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BAHIRDAR UNIVERSITY Institute of Technology

School of Computing and Electrical Engineering Thesis on Design and implementation of low power FM transmitter Submitted IN PARTIAL FULLFILMENT OF THE REQUIRMENTS FOR THE DEGREE OF BACHELOR OF SCIENCE

IN TVET IN ELECTRICAL ENGINEERING BY: AHMED MUHYE MENBERE SHITAW YEWLSEW MEKONEN

June 2012 Bahir Dar, Ethiopia

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Design and implementation of low power FM transmitter

by Ahmed Muhye Menbere Shitaw Yewlsew Mekonen A thesis submitted to School of CEE of Bahir Dar University In partial fulfillment of the requirements for the degree of Bachelor of Science in TVET in Electrical Engineering (Communication and Electronics) Advisor: Solomon Lule June 2012 Bahir Dar, Ethiopia ii

Project approval Students’ name and signature: Student:

Ahmede Muhye Menbere Shitaw Yewlsew Mekonen

School: School of Computing and Electrical Engineering Program: TVET in Electrical Engineering Thesis subject: Design and implementation of low power FM transmitter I certify that this thesis satisfies all the requirements as a thesis for the degree of Bachelor of Science.

Chairperson name and signature………………………….............date ……

I certify that this thesis satisfies all the requirements as a thesis for the degree of Bachelor of Science. Advisor name and signature………………………………..date ………

Examining committee members

signature

Date

1.

Chairman

____________

___________

2.

Examiner 1

____________

___________

3.

Examiner 2

____________

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It is approved that this thesis has been written in compliance with the formatting rules laid down by the school of the university.

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Acknowledgement We would like to gratefully extend our sincere thanks to all the people who gave generously their time, takes one and all. Specially our supervisor Mr. Solomon Lule for the guidance he showed us right though every stage of the project, from initial conception to final design and construction. We would also like to thank Mr. Solomon Haile who has the instructor of Bahir Dar University in the department of electrical engineering for giving the multisim software . We would also like to thank Mr. Bekele who is the lab assistance in electronics lab he gave us an introductory parts of how to use multisim software. Lastly, we would like to thank W/r Ayalnesh who has lab assistance of DSP lab and our partners’ for helped us to complete this project.

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Preface This project was written during the 8th semester final project of low power FM radio transmitter carried out at the department of TVET in Electrical Engineering at Bahir Dar University. The purpose of this report is to create low power FM radio transmitter. The report consists of four main chapters, the contents, list of figures, tables, abbreviations, appendices and symbols are presented in order for the shake of reading convenience. References within the text are given as numbers with in square brackets and they are listed at the end of this report. We would like to express our recognition to our advisor Mr. Solomon Lule for their guidance and disponibility throughout this project.

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Abstract The aim of the project is to develop a low power fm transmitter to be used in specialized application such as local area net work. Frequency modulation has several advantages over the system of amplitude modulation (AM) used in the alternate form of radio broadcasting. The most important of these advantages is that an FM system has greater freedom from interference and static Various electrical disturbances ,such as those caused by thunderstorms and car ignition systems, crate amplitude modulated radio signal that are received

as noise by AM receivers. A

well-designed FM receiver is not sensitive to such disturbances when it tuned to an FM signal of sufficient strength. Also the signal to noise ratio in an FM system is much higher than that of an AM system. FM broadcasting stations can be operated in the very high frequency bands at which AM interference is frequently sever, commercial FM radio stations are assigned frequencies between 88 and 108 MHZ and will be the intended frequency range of transmission.

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List of tables and figures Table 1 list of materials used in our project. Fig1. General Block diagram for communication system Fig 2. block diagram of Fm transmitter Fig3.schematic diagram for pre-emphasis Fig 4 . out put of pre-emphasis Fig 5 .schematic diagram for colpitt oscillator Fig . 6 Output of colpitt oscillator Fig 7 .schematic diagram for RF power amplifie Fig 8. out put of RF power amplifier Fig 9 .final FM transmitter circuit

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Table of Content Project approval ..................................................................................................................................... iii Acknowledgement.................................................................................................................................. iv Preface .................................................................................................................................................... v Abstract ................................................................................................................................................. vi List of tables and figures ........................................................................................................................ vii 1. Introduction ........................................................................................................................................ 1 1.1background of FM broadcasting station .......................................................................................... 3 1.1.1 Modulation ............................................................................................................................. 5 1.1.1.1 Frequency Modulation ..................................................................................................... 5 1.1.1.1.1FM Performance ......................................................................................................... 6 1.1.1.1.2 Bandwidth................................................................................................................. 6 1.1.1.1.3 Efficiency ................................................................................................................... 7 1.1.1.1.4 Noise ......................................................................................................................... 7 1.1.1.1.5 Frequency Modulation Advantages and Disadvantages .............................................. 8 1.1.1.1.6 Advantages of frequency modulation ........................................................................ 8 1.1.1.1.7 Dis- advantages of frequency modulation .................................................................. 9 1.2 motivation ..................................................................................................................................... 9 1.3problem description ....................................................................................................................... 9 1.4 Objective ..................................................................................................................................... 10 1.5 Organization of the project .......................................................................................................... 10 2. Literature review ............................................................................................................................... 13 2.1 Basic history of fm radio transmitter ............................................................................................ 13 2.2 Invention of radio ........................................................................................................................ 14 2.3Turn of the 19th to 20th century ................................................................................................... 14 3. Design and analysis /methodology/ ................................................................................................... 20 Oscillator ........................................................................................................................................... 20 Antenna ............................................................................................................................................. 20 3.1 Audio input/ Microphone ............................................................................................................ 20 3.1 .1 Sensitivity............................................................................................................................. 20 3.1 .2 Signal -to -noise ratio (SNR) .................................................................................................. 21 viii

