REGENT UNIVERSITY COLLEGE OF SCIENCE AND TECHNOLOGY
DESIGN AND CONSTRUCTION OF CRYSTAL LOCKED FM BUG USING FREQUENCY DOUBLER APPROACH
PRESENTED BY FUTA OSUMANU
THESIS SUBMITTED TO THE SCHOOL OF INFORMATICS AND ENGINEERING, REGENT UNIVERSITY COLLEGE OF SCIENCE AND TECHNOLOGY, TECHNOLOGY, IN PARTIAL FULFILLMENT OF THE REQUIREMENT FOR THE AWARD OF BACHELOR BACHELOR OF ENGINEERING DEGREE IN ELECTRONICS AND SYSTEMS ENGINEERING (INSTRUMENTATION OPTION)
FUTA OSUMANU B.Eng (Hons) Regent Ghana
DECLARATION
This dissertation has been accepted in substance for any degree and is not being concurrently submitted in candidature for any degree elsewhere. The thesis is a result of my investigation, except where otherwise stated. All sources used in the production of this thesis are acknowledged by appropriate citation and explicit reference and are included in the bibliography that is appended. I hereby declare that the preparation and presentation of the study were supervised in accordance with the guidelines and supervision laid down by Regent University College of Science and Technology.
……………………………………
…………………………
Student Signature
Date
(Futa Osumanu)
Supervisors Declaration This thesis is submitted for examination with my full knowledge and acceptance.
……………………………………
…………………………
Supervisors Signature
Date
(Emmanuel Affum Ampoma)
ii
DECLARATION
This dissertation has been accepted in substance for any degree and is not being concurrently submitted in candidature for any degree elsewhere. The thesis is a result of my investigation, except where otherwise stated. All sources used in the production of this thesis are acknowledged by appropriate citation and explicit reference and are included in the bibliography that is appended. I hereby declare that the preparation and presentation of the study were supervised in accordance with the guidelines and supervision laid down by Regent University College of Science and Technology.
……………………………………
…………………………
Student Signature
Date
(Futa Osumanu)
Supervisors Declaration This thesis is submitted for examination with my full knowledge and acceptance.
……………………………………
…………………………
Supervisors Signature
Date
(Emmanuel Affum Ampoma)
ii
ABSTRACT
Crystal lock FM transmitter is another way of keeping the frequency of a transmitter stable to avoid interference and more so, loss of information due to frequency drifting between the transmission and reception frequencies. This project focuses on designing a microphone transmitting equipment operating in parallel chains to ensure frequency stability by developing a simple and highly economical crystal oscillator that exhibits linear tuning characteristics. The crystal is employed to operate at 49MHZ with the oscillator components accurately selected so that the tuned circuit operates at 98MHZ.
iii
DEDICATION
I dedicate this project to my wife Hajarah Issaka and daughter, Zainab Futa for their consistent support support in many ways and the sacrifice they they made during these years. This will always be remembered and deeply appreciated. Most of all, my biggest thanks goes to Almighty God for giving me the strength and encouragement to complete this project.
iv
ACKNOWLEDGEMETNT
I will like to express my profound gratitude to all whose contribution has made this project a success, especially to Mr. David Celestine of David Broadcast Engineering Limited and his staff for their constant guidance, advice, encouragement and support in many ways in completing the circuit. I also appreciate the inspiration from all my lecturers, more especially, to my supervisor, Emmanuel Affum Ampoma, for his meaningful suggestions and contribution towards this project.
v
TABLE OF CONTENTS TITLE
PAGE
DECLARATION .......................................................................................................
ii
ABSTRACT ..............................................................................................................
iii
DEDICATION ..........................................................................................................
iv
ACKNOWLEDGEMENT ...........................................................................................
v
TABLE OF CONTENTS ............................................................................................... vi
CHAPTER ONE – INTRODUCTION
1.0
Introduction
……………………………………………………………………………….
1
1.1
Background
……………………………………………………………………………….
1
1.1.1 Frequency Doubling …………………………………………………………………….
1
1.1.2 The Crystal
……………………………………………………………………………….
1
1.2
Problem Statement ……………………………………………………………………………….
2
1.3
General Objective
2
1.4
Specific Objective of the Study
1.5
Scope of Study
………………………………………………………………………………. ………………………………………………………….
2
……………………………………………………………………………….
3
1.6
Significant of Study ……………………………………………………………………………….
3
1.7
Organization of Study
…………………………………………………………………….
4
1.8
Limitations
……………………………………………………………………………….
4
CHAPTER TWO – LITERATURE REVIEW
2.0
Literature Review
……………………………………………………………………………….
5
2.1
Introduction
……………………………………………………………………………….
5
vi
CHAPTER THREE – METHODOLOGY
3.0
Methodology
……………………………………………………………………………….
10
3.1
Introduction
……………………………………………………………………………….
10
3.2
The Hardware
……………………………………………………………………………….
10
3.3
The Software
……………………………………………………………………………….
15
CHAPTER FOUR – SYSTEM DESIGN, DEVELOPMENT AND IMPLEMENTATION
4.0
System Design, Development and implementation
………………………….
16
4.1
Component Selection and Measurement ……………………………………………….
16
4.2
Block Diagram
……………………………………………………………………………….
20
4.3
Audio Module
……………………………………………………………………………….
21
4.3.1 Microphone ……………………………………………………………………………….
22
BF199 - NPN Medium Frequency Transistor
…………………………………….
22
……………………………………………………………………………….
23
4.4.2 Application ……………………………………………………………………………….
24
BC547- NPN General Purpose Transistor ……………………………………………….
24
4.5.1 Features
……………………………………………………………………………….
24
4.5.2 Application ……………………………………………………………………………….
25
4.6
The Crystal
……………………………………………………………………………….
25
4.7
The Modulator
……………………………………………………………………………….
25
4.8
Frequency Doubler ……………………………………………………………………………….
