BAHIRDAR UNIVERSITY Institute of Technology
School of Computing and Electrical Engineering Thesis on
Design and and implementation implementation of low low power FM transmitter 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
i
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 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 Ethiopia ii
Project approval Students’ name and signature: Student: Student :
Ahmede Muhye Menbere Shitaw Yewlsew Mekonen
School: School: School School of Computing and Electrical Engineering Program: Program: TVET in Electrical Engineering Thesis subject: 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
____________
____________
It is approved that this thesis has been written in compliance with the formatting rules laid down by the school of the university.
iii
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 depart ment of electrical engineering for giving giving the multisim 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 assista nce of DSP lab and our partners’ for helped us to complete this project.
iv
Preface th
This project was written during the 8 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 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.
v
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.
vi
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
vii
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 A dvantages 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
ix
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
Receiver
channel
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
8
c = the speed of light = 300,000 km/s or 3.0 x 10 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 ( f c)……………………………………..88 -10MHz Chanel band width …………………………………….. 200kHz Frequency stability …………………………………… ±2kHz 3
Frequency deviation (at 100%) ………………….. ……±75kHz Frequency response…………………………………….. 50Hz -15kHz β ……………………………………………………… . 5 Harmonics
……………………………………………… <3.5%
Maximum power …………………………………………100kw Technical background
frequency
Designation
abbreviation
wavelength
3-30kHz
Very low frequency
VLF
100,000-10,000m
30-300kHz
low frequency
LF
10,000-1,000m
300-3,000kHz
medium frequency
MF
1,000-100m
3-30MHz
high frequency
HF
100-10m
30-300MHz
very high frequency
VHF
10-1m
300-3,000MHz
ultra-high frequency
UHF
1-10m
3-30GHz
supper-high frequency
SHF
10cm-1cm
30-300GHz
extremely- high frequency
EHF
1cm-1mm
4
1.1.1 Modulation The information signal can rarely be transmitted as is, it must be processed. In order to use electromagnetic transmission, it must first be converted from audio into an electric signal. The conversion is accomplished by a transducer . After conversion it is used to modulate a carrier signal. A carrier signal is used for two reasons: To reduce the wavelength for efficient transmission and reception (the optimum antenna size is ½ or ¼ of a wavelength). To allow simultaneous use of the same channel, called multiplexing . Each unique signal can be assigned a different carrier frequency (like radio stations) and still share the same channel. The phone company actually invented modulation to allow phone conversations to be transmitted over common lines. The process of modulation means to systematically use the information signal (what you want to transmit) to vary some parameter of the carrier signal. The carrier signal is usually just a simple, single-frequency sinusoid (varies in time like a sine wave). The basic sine wave goes like V (t) = V o sin (2 πf t +ɸ) where the parameters are defined below: V (t) the voltage of the signal as a function of time. Vo the amplitude of the signal (represents the maximum value achieved each cycle) f the frequency of oscillation, the number of cycles per second ɸ the phase of the signal, representing the starting point of the cycle. 1.1.1.1 Frequency Modulation
Frequency can be defined as the rate of change of phase of a signal. In this type of modulation, information is transferred through a carrier by varying its instantaneous frequency. Frequency modulation uses the information signal, V m (t) to vary the carrier frequency within some small range about its original value. Here are the three signals in mathematical form: 5
Information: V m(t) Carrier: Vc(t) = Vco sin ( 2 π f c t + ɸ) FM: VFM (t) = Vco sin (2 π[f c + (Δf/V mo) V m (t)]Vm (t) We have replaced the carrier frequency term, with a time-varying frequency. We have also introduced a new term: Δf, the peak frequency deviation . In this form, you should be able to see that the carrier frequency term: f c + (Δf/V mo) Vm (t) now varies between the extremes of f c - Δf and f c +Δ f. The interpretation of Δf becomes clear: it is the farthest away from the original frequency that the FM signal can be. Sometimes it is referred to as the "swing" in the frequency. We can also define a modulation index for FM, analogous to AM: β =Δf/f m, where f m is the maximum modulating frequency used. The simplest interpretation of the modulation index, β, is as a measure of the peak frequency deviation, Δf. In other words, β represents a way to express the peak deviat ion frequency as a multiple of the maximum modulating frequency, f m, i.e. Δf = β f m. 1.1.1.1.1FM Performance
The performance of fm measured by the following parameters as shown below . 1.1.1.1.2 Bandwidth
As we have already shown, the bandwidth of a FM signal may be predicted using: BW = 2 (β + 1) f m Where β is the modulation index and f m is the maximum modulating frequency used. FM radio has a significantly larger bandwidth than AM radio, but the FM radio band is also larger. The combination keeps the number of available channels about the same. 6
The bandwidth of an FM signal has a more complicated dependency than in the AM case (recall, the bandwidth of AM signals depend only on the maximum modulation frequency). In FM, both the modulation index and the modulating frequency affect the bandwidth. As the information is made stronger, the bandwidth also grows. 1.1.1.1.3 Efficiency
The efficiency of a signal is the power in the side-bands as a fraction of the total. In FM signals, because of the considerable side-bands produced, the efficiency is generally high. Recall that conventional AM is limited to about 33 % efficiency to prevent distortion in the receiver when the modulation index was greater than 1. FM has no analogous problem. The side-band structure is fairly complicated, but it is safe to say that the efficiency is generally improved by making the modulation index larger (as it should be). But if you make the modulation index larger, so make the bandwidth larger (unlike AM) which has its disadvantages. As is typical in engineering, a compromise between efficiency and performance is struck. The modulation index is normally limited to a value between 1 and 5, depending on the application.
