AM RADIO NAVIGATION USING CONVERSION PHASE · PDF filePrecise real time navigation is required...
Transcript of AM RADIO NAVIGATION USING CONVERSION PHASE · PDF filePrecise real time navigation is required...
AM RADIO NAVIGATION
USING DIRECT CONVERSION PHASE MEASUREMENTS
A Thesis
Submitted to the Faculty of Graduate Studies and Research
in Partial Fulfillment of the Requirements
For the Degree of
Master of Applied Science
in Electronic Systems Engineering
UNIVERSITY OF REGINA
BY
Anh Van Dinh
Regina, Saskatchewan
July 1997
@Copyright 1997: A. V. Dinh
395 Wellington Street 395, rue Wellington Ottawa ON K1A ON4 Ottawa ON K I A ON4 Canada Canada
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Precise real time navigation is required in many industries such as
farming, forestry and construction. These systems are in high demand since
they improve productivity. Numerous navigation systems are available today.
Unfortunately, they do not satisfy many of the requirements of users in these .
specific applications.
This thesis describes preliminary work toward the development of a low
cost, precise, real time navigation system. This system uses AM radio stations
as its primary beacons. The phase of AM carrier is used to provide disiance
ranging. Triangulation is then to be used ta determine position of a moving
vehicle.
This navigation system is based on a mixed analog and digital process
which is called software radio. The full AM radio spectrum is captured through a
wideband reœiver and digitized directly using a fast AID converter. Digital
signal processing is then be used to process data for phase measurements.
Frequencies of the AM carriers are very stable. Phase measurement
erms due to the frequency fluctuations are negligible. These high power
continuous waves cm be received over an extensive range. Modulation of the
carriers is the main difficulty in phase measurements of these CWs. The
moduiating signals are between 20 Hz to A0 kHz and create sidebands close to
the carrier. These unwanted sidebands can be considered as noise. lnsofar as
phase measurement is concemed, these sidebands make accurate
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using zero crossing. Circuit temperature drift also plays an important role in the
accuracy of phase measurement.
This thesis presents a number of approaches for precision navigation using
AM broadcasts and analog phase measurement techniques. By mixing signais
d o m to a low Intermediate Frequency (IF) and locking on with a Phase Lock Loop
(PLL), phase ciifferences m n be measured to within f0.5' acairacy. This provides
M.32 meters range accuracy with a 1300 kHz AM radio signal. Aithough this is
mmparable with commercial real tirne navigation systems such as DGPS, it is not
as accurate as the AGTRAK 2020 system developed at the University of Regina. It
also does not meet performanœ requirements in some specific applications. The
accuracy can be impmved by using Digital Signal Prooessing techniques. The
digital approach Mers higher selectivity, reduced cost and reduced variations due
to component toleranœs and drift.
I wish to express my gratitude to some of the people whose supervision,
guidance, advice and encouragement were helpful to this research. First, I
would like to extend my sincere gratitude to my advisor, Dr. Ralph D. Mason,
who provided support and assistance for this research. I thank my co-advisors,
Professor R. Palmer and Professor K. Runtz, for their valuable advice. I also
thank Engineering Faculty Members and Faculty of Engineering Staff to whom I
am very grateful over my years of study at the University of Regina. A special
thanks to Mr. Shing Ma, a graduate student at University of Regina, for his help
during my study.
I owe a great debt ta my family. I thank them most sincerely for their
patience, understanding, encouragement and unfailing moral support over the
long period of time spent on this reçearch.