29
4.9
Circuit diagram Description & Operation ……………………………………………….. 29
4.4
4.4.1 Features
4.5
4.9.1 Construction ……………………………………………………………………………….
vii
21
CHAPTER FIVE – RESULTS AND DISCUSSION
5.0
Results and Discussion
5.1
Results
…………………………………………………………………….. 32
……………………………………………………………………………….. 32
5.1.1 Test for frequency 4 KHz
………………………………………………………….. 32
5.1.2 Test for frequency 10 KHz …………………………………………………………... 33 5.1.3 Test for 49 MHz
…………………………………………………………… 33
5.1.4 Test for Frequency Doubler
………………………………………………… 35
5.2
Selectivity
………………………………………………………………………………… 35
5.3
Discussion
………………………………………………………………………………… 36
5.4
Cost of Components and Labour …………………………………………………………… 37
CHAPTER SIX – CONCLUSION AND RECOMMENDATION
6.0
Conclusion and Recommendation ………………………………………………………….. 39
6.1
Conclusion
……………………………………………………………………………….. 39
6.2
Recommendation
………………………………………………………………………………..
REFERENCES GLOSSARY LIST OF FIGURES LIST OF TABLES APPENDIX
APPENDIX A – PCB Layout APPENDIX B – Circuit Layout APPENDIX C – MatLab Codes
viii
39
CHAPTER ONE 1.0
Introduction
1.1
Background
1.1.1 Frequency Doubling
Frequency doubling [1] is a method used to separate oscillator circuit from the preceding stages. The aim is to eliminate RF energy from disturbing oscillator stability and also reducing superior level thereby providing clean output radio energy at the antenna end. The doubling is achieved by multiplying the frequency of the oscillator [2] by two (2). The resonant [3] after oscillator circuit is matched at 98MHz.The purpose is to isolate the oscillator from the antenna due to antenna influences on the frequency. However, this does not guarantee 100% stability, because there is problem with frequency drifting within 4MHz across the centre-frequency. For example, if the centre frequency is 98MHz; the drifting will occur between 98MHz-96MHz and 98MHz to 100MHz. The drifting is caused by temperature changes within oscillator component and the entire circuit itself. Increase in temperature tunes the frequency upwards and decrease in temperature tunes the frequency downwards. But at room temperature the frequency remains constant at 98MHz.
1.1.2 The Crystal
The crystal[4] used is a 49MHz device while the components in the oscillator stage have been chosen so that the tuned circuit is operating at 98MHz.The way a crystal works is caused by its capacitance changing abruptly at the frequency marked on it. The only problem with identifying the frequency of a crystal is that while some crystals are marked with their third overtone value others are identified with their fundamental frequency. For instance, crystals for Citizen Band (CB), remote control 1
cars and walkie talkies are generally 3rd overtone crystals and have a fundamental of about 9MHz while computer crystals are generally identified by their fundamental frequency.
1.2
Problem Statement
In order to stabilize frequency, some engineers tend to rely on Phase Locked Loop (PLL) ICs to accomplish their goal; however the PLL has several disadvantages such as •
The cost involved is so high that it makes telecommunication equipment very expensive and difficult to construct.
•
With the PLL, the signal must go through the Prescaler, crystal, Programmable ICs, Error Amplifier and loop Filter which makes the circuit complex.
1.3
General Objective
Frequency modulation [5] (FM) is increasing in the country despite the problems associated with its mode of operation. Generally, this project work is to make frequency modulation operation smooth with minimum defects and also to lower the cost involved in transmission, operation, and equipment.
1.4
Specific Objective of the Study
The specific objective of this project is to:
Produce a crystal locked transmitter using crystal and frequency doubling procedure.
2
Modulate audio frequency signal to a high level frequency by superimposing low-level frequency (AF) to a high level frequency by varying the frequency whilst the amplitude remains constant.
Ensure frequency stability by using crystal oscillator.
Reduce the cost involving Phase Locked Loop (PLL) ICs; which should have been present in the circuit to ensure frequency stability.
1.5
Scope of Study
Before starting this project it should be noted that having a fair skill in assembly and soldering is necessary. After all, this is one of the more complex designs and one should start with something simple if he/she wants to get the maximum understanding. However, time will not permit us to go through all these. Knowledge in resistor and capacitor codes, and components position on PCB boards is also important since working with high frequency projects such as FM to keep all the components as close to the board as possible due to leads inductance. This might change the characteristics of the circuit, consequently results in poor performance. The characteristics of the circuit mainly comprise of ‘Tank circuit’ and corresponding
impedance matching circuits.
1.6
Significance of the Project
To improve the existing knowledge about similar designs.
To
acquire
more
knowledge
in
the
field
of
telecommunication/information technology.
To provide literature for other students, researchers and others interested in the field of telecommunication.
To add up to existing knowledge in the field of communication.
To enhance our knowledge in frequency doubling procedures. 3
1.7
To boost our understanding on the use of Crystal Oscillators.
Organisation of Study
This project is organised as follows: Chapter two focuses on the Literature review with methodology captured in Chapter three. Chapter four also focuses on the system design, development and implementation of the project work with Chapter five concentrating on the results and discussions together with the cost analysis. Chapter six concludes the research with conclusion and recommendation of the entire project.
1.8
Limitations
Crystal lock [6] FM transmitter is another way of keeping the frequency of a transmitter stable to avoid interference and lost of information due to frequency drifting between the transmission and reception. Interference and frequency drifting are major problems encountered by radio frequency (RF) engineers o ver the past years. Due to these, engineers tend to rely on phase lock loop [7](PLL ICs) and other complicated circuits to accomplish their goals. The cost involved is so high that it makes Telecommunication equipment very expensive and difficult to construct.
