ahmad fitry bin kamaruzaman 30 may 1987 the establishment of the ...

AHMAD FITRY BIN KAMARUZAMAN
30 TH MAY 1987
THE ESTABLISHMENT OF THE REFRACTIVE INDEX
PROFILE FOR PROPAGATION STUDIES
2009/2010 II
√
870530 – 56 – 5279 ASSOC. PROF DR. JAFRI BIN DIN
1 ST MAY 2010 1 ST MAY 2010

DECLARATION
“I hereby declare that I have read this thesis and in my opinion this thesis is sufficient in
terms of scope and quality for the award of the degree of Electrical-Telecommunication
Engineering”
Signature : ....................................................
Name of Supervisor: ASSOC. PROF. DR. JAFRI BIN DIN
Date : MAY 2010

THE ESTABLISHMENT OF THE REFRACTIVE INDEX PROFILE FOR
PROPAGATION STUDIES
AHMAD FITRY BIN KAMARUZAMAN
A thesis submitted in partial fulfillment of the
requirements for the award of the degree of
Bachelor in Electrical Engineering (Telecommunication)
Faculty of Electrical Engineering
Universiti Teknologi Malaysia
MAY 2010

ii
DECLARATION
“I declare that this thesis entitled “The Establishment of The Refractive Index Profile For
Propagation Studies” is the result of my own project except as cited in the references. The
project report has not been accepted for any degree and is not concurrently submitted in
candidature of any other degree”
Signature : ....................................................
Name
: AHMAD FITRY BIN KAMARUZAMAN
Date : MAY 2010

iii
To Mak and Abah, Family, Friends,
And
To my supervisor
Thank You For Everything

iv
ACKNOWLEDGEMENT
First of all, I would like to express my deepest appreciation to my project
supervisor, Associate Professor Dr. Jafri bin Din for giving his insights and advices, and
also the one who guide me until I am successful in completing this project.
My appreciation also goes to my parents and family members who are consistently
giving supports and encouragement to me for all these years.
Finally, to my beloved colleagues who are also very supportive and helping me
during hard times. It has been a great experience by knowing all of you.

v
ABSTRACT
The refractive index is the important parameter that influences the propagation of
the electromagnetic waves during clear-sky conditions. It is largely depends on atmospheric
profile behavior which consists of temperature, atmospheric pressure and relative humidity.
Therefore, the purpose of this project is to observe the variability of the atmospheric profile
with altitude and computing the refractive index profile of the propagation medium based
on the atmospheric profile data. The project involves two main parts which are calculation
analysis part and hardware development part. The calculation analysis part is to obtain the
atmospheric profile and refractive index profile through the ITU-R Recommendation
Standards. Then, the hardware development is purposely done to measure the atmospheric
profile since the atmospheric profile database provides by the meteorological station only
covered specific location and it was used to represent the profile for the whole country.
Hence, the data collected by the hardware will be used in refractive index profile
computation for the particular range of area. It is an alternative to obtain better resolution of
the data collected compare with the database of the station. Finally, the results based on
measurement will be compared with the results based on calculation analysis to see the
deviations between those two. The results shown that the atmospheric profile particularly
temperature vary with altitude at the lower tropospheric region. The profile also affected by
the diurnal factor which made the difference in the profiles during day and night. Hence, it
brought the same effect towards the refractive index profile.

vi
ABSTRAK
Indeks biasan merupakan sebuah parameter penting yang mempengaruhi manamana
perambatan gelombang elektromagnet ketika keadaan langit cerah (clear-sky
condition). Kandungan indeks biasan bergantung kepada kalakuan profil atmosfera iaitu
kandungan suhu, tekanan atmosfera, dan kelembapan relatif. Oleh itu, tujuan projek ini
adalah untuk melihat bagaimana perubahan profil atmosfera ini dengan ketinggian dan
menggunakan profil atmosfera tersebut untuk mengira dan membentuk profil indeks biasan.
Umumnya, projek ini terdiri daripada dua bahagian di mana bahagian pertama adalah
analisis pengiraan dan yang kedua adalah pembangunan alat pengukuran. Analisis
pengiraan adalah bertujuan untuk mewmperoleh profil atmosfera dan profil indeks biasan
melalui piawaian yang telah ditetapkan ITU-R. Sementara itu, pembangunan alat
pengukuran dibuat untuk mengukur profil atmosfera dalam kawasan tertentu kerana data
yang dikumpul di stesen-stesen meteorologi hanya meliputi sebahagian kawasan-kawasan
tertentu sahaja dan digunakan untuk mewakili profil untuk seluruh negara. Justeru itu, data
yangt diperoleh oleh alat pengukur tersebut akan digunakan untuk mengira profil indeks
biasan. Penggunaan alat pengukuran ini merupakan suatu alternatif untuk mendapatkan
resolusi data yang lebih baik berbanding dengan data daripada stesen meteorologi.
Akhirnya, keputusan berdasarkan maklumat pengukuran akan dibandingkan dengan
keputusan berdasarkan analisis pengiraan demi untuk melihat perbezaan antara keduanya.
Keputusan yang diperoleh menunjukkan bahawa profil atmosfera dipengaruhi oleh faktor
‘diurnal’dimana terdapat perbezaan profil diantara siang dan malam. Justeru, hal ini akan
membawa kesan yang sama dalam pengiraan profil indeks biasan.

vii
CONTENTS
CHAPTER TITLE PAGE
TITLE
DECLARATION
DEDICATION
ACKNOWLEDGEMENT
ABSTRACT
CONTENTS
LIST OF FIGURES
LIST OF TABLES
LIST OF ABBREVIATIONS
LIST OF APPENDICES
i
ii
iii
iv
v
vii
xi
xiii
xiv
xv
1 INTRODUCTION 1
1.1 Overview 1
1.2 Problem Statement 2
1.3 Objectives 2
1.4 Scope of Project 3
1.5 Outline of Thesis 3

viii
2 LITERATURE REVIEW 4
2.1 Introduction 4
2.2 Radiowave Propagation 5
2.3 Modes of Radiowave Propagation 5
2.3.1 Groundwave Propagation 6
2.3.2 Spacewave Propagation 6
2.3.3 Skywave Propagation 7
2.4 Electromagnetic Wave Propagation In A Medium 7
2.5 Propagation Loss 9
2.6 Atmospheric Layers 10
2.7 Refraction In The Atmosphere 11
2.8 Refractivity, N and Refractive Index, n 13
2.8.1 Vertical Refractivity Gradient 13
2.9 Refractive Index Measurement 14
2.9.1 ITU-R Recommendation Standards
2.9.2 Refractive Index Computation Based On
ITU-R Recommendation
2.9.3 Refractive Index Computation Through
Atmospheric Profile Measurement
15
16
18
2.10 Research History on Refractive Index Equation 19
2.11 The Effects of Refraction 20
2.11.1 Ray Bending 20
2.11.2 Propagation In Ducting Layers 22

ix
3 METHODOLOGY 25
3.1 Introduction 25
3.2 Calculation And Analysis of Refractive Index Profile 25
3.2.1 Equation-based Atmospheric profile
Calculation
3.2.2 Equation-based Refractive Index profile
Calculation
3.2.3 Determination of Atmospheric Profile and
Refractive Index Profile Based on
Measurement
26
26
27
3.3 Hardware Design and Developmetn 27
3.3.1 5V Power Supply 28
3.3.2 Microcontroller PIC16F877A 29
3.3.2.1 Analog-to-Digital Input/Output 31
3.3.3 Temperature Sensor 33
3.3.3.1 Sensor Absolute Maximum Ratings 35
3.3.4 RF Module Transceiver 35
3.3.4.1 Serial Communications 39
3.4 Measurement Setup and Data Collection 40
3.4.1 Controllable Rope 42
3.4.2 Launching From High Place 44
3.4.3 Mechanical Structure 47
3.5 Software Implementation 49
3.5.1 Algorithm and Programming in MikroC
Compiler
49

x
4 RESULTS AND DISCUSSION 52
4.1 Introduction 52
4.2 The Results of the Equation-Based Atmospheric
Profile
4.3 Results of Equation-based Refractive Index Profile
Calculation
4.4 Results of Atmospheric Profile and Refractive Index
Profile Based on Measurement
4.5 Comparison between Theoretical and Measured
Temperature Values
4.6 Comparison between Theoretical and Measured
Refractive Index
52
55
57
60
63
5 CONCLUSION 66
5.1 Conclusion 66
5.2 Future Works and Recommendations 67
5.2.1 Hardware Advancement 67
5.2.2 Measurement Method 67
5.2.3 Measurement Readings 68
5.3 Summary 69
REFERENCES 70
APPENDICES 73

xi
LIST OF FIGURES
FIGURE NO. TITLE PAGE
2.1 Spacewave signal propagation 6
2.2 Skywave signal propagation 7
2.3 Ionospheric Layers in the Atmosphere 11
2.4 Temperature and Pressure Profiles in the
Atmospheric Layers
13
2.5 The Traditional Abbe Refractometer 15
2.6 Sensors of temperature, pressure and humidity used
in the measurement
18
2.7 Ray Bending Towards Earth Surface 21
2.8 Ducting Effect on the Radiowave 22
3.1 Integrated Circuit (IC) LM7805 28
3.2 Schematic Circuit of the +5V Power Supply 29
3.3 Pin Diagram of the PIC16F877A 31
3.4 The ADCON0 Register 32
3.5 IC LM35 Temperature Sensor 34
3.6 XBee and XBee PRO OEM RF Modules 36
3.7 Schematic Diagram of the Connections between
LM 35 Sensor, PIC16F877A and XBee Starter Kit
38