iii
TABLE OF CONTENTS
Abstract .......................................................................................................... i
Acknowledgments ........................................................................................ iii
Table of Contents ...................................................................................... iv
List of Figures .............................................................................................. vii
................................................................................................ List of Tables ix
....................................................................................... Glossary of Terms x
.................................................................................... 1 . INTRODUCTION 1
................................................................................... . 1 1 Navigation 1
................................................................................. 1.2 Applications 2
1.3 Existing technology ...................................................................... -3
.................................... ..............*.........*...... 1.4 Research objective ... -5
2 . PREClSlON NAVIGATION ................................................................... 8
2.1 LORAN-C ..................................................................................... 9
.......................................................... 2.2 Global Positioning System -11
2.3 Agtrak 2020 ................................................................................ -15
3 . AM BROADCASTlNG BASED NAVIGATION SYSTEM .......................... 18
3.1 Distance rneasurement using phase difference ........................ 18
3.2 Position determination using triangulation technique ............. 22
........................................................................... 3.3 Software radio 23
3.4 AM broadcasting radio navigation system .................................. 25
4 . AM BROADCASTING WIDEBAND RECEIVER ...................................... 28
4.1 Amplitude modulation signals .................................................. 28
.............. 4.2 AM Droaacasting wiaeDana receiver aesiyn apyi uaw I I
.......................................... 4.3 AM broadcasting wideband receiver 33
4.3.1 AM broadcasting wideband receiver circuit .................. 34
4.3.2 Circuit Construction ...................................................... 39
.................................................................................. 4.4 Test result 40
................................... ......................... 4.4.1 Bench tests .... 40
.................................................................... 4.4.2 Field tests 41
5 . PHASE MEASUREMENT USlNG DIRECT CONVERSION AM RADIO .. 45
.............................................. 5.1 Evaluation of AM Carrier Stability -45
...................................... 5.2 Phase rneasurement system overview 48
................................................................ 5.3 Phase measurements 50
..................................................... 5.3.1 Direct measurement 50
5.3.2 Mixing to DC .......................................................... 51
.................................................... 5.3.3 Low IF measurement 52
....... 5.3.4 High IF and band pass filter phase measurement 54
5.3.5 Low IF, PLL, and DC phase measurement .................. 55
5.3.6 Low IF, PLL, and phase meter measurement .............. 56
.................................... 5.3.7 Phase measurement summary 58
6 . CONCLUSIONS AND FUTURE WORK ............................................... 60
6.1 Conclusions ............................................................................... 60
................................................................................ 6.2 Future work 62
REFERENCES ........................................................................................... 65
n r r r ~ u i ~ i . iritwyr aieu WI GUIL +UUI IWLIUI 1 3 ......................................... vg
1 . ADSBOOU. 12-Bit. 40MHz Sampling. N D converter ..................... 69
2 . AD603AR. Low Noise. 9OMHz. Variable Gain Amplifier .... ... ........ 71
APPENDIX 2: Low Pass F ilter Frequency Response Simulation ............... 73
APPENDIX 3: Wideband Receiver Bench Tests ....................................... 74
.......................................... APPENDIX 4: Mathcad file for FFT calculation 77
...................................................................... APPENDIX 5: MC1496 Mixer 78
............................................................ APPENDIX 6: Distance calculation 79
................................................................ APPENDIX 7: Phase Lock Loop 80
Figure 2.1 : Hyperbolic navigation system .................................................. I O
Figure 2.2. Depiction of Global Positioning System triangulating .............. 13
Figure 2.3. The AGTRAK 2020 guidance system ...................................... 16
Figure 3.1 : Distance measurement ............................................................ 18
........................ Figure 3.2. Phase and distance of a single frequency CW 19
Figure 3.3. Time Of Arrival measurement .................................................. 23
Figure 3.4. Software Radio ......................................................................... 24
Figure 3.5. AM broadcasting radio navigation ........................................... 25
...................... Figure 4.1 : Time variation of an AM signal and its spectnim 29
Figure 4.2. Spectrum of 1 300 kHz double sideband AM radio signal ........ -30
Figure 4.3. AM broadcasting wideband receiver ........................................ 34
Figure 4.4. Power supply ........................................................................... 35
Figure 4.5. AM broadcasting wideband receiver schematic diagram ......... 36
Figure 4.6. tow pass filter ......................................................................... 38
Figure 4.7: Two AM wideband receiver housed in an aluminum enclosure . 40
Figure 4.8. Spectnim Analyzer field test cannection .................................. 41
Figure 4.9. A/D anverter field test connection .......................................... 42
Figure 4.10. AM broadcasting wideband receiver field tests ..................... 43
Figure 4.1 ? : Typical spectrum of an AM broadcasting wideband receiver
output .................................................................................... 44
Figure 5.1 : AhIl radio carrier frequency measurement ................................ 47
Figure 5.2. Phase measurement block diagram .......................................... 48