4
CHAPTER TWO 2.0
Literature Review
2.1
Introduction
Frequency Modulation (FM) is the method of varying a carrier wave's frequency proportionally to the frequency of another signal. Extensive studies was done by Kobayashi Kei et al when they researched on Analog frequency modulation detector for dynamic force microscopy [8] and presented a new analog frequency modulation (FM) detector (demodulator) for dynamic force microscopy (DFM). The detector utilizes the FM detection method where the resonance frequency shift of the force sensor is kept constant to regulate the distance between a tip and a sample surface. The FM detector employs a phase-locked loop (PLL) circuit using a voltage-controlled crystal oscillator (VCXO) so that the thermal drift of the output signal is negligibly reduced. Authors in [9] researched on Synchronously pumped mode‐locked dye laser pumped by a frequency‐doubled mode‐locked and Q‐switched diode laser pumped Nd:YAG laser and developed a powerful and efficient mode‐locked and Q‐switched diode laser pumped Nd:YAG laser. Mode
locking has been accomplished using intracavity frequency modulation (FM) to produce continuous‐wave mode‐locked pulses of 12 ps duration. Naicheng Shen
and the group [10] having done a comprehensive research on Frequency stabilization at
127
I2 Doppler-broadened line center near 532 nm using Nd:YVO 4
intracavity doubled lasers by employing an EOM crystal and FM spectroscopy method, locked the laser frequency to Doppler broadened lines of
127
I2 using
intracavity laser systems. The laser gain crystal is Nd:YVO 4, and the intracavity frequency doubling crystal is a KTP plate. It is estimated that the frequency stability of the stabilized laser is in the order of 10 -9. Reduction of FM Noise in Microwave Diode Oscillators by Cavity and Injection Stabilization was also analyzed by Ashley et al in [11] and concluded that a cavity
5
stabilized silicon avalanche diode oscillator used as a synchronizing signal to injection phase lock a Gunn oscillator has the best combination of low FM and AM noise. Still on noise the authors in [12] analyzed A Low-Noise Class-C Oscillator Using a Directional Coupler by using an oscillator using a directional coupler is proposed as a solution to the design of efficient low-noise high-power highfrequency oscillators. FM noise measurements are presented for microwave sources derived via varactor multipliers from several different transistor oscillators of this type. Further, design introduced an isolated port which can be used to achieve injection phase lock which is used to point out some of the interesting FM noise properties of these oscillators, the knowledge of which is important in the design and application of solid-state microwave sources. Finaly experimental results indicated how a low-noise microwave source can be built using a low-frequency crystal oscillator followed by a high-order varactor multiplier. Extensive work was also done by Bossard and the group when the researched on a Solid-State, OneWatt, Tunable Exciter for the 4.4 - 5.0 GC Communications Band [13] and describes a number of new techniques leading to the development of a completely solid-state source capable of delivering power in excess of 3 watts at a fixed frequency in ¿C¿ band, or power in excess of 1 watt rapidly tunable within an 18% bandwidth centered at 4.7 gc. With the system designed to carry multichannel FDM-FM, and is locked to a crystal source with a stability of one part in 106. Spurious responses of the exciter are, typically, 60 - 80 db below the output carrier frequency. Laser frequency stabilization by means of optical self-heterodyne beat-frequency control was also studied by Greiner et al and presented a new method for laser frequency stabilization based on control of a fiber interferometer-derived heterodyne beat signal that is proportional in specific limits to the laser frequency derivative. The output of an external-cavity diode laser equipped with an intracavity electro-optic crystal (EOC) is split and coupled into a Mach-Zehnder interferometer with one short and one long (fiber delayed) arm. The passage of light through the
6
short leg is acousto- optically frequency shifted by ΔνAOM relative to the initial laser frequency ν(t). The difference in optical path length between the two arms creates a time delay τD between the two fields. Thus, the resulting heterodyne signal as detected by the avalanche photodiode has a frequency ν h(t) given by νh(t)=ν(t)-ν(tτD)+Δν
AOM.
The output of the photodiode is subsequently coupled into a phase-
locked loop (PLL) operating as a FM demodulator. The PLL's output signal V(t) is proportional to the difference quotient of the laser's frequency during the time delay τD. AC coupling blocks the constant term and subsequent integration
electronics yield a voltage that in specific limits is proportional to the overall laser frequency excursion during the integration time. And concluded after appropriate amplification that, the voltage applied to the EOC provides negative feedback to the laser, stabilizing its frequency [14]. Phase modulation of a ring-laser gyro--Part II: Experimental results by Wax and the group [15] presented for the multimode ringlaser gyro with intracavity phase modulation indicated that by proper choice of modulator frequency, the oppositely directed traveling waves (ODTW) exist as either pulse trains or FM signals. And finally concluded that result is clearly useful for rotation sensing where rotation sensitivity is noise limited and shows an improvement of two orders of magnitude over the same system without modulation. When lock in does occur, it is accompanied by a hysteresis effect that is explained in terms of an optical damage effect in the KDP modulator crystal. The results also indicated that in the FM region of operation, the beat frequency between ODTW contains an offset that drifts with time and so this region of operation is not as useful for rotation sensing as is the pulse-train region. Authors in [16] researched on an FM-radio transmitter concept based on an alldigital PLL when they presented a stereo FM-radio transmitter with Radio Data System (RDS) support based on an all-digital PLL designed as a fully integrated single-chip transmitter in a 90-nm CMOS technology to be compatible with digital deep-submicrometer processes with target application of the proposed system as cointegration with baseband processors and transmitters for mobile communication 7
systems. Further, the proposed transmitter enables a mobile device to stream audio data to a FM receiver which is popular and existing in most households worldwide. RDS support allows sending additional information. And finally, concluded that the presented transmitter works on a 1 V supply voltage and is aimed for using a 32.768 kHz reference crystal oscillator instead of the commonly used 26 MHz reference oscillator while still providing wideband frequency modulation capability. Mann also did extensive studies on Active Stabilization of Crystal Oscillator FM Noise at UHF Using a Dielectric Resonator [17] and described a low-noise 600-MHz crystal oscillator circuit that uses a dielectric oscillator as the dispersive element of a discriminator in an active frequency stabilization loop which reduces the nearcarrier FM noise. The innovation in the circuit is an essentially noiseless active carrier suppression loop, which allows maximum utilization of a low-noise RF amplifier to reduce the discriminator threshold (Delta f rms) to 2.5x10-5 Hz in a 1-Hz bandwidth. The FM noise 1 kHz from the carrier was reduced by 44 dB to this threshold, equivalent to a phase-noise spectral density of -152 dBc/Hz. Optical frequency inter-modulation between two picoseconds laser pulses was studied in [18] where Vampouille and the group presented a method which transfers a nearly linear frequency modulation of bandwidth 3.5 THz (or 0.32 nm around 0.53 μm) to a frequency doubled single pulse of duration 30 ps emitted from a mode-locked laser. The experimental setup includes one stage to shape the pulses by a passive spectral filter, another to self-modulate their phase by non dispersive propagation through a single-mode optical fiber, and a final stage to multiply the pulse complex amplitudes in a harmonic-generating crystal. Finally, concluded that the proposed System is able to modulate sub-nanosecond laser pulses according to a wide variety of laws of temporal phase modulations. Driscoll also analyzed Oscillator AM-to-FM noise conversion due to the dynamic frequency-drive sensitivity of the crystal resonator [19]. The analysis made of the potential effects of AM-to-FM noise conversion in quartz crystal oscillators as a result of the dynamic frequency-drive sensitivity of the crystal resonator. The 8
analysis also indicates that it is quite possible for the FM noise resulting from AMto-FM conversion in the crystal resonator to equal or exceed that due to the conversion of oscillator open loop phase noise to closed loop frequency noise. This is especially true in oscillators designed to exhibit low white phase noise (floor) levels by operating the crystal resonator at relatively high drive level. In addition, the analysis reveals that, for the same drive sensitivity, the relative degradation in FM noise level due to this effect is more severe at lower relative oscillator operating frequencies. Djen and Shah also analyzed Implementation of a 900 MHz transmitter system using highly integrated ASIC [20], A highly integrated single-chip inphase and quadrature (I/Q) modulator is implemented for low power mobile applications (AMPS, ADC, GSM). A quadrature carrier is generated internally without having an external phase shift network. Baseband signals can modulate these carriers directly in the 900 MHz range. A variable gain amplifier with good linearity performance is incorporated to meet tough digital cellular requirements for linear modulation. It could be seen that crystal locked FM using frequency doubler approach, this project
seeks to designing
microphone transmitting equipment operating in
parallel chains to ensure frequency stability by developing a simple and highly economical crystal oscillator that exhibits linear tuning[21] characteristics . The crystal is employed to operate at 49MHZ with the oscillator components accurately selected so that the tuned circuit operates at 98MHZ.