1.1.1.1.4 Noise
FM systems are far better at rejecting noise than AM systems. Noise generally is spread uniformly across the spectrum (the so-called white noise, meaning wide spectrum). The amplitude of the noise varies randomly at these frequencies. The change in amplitude can actually modulate the signal and be picked up in the AM system. As a result, AM systems are very sensitive to random noise. An example might be ignition system noise in your car. Special filters need to be installed to keep the interference out of your car radio. FM systems are inherently immune to random noise. In order for the noise to interfere, it would have to modulate the frequency somehow. But the noise is distributed uniformly in frequency and varies mostly in amplitude. As a result, there is virtually no interference picked up in the FM receiver. FM is sometimes called "static free,” referring to its superior immunity to random noise. 7
1.1.1.1.5 Frequency Modulation Advantages and Disadvantages
FM is widely used because of the many advantages of frequency modulation. Although, in the early days of radio communications, these were not exploited because of a lack of understand of how to benefit from FM, once these were understood, its use grew. There are many advantages of FM, but also some disadvantages, and as a result it is suitable for many applications, but other modes may be more suited to other applications. An understanding of the disadvantages and advantages of FM will enable the choice of the best modulation format to be made. 1.1.1.1.6 Advantages of frequency modulation
There are many advantages to the use of frequency modulation. These have meant that it has been widely used for many years, and will remain in use for many years. Resilient to noise: One of the main advantages of frequency modulation that has been utilised
by the broadcasting industry is the reduction in noise. As most noise is amplitude based, this can be removed by running the signal through a limiter so that only frequency variations appear. This is provided that the signal level is sufficiently high to allow the signal to be limited. Resilient to signal strength variations: In the same way that amplitude noise can be removed,
so too can any signal variations. This means that one of the advantages of frequency modulation is that it does not suffer audio amplitude variations as the signal level varies, and it makes FM ideal for use in mobile applications where signal levels constantly vary. This is provided that the signal level is sufficiently high to allow the signal to be limited. Does not require linear amplifiers in the transmitter: As only frequency changes are required to be carried, any amplifiers in the transmitter do not need to be linear. Enables greater efficiency than many other modes:
The use of non-linear amplifiers, e.g. class C, etc means that transmitter efficiency
levels will be higher - linear amplifiers are inherently inefficient.
8
1.1.1.1.7 Dis- advantages of frequency modulation
There are a number of dis-advantages to the use of frequency modulation. Some are can be overcome quite easily, but others may mean that another modulation format is more suitable. Requires more complicated demodulator:
One of the minor dis-advantages of frequency
modulation is that the demodulator is a little more complicated, and hence slightly more expensive than the very simple diode detectors used for AM. Also requiring a tuned circuit adds cost. There are many advantages to using frequency modulation - it is still widely used for many broadcast and radio communications applications. However with more systems using digital formats, phase and quadrature amplitude modulation formats are on the increase. Nevertheless, the advantages of frequency modulation mean that it is an ideal format for many analogue applications.
1.2 motivation Our motivation to select this project title is that to design and implementation of low power fm transmitter and also to solve the problems of information accuses in our campus and mini-media service. Parallely we will understand the role of communication concept. Secondly we think that our project will be done by chip and easy components that are found in our compass in workshops, laboratories and stores.
1.3problem description When we do our project there was some problems, these are problems of to get internet access during on time. Due to this reason we start our project late in time than other students, until the program manger adjust the project room and lab class. There were also problems of power during working our project accidentally the power is off, even if we have not saved documents. The other is problem of software; the common software’s that was using in the lab class are not easily
simulating our project such as, circuit maker and tinna. Finally our advisor gives some
comment to use multisim software for simulation of our project. But multisim also little difficult to install and immediately license expired. Finally when we come to the implementation part they have been occurred shortage of materials, even if the equivalences of materials are not
9
found in the stores, labs and shops. Due to these challenges our goal of the project is not fully succeed. We hope that the next generation will be finishing this project better than ours.
1.4 Objective The aim of our project has the following objectives: To integrate the knowledge and skills acquired from major courses taken so far. To develop a low power FM transmitter to be used in specialized applications for local area entertainment purpose. Provide a reference for further study in a similar streams having having ambition to deal with low power FM transmitter design.
1.5 Organization of the project This section describes the introduction part of our project. It introduces basic concepts Fm 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 fm transmitter and the documents used to guide during our project. The third chapter discusses the design and analysis / methodology which describe the body of our project. It explains block diagrams, calculation parts, schematic diagrams and results/out puts. Finally the project also includes summary, conclusion, recommendation, references and appendix.
10
Table 1 shows list of materials used in our project.