k igure 3.3. rnase measurernenr using airecr rneasurernenr .................... au
Figure 5.4. Phase measurement using DC mixing ...................................... 52
Figure 5.5. Direct phase measurement using low IF .................................. 53
Figure 5.6. Direct phase measurement using high Q BPF on IF ................ 54
........... Figure 5.7. DC mixing phase rneasurement using low IF and PLL 55
Figure 5.8. Direct phase measurernent using PLLs .................................... 57
........................ Figure 6.1 : Digital Signal Processing phase measurement 63
.............................................. Figure A l : Definition of 1 dB compression 7 4
Figure A 2 Wideband receiver frequency response ................................... -76
Figure A3: Mixer schematic diagram and photograph ............................... 78
Figure A4: Phase Lock Loop schematic diargram and photograph ............ 80
Table 1 . 1. lndustrial navigation requirements ........................................... 3
Table 1.2. Current navigation systems ..................................................... 5
Table 4.1 : Local carrier signal levels .......................................................... 31
Table 4.2. Receiver performance ............................................................... 4 0
Table 4.3. Typical AM carrier signal output ............................................... -41
............................... Table 5.1 : Local AM radio stations carrier frequencies 47
................................................... Table 5.2. Phase measurement accuracy 59
Table A l : Receiver frequency response ..................................................... 75
. . N D .............................................................................................. Anaog to Digital
AM ....................................................................................... Amplitude Modulation
ARRL ................................................................. A m e n Radio Relay League
.............................................................................................. BPF Band Pass Filter
D/A ............................................................................................. Digital to Analog
dB .............................. Decibel, a logarithmic unit of relative power measurement
that expresses the ratio of two power levels
dBc .................................... The decibel value of a signal compared to the carrier
dBm ...................................... The decibel value of a signal campared to lmiliwatt
DECCA ...................................................... British Hyperbolic Navigation System
................................................................................ DFT Digital Fourier Transform
DSP ............................................................................. Digitat Signal Processing
CW ............................................................................................ Continuous Wave
emf .......................... .. ......................................................... e l e o i v e force
FCC ........................................................... Federal Communications Commission
FFT. .............................................................................. .Fast Fourier Transforrn
FIR ................................................................................ Finite Impulse Response
FPGA ............................................................. Field Programmable Gate Array
.............................. GLONASS ...................... ... Global Navigation Satellite System
GPS ........................................................................... G loba l Positioning System
IC ............................................................................................... lntegrated Circuit
IEEE ............................................ n s t t t e of Electrical and Electronics Engineers
~r ..................................................................................... ...--.-..------ . - ,
.......................................................................................................... kHz kiloHertz
.................................................................................................. LO Local Oscillator
.......................................................................... Loran L o n g Range Navigation
LPF ................................................................................................ Low Pass Fiiter
..................................................................................................... MHz .MegaHertz
.................................................................. MSPS M i l o n of Samples Per Second
NF ..................................................................................................... Noise Figure
........................................................ OMEGA Worldwide Radio Navigation System
....................................................................................... PCB Printed Circuit Board
......................................................................... PPS Precision Positioning Service
PLL ............................................................................................. Phase Lock Loop
RF ............................................................................................. Radio Frequency
........................................................................................ SA S e l v e Availability
...................................................................................... SNR Signal to Noise Ratio
SOC ............................................... S a Outline IC (surface mount package)
........................................................................ SPS Standard Positioning Service
SV ................................................................................................. Service Vehicle
TEM ..........................................................................T ransvse ElectroMagnetic
THD ............................................................................... Total Hamonic Distortion
............................................................................................ TOA T i m e Of Arrival
VRAT ......................................................... Variable Rate Application Technology
GHAP1 t K 1
INTRODUCTION
1.1 Navigation
Navigation is defined as the science of directing a craft or a person from
one place to another [Il. Some fundamental information is required to conduct
any form of navigation. Basic human navigation uses the senses to provide
information and intelligence to process that information. More complex
navigation uses radionavigation using transmitted etectronic signals.