9
CHAPTER THREE 3.0
Methodology
3.1
Introduction
The design procedures of this project were divided into two main sections, the hardware and the software. 3.2
The Hardware Testing of the components:Resistor
For example, a 10KΩ resistor Colours:
Translating colour to codes,
1st
Brown
2nd
Black
3rd
Orange
4th
Gold
1st
=1
2nd
=0
3rd
= Multiplier = 3 = 103
4th
= Tolerance = ± 5
= 10 KΩ Evaluating with the ohmmeter
Selected Ohmmeter range on the Multi-meter
Placed the meter probes at the two end wires of the resistor
Read the indicated value. 10
Capacitors
Used RLC meter to measure the capacitance and compared the value to that indicated on the capacitor. RLC Meter type – FLUKE PM6303A Trimmer Capacitor
Selected capacitance on RLC meter
Held capacitor with meter probe
Varied capacitance from minimum value to maximum
Monitored meter readings and compared with manufacturers data
Inductor
Used RLC meter to measure value of inductance
Selected Inductance on meter
Connected meter probes to the two end of Inductor
Read out indicated value and compared value with manufacturers data
Varied Inductor and monitored reading on RLC meter and state.
Transistor Type Identification: By Ohmmeter
Selected Ohmmeter range on Multi-meter
Attach meter’s common probe (-) to the base of transistor (see
illustration below)
Held meter’s other probe(+) to the emitter and observed meter reading (Ω) = Infinity
11
Changed positive probe to the collector and again observed meter readings (Ω) = Infinity
Attached Instruments positive probe to the base
Held meter’s common probe (-) to the emitter and observed meter reading (Ω) = 25Ω
Changed common probe (-) to the collector and observed meter readings (Ω) = 25Ω
Ω
Ω
C B
C
B
Ω
E
Ω
Fig. 3.1 (a) Transistor Test Step One
E
Fig.3.1 (b) Transistor Test Step two
Transistor Lead Identification
Selected ohms range on the multi-meter
Attached one meter probe to one of transistor lead.
Connected the other probe to the other lead alternatively while observing the meter reading.
Maintained probe at the lead which produced a very low resistance value and took the other probe to the other two lead alternatively.
12
Microphone Dynamic Microphone:
Hooked the two leads of a milli-voltmeter to the microphone terminals.
With variable intensity of audio signal applied to the microphone, the milli-voltmeter reading was observed.
v mV
A.S
Fig. 3.2 Test Setup for Microphone Quartz Crystal Oscillator
Connected the microphone, Xtal and C.R.O. as shown.
Applied audio signal to microphone
Monitored signal trace on C.R.O.
MIC. A.S
Xtal
C.R.O
Fig. 3.3 Test Setup for Crystal Oscillator PCB Preparation
Drilled 1mm diameter holes on copper clad board for component mounting
Diluted 100gramms of etching powder into 0.5 litres of water at 50˚C
Mounted components on board 13
Marked out components joining with etch resistance marker pen.
Removed component from board
Place board in solution for 10 minutes.
Remove board from solution and cleaned out remaining unwanted copper.
Assembling
All components were mounted at their positions and soldered
Heat sink was used on transistors during soldering to prevent damaging due to heat.
Mounted Antenna on Mica box by an aluminum bracket brackets fastened with 3mm x 4mm screws and nuts and soldered to circuit with a 1.5mm 2 flexible cable.
Microphone was soldered on circuit via a 1.5 mm 2 and 10 cm long flexible cable and brought out of enclosure and left dangling for ease of positioning.
Two interlocking push button switched are mounted on enclosure and joined to circuit via a 1.5 mm 2 flexible cable.
Mica was cut into 20cmx14cmx10cm and held together by a 4mmx10cm screw and nut is the enclosure of the prototype.
Meanwhile, the prototype was first mounted on the breadboard and tested.
Complete system Testing
The setup was powered by a 9v cell, and switched on.
Placed about 5meters away from a radio receiver.
A receiver was tuned to 98MHz.
14
3.3
The Software
Multism and MATLAB will be use to simulate the entire design to conduct performance analysis. Such as:
The performance of the Audio Amplifier at difference frequencies and it is expected that as the frequency increases the gain of the amplifier increases
The performance of the Crystal Oscillator to produced the exact frequency
Selectivity of the design transmitter, this deals with the ability of the transmitter to select 98MHz at zero decibels.
15
CHAPTER FOUR 4.0
System Design, Development and Implementation
4.1
Component Selection and Measurement
Before starting this project, a lot of research was made based on the functioning of the circuit with respect to selection of the components.
Fig. 4.1 Diagram showing some components
As we all know, radio frequency is based on imagination. There is no doubt that the component used for resonant frequency is an imaginary element [22] known as joperators namely, XL and XC.