3.1 .3 Frequency response ............................................................................................................. 21 3.1 .4 Distortion ............................................................................................................................. 21 3.1 .5 Directivity............................................................................................................................. 22 3.1 .6 Output impedance ............................................................................................................... 22 3.2 Design of pre –emphasis ............................................................................................................. 22 3.3 Designing of an oscillator ............................................................................................................. 25 3.4 Modulator ................................................................................................................................... 27 3.6 Antennas ..................................................................................................................................... 34 3.6.1 Design of antenna length ...................................................................................................... 34 3.6.2 Design of antenna cross sectional area .................................................................................. 34 3.6.3 Radiation resistance .............................................................................................................. 35 3.6.4 Impedance matching ............................................................................................................. 36 4. Conclusions and Recommendations ................................................................................................... 38 4.1 Summary ..................................................................................................................................... 38 4.2 Conclusion ................................................................................................................................... 39 4.3 Recommendation ........................................................................................................................ 40 REFERENCES .......................................................................................................................................... 41 APPENDIX .............................................................................................................................................. 42

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1. Introduction Communication system engineers attempt to design communication system that transmits information at a higher rate with a higher performance, using the minimum amount of transmitted power and band width. The purpose of any communication system is to transmit information signals from a source located at one point in space to the user/destination located at another point. The originating in put is frequently referred to as the source, where as the terminating /end is frequently referred to as the sink. If the message is understandable, then the information has been converted from the source to the destination. Mostly, the message produced by the source is not electrical in nature. But to carry them over an electrical system the message must be converted to an electrical signal in the same manner at receiver. The electrical signal must be reconverted in to an appropriate form. A transducer performs these functions. Thus, an input transducer used to convert the message generated by the source in to time varying electrical signal called the message signal. Basically, communication consists of three major parts. Transmitter Communication channel Receive

Source Fig

Transmitter

Transition channel

Receiver

Noise, distortion& interference

Fig.1 General Block diagram for communication system 1

Destination

Transmitter: The sub-system that takes the information signal and processes it prior to transmission. The transmitter modulates the information onto a carrier signal, amplifies the signal and broadcasts it over the channel. That means the main purpose of transmitter is to modify the message signal in to a form suitable for transition over the channel. It involves modulation and amplification. Channel: The medium which transports the modulated signal to the receiver. Air acts as the channel for broadcasts like radio. Receiver: The sub-system that takes in the transmitted signal from the channel and processes it to retrieve the information signal. The receiver must be able to discriminate the signal from other signals which may use the same channel (called tuning), amplify the signal for processing and demodulate to retrieve the information. It also then processes the information for reception (for example, broadcast on a loudspeaker). In other words the main purpose of the receiver is to reproduce version of transmitted signal after propagation through the channel, this accomplished by using a process of demodulation and amplification.

Modulation is employed in order to: More efficiently launch the radiated wave in to space. Permit multiplexing To improve the modulated signal to noise ratio. For efficient launching or reception of an electromagnetic wave or to obtain what is commonly called matching, the radiating or receiving device (antenna) must be a significant portion of wave length in size. The larger the antenna in the wave length, the greater the antenna’s radiation resistance. The antenna resistance can thus closely approximately the driving generator impedance and associated transmission line. The wave length of an electromagnetic wave in free space related to the velocity of light by the following relation. c=

f where: 2

c = the speed of light = 300,000 km/s or 3.0 x 108 m/s = the wavelength of light, usually measured in meter f = the frequency at which light waves pass, measured in units of per seconds (1/s). In communication system the information system, maybe transmitted by itself over the medium or may be used to modulate a carrier for transmission over a long distance. The former is a base band communication, while the later is band pass (modulated signal). The goal of communication system engineer to design systems that provide high quality service for the maximum number user with the smallest cost and least usage of limited resources. The resources to be conserved include hard ware for generating, transmitting and receiving information signal, the channel band width and the transmitter power.

1.1background of FM broadcasting station The comparatively low cost of equipment for an FM broadcasting station, resulted in rapid growth in the years following World War II. Within three years after the close of the war, 600 licensed FM stations were broad casting in the United States and by the end of the 1980s there were over 4,000. Similar trends have occurred in Britain and other countries. Because of crowding in the AM broad cast band and the inability of standard AM receiver to eliminate noise, the tonal fidelity of standard stations is purposely limited. FM does not have 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 broad casting has drawn increasing numbers of listeners to popular as well as classical music, so that commercial FM stations draw higher audience ratings than AM stations. Fm broad caste transition specification Frequency band ( fc)……………………………………..88 -10MHz Chanel band width ……………………………………..200kHz Frequency stability …………………………………… ±2kHz 3

Frequency deviation (at 100%) ………………….. ……±75kHz Frequency response…………………………………….. 50Hz -15kHz β ………………………………………………………. 5 Harmonics

………………………………………………