RESEARCH, DESIGN AND FABRICATION OF DIGITAL INFORMATION TRANSIMITER WORKING IN THE VHF BAND

List of FiguresFigure 2.1 Blog diagram of transmitter system...3 Figure 2.2 Diagram system...5 Figure 2.3 Diagram of operating circuit showing signal in time domain...6 Figure 2.4 Diagra

“I hereby declare that the work contained in this thesis is of my own and has not been previously submitted for a degree or diploma at this or any other higher education institution To the best of my knowledge and belief, the thesis contains no materials previously published or written by another person except where due reference or acknowledgement is made.”

Signature:………

SUPERVISOR’S APPROVAL

“I hereby approve that the thesis in its current form is ready for committee examination as a requirement for the Bachelor of Computer Science degree at the University of Engineering and Technology.”

Signature………

Foremost, I would like to express my deep and sincere gratitude to my supervisor

professor Bach Gia Duong for his continuous support of dissertation, for his motivation,

enthusiasm and immense knowledge His guidance has been of great value for me in all thetime of researching and writing of my thesis

My heartily thanks are due to Master Hoang Duc Long at the Research Center of

Electronics and Telecommunications for his invaluable help during the time I worked inthe laboratory

I would like to give my heartfelt thanks to all professors in University ofEngineering and Technology for their basic knowledge and dedicated guidance

Last but not the least, I owe my loving thanks to my family and my dear friendswho always encourage and being along with me

Sincerely,Van-The Nguyen

Currently high frequency technique is widely used in the field of communication.The wireless communications services are increasing powerful The deployment of thesetypes of communications in very high frequency band has become inevitable and essential.Especially boom in broadband communications to promote the exploitation of parallelfrequency channels in high frequency range that allow maximum usability bandwidth.Communications in high frequency bands have advantages in complex environments,especially where high-frequency waves transmitted directly between two parallel points ofcontact and communication through the ionosphere, in outer space In Vietnam,information transceiver system working VHF bands have a lot of important applications.Therefore, the study of information transceiver systems in the band VHF to understand thestructure, the transmission characteristics in order to master the technology to go tocomplete the set and apply the product on the fact that the purpose end of the study In theframework of this thesis, I have completed the following tasks:

-Study about the structure of transmitter system

-Study carefully VCO block in the transmitter system

-Study about delta modulation

-Design and fabricate successfully VCO circuit in VHF band and delta modulatecircuit