Components
s r o t s i s e R
r o t i c a p a c
s r o t c u d n I
transistor
Specific component
Theoretical value
R1
8Ω
R2
530m Ω
R3
1m Ω
R4
1m Ω
R5
127.58k Ω
R6
23k Ω
R7
5k Ω
R8
1.2k Ω
R9
39k Ω
C1
10 µF
C2
47nF
C3
47nF
C4
120mF
C5
120mF
C6
120mF
C7
22pF
C8
22pF
C9
2.2pF
C10
10pF
C11
22nF
L1
390 µH
L2
390uH
L3
211nH
L4
1µH
Q1=Q2=Q3
BC2329BP
11
Varactor diode MA372 Antenna 143cm 12v battery plug s t n e m e r i u q e r r e h t O
Signal input socket =3.5mm Breadboard Multimeter Frequency counter 12v battery Mic Digital radio Probe miliwatt
12
2. Literature review We have performed with high expectation to complete this final year project for the title ‘low power FM transmitter. By considering this project can be done for
in good result and the output
can be performing at fm radio smoothly. This chapter will review some similar project and studies, the solution s, of the project related, over view, on different approaches made by previous researchers and make comparism between my final year project and those similar projects. [1] Design and build a portable, miniaturized, Multichannel fm transmitter by Francis Mc Swiggan 9427406 in the University of Limerick, Limerick, Ireland in28/04/98.[2]Rudolf. Graf (2001).William sheets: Build Your Own Low power transmitter. [3]Stephan Jones. Ron Kovac (2003) introduction to communication technology. [4].en.wikipedia.orga/wiki/transmitter.[5 ]www.Cybercollege.com. 2.1 Basic history of fm radio transmitter
The first primitive radio transmitters (called Hertzian oscillators) were built by German physicist Heinrich Hertz in 1887 during his pioneering investigations of radio waves. These generated radio waves by a high voltage spark between two conductors. These spark-gap transmitters were used during the first three decades of radio (1887-1917), called the wireless telegraphy era. Short-lived competing techniques came into use after the turn of the century, such as the
Alexanderson
alternator and Poulsen Arc transmitters. But all these early technologies were replaced by vacuum tube transmitters in the 1920s, because they were inexpensive and produced continuous waves, which could be modulated to transmit audio (sound) using amplitude modulation (AM) and frequency modulation (FM). This made possible commercial radio broadcasting, which began about 1920. The development of radar before and during World War 2 was a great stimulus to the evolution of high frequency transmitters in the UHF and microwave ranges, using new devices such as the magnetron and traveling wave tube. In recent years, the need to conserve crowded radio spectrum bandwidth has driven the development of new types of transmitters such as spread spectrum.[4]
13
2.2 Invention of radio
James Clerk Maxwell showed mathematically that electromagnetic waves could propagate through free space. Heinrich Rudolf Hertz and many others demonstrated radio wave propagation on a laboratory scale.[5] Nikola Tesla experimentally demonstrated the transmission and radiation of radio frequency energy in 1892 and 1893 proposing that it might be used for the telecommunication of information. The Tesla method was described in New York in 1897. In 1897, Tesla applied for two key United States radio patents, US 645576, first radio system patent, and US 649621. Tesla also used sensitive electromagnetic receivers , that were unlike the less responsive coherers later used by Marconi and
other early experimenters. Shortly thereafter, he began to develop wireless remote control devices.In 1895, Marconi built a wireless system capable of transmitting signals at long distances (1.5 mi./ 2.4 km). From Marconi's experiments, the phenomenon that transmission range is proportional to the square of antenna height is known as " Marconi's law". This formula represents a physical law that radio devices use. The term wireless telegraphy is a historical term used today to apply to early radio telegraph communications techniques and practices, particularly those used during the first three decades of radio (1887 to 1920) before the term radio came into use. Guglielmo Marconi demonstrated application of radio in commercial, military and marine communications and started a company for the development and propagation of radio communication services and equipment. The field of radio development attracted many researchers, and bitter arguments over the true "inventor of radio" persist to this day.[4] 2.3Turn of the 19th to 20th century
Around the turn of the 19th to 20th century, the Slaby-Arco wireless system was developed by Adolf Slaby and Georg von Arco. In 1900, Reginald Fessenden made a weak transmission of voice over the airwaves. In 1901, Marconi conducted the first successful transatlantic experimental radio communications. In 1904, The U.S. Patent Office reversed its decision, awarding Marconi a patent for the invention of radio, possibly influenced by Marconi's financial backers in the States, who included Thomas Edison and Andrew Carnegie. This also allowed the U.S. government (among others) to avoid having to pay the royalties that were being claimed by Tesla for use of his patents. 14
For more information see Marconi's radio work. In 1907, Marconi established the first commercial transatlantic
radio
communications
service,
between
Clifden,
Ireland
and
Glace
Bay,
Newfoundland. Donald Manson working as an employee of the Marconi Company (England, 1906). Julio Cervera Baviera developed radio in Spain around 1902. Cervera Baviera obtained patents in England, Germany, Belgium, and Spain. In May – June 1899, Cervera had, with the blessing of the Spanish Army, visited Marconi's radiotelegraphic installations on the English Channel, and worked to develop his own system. He began collaborating with Marconi on resolving the problem of a wireless communication system, obtaining some patents by the end of 1899. Cervera, who had worked with Marconi and his assistant George Kemp in 1899, resolved the difficulties of wireless telegraph and obtained his first patents prior to the end of that year. On March 22, 1902, Cervera founded the Spanish Wireless Telegraph and Telephone Corporation and brought to his corporation the patents he had obtained in Spain, Belgium, Germany and England .