xii
3.8 The Parts of the Measurement Hardware 39
3.9 USART Data Packet 0xIF as Transmitted Through
the RF Module
40
3.10 The Measurement Setup Diagram 41
3.11 Hardware Setup before Measurement 41
3.12 The Illustration of the Controllable Rope Method 42
3.13 Flow Chart of the First Method, Controllable Rope 43
3.14 Flow Chart of the Second Method, Launch from
High Place
37
3.15 The Illustration if we launched from High Place 45
3.16 The Hardware Launched From High Place 45
3.17 Retrieving the Hardware After Arrive at the Ground 46
3.18 Example of the Received Data at X-CTU Software
in Hexadecimal Form
46
3.20 Front View of the Structure 47
3.21 Upper View of the Structure 48
3.22 Side View of the Structure 48
3.23 The Nylon Parachute 49
3.24 Flow chart of microcontroller’s main program 51
4.1 Graph of Measured Temperature vs. Theoretical
Temperature at Day Time
4.2 Graph of Measured Temperature vs. Theoretical
Temperature at Night Time
4.3 Graph of Measured Refractive Index vs. Theoretical
Refractive Index at Day Time
4.4 Graph of Measured Refractive Index vs. Theoretical
Refractive Index at Night Time
62
62
65
53

xiii
LIST OF TABLES
TABLE TITLE PAGE
3.1 Port Connection of PIC16F877A with Other Parts of 30
the System
3.2 Maximum Ratings of LM35 35
3.3 Some Specifications of the XBee OEM RF Module 37
4.1 Theoretical Atmospheric Profile at its Respective
54
Altitude
4.2 The Theoretical Refractivity Data, N and Refractive 56
Index Profile, n
4.3 Measured Temperature Results – Day and Night 58
4.4 Refractivity Data and Refractive Index Value Based
On Measured Temperature Results
59

xiv
LIST OF ABBREVIATIONS
BER - Bit-error-rate
EM - Electromagnetic
LOS - Line-of-sight
ITU - International Telecommunication Union
ITU-R - International Telecommunication Union -
Radiocommunication
CCIR - International Radio Consultative Committee
AP - Anomalous Propagation
ADC - Analog-to-Digital Converter
m - Meter
km - Kilometer
RF - Radio frequency
PAN - Personal Area Network
DSSS - Direct Sequence Spread Spectrum
TX - Transmitter
RX - Receiver
GHz - Gigahertz

xv
LIST OF APPENDICES
APPENDIX
TITLE
A - Project Schedule for FYP1 and FYP2
B - Sample Atmospheric Data Obtained From
National Meteorological Station
C - PIC16F877A Program Coding

CHAPTER 1
INTRODUCTION
1.1 Overview
Performance and reliability of microwave links depends mostly on the quality of
the propagation of electromagnetic waves between the transmitter and receiver [2]. The
quality of the propagation will depends on the transmission media that largely affected
by natural conditions such as daily weather. Bad propagation condition will lead to
various disadvantages for example, the increasing of signal distortion and severity of
error through the increment of bit-error-rate (BER).
Propagation is always associated with absorption and interference. Those two
factors are crucial for radio communication link budget. There is one type of fade,
called as the interference fades. Interference fade can caused the multipath fading
phenomena which largely influenced by the bending of electromagnetic waves in the
atmosphere.
The electromagnetic wave bending occurs due to the variation of refractive
index profile. The refractive index profile plays an important factor along the ground

2
layer of the atmosphere which is the troposphere. In troposphere region, there are
atmospheric profiles that influence the refractive index profile. Those atmospheric
profiles are temperature, pressure and relative humidity. Atmospheric profiles can be
measured at every altitude using various methods.
The calculation and analysis of the characteristics of refractive index profile will
be important since it is vital for the predictions of the probability of multipath fading
during clear sky conditions.
1.2 Problem Statement
It is important to have a good understanding on refractivity and the refractive
index profile to design the best radio communication networks since such system
performance depends on the refractive index profile through the quality of propagation
of electromagnetic (EM) waves.
1.3 Objectives
To compute the refractive index of the propagation medium based on the
atmospheric profile measurement for microwave links propagation studies and
investigate the variability of the atmospheric profile with altitude.

3
1.4 Scope of Project
The scope of this project will focused on the analysis of the refractive index
profile in the area of Kolej Perdana, Kolej Tuanku Canselor and Faculty of Electrical
Engineering, Universiti Teknologi Malaysia Skudai. All project findings will be applied
for ground wave propagation studies and further investigation regarding the
trospospheric refraction effects towards wave propagation. The scope of work for this
project is as follows:
i. Calculation and analysis of the refractive index
ii. Based on the results, the measurement hardware will be developed
iii. After the hardware development is completed, the measurement will be taken
1.4 Outline of Thesis
This thesis will consist of five main chapters:
i. Introduction
ii. Literature Review
iii. Methodology
iv. Results and Findings
v. Conclusion
As we proceed throughout the chapters, we will get to know what is actually
being done in this project and what is the goal at the end of this project.

CHAPTER 2
LITERATURE REVIEW
2.1 Introduction
Good understanding regarding the radio wave propagation is very important in
order to co-exist with the development of the radio communication service. As the radio
communication technology increased day by day, the requirement of the radio wave
spectrum or the frequency become more and more crucial. Therefore, a systematic
implementation in organizing the frequency spectrum needs to be done.
In designing a radio communication link, a good estimation and investigation of
the path parameters must be done in terms of its radio propagation model based on the
radio refractive index. The radio refractive index will depends on the altitude range of
the troposphere where it could be related with the radio communication distance.

5
2.2 Radio Wave Propagation
Propagation is a research on the behavior of a signal wave where it will
propagate physically through a medium. Signal wave or radio wave is consisting of
electromagnetic wave components (E-plane and H-plane). The propagation medium
could be anything but for wireless communication system, the medium will be freespace.
Free space propagation medium is commonly applied for long distance
communication.
During propagation, the electromagnetic signal will be refracted while
propagating through different layer of the atmosphere which had different density. The
lowest atmospheric layer will have low air density as the altitude increase thus
refraction occurs and the radio wave will bend towards earth surface and depends on the
communication path distance. The farther the communication distance, the bending
phenomena will be more crucial.
2.3 Modes of Radio Wave Propagation
There are three basic modes of propagation, which are ground wave, space
wave, and sky wave propagation. Mainly, the frequency wave will determine the
performance of propagation modes. The signal wave propagates are closely related to
the shape of the wave, earth surface atmospheric condition, diurnal or seasonal factors.
The activity in the sun could also give huge contribution towards signal
propagation such as the sunspot which can disturb the communication by disorienting
the pattern of the propagation in the common atmosphere or by giving noise and
interference.

6
2.3.1 Ground Wave Propagation
Ground wave is a kind of radio wave that travels along the earth surface. This
mode of propagation is limited for short range terrestrial communication. The main
factor that could give affect towards the ground wave propagation is the earth surface
characteristic or behavior such as hilly terrain or high mountains. This factor is the main
cause for the signal to attenuate.
As the frequency of the signal increase, the loss and attenuation will become
more severe in this mode of propagation. Therefore, this ground wave is suitable for
frequency below than 2MHz.
2.3.2 Space Wave Propagation
Space wave propagation consists of direct wave and reflected wave. The direct
wave will travel in the line-of-sight (LOS) path between the transmitter and the receiver
antenna and it is limited to that range only.
Figure 2.1: Spacewave Signal Propagation [20]

7
2.3.3 Sky Wave Propagation
Sky wave propagation is devoted for long distance communication. The wave is
not dedicated directly towards the recipient antenna but it shoots direct to the sky, then
reflected and refracted to the earth surface and reflected back to the sky until it arrives at
the receiver. This mode of propagation uses the ionosphere as a medium to propagate
the signal wave for establishing the communication around the world.
Figure 2.2: Skywave Signal Propagation [20]
2.4 Electromagnetic Wave Propagation in a Medium
As we all know, the fields that made the electromagnetic waves are electric
field, E and magnetic field, H. Those fields are perpendicular to each other.
In most cases, the propagation of the electric field at a distance, d from the
antenna is directly proportional with the square root of transmitted power, P t and
inversely proportional with the distance, d [7]. Therefore, the equation as follows:

8
(2.1)
Then, the received power could be defined as:
(2.2)
Where:
Pt = power transmitted from the transmitter antenna
Pr = power received at the receiver antenna
Gt = transmitter antenna gain
Gr = receiver antenna gain
λ= free space wavelength
d = the path distance between the transmitter and receiver
From the received power equation, the value of the received power will
increased when the denominator part decreased. Therefore, the denominator can be
defined as free space path loss ratio:
(2.3)

9
path loss:
Thus, when the ratio is change into its common form in decibel, the free space
(2.4)
Where d is the path distance and f is the carrier frequency in MHz.
2.5 Propagation Loss
There are some propagation effects that counted while designing a radio
communication link. One of them is the propagation loss. There are several factors that
might lead to the propagation losses such as:
i. Attenuation due to the atmospheric gases
ii. Fading due to the diffraction of the earth terrain
iii. Fading due to the multipath signal phenomena and random ray scattering
iv. Attenuation due to the precipitation or particles in the atmosphere
v. The off set between the angle-of-sight signal at the receiver and the angle-of-launch
at the transmitter.
vi. Reduction in the cross-polarization discrimination of the multipath signals or
precipitation condition
vii. Interference due to the frequency selective fading and during the multipath signals
propagation