Radionavigation enables a user to cornpute his position and provides
sufficient information to allow computations to navigate on a desired course.
Navigation systems use data from navigation sensors to determine the directions
required to guide a vehicle along a defined path. The navigation sensors define
the distance or bearing ta a reference station. Radionavigation systems can be
ground-based (such as LORAN) or space-based (such as Global Positioning
System). Highly accurate systems generally transmit a relatively short
wavelength (i.e., high frequency signal) and the user must rernain within lineaf-
sight. Systems broadcasting at a longer wavelength (i.e., low frequency signal)
are not limited to lin&-sight but are generally less accurate [Il.
One type of radionavigation utilizes the concept of time-of-arriva1 (TOA)
ranging to determine user position. TOA ranging measures the tirne it takes for
a Radio Frequency (RF) signal, transrnitted by an emitter (e.g., radio beacon,
satellite) at a known location, to reach a receiver. The emitter-to-receiver
distance can be obtained by multiplying the speed of the signal and the interval
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determine its position.
Most RF signals are either pulsed or continuous wave (CW). In general,
pulse systems are more expensive than CW systems because they require much
more complicated components for generating, tracking, receiving, and clocking
the signals. Continuous wave navigation systems based on phase
measurements, are primarily used in precise positioning.
1.2 Applications
There is a growing demand for precise real time navigation systems which
can provide accuracy of one tenth of a meter or better with an update period of
less than 100 milliseconds [2-51. Such systems could improve productivity in a
variety of industries such as agriculture, mining, forestry, road construction, and
military applications [2,4]. For exampte, it has been estimated that precise real
time navigation systems could reduce some operating costs by 15% in
agriculture [3,4]. Precise navigation could help avoid environmental disasters
such as oil tanker grounding. In surveying, a precise navigation system could
provide a significant saving by eliminating manual surveying techniques such as
manual recording and post processing of information. Similar operational
improvements could be realized for road construction, forestry, and mining. The
importance of the requirements for each industry varies somewhat as show in
Table 1.1 [6]. The potential market for automatic vehicle tracking systems and
navigation systems for land use is very large. The needs for these systems have
exista tor aecaaes; DU me tecnnoiogy was no1 yer avaiiarïre IO proviae me uesrimi
accuracy within acceptable costs [1].
Table 1 .l : Industrial navigation requirements
Application
Agriculture
Open pit Mining
Seismic Suweying
Road Construction
Forestry
Dredging
Range Absolute Position
Yes 1 Yes
Subiective Law 1 15 cm 1 Real 1 Reliable
Cost Accuracy Tirne I I I Yes 1 Yes 1 Yes 1 Yes
1.3 Existing technology
There are many different types of navigation systems in use today.
However, they do not address many of the following basic requirements: real
time updates, mobile, seif-contained, reliable, H.1 meter accuracy, and low cost
[1,2,3,8,9]. ln particular the requirement for high absolute accuracy, real time
performance and low cost can not be satisfied by any existing commercial
system. For example, Global Positioning System (GPS) may obtain an accuracy
of N.l meter when stationary; however, when moving in a relative positioning
mode, the accuracy is reduced to 1.2 meters [6]. Furtherrnore, GPS is not a self-
contained positioning system and user accuracy can be degraded by Selective
Availability (SA) and anti-spoofing [2,9]. A great deal of attention has been
fowsed on GPS as the solution for high precision applications. It has been
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accuracy and real time performance for many applications.[26].