[15]
He established the second
and third regular radiotelegraph service in the history of the world in 1901 and 1902 by maintaining regular transmissions between Tarifa and Ceuta for three consecutive months, and between Javea (Cabo de la Nao) and Ibiza (Cabo Pelado). This is after Marconi established the radiotelegraphic service between the Isle of Wight and Bournemouth in 1898. In 1906, Domenico Mazzotto wrote: "In Spain the Minister of War has applied the system perfected by the commander of military engineering, Julio Cervera Baviera (English patent No. 20084 (1899)). "
[16]
Cervera thus achieved
some success in this field, but his radiotelegraphic activities ceased suddenly, the reasons for which are unclear to this day. Using various patents, the company called British Marconi was established in 1897 and began communication between coast radio stations and ships at sea. This company along with its subsidiary American Marconi, had a stranglehold on ship to shore communication. It operated much the way American Telephone and Telegraph operated until 1983, owning all of its equipment and refusing to communicate with non-Marconi equipped ships. Many inventions improved the quality of radio, and amateurs experimented with uses of radio, thus the first seeds of broadcasting were planted. The company Telefunken was founded on May 27, 1903 as "Telefunken society for wireless 15
telefon" of Siemens & Halske (S & H) and the Allgemeine Elektrizitäts-Gesellschaft ( General Electricity Company) as joint undertakings for radio engineering in Berlin. It continued as a joint
venture of AEG and Siemens AG, until Siemens left in 1941. In 1911, Kaiser Wilhelm II sent Telefunken engineers to West Sayville, New York to erect three 600-foot (180-m) radio towers there. Nikola Tesla assisted in the construction. A similar station was erected in Nauen, creating the only wireless communication between North America and Europe. The invention of amplitude-modulated (AM) radio, so that more than one station can send signals (as opposed to spark-gap radio, where one transmitter covers the entire bandwidth of the spectrum) is attributed to Reginald Fessenden and Lee de Forest. On Christmas Eve 1906, Reginald Fessenden used an Alexanderson alternator and rotary spark-gap transmitter to make the first radio audio broadcast, from Brant Rock, Massachusetts. Ships at sea heard a broadcast that included Fessenden playing O Holy Night on the violin and reading a passage from the Bible. In 1909, Marconi and Karl Ferdinand Braun were awarded the Nobel Prize in Physics for "contributions to the development of wireless telegraphy". In April 1909 Charles David Herrold, an electronics instructor in San Jose, California constructed a broadcasting station. It used spark gap technology, but modulated the carrier frequency with the human voice, and later music. The station "San Jose Calling" (there were no call letters), continued to eventually become today's KCBS in San Francisco. Herrold, the son of a Santa Clara Valley farmer, coined the terms "narrowcasting" and "broadcasting", respectively to identify transmissions destined for a single receiver such as that on board a ship, and those transmissions destined for a general audience. (The term "broadcasting" had been used in farming to define the tossing of seed in all directions.) Charles Herrold did not claim to be the first to transmit the human voice, but he claimed to be the first to conduct "broadcasting". To help the radio signal to spread in all directions, he designed some omnidirectional antennas, which he mounted on the rooftops of various buildings in San Jose. Herrold also claims to be the first broadcaster to accept advertising (he exchanged publicity for a local record store for records to play on his station), though this dubious honour usually is foisted on WEAF (1922). In 1912, the RMS Titanic sank in the northern Atlantic Ocean. After this, wireless telegraphy using 16
spark-gap transmitters quickly became universal on large ships. In 1913, the
International
Convention for the Safety of Life at Sea was convened and produced a treaty requiring shipboard radio stations to be manned 24 hours a day. A typical high-power spark gap was a rotating commutator with six to twelve contacts per wheel, nine inches (229 mm) to a foot wide, driven by about 2,000 volts DC. As the gaps made and broke contact, the radio wave was audible as a tone in a magnetic detector at a remote location. The telegraph key often directly made and broke the 2,000 volt supply. One side of the spark gap was directly connected to the antenna. Receivers with thermionic valves became commonplace before spark-gap transmitters were replaced by continuous wave transmitters. On March 8, 1916, Harold Power with his radio company American Radio and Research Company (AMRAD), broadcast the first continuous broadcast in the world from Tufts University under the call sign 1XE (it lasted 3 hours). The company later became the first to broadcast on a daily schedule, and the first to broadcast radio dance programs, university professor lectures, the weather, and bedtime stories.
[18]
Inventor Edwin Howard Armstrong is credited with developing many of the features of radio as it is known today. Armstrong patented three important inventions that made today's radio possible. Regeneration, the super heterodyne circuit and wide-band frequency modulation or FM. Regeneration or the use of positive feedback greatly increased the amplitude of received radio signals to the point where they could be heard without headphones. The superhet simplified radio receivers by doing away with the need for several tuning controls. It made radios more sensitive and selective as well. FM gave listeners a static-free experience with better sound quality and fidelity than AM. In the mid-30s, Major Edwin Armstrong, an inventor who had already devised a successful circuit to improve AM radio, came up with a whole new approach to transmitting radio signals. Armstrong was clearly a technical genius. Although his life was cut short, he's still considered the most prolific inventor in radio's history. Even though he had improved AM radio in significant ways, Armstrong was well aware of AM 17
radio's major limitations: static interference from household appliances and lighting limited audio quality (frequency response and dynamic range) nighttime interference between many stations (cochannel interference), because of ionospheric refraction. Armstrong's new approach to encoding audio for transmission eliminated these problems. Recall that in Module 17 we explained the technical differences between the AM and FM systems of transmission. Armstrong took his invention to a friend, David Sarnof, who was head of RCA and who said he would help him develop it. RCA bought into the patents and helped Armstrong develop an experimental radio station. But, then it became evident that Sarnof and RCA were out to protect their existing AM radio empire and they didn't want the competition from a new (although much better) form of radio. Years of costly legal battles ensued that RCA could afford and Armstrong couldn't.
