

Green, D.C. (1994). Electronics III, Fourth Edition. Essex: Longman. Burnt Mill Harlow.

Ihemelandu, J.C & Manyahaya, S. (2011). Telecommunication Systems. Minna: Mak Publishers.

Kogawa (1997). Television Transmitter Systems. Retrieved from www.poptronix.com. 13/10/14

Kolawole, O. (2006). Design and Construction of a 50w Colour Television Transmitter. Fed.Poly Bida, Niger State.

Mark (2007). Transmitter Propagation. Retrieved from www.semtech.com. 08/10/14

43

Spinak (1999). Design and construction of 20w audio video wireless sender. Retrieved from www.diy-electronics.com. 08/10/14

Whathfi (2010). History of Television Transmitter. Retrieved from www.whathfi.com. 01/10/14

APPENDIX A

44

Fig A1 Pictorial view of the internal circuitry of the 50w TV transmitter

45

Fig A2 Pictorial view of the etched board of the 50w TV transmitter.

APPENDIX B

46

Fig B2 Pictorial view of the casing and antenna of the 50w TV transmitter

47