TABLE OF CONTENTS

AUTHORSHIP i

SUPERVISOR’S APPROVAL ii

ACKNOWLEGEMENT iii

ABSTRACT iv

TABLE OF CONTENTS v

List of Figures vii

List of Table ix

ABBREVATIONS x

Chapter 1 INTRODUCTION 1

1.1,Overview of VHF frequency band 1

1.2 Propagation characteristics 1

1.3 Thesis objectives and structure 1

Chapter 2 THE STRUCTURE OF TRANSMITTER 3

2.1Blog diagram of transmitter 3

2.1.1 Function of modules in the system 3

2.2 Voltage-controlled oscillator 5

2.3 Three-point oscillator 6

2.4 Capacitive three-point circuit 8

Chapter 3 CONTINUOUSLY VARIABLE SLOPE DELTA MODULATION 11

3.1 General 11

3.2 General descriptions 12

3.2.1 Delta Modulation 12

3.2.2 CVSD Converter 12

3.3.Detailed descriptions 13

3.3.1 Input Band Pass Filter 13

3.3.2 Comparator 13

3.3.5 Syllabic Filter 14

3.3.6 Pulse Amplitude Modulator 14

3.3.7 Reconstruction Integrator 14

3.3.8 Output Low-Pass Filter 14

3.3.9 Typical CVSD Decoder Output Envelope Characteristics 14

3.4 Reference Level 15

3.5 CVSD Characteristics 15

3.5.1 Input and Output Impedances 15

3.5.2 Data Signaling Rates 16

3.5.3 Input and Output Filters 16

3.5.4 Overload Algorithm 16

3.5.5 Compression Ratio 16

3.5.6 Syllabic Filter 16

3.5.7 Reconstruction Integrator Time Constant 16

3.5.8 Analog-to-Digital Conversion 16

3.5.9 Digital-to-Analog Conversion 16

3.5.10 CVSD Converter Performance 17

5.10.4 Variation of Gain With Input Level 19

5.10.5 Idle Channel Noise 20

5.10.6 Variation of Quantizing Noise With Input Level 20

5.10.7 Variation of Quantizing Noise With Frequency 21

Chapter 4 EXPERIMENT AND RESULTS 23

4.1 Design and fabricate VCO using 2SC3355 23

4.2 Results and discussion 26

4.3 Delta Modulation 30

4.3.1 Brief descriptions 30

CHAPTER 5 35

CONCLUSION 35

5.1 Thesis Summary 35

5.2 Future works 35

References 36

List of Figures

Figure 2.1 Blog diagram of transmitter system 3

Figure 2.2 Diagram system 5

Figure 2.3 Diagram of operating circuit showing signal in time domain 6

Figure 2.4 Diagram of feedback circuit 6

Figure 2.5 Diagram of general 3-point circuit oscillators 7

Figure 2.6 Capacitive three-point oscillator circuit 8

Figure 2.7 a VCO Colpitts parallel tuning 10

Figure 3.1 Typical CVSD encoder 11

Figure 3.2 Typical CVSD decoder 11

Figure 3.3 Typical Envelope Characteristics of the Decoder Output Signal for CVSD 15

Figure 3.4 Interface Diagram for CVSD Converter 17

Figure 3.5 Insertion Loss vs Frequency for CVSD (16 kbps) 18

Figure 3.6 Insertion Loss vs Frequency for CVSD (32 kbps) 19

Figure 3.7 Variation of Gain With Input Level for CVSD (16 kbps) 19

Figure 3.8 Variation of Gain With Input Level for CVSD (32 kbps) 20

Figure 3.9 Signal to Quantizing Noise Ratio vs Input Level for CVSD (16 kbps) 21

Figure 3.10 Signal to Quantizing Noise Ratio vs Input Level for CVSD (32 kbps) 21

Figure 3 11 Signal to Quantizing Noise Ratio vs Frequency for CVSD (16 Kbps) 22

Figure 3.12 Signal to Quantizing Noise Ratio vs Frequency for CVSD (32 Kbps) 22

Figure 4.1 Gain of 2SC3355 23

Figure 4.2: Calculate the value of Oscillate Tank 24

Figure 4.3:Complete diagram 25

Figure 4.4 Layout of VCO 26

Figure 4.5 Fabricated VCO circuit using 2SC3355 26

Figure 4.6 Measure the results 27

Figure 4.7 VCO at 117.56 MHz 27

Figure 4.8 VCO at 134 MHz 28

Figure 4.9 VCO at 161 MHz 28

Figure 4.10 The output frequency versus voltage 29

Figure 4.13 Delta modulation circuit 33 Figure 4.14 Measure the results 34 Figure 4.15 Delta signal 34

List of Table

Table 2.1 Block’function 5

Table 3.1 Decoder Reference Digital Patters for CVSD 17

Table 3.2 Insertion Loss Limits for CVSD 18

Table 3.3 Idle Channel Noise Limits for CVSD 20

Table 4.1 Changing of frequency under the adjustment of voltage 29

Chapter 1 INTRODUCTION

1.1,Overview of VHF frequency band

Very high frequency(VHF) is the ITU-designated range of radio frequencyelectromagnetic waves from 30 MHz to 300 MHz,with corresponding wavelengths of one

to ten meters.Common uses for VHF are FM radio broadcasting ,televisionbroadcasting,land mobile stations,long range data communication up to several tens ofkilometres with radio modems,amateur radio, and marine communications.Air trafficcontrol communication and air navigation systems work at distances of 100 kilometres ormore to aircraft at cruising altitude

1.2 Propagation characteristics

VHF propagation characteristics are ideal for short distance terrestricalcommunication,with a range generally somewhat farther than line of sight from thetransmitter.Unlike high frequency(HF),the ionosphere does no usually reflect VHF waves

so transmissions are restricted to the local radio horizon less than 100 miles.VHF is alsoless affected by atmospheric noise and interference from electrical equiqment than lowerfrequencies.While it is blocked by land features such as hills and mountains,it is lessaffected by buildings and can be received indoors,although multipath television receptiondue to reflection from buildings can be a problem in urban areas