10
2.6 Atmospheric Layers
Generally, atmosphere consists of three layers which are troposphere,
stratosphere, and ionosphere. Troposphere range begins from the earth surface up until
17km in the middle latitudes. It is deeper in the tropical regions, up to 20 km (12 mi),
and shallower near the poles, at 7 km (4.3 mi) in summer, and indistinct in winter. 99%
of its composition contains water vapor and aerosols. The lowest part of the
troposphere, where friction with the Earth's surface influences air flow, is the planetary
boundary layer. This layer is typically a few hundred meters to 2 km (1.2 mi) deep
depending on the landform and time of day. The border between the troposphere and
stratosphere, called the tropopause, it is a temperature inversion [21].
Stratosphere range starts at the boundary of troposphere up to 30km.
Stratosphere is stratified in temperature, with warmer layers higher up and cooler layers
farther down. This is in contrast to the troposphere near the Earth's surface, which is
cooler higher up and warmer farther down.
The last major layer is the ionosphere. Ionosphere range starts at the boundary of
stratosphere up to more than 900km distance. The ionosphere is a shell of electrons and
electrically charged atoms and molecules that surrounds the Earth. It owes its existence
primarily to ultraviolet radiation from the sun. Ionosphere is divided into three main
layers which are D layer, E layer, and F layer. F layer is divided into two more layer
which are F1 layer (lower layer) and F2 layer (upper layer).
The presence of those layers in ionosphere and its altitude from earth changes
with the position of the sun. At noon, the sun light in the ionosphere is high, therefore
the ionization process of the ions become active. However, at night the light is very low
so when there is no presence of light, most of the ionized ions will be combined

11
together. The time lapse between these processes will cause the size and magnitude of
the ionized layer in ionosphere change. Figure below shows the ionospheric layers
where the size of the layers had been estimated.
Figure 2.3: Ionospheric Layers in the Atmosphere [12]
2.7 Refraction in the Atmosphere
As the electromagnetic energy propagates through the atmosphere, it is will
experience attenuation by absorption and scattering. The major gaseous absorbers in
the atmosphere are water vapor, carbon dioxide, ozone, and oxygen. Each of these
gaseous absorbers is selective about what it absorbs, for example oxygen absorbs
ultraviolet energy. However in radar application, absorption is fairly negligible in terms
of its effect on electromagnetic propagation [6]. The electromagnetic energy is also
scattered by liquids and solids in the atmosphere. This effect is greatly dependent on

12
the size of the particle in relation to the wavelength, but as with absorption, scattering
represents a small factor in electromagnetic propagation.
Changes in temperature, water vapor, and pressure in the atmospheric column
cause a change in atmospheric density, which in turn causes variations in the speed of
electromagnetic waves in all possible ways. These changes in speed could lead to
changes in the propagation direction or inducing the wave bending phenomena. The
bending of electromagnetic waves as they pass through the atmosphere is an example of
refraction.
Refraction is always such that the waves turn toward or much more into the
medium. The waves will travel more slowly, as they pass from a faster speed medium
into a slower speed medium. This is the case shown in the figure below, where medium
A is the faster speed medium. Refraction causes waves to turn back toward the slower
speed medium as they pass from the slower into the faster medium.

13
Figure 2.4: Temperature and Pressure Profiles in the Atmospheric Layers
2.8 Refractivity, N and Refractive Index, n
Refractive index is defined as the ratio of velocity of the propagating radio wave
in free space towards the velocity of the propagating wave in the specified medium. The
value of the refractive index, n is about 1.0003 for standard atmosphere that closest to
the earth surface (troposphere). Therefore, the approach of scaling-up the refractive
index value is needed and it was named as refractivity, N.
2.8.1 Vertical Refractivity Gradient
The vertical refractivity in the lowest layer of the atmosphere are important
parameters for the estimation of path clearance and propagation associated effects such

14
as ducting, surface reflection and multipath fading and also distortion on terrestrial lineof-sight
links [1].
For the first kilometer of the atmosphere, the change in radio refractivity, ∆N
shown as follows:
(2.5)
N 1 is the radio refractivity at a height of 1km above the surface of the earth. The
∆N values were not reduced to a reference surface. Refractivity gradient statistics for
the lowest 100m from the surface of the earth are used to estimate the probability of
occurrence of ducting and multipath conditions.
2.9 Refractive Index Measurement
Refractive index can be measured directly by using the refractometer as the
measurement tool. The refractive index is calculated from Snell's law and can be
calculated from the composition of the material using the Gladstone-Dale relation [23].
There are four main types of refractometers: traditional handheld refractometers, digital
handheld refractometers, laboratory or Abbe refractometers, and inline process
refractometers. There is also the Rayleigh Refractometer used (typically) for measuring
the refractive indices of gases.
Refractometer is likely to be used because of its precision. However,
refractometer is very expensive in cost and it is also relatively complex in its design.

15
This device is also requiring a high skill handling. Therefore, because of those reasons,
this device is less used.
The indirect way to measure the refractive index is by measuring the
atmospheric profile (temperature, atmospheric pressure, and humidity) at a particular
place and use the values obtain to compute the refractive index profile through the
proposed equation by the standards.
Figure 2.5: The Traditional Abbe Refractometer
2.9.1 ITU-R Recommendation Standards
International Telecommunication Union (ITU) is previously known as
International Radio Consultative Committee (CCIR). Its roles are to fulfill the needs of
the Union as been noted in Article 1 from International Telecommunication
Constitution, Geneva 1992 regarding the radio communication affairs. Therefore, the
ITU-R Recommendation in 1994 has been used as reference in this project by
considering all parameters involved [5].

16
2.9.2 Refractive Index Computation Based on ITU-R Recommendation
The indirect method had been discussed here in order to measure the refractive
index value where the determination of the atmospheric profile needs to be done first.
Based on ITU-R Recommendation P.835-4, it states that Malaysia was classified as the
low latitude country (smaller than 22 0 ). Thus seasonal variations are not very important
and a single annual profile could be used for atmospheric profile measurement [3].
Therefore, there are equations to compute the atmospheric profile value as a function of
altitude. For specific altitude, the atmospheric profile could be known.
The equations for the atmospheric profile computation as recommended by ITU-
R P.835-4 are shown below. It is specified for certain range of altitude and those
equations are applicable for frequency up 100 GHz:
Based on the equations above, water vapor is being introduced instead of
relative humidity component. Therefore, the water vapor values obtained will be used to

17
compute the water vapor pressure (in hPa). Furthermore, water vapor pressure is a
function of humidity and also the water vapor. In this project, the term water vapor
pressure will be used afterwards to represents the relative humidity profile.
After obtaining those atmospheric profiles, the refractive index profile can be
computed using the refractivity and refractive index equations proposed in ITU-R
Recommendation P.453-9.
Where:
(2.6)
(2.7)
(2.8)
(2.9)

18
2.9.3 Refractive Index Computation through Atmospheric Profile Measurement
Instead of using the equation of atmospheric profile as a function of altitude, the
refractive index can be computed through the measurement of the atmospheric profile
by using specified sensors which are the temperature, pressure and humidity sensors.
According to the research done by Martin Grabner and Vaclav Kvicera from the
Faculty of Electrical Engineering of Czech Technical University in Prague, they
measured the atmospheric profile at the TV Tower Prague. Both temperature and
humidity sensors were placed at three different altitude which at 12 m, 126 m, and 191
m. However, pressure sensor was placed only at the altitude of 126 m because the
pressure changes significantly at that altitude range [2]. After analyzing all the collected
data, it will be used to compute the refractive index profile by using equations 2.6 until
2.9 which had been previously shown.
Figure 2.6: Sensors of temperature, pressure and humidity used in the measurement [2]

19
2.10 Research History on Refractive Index Equation
Refractive index equation has its origin before the established equation proved
for the standards. In 1965, Bengt Edlen from University of Lund, Sweden has derived
the equation of refractive index of air [9]. The equation involves the dependence of
refractivity towards pressure and temperature. However, there are series of revisions
done in order to improve the equation for more precise computation of the refractive
index. The original Edlen equation of refractive index as follows:
(2.10)
However, in 1990, K.P Birch and M.J Downs have come out with the new
revised of Edlen equation. The equation was made for dry air condition which contains
78.09% of nitrogen, 20.95% of oxygen, 0.93% of argon, 0.03% of carbon dioxide.
(2.11)

20
These findings have been continuously improved by other scholars and
researchers until it was fixed to the standards as what we are applying nowadays. The
standards which refer to the ITU-R Recommendation would be the best reference for
refractivity and refractive index studies.
2.11 The Effects of Refraction
The effects of refraction are called as refractive effects. The refractive effects
particularly in the troposphere of the atmosphere are including ray bending, ducting
layers, the effective earth radius, the apparent elevation and boresight angles in earth
space paths and the effective radio path length. Appropriate calculation procedures for
assessing the refractivity effects on radio signals must be done especially for terrestrial
and earth-space links [4]. In this thesis, the effects that will be discussed are ray bending
and ducting layers.
2.11.1 Ray bending
A radio ray passing through the lower (non-ionized) layer of the atmosphere
undergoes bending due to the gradient of the refractive index. It is known that refractive
index varies mainly with altitude; therefore only vertical gradient of the refractive index
is generally considered. The curvature at a point is therefore contained in the vertical
plane.