Impedance Z X = XL - XC Reactance
Resistance R
(4.1)
Fig. 4.2 Impedance Triangle
Impedance, 2
Z=
R + XL
16
2
(4.2)
Inductive reactance, X L
XL = 2fL
(4.3)
Where: XL is reactance in ohms ( ), f is frequency in hertz (Hz) and L is inductance in henrys (H).
Capacitive reactance, Xc Xc =
1
(4.4)
2 fC Where: Xc is reactance in ohms ( ), f is frequency in hertz (Hz) and C is capacitance in farads (F).
Components selection was also based on the Transition [23] frequency (F t). The Ft value determines maxi, frequency the gain of the transistor will be zero. And at this point the transistor cannot generates any signal, rather begin to give up a lot of heats. The second step was to analyze the transistors H EF for each transistors using digital multi-meter. The amount of current amplification is called the current gain,[24] symbol hFE. The HEF connector is also used to determine the type of transistor (NPN or PNP) in hand. Not all transistors have the same lead configuration. The figure below shows different type of transistors with three (3) terminal leads but with different connections.
17
Fig. 4.3 Diagram showing different types of transistors
Fig. 4.4 Circuit symbol for BJT Transistors
The leads are labeled base (B), collector (C) and emitter (E).These terms refer to the internal operation of a transistor but they are not much help in understanding how a transistor is used, so we just treat them as labeled. The leads [25] can be identified by using analogue or digital multi-meter. Basic analysis on Resistance depends on resistors in series or parallel as shown below
18
R = R1 + R2+… (Series)
(4.5)
Fig. 4.5 Resistors in Series
R = R1 × R2 / R1 + R2 (parallel)
(4.6)
Fig. 4.6 Resistors in parallel
Resistance of a resistor is measured using Ohmmeter. Most ohmmeters are built in Digital/ Analogue multi-meters. Secondly, resistance of a resistor can be determined by using resistance color code [26]. Now, series resistance is used to divide the apply voltage as shown in the main circuit diagram.
19
Fig. 4.7 Voltage Divider Network
To calculate V0, V0 = Vs × R2 /R1 + R2
(4.7)
Where: Vo is Output Voltage and Vs is the Supply Voltage. As you can see, the circuit made use of basic resistor theory to actually arrive to practicable values.
4.2
Block Diagram
The FM transmitter system can be superficially broken down into component illustrated in the figure 4.8 below. ANTENNA
MICROPHONE
A.F AMPLIFIER
FREQ. MODULATOR
CRYSTAL OSCILLATOR
FREQ. MULTIPLIER
POWER AMPLIFIER
Fig. 4.8 Block Diagram of Crystal Locked Bug FM Transmitter
For design and subsequent analysis, it is more appropriate to consider the system using the following models and sub-models. 20
Audio Module o
Microphone
o
Audio Signal Conditioning
Fm Transmitter o
FM Modulator
o
RF Amplifier
o
Antenna
The physical layout of this module is illustrated in Figure 4.9. The modules will be broken down and subsequently discussed throughout this document.
Fig. 4.9 Complete Circuit Diagram of the FM Transmitter
4.3
Audio Module
The Audio Module in the first stage of the FM transmitter that converts a voice audio signal to usable electrical signal. The Sub-modules are described in the following section.
21
XSC1
Ext Trig + _ B
A +
_
+
_
Fig. 4.10 Circuit Diagram for the Audio Amplifier
4.3.1 The Microphone
The microphone component of the system has one simple requirement – quality. If the microphone is low quality, the attenuation [27] and distortion may occur to a degree such that the resulting signal may be unrecoverable or unusable even before it undergoes any processing.
4.4
BF199 - NPN Medium Frequency Transistor BF199 is a high frequency transistor covering a wide range of unity gain up to
400MHz and at 200MHz; it has a unique low noise figure (ie. 4.5dB at IC= 5mA). The datasheet of BF199 has a complete electrical characteristic. To which the designer/engineer has no choice than to use in design calculations. 22
BF199 is intended for oscillators design and small signals amplifications. Internal bonding, that is base spreading capacitance, output/diffusion capacitance is so small that parasitic oscillations are minimal. The figure 4.11 below shows the pin connection and symbol of the BF199 medium frequency transistor.
Fig 4.11 Pin Connection and Symbol of BF199 Transistor
BF199 is an RF transistor featured for small signal amplifiers. The unity gain of this device is up t o 400MHz. Making the device available for TV receivers’ design and IF amplifiers design for community radios and SSB meters radios. The transition frequency is determined by the unity gain bandwidth. The D.C. gain hfe of 220 enables the device to be used in class A, classB and class C amplifiers [28]. High stability is guaranteed when used as buffer amplifiers in RF stage. BF199 is good for oscillators design and small signal amplification. The required scattering parameters enable the designer to design stable oscillator and amplifiers by using smith chart. The use of this device as modulator is a suitable choice, since the signal modulated will be purely (sinusoidal) electromagnetic waves.
4.4.1 Features
Low current (max. 25 mA)
Low voltage (max. 25 V).
23
4.4.2 Applications
Output stage of a vision IF amplifier.
However it’s difficult to come by these components i.e. hardly to find in Africa.
4.5
BC547- NPN General Purpose Transistor
BC547 is a medium gain, general-purpose transistor purposely for signal generation, audio amplifiers applications and low power consumptions. Usually the frequency is about 250MHz and is of 330. BC547 is a small signal general-purpose silicon transistor. D.C. gain and Fт of BC547 ensures wide usage. The figure 4.12 below shows the pin connection and symbol of the BC547 NPN General purpose Transistor.
Fig. 4.12 Pin Connection and Symbol of the BC547 NPN General Purpose Transistor
4.5.1 Features
Low current (max. 100mA)
Low voltage (max.65V). 24
4.5.2 Applications
General purpose switching and amplification
4.6
The Crystal
The crystal used here is 49MHz device while the components in the oscillator stage have been chosen so that the tuned circuit is operating at 98MHz.The way a crystal works is caused by its capacitance changing abruptly at the frequency marked on it. The only problem with identifying the frequency of a crystal is some crystals are marked with their third overtone value while others are identified with their fundamental frequency, For instance. 27MHz crystals for CB's, remote control cars and walkie talkies are generally 3rd overtone crystals and have a fundamental of about 9MHz while computer crystals are generally identified by their fundamental frequency.
4.7
The Modulator
The figure 4.13 and 4.14 below shows the basic principle of operation of a frequency modulator.