Strongly believing in his invention, Armstrong started to develop FM radio on his own. He sold rights to manufacture FM radios to several companies. By 1941, 50 FM stations were on the air. Then the Japanese bombed Pearl Harbor. The ensuing war diverted resources and froze development. David Sarnof and RCA, still out to hold control of their radio empire, pressured the FCC to change all of the FM radio frequencies — a move they knew would instantly obsolete all of the exiting FM radios, and cause Armstrong to lose his personal investment in FM radio. Listeners were understandably upset at having their radios suddenly rendered useless. And having been "burned once," they were reluctant to immediately go out and buy new FM radios. Since most radio station owners didn't want to go to the expense of creating high-fidelity
18
programming just for their FM stations, the FCC allowed them to simulcast — simultaneously broadcast the same programming on both their AM and FM stations. Of course, this didn't show off FM's quality advantages and it did nothing to help the cause of FM. (Years later, the FCC ruled against the practice of simulcasting.) Once TV started to evolve (to be covered in an upcoming module), interest in FM radio further diminished and by 1949, many FM stations had shut down.
On January 31, 1954, Edwin Armstrong, gave up his long, taxing battle against Sarnof and RCA. He wrote a note to his wife apologizing for what he was about to do, removed the air conditioner from his 13th story New York apartment, and jumped to his death. A few weeks later RCA announced record profits. Armstrong never lived to see the great success of his invention. Nor will we know what other inventions this genius of electronics might have contributed if his personal and financial resources hadn't been devastated by years of legal battles.Once FM radio started to make money, RCA quickly started pushing its development and subsequently made millions of dollars from the sale of FM transmitters and equipment.[5] As you can see from the graph below, FM radio not only climbed out of the cellar of popularity after Armstrong's death, but today it leads AM radio in both number of stations and listeners. The green line represents the growth of noncommercial and National Public Radio (NPR) stations. We'll cover public broadcasting both radio and television in an upcoming module. Among
other
things
RCA
closed
down
the
FM
station
that
they
had
helped
Armstrong build. Our final year project is different from researcher indicated by [1] in the above called Francis Mc Swiggan he used to design his project for tour guide, for vacant spot or multichannel purpose. Also his design methodology is different from our project. Which means our project design methodology and using of material and components are different , such as our project uses for fixed channel (104.5MHz) frequency and use low power consumption (40mW). 19
3. Design and analysis /methodology/ Frequency modulation is used for sound broad casting in the VHF bands for VHF and UHF mobile systems and for wide band UHF and SHF radio relay systems.FM transmitters are used to generate high frequency signal.[2][1] Block diagram of FM transmitter
Audio i/p
Pre-emphasis
Modulator
VHF power am lifier
Antenna
Oscillator
Fig.2 block diagram of Fm transmitter
3.1 Audio input/ Microphone Microphone is a transducer, which converts sound pressure variations in to electrical signals of the same frequency and of amplitudes in the same proportion as a pressure variation. Quality of a microphone is determined by the following characteristics:-Sensitivity, Signal to noise ratio (SNR), Frequency response, and Distortion, Directivity and Output impedance. These characteristics are defined as:-
3.1 .1 Sensitivity It is defined as output in mill volts (in DB below volt) for the sound pressure of one micro bar (0.1pa)at 1000Hz. As the normal level of speech provides sound pressure of 1micro bar, the 20
sensitivity based on these criteria is more appropriate and has been used. For instance, sensitivity of microphone is 120dB below 1 volt, and its output becomes 20log (1/E o) =120therefore, -6
1/Eo=10 =1µv. 3.1 .2 Signal -to -noise ratio (SNR)
It is generated inside the microphone due to resistance of the circuit, built in transformer, etc.it is represented in terms sound pressure, which would give the same output as the noise output. The output is measured by passing it through a weighting filter, which accounts for the reduced sensitivity of the ear at high and low audio frequencies. S/N=20log (output in the pressure of sound /output in the absence of sound). 3.1 .3 Frequency response
The Frequency response of a micro phone is defined by the band width of audio frequencies in the out of micro phone plus or minus of the out at 1000Hz. although the complete audio frequencies range of sound is 16 to 20hz,a micro phone which gives flat response within plus or minus dB for frequencies 40-to-15Hz is considered good for high fidelity audio systems. 3.1 .4 Distortion
Besides frequency distortion (un-even frequency response) described above, the microphone has two types of distortion these are: None linear distortion: distorts the amplitude of the audio signal ,which results in production of such harmonics in the output that are not present in the input sound for quality microphones , such distortion should be less than 5% . For high fidelity sound systems, distortion should not be more than 1%. Phase distortion: may cause change of phase relationships between components of a complex sound wave. It occurs when multiple microphones are used causing relative path from the source sound.