Besides GPS, Global Navigation Satellite Systern (GLONASS) is a
Russian space-based radionaviagtion system that provides the capacity for 3-
dimensional position and velocity determination. It also serves as a world wide
time base. GLONASS provides separate civil and military services. The actual -
measured civil accuracies are better than standard positioning service of GPS
since the GLONASS does not employ selective availability [l ,1 O]. However this
system is not widely used. System constellation has not been completed and
fully operational capability has not been declared. User equipment tends to be
larger and heavier than comparable GPS receivers [ l O].
LORAN-Cl OMEGA, and DECCA are popular navigation systems.
Unfortunately, they can not achieve submeter accuracy over short ranges of a
few kilometers [8]. Carrier wave interference is also a serious problem in
LORAN-C systems 11 41. These systems are mostly outdated and much more
expensive to operate and maintain compared with GPS fi].
One system that has been researched, developed, and marketed locally
is the Agtrak 2020 [12,13,14]. This system uses terrestrial beacons and a
unique application of adaptive filtering to position a moving object. It is a real
time perfonning system for precise, short range navigation and positioning. This
system can detemine absolute position to within M.1 meters in real time with
excetient reliability [13,14]. The major limitations of this system are the range of
the transmitted signal ( l es than 3 km), the requirement for local transmitter
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several paths due to reflection.
A summary of how some existing navigation systems meet the
requirements of the defined applications is shown in Table 1.2 [6].
Table 1.2: Current navigation systems
Navigation 1 3 km 1 ~ocalized ( Low Range Absolute Cost
1 Differential LORAN 1 Yes 1 No 1 Yes
DECCA
1 Differential OMEGA 1 Yes 1 No 1 No
IDifferential GPS 1 Yes 1 No 1 NO
Yes Position 1
No 1 NO No 1 Yes
15 cm Accuracy
Reliable 4 Real Tirne
1.4 Research objective
The objective of this research is to develop techniques ta overcome the
limitations of the current Agtrak 2020 system and yet to maintain the same level
of accuracy of it. Based on this work, an improved navigation system could be
developed through additional research. The new system should have wider
application with a wider operational range, lower cost and easier installation,
operation and maintenance.
1.4.1 Approach
This low cost, precise, real time positioning system would use transmitted
signals from local AM radio stations. These stations broadcast high power,
stable carrier frequencies that may have predictable phase relationships
between stations. Suitable AM radio carriers wuld be used as CWs for phase
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be used to determine the position of the vehicle for navigation.
1.4.2 Methodology
One of the most promising advances in radio technology has been the
development of so called "software radion. This new approach applies direct RF
sampling and uses Digital Signal Processing (DSP) to process radio signals.
The technique greatly reduces the analog functions within a radio system
11 5,16,17].
A navigation system, based on 'software radio", would use a wideband
receiver with a suitable filter placed at the front end of the system to capture al1
channels in an AM radio band. The desired spedrum is then digitized and
individual channels are processed using digital signal processing techniques to
detect their phases. Modem DSP technology and advanœs in data converters
can achieve the speed necessary to provide the system with real time updates.
The system would also be flexible due to the programmable DSP function. The
use of multiple AM broadcasting signals would eliminate the need for multiple
redundant beacons. High power broadcasting of the carrier frequencies woutd
increase the Agtrak 2020 range far beyond that of the current system.
1.4.3 Summary
This thesis outlines proposed receiving and phase measurement systems
and diswsses phase measurement accuracy that can be obtained using
different analog measuring techniques. Chapter two surnmarizes the
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three describes an AM broadcasting based systern that uses phase
measurement for positioning. Chapter four describes a wideband AM radio
receiver that is used as the front end of the proposed receiving and phase
measurement system. Chapter five addresses six methods of phase
measurernent and presents the resuks achieved during field testing. Chapter six
presents the conclusions reached in this research and the areas where future
research may be conducted.