21
The ray curvature is defined as positive for ray bending towards Earth’s surface.
This phenomenon is virtually dependent of frequency, if the index gradient does not
vary significantly over a distance equal to the wavelength.
The atmosphere can cause an abnormal ray bending (abnormal bending of the
energy) and at this time anomalous propagation (AP) occurs. AP takes place when an
unusual, other-than-normal vertical distribution of temperature, moisture, and pressure
exists within the atmosphere.
Figure 2.7: Ray Bending Towards Earth Surface
Ray bending is most likely to occur in the early morning hours just after dawn,
and the early evening hours just after sunset. It's least likely to occur at mid-day when
the atmosphere is most stable. However, the passage of weather fronts, storms, and
others can produce this phenomenon at any time of the day or night.

22
2.11.2 Propagation in Ducting Layers
The existence of ducts is important because they can give rise to the anomalous
propagation (AP), particularly on terrestrial or very low angle earth-space links [6].
Ducts provide a mechanism for radio wave signals of sufficiently high frequencies to
propagate far beyond their normal line-of-sight range, giving rise to potential
interference with other services. They also play an important role in the occurrence of
multipath interference although they are neither necessary nor sufficient for multipath
propagation to occur on any particular link.
Figure 2.8: Ducting Effect on the Radiowave [23]
When a transmitting antenna is situated within a horizontally stratified radio
duct, rays that are launched at very shallow elevation angles can become ‘trapped’
within the boundaries of the duct. For the simplified case of a ‘normal’ refractivity
profile above a surface duct having a fixed refractivity gradient, the critical elevation
angle α (rad) for rays to be trapped is given by the expression:
(2.12)

23
Where dM/dh is the vertical gradient of modified refractivity and ∆h is the
thickness of the duct which is the height of duct top above transmitter antenna. Figure
2.9 gives the maximum angle of elevation for rays to be trapped within the duct. The
maximum trapping angle increases rapidly for decreasing refractivity gradients below -
157 N /km and for increasing duct thickness.
The existence of a duct, even if suitably situated, does not necessarily imply that
energy will be efficiently coupled into the duct in such a way that long-range
propagation will occur. In addition to satisfying the maximum elevation angle condition
above, the frequency of the wave must be above a critical value determined by the
physical depth of the duct and by the refractivity profile. Below this minimum trapping
frequency, ever-increasing amounts of energy will leak through the duct boundaries.
The minimum frequency for a wave to be trapped within a tropospheric duct can
be estimated using a phase integral approach. Figure 2.10 below shows the minimum
trapping frequency for surface ducts (solid curves) where a constant (negative)
refractivity gradient is assumed to extend from the surface to a given height, with a
standard profile above this height. For the frequencies used in terrestrial systems
(typically 8-16GHz), a ducting layer of about 5 to 15m minimum thickness is required
and in these instances the minimum trapping frequency, f min is a strong function of both
the duct thickness and the refractive index gradient.
In the case of elevated ducts an additional parameter is involved even for the
simple case of a linear refractivity profile. That parameter relates to the shape of the
refractive index profile lying below the ducting gradient. The dashed curves in the
figurey show the minimum trapping frequency for a constant gradient ducting layer
lying above a surface layer having a standard refractivity gradient of -40 N /km [4].

24
Figure 2.9: Maximum Trapping Angle for a Surface Duct of Constant Refractivity
Gradient over a Spherical Earth
Figure 2.10: Minimum Frequency for Trapping in Atmospheric Radio Ducts of
Constant Refractivity Gradients

CHAPTER 3
METHODOLOGY AND APPROACH
3.1 Introduction
This project is consisting of two major parts, the hardware development part and
calculation analysis part. Both parts will be done simultaneously through the project.
The calculation analysis will be largely depends on the theoretical standards that have
been used in recent years and being widely used by most researchers.
3.2 Calculation and Analysis of Refractive Index
All values of the atmospheric profile (temperature, atmospheric pressure, and
water vapor pressure) in the equation will be taken from the database of National
Meteorological Department of Malaysia. The data collected from the station will be the
data from two locations which are Skudai and Petaling Jaya. Those data will be on daily
basis starting from January 2006 up until September 2009.

26
From the analysis, it could show the trend of the refractive index over the certain
range of altitude. Besides that, it can be seen at which range of altitude that the
atmospheric profile have significant changes. Therefore, analysis could be made and it
could be determined whether the location is highly influenced by the refractivity and the
refractive index value.
3.2.1 Equation-based Atmospheric Profile Calculation
The atmospheric profile could be determined by using the equation in ITU-R
Recommendation P.835-4 where the equation is in a function of altitude. The equation
profile is suitable for low latitude country like Malaysia where such single annual
profile is enough to predict the variations with altitude. The results from this calculation
are called as theoretical atmospheric profile.
3.2.2 Equation-based Refractive Index Profile Calculation
By using the calculated atmospheric profile before, the refractive index profile
could be established by using the equations in ITU-R Recommendation P.453-9. The
equation is divided into two main components, dry refractive index, N dry and wet
refractive index, N wet where the atmospheric profile value is required in the equations.
This refractive index profile obtained is named as theoretical refractive index.

27
3.2.3 Determination of Atmospheric Profile and Refractive Index Profile Based on
Measurement
In order to achieve the objective of the project, the atmospheric profile and
refractive index profile must be measured in real time. For atmospheric profile, the only
parameter that will be measured is temperature and for other parameters like water
vapor pressure and atmospheric pressure will be obtained from the National
Meteorological Station (NMS) database. The measurement of temperature profile will
depends on the hardware development which will be explained afterwards.
The result from the measurement is named as measured atmospheric profile.
Then, the result obtained and the values from the NMS database (for relative humidity
and pressure) will be used to compute the refractive index profile using the same
equation in ITU-R Recommendation P.453-9. Hence, the refractive index profile
obtained named as the measured refractive index and comparison will be made between
theoretical and measured results.
3.3 Hardware Design and Development
The purpose of developing the measurement hardware:
i. For ambience temperature measurement
ii. The database provide by the meteorological station only covered specific
location and in fact, it was used to represent the profile for the whole country
which may lead to the inaccuracy of the data presented
iii. To obtain better resolution of the data collected especially for temperature
compare with the database of the station

28
iv. Provide versatility in measuring the atmospheric profile at particular location
The hardware mainly comprises of several parts such as the main board, sensor
board, communication board, and the outer shell or casing. The main board is consists
of microcontroller and 5V power supply while the sensor board consists of the
temperature sensor. Then, for the communication board, it will be the RF module
transceiver. There will be two RF module transceivers made for both on board and
ground station setup.
The main parts of the hardware will be design on a simple ‘donut’ board with a
dimension of (W x L) = 4cm x 10 cm. Then, for the RF transceiver, its dimension will
be 5cm x 8cm. Total weight of the hardware is about 330 grams.
3.3.1 5V Power Supply
Mainly in most digital logic circuits and processors, a +5V power supply is
needed for the circuit to operates. In order to realize this, a regulated +5V source will be
built. The unregulated power supply should be ranging between 9V to 24V DC.
The main component for the +5V regulator is LM7805 voltage regulator IC.
Figure 3.1: IC LM7805

29
5V output.
The placement of the capacitors is to eliminate the noise in order to obtain a better
Figure 3.2: Schematic Circuit of the +5V Power Supply
3.3.2 Microcontroller PIC16F877A
Microcontroller is the most important part in the operation of the electronic
circuitry system. It is a chip that considered as the brain of the system i.e. in common
computer system it is called a microprocessor. The functions of both components are the
same but they also have their own differences. In this project, the type of
microcontroller used is the PIC16F877A. This type of PIC developed by Microchip has
several advantages that make it useful for various kinds of device or projects [8]:
i. Small in size and equipped with sufficient output ports without the needs of
decoder or multiplexer.
ii.
iii.
It has low current consumption and high portability.
It has a built-in Analog-to-Digital Converter (ADC) which makes it easy for
designers to collect and analyze the analog input.

30
iv.
It is proven as a simple but powerful microcontroller compare to other kinds of
microcontroller since the users would only need to learn 35 single word
instructions in order to program the chip.
v. It is user friendly, easy to programmed using the high-level language and also
easy to reprogrammed.
Table 3.1: Port Connection of PIC16F877A with Other Parts of the System [21]
Pin Name Pin Number Description Application
VDD 11 & 32 Positive Voltage Supply Power Supply To The PIC
(+5V)
VSS 12 & 31 Ground Reference Ground Reference
OSC1 13 For Oscillator or Connected to 20MHz
OSC2 14
Resonator
Crystal Oscillator with
two 22pF capacitors
MCLR 1 Reset Input Connected to the +5V
RE2 10 Analog Input/Output Port Voltage Input From LM35
Sensor Represent The
Temperature Value
RC6 25 Transmitter Port For
USART
Connect To The RF
Module RX Port
RC7 26 Receiver Port For USART Connect To The RF
Module TX Port

31
Figure 3.3: Pin Diagram of the PIC16F877A [21]
3.3.2.1 Analog-to-Digital Input/Output in PIC16F877A
The analog-to-digital (A/D) converter module has eight inputs for the 40/44-pin
devices. The conversion of an analog input signal results in a corresponding 10-bits
digital number. The A/D module has high and low voltage reference input that is
software selectable to some combination of V DD , V SS , RA2 or RA3.
The A/D converter has a unique feature of being able to operate while the device
is in sleep mode. To operate in sleep mode, the A/D clock must be derived from the
A/D’s internal RC oscillator. The A/D module has four registers:
i. A/D Result High Register (ADRESH)
ii.
iii.
iv.
A/D Result Low Register (ADRESL)
A/D Control Register 0 (ADCON0)
A/D Control Register 1 (ADCON1)