21
3.1 .5 Directivity It is defined with the help of a polar diagram. The angle for half power points in a polar diagram represents directivity of a microphone. Mathematically, microphone is defined as the ratio of actual output when placed in a direction of maximum response to the output which an Omni directional microphone in the same direction would have given, keeping the intensity of sound constant. D=E/Eo in dB, D=20logD Where, E= actual output in the direction of maximum output Eo= output in that direction has the microphone been Omni directional. D = directivity . 3.1 .6 Output impedance
A microphone has output impedance, which is represented in a ohms. This is an important parameter which is used to determine which type of matching transformer would be needed to transfer the power efficiently from , microphone to the transmitting line and then to the amplifier. some microphones like dynamic microphones have quite low output impedance, and therefore have built in step up transformer match line impedance. 3.2 Design of pre –emphasis
The circuits are the transmitting side of the frequency modulator. It is used to increase the gain of the higher frequency component as the input signal frequency increased, the impendence of the collector voltage increase. If the signal frequency is lesser then the impendence decrease which increase the collector current and hence decrease the voltage. ω1 =1/rc ……………………. (1) 22
ω2=1/RC ………………… (2) ω1 and ω2 is break frequency. For FM broad cast purpose, the lower break frequency f 1 is about
2.1 kHz and the higher break frequency f 2 is chosen to be much higher than the highest frequency term in the message band, so that f 2 lies outside the baseband spectral range. For audio rang, f 2 may be taken as 30 KHz. ω1 =1/rc let c=10µF & f 1 =2.1 kHz
2πf 1=1/rc =1/r*10µF r =1/ 2πf 1 (10µF) r=1/2*3.14*2.1k*10µF -3
r=1/2*3.14*2.1*10 Ω -3 r =1/131.95*10 Ω
r=0.007578628k Ω ≈7.58Ω or 8Ω ω2=1/RC let c=10µF & f 2 =30 kHz
2πf 2=1/RC 2*π*30 kHz = 1/R*10µF R=1/2π*30 kHz*10µF R=1/2π*30*10m F R=1/1884.95m R=0.000530516k Ω ≈0.53Ω
23
Fig. 3 schematic diagram for pre-emphasis
Fig. 4 out put of pre-emphasis
24
3.3 Designing of an oscillator Oscillators are necessary in any low power transmitter because they generate a necessary RF signal. The Colpitt’s oscillator is designed for generation of high frequency sinusoidal oscillations .Colpitt's oscillator is same as Hartley oscillator except for one difference. Instead of using a tapped inductance, Colpitt's oscillator uses a tapped capacitance. The circuit diagram of Colpitt’s oscillator using BJT is shown in Fig. It consists of an R -C coupled amplifier using an np-n transistor in CE configuration. R1 and R2 are two resistors which form a voltage divider bias to the transistor. A resistor RE is connected in the circuit which stabilizes the circuit against temperature variations. A capacitor CE is connected in parallel with RE, acts as a bypass capacitor and provides a low reactive path to the amplified ac signal. The coupling capacitor CC blocks dc and provides an ac path from the collector to the tank circuit.[1]
The feedback network (tank circuit) consists of two capacitors C1 and C2 (inseries) which placed across a common inductor L. The centre of the two capacitors is tapped (grounded). The feedback network (C1, C2 and L) determines the frequency of oscillation of the oscillator. The two series capacitors C1, and C2 form the potential divider led for providing the feedback voltage. The voltage developed across the capacitor C2 provides regenerative feedback which is essential for sustained oscillations. There are different type’s oscillator configuration such as Hartley, Winebridg, colipits and other. Because of good stability and high resonant frequency operation so we take colippit oscillator. When the collector supply voltage Vcc is switched on, collector current starts rising and charges the capacitors C1 and C2. When these capacitors are fully charged, they discharge through coil L setting up damped harmonic oscillations in the tank circuit. The oscillatory current in the tank circuit produces an a.c. voltages across C1, C2. The oscillations across C2 are applied to base-emitter junction of the transistor and appears in the amplified form in the collector circuit and overcomes the losses occurring in the tank circuit. The feedback voltage ( across the capacitor C2) is 180° out of phase with the output voltage ( across the capacitor C1), as the centre of the two capacitors is Grounded. The following figure show us Colipit oscillator circuit diagram.[6]
25
Formula: the frequency of oscillation the oscillator f =
1 2√
Where L = Self inductance of the coil (H) C = Capacitance of the condenser (F)
C=
12 =Resultant capacitance of the series combination 1+2
C1, C2 = capacitances of the two capacitors in the tank circuit.
Fig .5schematic diagram for colpitt oscillator
26
Fig. 6 Output of colpitt oscillator
3.4 Modulator An RF modulator (or radio frequency modulator) is a device that takes a baseband input signal and outputs a radio frequency-modulated signal. 3.5 Design procedure for CE power amplifier
1. Selection of transistor: select the transistor according to the frequency of operation, power requirement and h fe. For example PN3563 (TO-92) has frequency of operation up to 600MHz, hfe <200 and wattage=310mW. There for, the transistor must be selected in such way that the minimum h fe should be greater than or equal to the Av required. 2. Selection of the supply voltage VCC and setting of quotient voltage VCEQ :
27
The supply voltage v cc must be selected in- such a way that the quotient voltage V CEQ
≤50%
VCC should give distortion less output and protect from thermal stability. This means, the output voltage swing in either positive or negative direction with half of V CC. Therefore, the design criteria is
VCEQ≤
2
Let VCC =12V
3. The data sheet: go through the data sheet and make note of the important parameters.
From the data sheet of TO-92, we can find the following specifications. Maximum rating : VCB=30V, VCE=12v, VEB=4v, IC=50mA Normal rating: V CE=10v, IC=8mA, hfe=20 to 200 4. Selection of the collector current IC: collector current will be given in data sheet.