25
Fig. 4.13 Basic Frequency Modulator
XSC1 XFC1 Ext Trig +
123
_ B
A +
_
+
_
Fig. 4.14 Circuit Diagram for the Modulator
Before VHF sine wave radiates from an oscillatory circuit the entire reactance network must be in AC network. The reactance inductor and capacitor (LC) is connected such that it will course the transistor to switch ON and OFF in microseconds (μs). The time or period been controlled by LC time constant.
26
With these, the cycle is repeated over and over as long as the device is kept ON. The relation below determines the time:
(4.8)
Where: T is Period measured in seconds, L is Inductance and C is Capacitance.
(4.9)
where: F is Resonant Frequency. In the circuit L1 has 6 turns and has a diameter of 5.5mm and has a length of 4.5mm. Based on the formula for an air cored inductor:
or
(4.10)
Where: L1 is inductance in µH, r is radius of coil in inches, L is length of coil in millimeters (mm) and n the number of turns on coil.
Fig. 4.15 AC Impedance Network
27
The above sketches can be explained in this way, Re, R1 and R2 in fig. 4.16 provides D.C. bias characteristics by powering the transistor to operate. The resistors provide currents and voltages necessary to turn ON the transistor. However, the actual D.C. bias circuit is shown below:
Fig. 4.16 D.C Bias Circuit
Take Vbe to be 0.7v. From the base side of the transistor, R1 and R2 have a potential divider arrangement. So using
(4.11)
Base voltage, Vb can be calculated. Since the supply voltage Vcc is 9v then we can conclude that Vb = 4.5v because R1=R2 =27kΩ. Also using
(4.12)
Where IE =Ic, emitter resistor is calculated to be 680Ω.
28
4.8
Frequency Doubler
XFC1 XSC1
123 Ext Trig + _ B
A +
_
+
_
Fig. 4.17 Frequency Doubler Circuit
4.9
Circuit Diagram Description & Operation
FM microphone bug is a miniature FM wireless microphone transmitter of type “narrow band frequency modulation wireless microphone” (NBFMWM’s). It is
designed to monitor secret conversation, detect lies and use as public address cordless mic. Since the development of telephone for the past years, many experiments have been carried out to make communication simple and convenient. However the discovery of radio waves accelerated the development of telecommunication equipment. The theories were based on Prof. James Maxwell’s Equations. In this case there is no need to wire the entire community, society or even the whole country. Since this will involve a lot of money and telecom equipment /switches for installation. It is also true to say that the process involved is too tiresome and complicated.
29
Mounting poles and wiring from one place to another can also result in wrong connections. The only things left to discuss are the minor features like the 100n capacitors across the power rails. These are designed to tighten up the rails so that each of the stages works correctly without interfering with each other. This is especially important with the output stage as the transistor is connected directly across the rails via a very low resistance coil. The coil is only few turns of wire around a slug and appears to be almost a short circuit as far as the transistor is concerned. But at the frequency at which the circuit is operating, the coil becomes an inductor in which a voltage is developed across the turns. The characteristic of developing a voltage like this is one of the amazing features of impedance and it is the generation of this voltage that prevents excessive current flowing. How this occurs is very complex and will be discussed in another article but basically excessive current does not flow because it takes time for current to start to flow in an inductor and the transistor is only turned on for a very short period of time (up to
the
time
when
the
maximum
current
just
starts
to
flow).
The transistor then turns off and the current that was flowing in the coil has produced magnetic flux. This magnetic flux now collapses and produces a voltage across the turns of the coil. This voltage is of opposite sign to the supply voltage and can be of much higher amplitude and since the transistor is turned off, the only path for it; is to flow along the antenna lead. I know you are going to say the antenna does not form a closed circuit but when we are talking about high frequencies, energy is capable of flowing along a lead and in doing so it produces radiation to the air, called electromagnetic radiation or radio waves. This converts energy from the circuit into a radiated signal. The 100k resistor on the base of the output transistor is designed to turn the
30
transistor ON a small amount (about half) so that the signal from the 10p capacitor can modulate the transistor (turn it on and off). At 98MHz, the antenna lead appears to the output stage as a low impedance load and energy from the coil will readily flow into it and be converted to radiate signal as mentioned above. This is how energy from the battery passes through the output stage to the antenna.
4.9.1 Construction
Before starting this project one should have a fair degree of skill in assembly and soldering. After all, this is one of our more complex designs and one should start with something simple if you want to get the maximum understanding. However, the time will not permit me to go through all these boring details of construction. That knowing your resistor and capacitor codes, and components position on PCB boards. It is so because when working with high frequency projects such as FM transmitters, it is important to keep all the components as close to the board as possible due to leads inductance. This might change the characteristics of the circuit consequently results in poor performance. The characteristics of the circuit mainly comprise of ‘Tank circuit’ and corresponding
impedance matching circuits. Component Layout
Component layout for the circuit can either be PCB etched or PCB breadboard or Vero-board wiring. For PCB etching, provide a clean output RF power with little or no interference. The
lead inductance is reduced. For Vero-board, the wiring is done by soldering the leads of the component
together.
31
CHAPTER FIVE 5.0
Result and Discussion
5.1
Introduction
Performance analysis on audio signal at different frequencies i.e. at 4 KHz and 10 KHz.
5.1.1 Performance Analysis at 4 KHz
Fig. 5.1 Input and Output Frequency at 4 KHz
This is the graph showing the input and the output signals at 4 KHz. The blue color shows the input signal while the red color shows the output signal. With the input set at 13.841 mV, the output was 125.35 mV which shows the amplification of the input signal. 32
5.1.2 Performance Analysis at 10 KHz
Fig. 5.2 Input and Output Frequency at 10 KHz
This is the graph showing the input and the output signals at 10 KHz. The blue color shows the input signal while the red color shows the output signal. With the input set at 12.393 mV, the output was 110.200 mV which shows the amplification of the input signal. Comparing the two graphs, it shows that the two signals were amplified as expected. The frequency increases as the gain increase.
5.1.3 Performance Analysis of the 49 MHz Crystal Oscillator
At the output, we are measuring the frequency of the modulator and as well monitoring the output wave form. The result are shown below
33
Fig. 5.3 Diagram Showing the Crystal Oscillator and Output Wave form
The crystal oscillator analysis using Multism in figure 5.3 above produced the exact 49 MHz frequency as required.