Much effort has been carried out to provide high accuracy real time
navigation systems for the applications listed in Chapter 1. Different site specific
applications need different levels of precision. Many applications require low
cost, high reliability navigation systems with real time performance and an
absolute accuracy of 15 cms over a range of up to 3 krns [3,4]. There are two
general classes of radionavigation systems in use today, ground based and
spaced based systems. Space based systems utilize satellites as the primary
beacons. They include Sequential Collation of Range (SECOR), TRANSIT,
TIMATION, PARUS, TSIKADA, TSYKLON, Global Positioning System (GPS),
Global Navigation Satellite System (GLONASS) and their augmentations such
as International Maritime Satellite Organization (INMARSAT), and Wide Area
Augmentation System (WAAS) [Il. Ground based systems use land-based radio
transrnitters as their beacons. DECCA, GEE, LORAN-A, Omega, LORAN-C and
Maritime Beacons navigation systems fall into this category. Common
navigation systems used today are LORAN-C and GPS. Locally owned based
systems such as Agtrak 2020 are preferred in many applications which do not
require long range but do require a high degree of accuracy.
Three of the most accurate systems (LORAN-Cl GPS and AGTRAK 2020)
will be discussed in terms of both of their advantages and disadvantages.
A. 1 LVnmlU-%4
LORAN is an acronym for Long Range Navigation. LORAN-C was
developed in the 1950s to provide a radionavigation capacity with longer range
and much greater accuracy than its predecessor, LORANA. LORAN-C is a low
frequency (90 to 110 kHz), pulsed, hyperbolic radio navigation system. It
consists of transmitting stations arranged in groups forming chains. At least
three transmitting stations make up a chain. One station is designed as a
master while the others are called secondaries.
The master station and the secondaries transmit radio pulses at precise
time intervals. LORAN-C receivers measure the diifference in time for these
pulsed signals to reach the user. This tirne difference is a measure of distance
from the user to each of the stations. The lacus of points having the same time
difference from a specific master-secondary pair is a curved line of position, as
shown in Figure 2.1.
These curved lines are spheroidal hyperbolas on the curved surface of
the earth. The intersection of two or more lines detemines the position of the
user. In practice, the user reads the observed tirne differences (td) from the
receiver and converts these readings into latitude and longitude using special
charts. The accuracy af LORAN-C depends upon the user's ability to measure
the time differences and knowledge of propagation conditions so that tines of
position can be deterrnined. The signal pulse shape has to be perfectly
wntrolled ta ensure a proper wmparison point for identification by the receiver
11 83
Figure 2.1 : Hyperbolic navigation system
LORAN-C average extends over North America and many other areas of
the world. It is available continuously, 24 hours. a day and has a predidable
error of less than 400 meters. The repeatable and relative acairacy depends
upon the chah geometry and is usually b&w88~ 18 and 90 meters. LORAN-C
can have an operation range up to few thousands kilometers depending on the
mode of the waves used. The skywave m r a g e at night is much greater than
the groundwave during the daytime. Since LORAN-C is intended for longrange
applications and is relatively inaccurate, it does not provide sufficient acairacy
to meet the requirements for many precision navigation applications. At present.
the cost of LORAN-C reœivers is higher than GPS user equipment. There is a
trend for switching from LORAN-C to GPS systems since GPS has adrieved its
initial operational capability. The use of the LORAN-C system is expected to
have no growth in the near ten. As the user equipment becornes outdated, the
transition away from LORAN-C to GPS is now underway. The continued
operation of LORAN-C depends on validating requirements that c m not be met
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operate. In the year 2000, the need for LORAN-C will be re-evaluated 1191.
2.2 Global Positioning System
Spaced based navigation systems have been under development by the
United States and the Soviet Union since the 1970's and have bewme -
operational towards the end of the 1980's. GPS was designed to be a passive,
survivable, continuous system. The system provides any suitably equipped user
with three-dimensional position, velocity and precise tirne information. The
Standard Positioning Service (SPS) is made available free of charge to any
user. The higher levels of acwracy provided by the Precision Positioning
Service (PPS) are denied to unauthorized users.