Normally the collector current of the power amplifier will be at ampere range; however those of normal transistors will be at mA range. Collector current I C is the biased current at which hfe is measured. Therefore, the collector current I C is selected based up on h fe which is obtained from the datasheet. In this design, let we select I
C
=8mA.
5. DC biasing condition: As a design criteria, normally,40%V CC is allocated for the
collector resistor R C , 50%VCC is allocated for the quotient drop V CEQ , and 10% V CC is allocated for the emitter resistor R E. therefore, the design criterion is VC ≥40%VCC =0.4 VCC=0.4× 12=4.8v
28
VCEQ ≤ 50%VCC=0.5× VCC=0.5×12=6v VE ≤10 %VCC =0.1×12=1.2v
6. Design of RE: therefore, the emitter resistor should be R E =
Where, VE ≤
10
1.2
≤ 8×10 -3 ≤ 0.15Kῼ.
≤0.1×12=1.2v
7. Design of RC: the collector resistor should be RC
≥
0.4
4.8
≥ 8×10 -3 ≥ 600ῼ
8. Design of voltage divider or biasing resistors R1 and R2: the value of I B is obtained
using the relation I B=
=
8×
ℎ (min )
20
=0.4mA. However for better design, the current
flowing through the resistor R 1 should be 10I B.With this assumption, 9I B flows through the resistor
R2.
Now the values of R 1 and R2 can be calculated from the DC potential
created by the respective currents.[6] Voltage across R 2:V2=9IB×R2=VBE+VE=0.7+1=1.7V Or
9× 0 . 4 ×10-3 ×R2=1.7V 1.7
R2=
9×0.4×10 −3
=0.47kῼ
Voltage across R 1=VCC-V2=10IB× R1 Or
-3
10v-1.7v=10×8×10 ×R1 R1=
8.7
10×8×10 −3
8.7
=
80
kῼ= 108.7ῼ
29
9. Design of RL: the voltage gain of the CE amplifier can be obtained by using the relation Av= =e
|| but re=25mv/I E =25mv/8mA=3.125ῼ ≈/
Let the required gain be 100 (i.e. Av=100). Substituting back we get
100=
+ .
using cross multiplication we get
=-1250 +
RL=414ῼ
10. Design of coupling capacitor C1and C2: the purpose of the coupling capacitor is to
couple the AC signal to the input of the amplifier and block DC. it also isolates the input signal source and the voltage divider network. The value of the coupling capacitor C
C
is
set in such a way that the reactance X C at the lowest frequency(say 104.5MHz) , should be equal to one tenth or less of the series impedance that is being driven by the signal passing through the capacitor. That is X C ≤
10
Design of coupling capacitor C 1: XC ≤
10
But, Rin=R1 || R2|| hie =108.7 || 470 || 20=1.7kῼ Therefore,
1 2 1
ῼ
1.7k ≤ 2∗104.5∗ 1 10
=
1
∴ C1≥8.9*10-12 F ≈8.9pF Design of coupling capacitor C 2: 30
XC2 ≤
10
But, Rout=RC= 600ῼ Therefore,
1 2 2
C2
1
≤ 2∗ 104.5∗2
=
600 ῼ 10
≥ 2.54uF
11. Design of the emitter by-pass capacitor CE: the purpose of the by- pass capacitor is to
bypass the signal currents to the ground. To bypass lowest frequency component the reactance XE at the lowest frequency (say 104.5MHz) , should be equal to one tenth or less of the emitter resistance.[6] That is XCE ≤
Therefore,
1 2
=
10
= 0.1RE =0.1*1500ῼ=150ῼ
1
2∗104.5 ∗
≤150ῼ
CE ≥ 0.1p F
12. Calculate the signal resistance in the base leg ( rb). rb = Rb1 || Rb2 = 108.7 ῼ || 0.47k ῼ = 88 ῼ 13. Multiply the emitter leg signal resistance times beta. (Assume beta equals 20.)
× re =200 × 3.125 = 625 ῼ 14. Calculate the circuit input impedance by finding the parallel equivalent of the signal base resistance and the signal emitter path resistance.
zin = rb ||β re =88||625 =77.14 ῼ 31
15. Calculate the output impedance. zout = Rc = 600 ῼ 16. The voltage gain of the common emitter amplifier is Av = rc/re,
Av= 600/3.125 =192
Fig.7 schematic diagram for RF power amplifier
Resistor R1 and R2 form voltage divide that provide the base biased voltage. The resistor R e allows the emitter to raise the above ground potential. 32
The capacitor c used to coupled Ac signal voltage from source to voltage divider point and the capacitor block Dc-Ac source an affected by Dc level but ac signal is pass through the capacitor. CE is by pass capacitor this capacitor (by pass) of shunt any Ac signal parallel to component to ground and there for increase Ac signal voltage gain. Cc is blocking capacitor it block Dc and provide Ac signal path from point to point.
Fig .8 out put of RF power amplifier
33
3.6 Antennas The final stage of any transmitter is the antenna; this is where the electronic FM is converted to electromagnetic waves, which are radiated into the atmosphere. Antennas can be vertically or horizontally polarized, which determined by their relative poisonwith the earth’s surface (i.e antenna parallel with the gro und is horizontally polarized) A transmitting antenna that is horizontally polarized transmits a better to a receiving antenna that is also horizontally polarized, this is also true for vertically polarized antennas.