34
5.1.4 Performance of the Frequency Doubler
Fig. 5.4 Frequency Doubler Waveform
After tuning to second harmonics, the frequency from the Crystal oscillator was doubled as shown in the graph above.
5.2
Selectivity
The ability of the transmitter to select exact frequency, if not it will cause interchannel cross talk in other networks.
35
Fig. 5.5 The Graph of Received Signal Against Frequency
After measuring the received signals at various levels, the received signal in decibel (dB) was plotted against frequency. The more the distance between the transmitter and the receiver, the signal level reduces. But when attenuation is zero, there is no loss and the frequency will be exactly 98 MHz.
5.3
Discussion
The board used in the project is the PCB board. The active and passive are switching device (transistor), inductors, capacitors and resistors. Occasionally, scaling of iron bit occurs and therefore has to be cleaned with sand paper and thinned. Obtaining the values of the inductors and setting values of the trimming capacitors is difficult. Also, variation in transistor parameters due to change in temperature stands as another difficulty. 36
5.4
Cost of Components and Labour Table 5.1
Parts List
PART NUMBER
QUANTITY
DESCRIPTION
COST (GH¢)
470Ω
1
½ Watts Resistor
0.6
680 Ω
2
½ Watts Resistor
0.6
1k Ω
1
½ Watts Resistor
0.6
10k Ω
2
½ Watts Resistor
0.6
27k Ω
4
½ Watts Resistor
0.6
47k Ω
1
½ Watts Resistor
0.6
100k Ω
1
½ Watts Resistor
0.6
1M Ω
2
½ Watts Resistor
0.6
3-30pF
2
Ceramic Disc Capacitor
2.0
10pF
1
Ceramic Disc Capacitor
2.0
15pF
1
Ceramic Disc Capacitor
2.0
27pF
1
Ceramic Disc Capacitor
2.0
47pF
1
Ceramic Disc Capacitor
2.0
120pF
1
Ceramic Disc Capacitor
2.0
1nF
1
Ceramic Disc Capacitor
2.0
22nF
2
Ceramic Disc Capacitor
2.0
100nF
4
Ceramic Disc Capacitor
2.0
49MHz Crystal
1
Xtal (Crystal)
100.0
BC547
4
NPN General Purpose
3.0
Bf199/2n5179
2
RF Transistor
3.0
Electret
1
Microphone
5.0
Transistor
Microphone 9V DC Battery
1
5.0
37
Mini
Slide
1
5.0
Antenna
1
4.0
Switch 17cm Wire Enamelld
3.0
Copper Wire Copper
Clad
1
5.0
1
4.0
6 yards
3.0
1
20.0
Board Soldering Iron Soldering
Lead
(60/40) Enclosure/Case
Total
181.8
= GH¢ 100.0
Cost of Labour –
Total Cost = GH¢ 281.8
The construction of a transmitter using doublers approach reduces the number of components and the cost of construction.
38
CHAPTER SIX 6.0
Conclusion and Recommendation
6.1
Conclusion
The performance analysis on the Audio Amplify shown in figure 5.1 and 5.2 respectively indicated that as the frequency increase the gain of the audio signal also increased with the scale divisions. The crystal oscillator analysis using Multism in figure 5.3 produced exact 49 MHz and the frequency doubler producing approximate frequency of 98 MHz in figure 5.4. In other to prevent inter-channel crosstalk of the Transmitter the selectivity analysis was done as shown in figure 5.5, interestingly, the filter employed after the simulation at zero attenuation selected the resting frequency of 98MHz frequency. This makes the design perfect as selectivity is the ability of the transmitter to transmit on the exact resting frequency. Finally, the analysis carried depicts the advantages of the Frequency Doubler technology for FM Transmitters far outweighs that of the PLL technology because inter-channel crosstalk is minimize as a result of perfect selectivity. 6.2
Recommendation
Communications Authorities do not tolerate interference in radio frequency because of unwanted signals detected at the receiver end. Interestingly, most cordless microphone employed by churches, musicians and public address systems somehow interferes with one another. Some FM broadcast transmitters do cause interference to each other though the frequency is locked with PLL circuitry. This is caused by self-oscillation within the transmitter amplifiers themselves and can be eliminated by adding bias circuit or grounding the power supply lines. This project is to keep the frequency of a transmitter stable by using crystal oscillator approach with minimal parts count. Self-oscillation is minimal due to the frequency doubling approach. The success of this project will definitely
39
encourage many young engineers to develop more of half-duplex systems for themselves as well as the nation.
40
REFERENCES
[1]
Rowan Gilmore, Les Besser, “ Practical RF Circuits design for Modern wireless systems”, Pearson Education, Inc, New Jersey, vol. II, Nov. 2002.
[2]
D.C. Green, “Electronics IV” Third Edition, Pearson Education, Inc, 1998.
[3]
C. Arcado, “Technical Standards and Operating Requirements for FM Broadcasting Stations”. Third Edition, Prentice Hall PTR, Philippines, 1991.
[4]
Paul Tobin, “ Pspice for Analog Communication”, First Edition, Artech House, Jan. 2009.
[5]
Theodore Rapport, “Wireless Communications” Second Edition, Pearson Education, Inc, New Jersey, 2002.
[6]
Devendra K, Misra., “ Radio Frequency and Microwave Communication Circuits Analysis and Desig” Second Edition, Wiley Interscience, pp. 7-10, 2004.
[7]
E. Roland, “ Phased-locked loops Design, Simulation and Applications”, Sixth Edition, Irwin/Mc Graw – Hill, Inc, New York, USA, 2007.
[8]
Kobayashi Kei, Yamada Hirofum, Itoh Hiroshi, Horiuchi Toshihisa, Matsushige Keizumi, “ Analog frequency Modulation Detector for Dynamic Force Microscopy”, Review of scientific instruments, IEEE, vol. 72, pp. 4383 – 4387, Japan, Dec., 2001.
[9]
G.T. Maker, A.I.Ferguson, “Synchronously pumped mod-locked dye laser pumped by a frequency-doubled mode-locked and Q-switched diode laser pumped Nd:YAG laser ”, Applied Physics Letters, IEEE, vol.55, pp. 525 – 527. UK. Aug., 1989.