32
The ADCON0 register, shown in figure below, controls the operation of the A/D
module. The ADCON1 register, shown in Register 11-2, configures the functions of the
port pins. The port pins can be configured as analog inputs (RA3 can also be the voltage
reference) or as digital I/O.
Figure 3.4: The ADCON0 Register [21]
The ADRESH: ADRESL registers contain the 10-bit result of the A/D
conversion. When the A/D conversion is complete, the result is loaded into this A/D
result register pair, the GO/DONE bit (ADCON0) is cleared and the A/D interrupt
flag bit ADIF is set. After the A/D module has been configured as desired, the selected
channel must be acquired before the conversion is started. The analog input channels
must have their corresponding TRIS bits selected as inputs.
Then, A/D conversion steps:
i. Configure A/D module
ii.
iii.
iv.
Configure A/D interrupt
Wait the required acquisition time
Start conversion by setting the GO/DONE bit (ADCON0) and wait for
completion
v. Read A/D result register pair

33
3.3.3 Temperature Sensor
The type of temperature sensor used is LM 35. The output voltage is linearly
proportional to the Celsius (Centigrade) temperature. Some features of this temperature
sensor are as follows [18]:
i) Calibrated directly in Celsius
ii)
iii)
iv)
Linear +10.0 mV/degree Celsius scale factor
0.5 degree Celsius accuracy guarantee able
Operates from 4 to 30 volts
v) Less than 60 micro Ampere current drain
For this project, the sensor will be supplied by the +5V power supply through
the +5V regulator. The sensor will received an analog input signal which is the
ambience temperature and represented the data in voltage values. The values then will
be processed by the microcontroller and converted it to digital signal through the builtin
ADC of the microcontroller.
To interface LM35 with microcontroller, it will be based on both, sensor features
and the ADC behavior. As for PIC16F877A ADC, it has 10-bits resolution where for
0V we will get count zero and for full scale +5V power supply we will get a count of
1024. Hence, in this project each bit represents 5/1024 = 4.9x10 -3 mV/ºC. However,
based on the sensor features, LM35 has a resolution of 10mV/ºC thus each bit of ADC
represents (4.9x10 -3 )/10x10 -3 =0.49V/ºC. Therefore, to get the exact value of
temperature the ADC value has to be multiplied by 0.49. Since multiplication of this
floating-point number consumes enormous memory area and also adds overhead of
inefficient calculation we can approximate it to 0.5=1/2. Hence ADC value will be

34
divided by 2. This makes the program coding more efficient, simpler with less program
memory area [17].
Figure 3.5: IC LM35 Temperature Sensor [18]
Otherwise, we could check the direct output voltage from the sensor through any
measuring device and it can be converted into temperature by using this equation:
(3.1)

35
3.3.3.1 Sensor Absolute Maximum Ratings
Every sensor including this temperature sensor has its own maximum rating for
users to appreciate as the ratings are important during the interfacing of the sensor with
other elements such as power supply and microcontroller. The table below shows the
maximum ratings of the sensor:
Table 3.2: Maximum Ratings of LM35 [18]
Item
Supply Voltage
Output Voltage
Output Current
Soldering Temperature
Rating
+35V to -0.2V
+6V to -1.0V
10mA
300 0 C within 10 seconds
Operating Temperature Range 0 0 C to +100 0 C
3.3.4 RF Module Transceiver
The type of transceiver used is the XBee OEM RF Module which is purposely
engineered to meet IEEE 802.15.4 standards and support the unique needs of low cost
and low power wireless sensor network. There are several advantages of using this
module. The most useful advantages are its long range data integrity and low power
consumption [16].

36
For XBee RF Module, it offers a communication range up to 30m for indoor
usage and up to 100m for outdoor line of sight range. Actually, there are other types of
XBee which is XBee PRO which offers greater range of communication coverage. The
communication range can achieved about 100m for indoor application and up to 1500m
line of sight for outdoor communication application. The version of the XBee module
used is 1084. Specifications of the XBee RF Module are shown in the table on the next
page.
This XBee RF Module could be used for point-to-point or point-to-multipoint
communication especially in short distance range. Other than that, this RF Module is
applicable for unicast and broadcast communications for example in Personal Area
Network (PAN) application. The RF Module has great robustness against other signal
interference since it used the Direct Sequence Spread Spectrum (DSSS) technique for its
signal transmission where each direct sequence channels has over 65000 unique
addresses available.
Figure 3.6: XBee and XBee PRO OEM RF Modules [16]

37
Table 3.3: Certain Specifications of the XBee OEM RF Module [16]
Specification XBee XBee
Indoor/Urban Range Up to 30m Up to 100m
Outdoor RF line-ofsight
Up to 100m
Up to 1500m
Range
Transmit Power
Output
1mW (0dBm)
60mW(18dBm)
conducted,
100mW(20dBm) EIRP
RF Data rate 250000 bps 250000 bps
Serial Interface Data 1200 – 115200 bps 1200 – 15200 bps
Rate
Receiver Sensitivity -92dBm(1% packet error rate) -100dBm(1% packet
error rate)
Supply Voltage 2.8 – 3.4 V 2.8 – 3.4 V
Operating Frequency ISM 2.4GHz ISM 2.4GHz
Antenna Options Integrated Whip, Chip or
U.FL Connector
Integrated Whip, Chip or
U.FL Connector
Since the RF Modules comes with small pin and requires the 3.3V operation, a
starter kit have been use to convert the 3.3V into 5V operation and it offers connection
to PC with USB for ground station setup. The starter kit XBee has been designed for 5V
TTL logic interface which requires no extra voltage divided. It prepares the XBee with
minimum interface and it is ready to connect to microcontroller for embedded XBee
development. In addition, the on board USB to USART converter offers easy yet
reliable communication to PC for functionality tests. Therefore, starter kit XBee had
been used for this project as the on board RF transceiver and also for ground station
transceiver [24].

38
The connection schematic is shown in the figure on the next page. As we can
see, the LM35 sensor is connected to the analog port RA0 of the PIC16F877A as the
input. Then, the XBee Starter Kit is connected through the USART ports of
PIC16F877A which are the RC6, transmitter port and RC7, the receiver port. These
ports are cross connected with the USART ports (TX and RX ports) of the XBee Starter
Kit in order to establish the communication interface between both components.
GND
LM3
5
V out
PIC16F877
.
XBee Starter Kit
Figure 3.7: Schematic Diagram of the Connections between LM 35 Sensor,
PIC16F877A and XBee Starter Kit

39
Figure 3.8: The Parts of the Measurement Hardware
3.3.4.1 Serial Communications
Universal Synchronous Asynchronous Receiver Transmitter (USART) is a
module or function that available in the RF transceivers in order to transmit and receive
a signal from other transceiver. This USART is also called as UART where the
synchronous trait is not available for certain modules or devices. For XBee OEM RF
Module, data enters the module USART through D1 pin as an asynchronous serial
signal. The signal should idle high when no data is being transmitted. Each data byte
consists of a start bit (low), 8 data bits (least significant bits first) and a stop bit (high).
The following figure illustrates the serial bit pattern of data passing through the module.

40
Figure 3.9: USART Data Packet 0xIF as Transmitted Through the RF Module [16]
3.4 Measurement Setup and Data Collection
The purpose of this measurement and data collection is to obtained the temperature
profile at the particular area and use it for the computation of the refractive index.
Figure below is the measurement setup flows which give us an idea on how the
hardware will do the measurement. Ideally, the hardware will measure the temperature
value at every level in the range of the specified altitude and transmit it at every two
seconds interval towards the ground station. Then, the raw received data will display on
screen. However, the best measuring techniques are needed to be considered in order to
obtain the reliable and consistent data. Therefore, there are several methods discussed
for the measurement method.

41
Moving gradually
downwards
Figure 3.10: The Measurement Setup Diagram
Figure 3.11: Hardware Setup before Measurement

42
3.4.1 Controllable Rope
One of the methods to do the measurement is by using the controllable rope.
Two nylon ropes will be used for this method where each length is about 60m .The first
rope named as a ‘path’ rope where one end of the rope will be tied at one point at the
place of 50m height. Then, the ‘path’ rope will be stretched and the other end of the
rope will be placed tensely slanting towards ground. The second rope act as a controlled
rope as it will control the movement of the hardware while going downwards through
the ‘path’ rope. This rope is tied to the hardware. There are minimum two people
required to apply this method. One person will be on the high upper point to setup the
ropes placement and control the attached hardware. The second person role is to
monitor the ground station unit and make sure that the hardware arrives at the ground
safely. The illustration and the flow chart of this method are shown as follows.
Figure 3.12: The Illustration of the Controllable Rope Method

43
Preparing the hardware and make all
components are well placed
Take one rope and tie up its one end at
the point of about 50m height. Then,
pull the other end slanting to the
ground to make it as a ‘path’ rope
Use another rope act as a controlled
rope to control the movement of the
hardware along the ‘path’ rope
Starting at the highest point, attached
the hardware through the built-in hooks
to both controlled and ‘path’ rope
Release the control rope bit by bit as
the hardware move down along the
slanting ‘path’ rope. Along the way,
data transmission will be occurred at 2
seconds interval
Finally, the data received will be display
and the hardware will be safely arrived
at the ground
Figure 3.13: Flow Chart of the First Method, Controllable Rope

44
3.3.1 Launching From High Place
For this second method, the hardware will be brought up to about 50m. Then,
it will be released from that particular height. However, the fall will be slower because
of the presence of the parachute. The parachute role is to stabilize the movement of the
hardware in the air. Therefore, at the same time the hardware will keep transmitting the
data collected from the sensor.
Preparing the hardware and make all
components are well placed
Setup the parachute; tie it nicely to the
hooks. Make sure that the parachute
chords do not tangled with each other.
Be prepared and make sure everything
is fully set up. Then, release the
hardware and let it flows down. The
data will be transmitted within 2
seconds interval
Finally, the data received will be display
and the hardware will be safely arrived
at the ground
Figure 3.14 Flow Chart of the Second Method, Launch from High Place
This method is quite risky since the flow of the hardware is exposed to the wind
flow. It is best to apply this method at field ground since there will be broad range of
area for the hardware to move.