GPS systems consist of three portions: space, control and user segments.
The satellite constellation wnsists of 24 satellites called Space Vehicles (SV)
arranged in 6 orbital planes with four SVs in each plane. The orbits are about
20,200 km above the earth. The orbit planes are equally spaced (60 degrees)
and indined at ffty-five degrees with respect to the equatorial plane. The
constellation provides the users with between five and eight SVs visible frorn any
point on the earth. A worldwide ground controllmonitoring network monitors the
health and status of the satellites. The Master Control station located at Falcon
Air Force Base in Colorado uploads ephemeris (variation errors) and dock data
to the SVs [20]. The SVs then send subsets of the orbital ephemeris data to
GPS receivers over radio çignals. The user segment consists of GPS receivers
ana rne user wmmuniry. i r ie I wwivurii wrivur r a v siyriais i r iiu )JUSILIUI 1, v w r u ~ i r y
and time. GPS receivers are used for navigation, positioning, time
dissemination and other research.
GPS can provide service to an unlimited number of users since user
receivers operate passively. The system utilizes the concept of one-way time of
arriva1 ranging. The satellites broadcast ranging codes and navigation data on
two carrier frequencies called L I (1 575.42MHz) and L2 (1 227.60MHz). The
carriers are modulated by two pseudo-randorn code signals. Another frequency
(L5) is a contrad option on the Block nF satellite (to replace failing Block IIR) to
increase civilian GPS accuracy [ZI].
The basic operation of GPS is the triangulation of signals from the
satellites. To triangulate, the receiver measures distance using the travel time of
a radio message from the satellite to the receiver. GPS uses accurate docks in
the satellite to measure travel time. Timing information is embedded within the
satellite ranging signal that enables the receiver to calculate when the signal left
the satellite. By noting the time when the signal was received, the satellite-to-
user propagation time can be mmputed. The product of this time and the speed
of light yields the satellite-to-user range. Once distance to a satellite is known,
knowledge of the satellite's location in space is used to complete the calculation.
GPS receivers triangulate a precise position on earth as depicted in
Figure 2.2. Two satellite measurements determine an intersection of two
spheres. A third measurement identifies two points mmmon to the spheres,
while the fourth measurement determines the specific point.
Figure 2.2: Depiction of Global Positioning System triangulating
GPS provides Standard Positioning Service (SPS) to al1 users worldwide.
The SPS predictable accuracies are 100 meters (95%) in the horizontal plane
and 156 meters (95%) in the vertical plane. The acairacy of this SPS is
intentionally degraded to protect US national sewrity interest. This process,
called Selective Availability (SA), controls the availability of the system's full
capabilities. SA was fomially implemented in March 1990. There is a policy
which intends ta discontinue the use of GPS selective availability in the near
future [22]. With the advance of today's integrated circuit technology, GPS
receivers are now small, low cost units. Most experts agree that GPS will
replace most of the navigation systems being used in the past 20 years [23].
Many factors affect the accuracy of GPS systems. Selective Availability is
the single largest source of error for standard positioning service users. With
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erroneous ranging determination. Ephemeris prediction also has errors which
give wrong satellite positions in space. Free electrons in the ionosphere
influence the electrornagnetic wave propagation of satellite radio signals.
Atmosphere affects the propagation speed when the signals enter this layer.
Local temperature, pressure and relative humidity of the troposphere also delay
phase and group velocity of GPS carrier and signal information. Besides noise
and resolution, multipath and shadawing are major sources of error of GPS
receivers on the earth surface. With multipath, a signal arrives at the receiver
via multiple paths due to refledions frorn the earth and nearby objects. Multipath
not only distorts the codes and navigation data but also the phase of the carrier
itself. Another concern with using GPS navigation is signal interruption.
Shading of the antenna by terrain or manmade structures causes interruption. A
"dead-reckoning" navigation system can be employed to reduce errors during
these shadowing periods [24]. In addition, GPS receiver antennas must have
line-of-sight visibility of the entire sky. Depending upon the specific application,
such as navigation of a mobile vehicle, this may present a major problem.