3.6.1 Design of antenna length If an audio frequency is translated to a radio frequency carrier 104.5 MHz, the antenna height required will be 2
but λ=C/f where C=3*10
There for
L=
. 2
λ =
8
∗ = = 104.5000000 104.5
=2.87m
m
L=1.43m So, this antenna height can be practically achieved. 3.6.2 Design of antenna cross sectional area
the electrical resistance of a wire would be expected to be greater for a longer wire, less for a wire of larger cross sectional area, and would be expected to depend upon the material out of which the wire is made (resistivity) . Experimentally, the dependence upon these properties is a 34
straightforward one for a wide range of conditions, and the resistance of a wire can be expressed as R=
Where, R is the electrical resistance of copper ( Ω )
is the resistivity of conductor material ( Ω m) L is length of copper (m)
1.43 ∗1.68 ∗ 10 −8 2 = =40.04*10−6 mm 600
A=
40.04 ∗10 −6
D=
3.14
= 12.75∗ 10−6 mm
Radius(r) =6.375 ∗ 10−6 mm. 3.6.3 Radiation resistance The power radiated by an antenna is give by the pointing vector theorem
= × watt/m2
.getting the cross product of E(electric field strength) and H (magnetic field strength) fields, multiply by a certain area( . ) ant equating the resulting power to I .Rr , Rr the radiation 2
2
resistance may be obtained.
2 2 2 n I .Rr = power = 80. .I ( )
2 n Rr = 80. ( )
Where l is the length of the antenna, λ is the wave length and n is an exponent value that can be
found by using ( ) on the y- axis and then can found on the x-axis.
35
For l half wave length ,n is found to be 3.2 , l= 1.43m, λ= 2.87m then when we substitute this values into the following formula we get
Rr = 80. ( ) 2
Rr = 80. ( 2
n
1.43 2.87
) 3.2 Ω
2 3.2 Rr = 80. (0.5) Ω
Rr = 80. *0.1 Ω 2
Rr = 80. *0.1 Ω 2
Rr = 78.9 Ω
3.6.4 Impedance matching Between the final power amplifier of the transmitter and the antenna, an impedance matching network may be considered. One of the possible surprises in power amplifiers is the realization. That out put impedance matching is not based onn the maxumem power crateria.one reason for this , is the fact that matching the load to the device out put impedance results in power transfer at 50% efficiency. The purpose of the impedance network is to transform a load impedance to an impedance approprite ro optimum curcuit operation.[7]
36
Fig. 9 final FM transmitter circuit
37
4. Conclusions and Recommendations 4.1 Summary 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. Basically, communication consists of three major parts. Transmitter, Communication channel, Receive. Frequency modulation is used for sound broad casting in the VHF bands for VHF and UHF mobile systems and for wide band UHF and SHF radio relay systems.FM transmitters are used to generate high frequency signal. Microphone is a transducer, which converts sound pressure variations in to electrical signals of the same frequency and of amplitudes in the same proportion as a pressure variation. Pre – emphasis is used to increase the gain of the higher frequency component as the input signal frequency increased, the impendence of the collector voltage increase. Oscillators are necessary in any low power transmitter because they generate a necessary RF signal. The Colpitt’s oscillator is designed for generation of high frequency sinusoidal oscillations. The RF power amplifier used to amplify the signal which is coming from the modulator. The carrier frequency used to carry the message signal to reach the destination/receiver.
38
4.2 Conclusion In conclusion the FM transmitter with a variable inductor design was a success. The FM transmitter was able to broadcast at frequency 104.5MHz. A lot was learned from the experiment without the aid of a variable inductor schematic. Even though much guidance was given from other schematics, it still took some time to complete the final project. Also a better understanding of BJT transistors, amplifiers, modulators, oscillators, capacitors and inductors were developed. In addition, a better understanding of the oscilloscope was also achieved. The mastering of horizontal and vertical position controls to find the output frequency took some patience. In the future, an oscilloscope could be used to find the precise frequency. Also, better components and a higher voltage supply would allow for a larger transmitting distance.
39
4.3 Recommendation The design used for this project is essentially quite the difficult one, and it is using the last effort of which partially brings it down when it comes to the overall reliable performance. The main area of to do this project is that, the design parts and collecting of the necessary components of materials that have used to done the suitable ways. In order to doing this final project we are early expected to simulated and implemented of the final achievements. In this case when we started from the beginning to the end the members /teams are participated actively in order to collecting the data and gathering information from different areas/ parts to fulfill the necessary documents. During we do this final project we have got aulthigment knowledges, skills, and experiences throughout our life. When we are seen those, that have using different designs parts of micraphone, modulation, pre- ephasise, oscillator, power amplifier and the antennas. Those designs are connected each other and how to get the formulas to done in a correct ways in the real world. In the other ways when we do this project we are faced different problems like to get the exact components of the design materials. But with the help of our advisor and our partners most of the problems would be removed/ faced. Generally this project has been done well and what we are expected to achieve our goals.
40
REFERENCES [1]. Design and build a portable, miniaturized, Multichannel fm transmitter by Francis Mc Swiggan 9427406 in the University of Limerick, Limerick, Ireland in28/04/98.
[2]. Rudolf. Graf (2001).William sheets: Build Your Own Low power transmitter. [3]. Stephan Jones. Ron Kovac (2003) introduction to communication technology. [4].en.wikipedia.orga/wiki/transmitter. [5] . www.Cybercollege.com. [6]. Theodore F. Bogart, Jeffrey S. Beasley, Guillermo Rico [7] www.ebookee.net/ antenna- theory- balanice-dl/ -
41