1.3 Thesis objectives and structure.

In this thesis,I will clarify the roles and the need of a information digital transmitter

in VHF band Study the function of each block in a transmitter system and especially aVCO block will be studied.Study about delta modulation Finally, the experience is design,fabricate a VCO and delta modulation using FX609J.This thesis is organized in fivesections:

-Chapter 1:Provide an overview of VHF frequency band,propagation characteristicand objectives and structure of this thesis

-Chapter 2: Study in detail about VHF transceiver system and VCO block

-Chapter 4: Design, Fabrication a VCO circuit,delta modulation circuit andachievement results.

-Chapter 5: Summarization what have been done in the thesis

Chapter 2 THE STRUCTURE OF TRANSMITTER

2.1Blog diagram of transmitter

Figure 2.1 Blog diagram of transmitter system 2.1.1 Function of modules in the system

Adding two input signals to produce amicro wave signal

Upconversion

A driver amplifier can be simply considered as

a driver (to amplify power) that is capable ofproviding sufficient current (power) to drive thefollowing stage of the circuit

The maximum output power at transmitters is1W with the assumption 2 antennas in the light

of sigh the transmission distance can be 10km

A voltage-controlled oscillator or VCO

is an electronic oscillator whose oscillationfrequency is controlled by a voltage input Theapplied input voltage determines theinstantaneous oscillation frequency

Low-noise amplifier (LNA) is anamplifier which located very close to thereceiver to reduce losses in the feed line Itsmain function is amplifying the weak signal atthe receiver with suitable gain and adding verylittle noise

The nature of downconversion is thesame with upconversion, the difference is inputsignal and the position in system If theupconversion be used in transmitter,downconversion is inversely at the receiver.The microwave signal go through this blockwill turn into intermediate signal IF carry theinformation

Accepts the intermediate frequencysignal from the converter, amplify and passsignal on to either, the next stage (if the receiverhas one), or to the detector stage

Detect the desire signal

The function of an audio amplifier is toamplify signal without making any otherchanges in it before playing in the speaker

Speaker: used to play the sound

Antenna: transmit or receive signal

Table 2.1 Block’function

2.2 Voltage-controlled oscillator

A voltage-controlled oscillator or VCO is an electronic oscillator whose oscillationfrequency is controlled by a voltage input.The applied input voltage determines theinstantaneous oscillator frequency.Consequently,modulating signals applied to controlinput may cause frequency modulation (FM) or phase modulation (PM).A VCO may also

be part of phase-locked loop

*The basic parameter of oscillator

+ Resonant frequency

+ The amplitude of the output voltage

+ The stability of output frequency

+Output power

+ Circuit performance

*The output signal can be created by two principles

+Using amplifier circuit with positive feedback

+Using circuit analysis method

*A good oscillator circuit has to satisfy

+Condition of amplitude stability

+Condition of phase stability

Figure 2.2 Diagram system

The rate of output to input voltage:

Figure 2.3 Diagram of operating circuit showing signal in time domain.

Figure 2.4 Diagram of feedback circuit

When K 

the circuit will oscillates

The equation above can be written more detail:

Figure 2.5 Diagram of general 3-point circuit oscillators

Oscillator circuit LC has 3 common points between resonant tank and the circuit so

we call it is 3-point circuit oscillators The positive feedback is implemented through theinductor or capacitor First, we consider the general principle as the diagram in Figure 2.5Where Z1, Z2, Z3 are the element of the serial resonant circuit system with:

Condition (3) will be:

Z Z Z

Z

Z Z

Z Z

Z Z Z K

3 2 1

3 2 2

1 2 3

2 1

2 1

X X S

K

3 2 1 3 2 1

XSX

3 2 1

2.4 Capacitive three-point circuit

Figure 2.6 Capacitive three-point oscillator circuit

In Capacitive three-point circuit, we have X1 = XCB = L > 0

1

- input resistance of transistor to resonant tank

The condition (3) becomes:

ehneh

When the oscillation is established n will receive the value of n1 or n2

The resonant frequency will be:

CC

The operating frequency of circuit:

ω2L=[1/(C2+Cvar)]+(1/C3)+(1/C4)

Figure 2.7 a VCO Colpitts parallel tuning

Chapter 3 CONTINUOUSLY VARIABLE SLOPE

DELTA MODULATION

3.1 General

The continuously variable slope delta(CVSD) modulation is a nonlinear,sampleddata,feedback system which accepts a band-limited analog signal and encodes it intobinary form for transmission through a digital channel.At the receiver,the binary signal isdecoded into a close approximation of the original analog signalA typical CVSD converterconsisting of an encoder and decoder is show in Figure3.1,Figure3.2

Figure 3.1 Typical CVSD encoder

Figure 3.2 Typical CVSD decoder

3.2 General descriptions

3.2.1 Delta Modulation

Delta modulation is an A-D conversion technique resulting in a form of digitalpulse modulation A delta modulator periodically samples the amplitude of a band-limitedanalog sinal and the amplitude differences of two adjacent samples are coded into n bitcode words.This nonlinear,sampled-data feedback system then transmits the encoded bitstream through a digital channel.At the receiver end ,an integrating network converts thedelta-modulated bit stream through a decoding process into a close approximation of theorginal analog signal

3.2.2 CVSD Converter

A typical CVSD converter consists of an encoder and a decoder(see Figure 3.1 andFigure 3.2).The analog input signal of the CVSD encoder is band-limited by the inputband,pass filter.The CVSD encoder compares the band-limited analog input signal with ananalog feedback approximation signal generated at the reconstruction integrator output.Thedigital output signal of the encoder is the output of the first register in the counter.thedigital output signal is transmitted at the clock(sample) rate and will equal”1” if the analoginput signal is greater than or equal to the analog feedback signal at the instant of thesampling.For this value of the digital output signal,the pulse amplitude modulator(PAM)amplies a positive feedback pulse to the reconstruction integrator;otherwise a negativepulse is applied.This function is accomplished by the polarity control signal,which is equal

to the digital encoder output signal.the amplitude of the feedback pulse is derived bymeans of a 3 bit shift register,logic sending for overload and a syllabic lowpass filter.When

a string of three consecutive ones ar zeros appears at the digital output ,a discrete voltagelevel is applied to the syllabic filter,and the positive feedback pulse amplitude increasesuntil the overload string is broken.In such an event,ground potential is fed to the filter bythe overload algorithm,forcing a decrease in the amplitude of the slopevoltage out of thesyllabic filter.the encoder and decoder have identical characteristics except for thecomparator and filter functions

The CVSD decoder consists of the input band pass filter, shift register, overloadalgorithm, syllabic filter, PAM and reconstruction integrator used in the encoder, and an

through the low-pass filter Other characteristics optimize the CVSD modulation techniquefor voice signals These characteristics include the following.

+ Changes in the slope of the analog input signal determine the step-size changes ofthe digital output signal

+ The feedback loop is adaptive to the extent that the loop provides continuous orsmoothly incremental changes in step size

+ Companding is performed at a syllabic rate to extend the dynamic range of theanalog input signal

+ The reconstruction integrator is of the exponential (leaky) type to reduce theeffects of digital errors

3.3.Detailed descriptions

3.3.1 Input Band Pass Filter

The input filter provides band-limiting and is typically a second- or higher-orderfilter

3.3.2 Comparator

The comparator compares the band-limited analog input signal from the filter withthe output signal of the reconstruction integrator This comparison produces the digitalerror signal input to the 3-bit shift register The transfer characteristic of the comparator issuch that the difference between the two input signals causes the output signal to be driven

to saturation in the direction of the sign of the difference

3.3.3 Bit Shift Register

The 3-bit shift register acts as a sampler which clocks the digital error signal fromthe comparator at the specified data signaling rate and stores the current samples and twoprevious samples of the error signal The digital output signal is a binary signal having thesame polarity as the input signal from the comparator at the time of the clock signal Thedigital output signal is also the digital output of the encoder and is referred to as thebaseband signal Further processing for transmission such as conditioned diphasemodulation may be applied to the baseband signal It is necessary that the inverse of anysuch processing be accomplished and the baseband signal restored before the CVSDdecoding process is attempted