45
Figure 3.15: The Illustration if we launched from High Place
Figure 3.16: The Hardware Launched From High Place

46
Figure 3.17: Retrieving the Hardware After Arrive at the Ground
Figure 3.18: Example of the Received Data at X-CTU Software in Hexadecimal Form

47
3.4.3 Mechanical Structure
It is important to have a good casing or shell in order to protect the circuit boards
from being damaged while doing the measurement i.e. it will increase the robustness of
the hardware due to the nature of the measurement setup itself. For safety purposes, the
hardware will be placed inside an oval-like shaped casing with 12cm in diameter and
5cm of height. The casing or the shell will be designed with embedded hooks for the
parachute attachment. The parachute used is made from nylon and the shell was made
of solid plastic-based material. It was light in mass, high flexibility and solid in form.
Figure 3.20: Front View of the Structure

48
Figure 3.21: Upper View of the Structure
Figure 3.22: Side View of the Structure

49
Figure 3.23: The Nylon Parachute
3.5 Software Implementation
MikroC Compiler by Mikroelektronika is used to program the microcontroller in
C language. For burning process the PICkit 2 v2.55 programming software had been
used with UIC00A bootloader. Besides that, X-CTU software has been used for
receiving and monitoring the transmitted data from the measurement hardware.
3.5.1 Algorithm and Programming in MikroC Compiler
Microcontroller is the brain of the system where any data collected by the
temperature sensor will be processed and transmitted to the ground station RF
transceiver until the hardware arrives at the ground. The data that received will be in the
form of hexadecimal.

50
An algorithm has to be developed to make the order to read the input and
respond accordingly. Therefore, a flow chart needs to be made first before translating it
into the C language and compiled it using MikroC Compiler. The program in C
language can be referred in Appendix A.
The program will begin with function and variable declaration plus initializing
all the microcontroller specific parameters. Next, the main program will focus on
retrieving data from the sensor. Once the data collected by the sensor, it will be
converted by the ADC and transmitted directly to the ground station through the
USART ports.

51
Start
Initialization
Initialize PORT
Initialize ADC
Initialize USART
Delay Setup
Obtain data from
LM35 sensor
No
Yes
Test PORTA.0 = 1
No
Yes
Processing the data
Test PORTC.6 =1
No
Yes
Transmit the data
Figure 3.24: Flow chart of microcontroller’s main program

CHAPTER 4
RESULTS AND DISCUSSION
4.1 Introduction
All results and findings including calculation process will be done and analyzed
using MATLAB R2006a software. The software has a feature called Curve Fitting Tool.
This feature is useful in obtaining the smooth estimation through the results obtained
and it will be used to represents the results in graphical form later on in this chapter.
4.2 The Results of the Equation-Based Atmospheric Profile
Based on ITU-R Recommendation P.835-4, for low latitudes (smaller than 22 0 )
the seasonal variations are not very important and a single annual profile can be used
[3]. Therefore, to calculate the theoretical atmospheric profile at tropospheric region,
this equation had been used:

53
For temperature,
(4.1)
For atmospheric pressure,
(4.2)
For water vapor pressure, it can be a function of humidity, H and temperature, T.
The relationship between water vapor pressure, water vapor density and temperature is
given by equation 4.3 and 4.4:
With:
(4.3)
(4.4)
Where:

54
Table 4.1 below shows the atmospheric profile which is temperature,
atmospheric pressure, and water vapor pressure. Since this project involves the study in
tropospheric region, the results will be calculated starting from 0m up to 100m altitude.
Besides that, the theoretical atmospheric profile calculated are based on the equation
that solely depends on altitude. Therefore, there are no influences of day and night
factor.
Table 4.1: Theoretical Atmospheric Profile at its Respective Altitude
Height, m Temperature, K Atmospheric Pressure, hPa Water Vapor Pressure, hPa
0 300.422 1012.03 31.2965
10 300.359 1010.94 31.1811
20 300.295 1009.85 31.0643
30 300.232 1008.76 30.9496
40 300.168 1007.67 30.8336
50 300.104 1006.59 30.7179
60 300.041 1005.50 30.6043
70 299.977 1004.42 30.4894
80 299.914 1003.33 30.3766
90 299.850 1002.25 30.2624
100 299.787 1001.17 30.1504

55
4.3 Results of Equation-based Refractive Index Profile Calculation
The equations used are based on ITU-R Recommendation P.453-9 for refractive
index profile calculation.
The refractive index calculation is as follows:
Where:
(4.6)
For N dry :
(4.7)
For N wet :
(4.8)
Where:
(4.9)

56
The water vapor pressure and temperature values will be obtained by using the
same equation and method as in the previous section. However, for this refractive index
profile calculation, the atmospheric pressure parameter will be put as a constant
parameter in order to be consistent with the objective to observe the effects of
temperature towards the refractive index profile. Table 4.2 shows the calculation results.
Table 4.2: The Theoretical Refractivity Data, N and Refractive Index Profile, n
Height, m Refractivity Data, N Refractive Index, n
0 390.1432 1.000390143
10 389.7748 1.000389775
20 389.4019 1.000389402
30 389.0357 1.000389036
40 388.6656 1.000388666
50 388.2963 1.000388296
60 387.9337 1.000387934
70 387.5670 1.000387567
80 387.2069 1.000387207
90 386.8424 1.000386842
100 386.4850 1.000386485

57
4.4 Results of Atmospheric Profile and Refractive Index Profile Based on
Measurement
As what been explained in the previous chapter, a hardware was built in order to
measure the ambience temperature thus establishing the temperature profile for 100m
altitude range.
With our current situation to complete this project, it is hard to measure the
temperature exactly from 0m up to 100m. Therefore, with our limited sources, an
approximate 50m of altitude had been taken as the measurable altitude range. It was
already specified in the previous chapter that the actual altitude range of the
measurement hardware is about 50m.
Hence, the data obtained during measurement for the 50m altitude range will be
extrapolated up to 100m. The analysis is done in MATLAB. The results shown in Table
4.3 are made from the average data collected through the several days of measurement.

58
Table 4.3: Measured Temperature Results – Day and Night
Height, m Day Night
Temperature, K
Temperature, K
0 307 301.25
10 306.5 300.75
20 305.5 300.5
30 305.5 300.5
40 305.25 300.5
50 304.75 300.5
60 304 300.75
70 304 301
80 303 301
90 302.5 301
100 302.25 300.0
After analyzing the measured temperature data in Kelvin, it will be used to
compute the refractive index profile. The computed values are shown in the Table 4.4
below.

59
Table 4.4: Refractivity Data and Refractive Index Value Based On Measured
Temperature Results
Height,
m
Day Time
Night Time
Refractivity Data, N Refractive Index, n Refractivity Data, N Refractive Index, n
0 437.2131 1.000437213 396.2907 1.000396291
10 433.2371 1.000433237 393.2486 1.000393249
20 425.4228 1.000425423 391.7469 1.000391747
30 425.4228 1.000425423 394.7469 1.000394747
40 423.5486 1.000423549 391.7469 1.000394747
50 419.8444 1.000419844 391.7469 1.000394747
60 414.4414 1.000414441 393.2486 1.000393249
70 414.4414 1.000414441 394.7503 1.000394750
80 407.5504 1.000407550 394.7503 1.000394750
90 404.2704 1.000404270 394.7503 1.000394750
100 400.9904 1.000400990 388.8195 1.000388820
Based on the measurement results and findings, it shows that the refractive index
profile is gradually decreasing as the altitude increased. The trend for this measurement
result is consistent with the theoretical results which is also its refractive index profile
inversely proportional to the altitude.

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4.5 Comparison between Theoretical and Measured Temperature Values
The theoretical result which is based from calculation analysis will be compared
with the measurement results. Figure below shows the comparison between measured
temperature values and theoretical temperature values in two sessions, day and night.
Results on both sessions will be compared with the same theoretical results. The red line
marks the theoretical results and the blue line marks the measured results. The
theoretical profile will be looked as a reference to analyze the measured results. The
profiles obtain are based on the average temperature values collected from several days
of measurement.
Based on Figure 4.1, the highest temperature measured during day time is 307K
at ground level (0m) and the lowest is 302.25K at the highest point measured (100m).
The temperature profile obtain is inversely proportional with the altitude. It is precisely
consistent with the theory which proves that as the altitude increase in the atmospheric
layers, the degree of atmospheric temperature will decreased. This is where the
temperature inversion behavior applies. Temperature inversion is a thin layer of the
atmosphere where the decrease in temperature with height or altitude is much less than
normal (or in extreme cases, the temperature increases with height).
An inversion which is also called a "stable" air layer, effectively suppress
vertical air movement and thus acts like a lid, keeping normal convective overturning of
the atmosphere from penetrating through the inversion. Instead of refraction effects,
usually this can cause several weather-related effects. One is the trapping of pollutants
below the inversion, allowing them to build up. If the sky is very hazy, or is sunsets are
very red, there is likely an inversion somewhere in the lower atmosphere [25].