[10]
Naicheng Shen., ErJun Zang, Jianping Cao chengyangli, “ Frequency Stabilization at 127 I 2 Doppler-broadened line Center near 532 nm using Nd: YVO4 Intra-cavity doubled lasers”, Quantum Dept., Nat. lust of Metrol, Beijing, pp. 465 – 466 Aug. 2002.
[11]
J.R. Ashley, F.M. Palka, “ Reduction of FM Noise in Microwave Diode Oscillators by cavity and injection stabilization”, IEEE Microwave Symposion Digest, pp. 94 – 95, May 1971.
[12]
H.J. Peppiatt, J.A. Hall, A.V. Mc Daniel, “ A low-Noise- C Oscillator using a Directional Coupler ” Microwave Theory and Technique, IEEE, pp. 748 – 752, vol. 16, Sep. 1968.
i
[13]
B. Bossard, S. J. Mehlman, and A. Newton, “ A Solid State, one-watt, Tunable Exciter for the 4.4-5.0 GC Communications Band ”, IEEE RCA Surface communications systems laboratories, pp. 3.3.1-1, Oct.,1963
[14]
C. Greiner, B. Boggs, T. Wang, and T.W. Mossberg, “ Laser frequency Stabilization by means of optical Self-heterodyne beat-frequency Control ”, Dept. pp. 242 – 243, May, 1998.
[15]
S. Wax, and M. Chodorow, “ Phase Modulation of a ring-laser gyro — part II: Experimental results”, Quantum Electronics, IEEE, vol. 8. pp. 352 -361, Mar. 1972.
[16]
S. Milki, T. Nyuji, S. Ninomiya, “Thin Radio Receiver by using PLL Synthesizer Digital tuning Techniques”, Consumer Electronics, IEEE, vol. 4, pp. 597-605, Aug. 1979.
[17]
M. Vanpouille, J. Marty, C. Freohly, “ Active Stabilization of Crystal Oscillator FM Noise at UHF using a Di electric Resonation”, Quantum Electronics, IEEE, vol.2. pp. 192-194, Jan 1986, USA.
[18]
V. Thompson, “Optical Frequency Inter -modulation between two pico-second laser pulses”, Photonic Society, IEEE, vol. 22.pp. 192-194, USA.
[19]
M. Driscoll, “Oscillator AM – to – FM Noise conversion due to the dynamic frequency – drive sensitive of the crystal resonator ”, Frequency Controlled Symposium, IEEE, pp. 672 – 676, United Kingdom.
[20]
W.S. Djen, P.M. Shah, , “Implementation of a 900 MHz Transmitter System using highly integrated ASIC”, Vehicular Technology conference, IEEE, vol.2, pp. 1341 – 1345, Jun. 1994, Canada.
[21]
Harry Kybett, Earl, Boysen, “ All New Electronic Self Teaching Guide”, Third Edition, pp. 241 – 256, Pearson Education , May 2006, USA.
[22]
Owen Bishop., “Understand Amplifiers”, Fourth Edition, Newners, an imprint of Butterworth – Heinemann, Dec. 2004, United Kingdom
[23]
K. Devendra, M. Misra, “ Radio Frequency and Microwave Communication Circuits”, Analysis and Design, Second Edition, John Wiley Interscience, pp. 7-10, 2004, Carlifornia, USA.
ii
[24]
M. David, H. Pozar, “ Microwave and RF wireless systems”, Third Edition, John Wiley and Sons companies, Inc, New York, USA, 2007.
[25]
John G. Proakis, Masoud Salehi, “Communication System Engineering ” Second Edition, Irwin/McGraw-Hill, an imprint of the Mcgraw-Hill Companies, Inc, New York, USA, 2002.
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Ian R. Sinclair , “ Audio and Hi-fi Hand book ”, Third Edition, Newness, an imprint of Butterworth – Heinemann, Oxford. UK 1998.
[27]
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[28]
A.B. Grebene, H.R. Camenzind, “ Phase Locking As a New Approach for Tuned Integrated Circuit”, ISSCC Digest of Technical papers, pp. 100 -101, Feb. 1969.
iii
GLOSSARY
FM
Frequency Modulation
MHz
Mega Hertz
Hz
Hertz
CB
Citizen Band
TV
Television
AF
Audio Frequency
PLL
Phase Lock Loop
PCB
Printed Circuit Board
RF
Radio Frequency
AM
Amplitude Modulation
MIC
Microphone
R
Resistor
C
Capacitor
L
Inductor
ECM
Electrets Condenser Microphone
JFET
Junction Field Effect Transistor
ADC
Analogue-to- Digital Converter
SPL
Sound Pressure Levels
dB
Decibel
SNR
Signal to Noise Ratio iv
AC
Alternating Current
VHF
Very High Frequency
Z
Impedance
Vb
Base Voltage
Ant.
Antenna
X
Reactance
C.R.O
Cathode Ray Oscilloscope
v
LIST OF FIGURES FIGURE
TITLE
PAGE
3.1
Transistor Test Step (a) and (b)
12
3.2
Test Setup for Microphone
13
3.3
Test Setup for Crystal Oscillator
13
4.1
Diagram showing some Components
15
4.2
Impedance Diagram
15
4.3
Diagram showing different type of transistor
16
4.4
Circuit symbol for BJT Transistor
16
4.5
Resistors in series
19
4.6
Resistors in parallel
19
4.7
Voltage Divider Network
20
4.8
Block Diagram of Crystal locked Bug FM transmitter
20
4.9
Complete Circuit Diagram of the FM Diagram
21
4.10
Circuit Diagram for the Audio Amplifier
22
4.11
Pin Connection and symbol of BF199 Transistor
23
4.12
Pin Connection and Symbol of the BC547 NPN General Purpose Transistor
24
4.13
Basic Frequency Modulator
26
4.14
Circuit Diagram for the Modulator
26
4.15
Ac Impedance Network
27 vi
4.16
DC Bias Circuit
28
4.17
Frequency Doubler Circuit
29
5.1
Input and Output Frequency at 4 KHz
32
5.2
Input and Output Frequency at 10 KHz
33
5.3
Diagram showing Modulator Frequency and output waveform34
5.4
Frequency Doubler Waveform
35
5.5
The graph of received Signal against Frequency
36
vii
LIST OF TABLES TABLE
TITLE
5.1
Part List
PAGE
38
viii
APPENDIX APPENDIX A – PCB LAYOUT
ix
APPENDIX B – CIRCUIT LAYOUT
x