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At night, temperature profile is quite unstable which can be seen in Figure 4.2
below. The highest temperature measured is 301.25K at 0m and the lowest temperature
measured is 300K at 100m. There are ups and downs of the values which show the
inconsistency along the data profile. However through the curve fit analysis using the
curve fit tool in MATLAB, it shows here that the temperature profile also decreased as
the altitude increased. The reason for this is due to the temperature inversion behavior in
the tropospheric region.
It was shown in the figures that during day time, the temperature values hugely
vary with altitude compare to the temperature values during night time. One of the
reasons for this difference is during day time; the radiation from the sun enlightened the
earth ground which will heat up immediately. When the ground is heated, the ground
temperature will increase rapidly as it will induce the heat towards nearer level from it
thus rising up the temperature level in the surrounding. Then, during night time, with no
presence of the sun, the ground also cools rapidly. Hence, the temperature will decrease
very fast and that shows a significant difference in the temperature profile for both
sessions.
Besides that, the measured temperature values also have a significant difference
with the theoretical temperature values. In other words, we could say that the variations
of the temperature changes the air density in the altitude range drastically thus will
contribute huge effects towards the refractive index profile computation.

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Figure 4.1: Graph of Measured Temperature vs. Theoretical Temperature at Day Time
Figure 4.2: Graph of Measured Temperature vs. Theoretical Temperature at Night Time

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4.6 Comparison between Theoretical and Measured Refractive Index
The comparison between theoretical and measured refractive index profile have
been shown here. The measured refractive index profile obtained based on the
temperature measurement results and the theoretical refractive index profile obtained
based on the calculated atmospheric profiles which all of these have been done
previously.
The comparison is made between two sessions, day and night and the results for
both sessions will be compared with the same theoretical refractive index profile results.
From Figure 4.3 and Figure 4.4, the red line represents the theoretical profile and the
blue line represents the measured profile. Theoretically, the variations of the refractive
index with 100m altitude range are very small. However, the measured result shows
significant variation with 100m altitude range.
During day time, the refractive index profile consistently varies with the altitude
which means it is inversely proportional with altitude. The highest value of refractive
index achieve is at ground level (0m) with the value of 1.000437213 and the lowest
value is 1.000389775 at 100m height. The ground level is having the highest refractive
index value would be largely contributed by the temperature factor. Previously, it was
shown that the highest temperature noted there was at the ground level too. For the
theoretical refractive index values, the highest calculated value is 1.000390143 at
ground level and the lowest calculated value is 1.000386485 at 100m height. Thus,
shows that theoretical values do not significantly differ in that range of altitude.
At night, the refractive index profile obtained is more inconsistent throughout
the altitude range. The results have been shown with the theoretical refractive index
profile. However, through the curve fit tool in MATLAB software, it can be shown that

64
the refractive index profile trend is inversely proportional with the altitude. The highest
refractive index value obtained is 1.000396291 at ground level and the lowest refractive
index value is 1.000388820 at the highest point of altitude range.
Between the refractive index profile during day time and night time, there are
quite huge differences. As we can see from the graph, the difference can be assured
through the gradient of the profiles. During day time, the refractive index profile
gradient is greater than the refractive index profile gradient during night time. It can be
said that the refractive index profile experienced a diurnal variations. Diurnal variation
involves the occurrence behavior in a 24 hours period. For this project, it is associated
with the temperature values measured in the altitude range.

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Figure 4.3: Graph of Measured Refractive Index vs. Theoretical Refractive Index at Day Time
Figure 4.4: Graph of Measured Refractive Index vs. Theoretical Refractive Index at Night Time

CHAPTER 5
CONCLUSION
5.1 Conclusion
Based on the results, it is proven that at the lowest region of the tropospheric area
the temperature decreased as the altitude increased. According to the most researchers
such as Tjasyono HK and Djakawinata [13] regarding the influence of meteorological
factor towards tropospheric refraction, they say that temperature together with other
atmospheric profile parameters decreases with altitude. The behavior of the temperature
profile did influence the refractive index profile as shown in the result where the
refractive index profile is proved to be inversely proportional with altitude.
Other than that, ITU-R Recommendation P.835-4 shows the atmospheric profile
data decreased as the altitude increased. The data shows collected by the World
Meteorological Organization from Meteorological Station 10410, location in Essen,
Germany through the ten years of radiosonde data [3].
The refraction which occurs in the tropospheric region will produce some effects
towards radio wave signal that must be studied for predicting the propagation of the

67
signal through a medium. Those effects are electromagnetic wave bending, effective
radio path length, production of ducting layers due to the super refraction phenomena,
and many other tropospheric refraction effects that important in propagation studies. For
analysis, those effects will used the refractive index profile as main parameter.
5.2 Future Works and Recommendations
There are numbers of recommendation that will be suggested in this section
particularly in the measurement part. The advancement must be made in order to obtain
more precise refractive index profile.
5.2.1 Hardware Advancement
The hardware could be improved in terms of its function as for now the function
is only to measure collect the temperature values. Therefore, make an additional in
terms of sensor such as barometric pressure sensor and humidity sensor. Those
additional sensors are capable to measure the atmospheric pressure and relative
humidity. There will be a lot more work to be done to interface those sensors with other
components of the hardware such as the PIC microcontroller and RF Module
transceivers. Hence, the data collection procedure will be complicated. However, this
will guarantee a better accuracy of the refractive index profile computed.
5.2.2 Measurement Method
Measurement method is important in assuring the reliability of the data. The way
of measuring must be improved using a better way compare with the current method

68
used. The method must ensure the data collected is consistent thus most likely will
increased the precision of the end results.
Another method to do the measurement process would be by using a remotecontrolled
helicopter. The hardware will be attached to the helicopter and it will fly the
hardware freely as at the same time a user will handle the remote to control the position
of the helicopter. Therefore, it is possible to do the measurement at any height as long as
it is in the range of the helicopter remote-control coverage. However, one must concern
about the weight of both helicopter and the hardware itself whether it is capable enough
to lift the hardware from the ground.
Besides using the remote-controlled helicopter, we can use the controlled helium
balloon to bring up the measurement hardware at the specified height. As we all know
that helium is the most less-weighted gas in the world, therefore it can be used to lift the
hardware through the balloon. The lift of the balloon is controlled by the user at the
ground using the control rope. Therefore, in a wide location or area this method could
be applied as the user freely to adjust the position of the balloon that carries the
hardware at any altitude level. Hence, an accurate and precise reading at any particular
level can be obtained.
5.2.3 Measurement Readings
The measurement must be done in the long run which means in the range of
several months or up for one year measurement. Therefore, a consistent measurement
need to be done so that more accurate readings can be obtained thus the probability to
have the closest results with the theoretical one is high.

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5.3 Summary
Even the objectives have already been achieved; those future works and
recommendations must be done in order to produce a better refractive index profile
through more precise method. Hoping this project will give an insight and in depth
views for people who practice engineering especially for ground wave propagation
studies. It is important for engineers to have such a strong knowledge regarding the
refractivity and refractive index phenomena in order to design good radio
communication link.

REFERENCES
[1] Rec. ITU-R P. 453-9, “The radio refractive index: its formula and refractivity data”,
2003.
[2] Martin Grabner, Vaclav Kvicera, “Refractive Index Measurement at TV Tower Prague”,
Radioengineering Vol. 12, No. 1, Prague, Czech Republic, April 2003
[3] Rec. ITU-R P. 835-4, “Reference standard atmospheres”, 2005
[4] Rec. ITU-R P.834-6, “Effects of tropospheric refraction on radiowave propagation”,
2007
[5] Basri Abu Bakar, Jafri Din, “Analisa Indeks Biasan Radio Berdasarkan Pengumpulan
Data Kajicuaca Tempatan”, University Technology of Malaysia, September 1997
[6] Bruce W. Ford, “Atmospheric Refraction: How Electromagnetic Waves Bend in the
Atmosphere and Why It Matters”, 1995
[7] Roger L. Freeman, “Radio System Design for Telecommunication (1 to 100GHz)”, 1 st
Edition, John Wiley Sons, Inc. United States, 1987
[8] Lawrence A. Duarte, “The Microcontroller Beginner’s Handbook. 2 nd Edition”, United States
of America: Prompt Publication. 3-5; 1998
[9] Bengt Edlen, “The Refractive Index of Air”, Metrologia Vol. 2, No. 2, University of Lund,
Sweden, 1966

[10] K.P Birch, M.J Downs, “An Updated Edlen Equation for Refractive Index of Air”, Metrologia
Vol. 30, No. 155-162, 1993
[11] G. Bonsch, E. Potulski, “Measurement of The Refractive Index of Air and Comparison with
Modified Edlen’s Formulae”, Metrologia Vol. 35, No. 133, 1998
[12] Gary M. Miller, “Modern electronic Communication” 4 th Edition, Prentice Hall, United
States, 1993
[13] Bayong Tjasyono HK, Djakawinata S. “The Influence of Meteorological Factors on
Tropospheric Refractive Index over Indonesia”, JMS Vol. 4, No. 1, Bandung Institute of
Technology, Bandung, Indonesia, April 1999
[14] “Atmospheric Profile Data of Senai and Petaling Jaya from 2008 to 2009”, National
Meteorological Station of Malaysia
[15] Benoit Roturier, Beatrice Chateau, “Anomalous Propagation (Ducting) Effects In
Aeronautical VHF Band”, Aeronautical Mobile Communication Panel (AMCP), Honolulu,
Hawaii, January 1999
[16] “Product Manual v1.xAx – 802.15.4 Protocol: XBee/XBee-PRO OEM RF Module”,
United States, Max Stream Inc. 2006
[17] http://embeddedsystemdesign.blogspot.com/2007/12/temperature-controller-usingpic16f877a.html
[18] http://www.alldatasheets.com/lm35, “LM35: Precision Centigrade Temperature Sensor”,
November 2000
[19] Korak Saha, Suresh Raju, K. Parameswaran, “ Neutral Atmospheric Refraction on
Microwave Propagation and Its Implication on GPS Based Ranging System”, Vikram
Sarabhai Space Centre, Kerala,

[20] Norhisham Hj. Khamis, “Radiowave Propagation Notes for Antenna and Propagation
Course”, University Technology of Malaysia
[21] Danielson, Levin, Abrams, “Meteorology”, McGraw Hill, 2003
[22] http://www.microchip.com, the Microchip official website
[23] http://www.wikipedia.com, an open source information
[24] http://www.tpub.com/content/neets/14190/css/14190_29.htm
[25] “SKXBee User Manual”, Cytron Technologies, August 2008
[26] http://www.weatherquestions.com/

APPENDIX A
Project Schedule for FYP 1 and FYP 2
ITEM
FYP Briefing
Supervisor identity
Topic choosing
Project proposal
Literature review
Study the refractive
index concept
Design the measurement
hardware
Presentation preparation
FYP1 presentation
Report preparation
Report submission
WEEK
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
ITEM
Theoretical
calculation and
analysis
Hardware
development
Temperature
measurement
Result and analysis
Writing thesis
Presentation
preparation
FYP2 Presentation
Thesis submission
WEEK
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16

APPENDIX B
Sample Atmospheric Data Obtained From Meteorological Station – Petaling Jaya Station
24 Hour 24 Hour
24 Hour Mean Mean
Mean Relative MSL
Temp. Humidity Pressure
Stnno Year Month Day ( ° C ) ( % ) (Hpa)
48648 2008 1 1 27.1 74.7 1008.3
48648 2008 1 2 27.1 69.4 1009.4
48648 2008 1 3 26.5 72.8 1010.5
48648 2008 1 4 26.2 76.3 1010.7
48648 2008 1 5 25.8 80.7 1010.6
48648 2008 1 6 25.7 81.0 1011.1
48648 2008 2 1 26.1 82.7 1008.0
48648 2008 2 2 25.6 86.2 1007.7
48648 2008 2 3 25.2 85.1 1008.5
48648 2008 2 4 26.4 76.5 1007.6
48648 2008 2 5 27.7 71.8 1007.8
48648 2008 2 6 28.1 70.3 1007.6
48648 2008 2 7 -1.1 -1.1 -1.1
48648 2008 2 8 -1.1 -1.1 -1.1
48648 2008 2 9 28.0 66.3 1009.0
48648 2008 2 10 27.7 60.0 1009.2
48648 2008 2 11 27.1 60.6 1009.6
48648 2008 2 12 27.3 62.1 1009.1

24 Hour 24 Hour
24 Hour Mean Mean
Mean Relative MSL
Temp. Humidity Pressure
Stnno Year Month Day ( ° C ) ( % ) (Hpa)
48648 2008 3 1 24.7 88.0 1009.1
48648 2008 3 2 26.2 80.9 1009.0
48648 2008 3 3 25.1 85.8 1009.5
48648 2008 3 4 25.4 81.9 1008.9
48648 2008 3 5 27.1 74.6 1009.0
48648 2008 3 6 27.1 77.8 1009.1
48648 2008 3 7 25.9 84.5 1008.9
48648 2008 3 8 26.5 78.2 1008.8
48648 2008 3 9 26.7 81.6 1008.3
48648 2008 3 10 26.0 82.6 1008.3
48648 2008 3 11 26.2 83.7 1007.8
48648 2008 5 1 29.4 71.4 1006.8
48648 2008 5 2 28.5 75.0 1006.2
48648 2008 5 3 28.0 76.4 1006.9
48648 2008 5 4 29.6 65.6 1007.3
48648 2008 5 5 28.8 72.1 1007.7
48648 2008 5 6 28.6 72.1 1007.4
48648 2008 5 7 27.2 80.3 1008.3
48648 2008 5 8 27.8 76.9 1008.1
48648 2008 5 9 28.1 74.4 1007.7
48648 2008 5 10 29.0 72.5 1007.6
48648 2008 5 11 28.6 71.1 1007.7
48648 2008 5 12 29.4 64.8 1008.1
48648 2008 5 13 29.8 64.0 1008.2
48648 2008 5 14 28.4 74.2 1008.9
48648 2008 5 15 29.4 69.6 1009.1
48648 2008 5 16 29.7 68.3 1009.4
48648 2008 5 17 29.6 66.9 1008.4

Sample Atmospheric Data Obtained From Meteorological Station – Senai Station
24 Hour 24 Hour
24 Hour Mean Mean
Mean Relative MSL
Temp. Humidity Pressure
Stnno Year Month Day ( ° C ) ( % ) (Hpa)
48679 2008 1 1 24.9 85.2 1009.7
48679 2008 1 2 24.4 89.9 1010.9
48679 2008 1 3 24.4 89.8 1011.7
48679 2008 1 4 25.5 86.0 1011.8
48679 2008 1 5 25.1 89.3 1012.0
48679 2008 1 6 25.0 88.8 1012.2
48679 2008 1 7 25.4 88.8 1012.0
48679 2008 1 8 24.4 95.0 1011.3
48679 2008 2 1 24.6 89.3 1009.0
48679 2008 2 2 23.8 94.1 1008.7
48679 2008 2 3 23.7 91.7 1009.7
48679 2008 2 4 24.4 90.7 1009.0
48679 2008 2 5 25.0 90.0 1009.6
48679 2008 2 6 26.4 80.7 1009.4
48679 2008 2 7 25.9 78.5 1009.2
48679 2008 2 8 26.0 81.8 1009.8
48679 2008 2 9 25.8 83.0 1010.6
48679 2008 2 10 25.4 83.5 1010.7
48679 2008 3 1 24.2 90.0 1010.2
48679 2008 3 2 24.8 92.5 1010.2
48679 2008 3 3 25.0 87.3 1010.4
48679 2008 3 4 24.3 88.9 1010.0
48679 2008 3 5 25.0 87.9 1010.4
48679 2008 3 6 24.3 93.7 1010.7
48679 2008 3 7 25.5 85.1 1010.2
48679 2008 3 8 26.1 83.1 1010.2
48679 2008 3 9 24.7 91.3 1009.8

24 Hour 24 Hour
24 Hour Mean Mean
Mean Relative MSL
Temp. Humidity Pressure
Stnno Year Month Day ( ° C ) ( % ) (Hpa)
48679 2008 4 1 26.8 82.9 1010.0
48679 2008 4 2 26.3 86.2 1010.3
48679 2008 4 3 25.7 87.6 1009.8
48679 2008 4 4 25.6 85.8 1009.3
48679 2008 4 5 25.4 88.6 1009.9
48679 2008 4 6 25.6 88.2 1010.7
48679 2008 4 7 25.4 88.3 1009.4
48679 2008 4 8 25.2 90.5 1008.5
48679 2008 4 9 27.2 78.5 1008.0
48679 2008 5 1 28.1 81.8 1008.0
48679 2008 5 2 27.2 80.0 1007.3
48679 2008 5 3 27.2 86.0 1008.0
48679 2008 5 4 26.1 91.0 1008.8
48679 2008 5 5 26.2 86.8 1008.8
48679 2008 5 6 26.6 86.4 1008.6
48679 2008 5 7 25.7 92.2 1009.2
48679 2008 5 8 25.4 93.8 1009.0
48679 2008 5 9 27.3 83.1 1008.5
48679 2008 6 1 25.8 91.0 1008.6
48679 2008 6 2 25.8 89.3 1009.0
48679 2008 6 3 25.9 91.6 1010.0
48679 2008 6 4 25.9 91.3 1009.8
48679 2008 6 5 25.8 90.1 1008.6
48679 2008 6 6 26.2 90.4 1008.1
48679 2008 6 7 24.9 93.1 1009.1
48679 2008 6 8 25.4 90.5 1009.4
48679 2008 6 9 26.5 87.4 1009.0

APPENDIX C
PIC16F877A Program Coding
/*
* offset reference of the sensor : 0°C is 500 mV => 102.4
* since the sensor is factory calibrated, there is no need for adjustment
*/// offset is multiplied by 10 to get tenth of degree
*****************************************************************************
unsigned long temp;
unsigned long temp2;
*/ program entry
*/***************************************************************************
void main()
{
USART_Init(9600); // Initalize USART (9600 baud rate, 1 stop bit, ...
//clear A/D result
ADCON1 = 0; // All porta pins as analog, VDD as Vref
TRISA = 0xFF; // PORTA is input
TRISD = 0x00;
do
{
/*
* read the sensor
*/
temp = Adc_Read(0)>> 2;
temp2 = temp/2;
USART_Write(temp2);
Delay_ms(1000);
//* sensor temperature coefficient is +10mV/°C
//*ADC resolution is 5000/1024 = 4.88 mV
//*so one ADC point is approx. 0.5°C
*/write sensor data to USART for transmission
// clear counter
}
} while(1);