Efforts have been put into developing more accurate GPS systems.
These include Differential GPS (DGPS), International Maritime Satellite
Organization systems (INMARSAT), Wide Area Augmentation System (WAAS)
and the integration of GPS with other systems to provide reliability and integrity
of navigation information. At the present time, commercially available differential
GPS services allow commercial users to routinely obtain 1 meter accuracy
L&Y,LWJ. w ivirv r u i , ui w ri--- ri-, ri--- i irrr . . .--- .. .- . -.. .-. .-- -. -- -- - - - . -.
localized application such as precision farming.
A more accurate technique for using GPS is to use the carrier as the
basic signal to obtain the distance to the satellites instead of using code
modulation. The carrier phase measurements can be made to within a few
degrees, corresponding to a distance of a few millimeters. Although phase can
be rneasured precisely, the exact number of carrier cycles between the satellite
and the receiver is unknown. High precision measurements in real time can only
be achieved when this carrier cycle ambiguity problern is solved to provide low
cost GPS systems [25].
2.3 Agtrak 2020
An electronic positioning and navigation system has been developed and
is being tested by Accutrak Systems Ltd. [14]. The Agtrak 2020 (Morris and
Palmer, 1994) is an RF system that has accurades in the order of 15 cm for a
moving vehicle with a maximum velocity of 40 krnlhr. It uses reference beacons
and it is a cornpletely independent land based system. It provides up to 10
position reports per second. The Agtrak 2020 currently has a range of 3 km and
was designed to address the needs of the level 2 Variable Rate Application
Technology (VRAT), namely the guidance and accurate placement of the
application vehicle 1271. VRAT or SiteSpecific Faming requires real time
position information for the application vehicle. There are 3 levels of accuracy in
VRAT: a) level 1 requires a position accuracy of several meters, b) level 2
should have accuracies 01 petter man -13 cm, C) leve1 3 ~ U S I rwve puuiiiuri
accuracies of 1 cm [27]. The Agtrak 2020 navigation system c m be applied in
surveying, rnining, faming and any other industries which require accurate
positioning in real tirne.
The curent Agtrak 2020 system consists of a navigation wmputer, a
rnaster mobile unit and three to eight stationary beacon units (Figure 2.3). The
system operates by measuring straight line distances from the master mobile
units ta the beacons. The wmputer uses these straight Iine distances and the
coordinates of the beacons to calculate the x-y coordinate of the mobile unit.
1 Remob beacon station Remote h a n staîion 1
Modr Mobile Unit can be Remota beamn station
uaed to navigatm a variety of vehides fmm mmob todons, or driver assisbed by an onboord display.
Remobs bacon station cm be permanent installalions or mmpietely protable, as mquired.
Figure 2.3: The AGTRAK 2020 guidance system
The system electronics includes a microprocessor, digital logic, RF mixers
and transmitters. The carrier and intermediate frequencies are all derived from
one cornmon frequency using Phase Locked Loops and a digital phase detection
system. The critical function of the system is to measure the phase of an
inwrning signai reiarive LU a ni iuwi i i tiiclr clr ir;a uawi ia iu~ . I 1 IF 1 CZ~GI QI uawiraiui
phase can be digitally offset to any desired value prior to transmission. By
perfoming these two functions, it is possible to measure the phase angle whicti
is a measure of the distance from a known location. Several ranges can be used
to compute an x-y wordinate for a moving vehicfe. Currently these functions, as
well as a number of other digital functions, are implemented on a XlLlNX 3030~
series Field Programmable Gate Array (FPGA).
The major limitations of the system are the need for local transrnitter
beawns, the limited signal range and multipath rejection. As a result, the
system requires a minimum of three beacons within a three kilometer radius from
the vehicle being navigated. Boosting the transmitted RF power to increase
navigation range is just a partial solution as the wst of system operation and
maintenance is increased. Due to the range limitations and high wst, an
alternative implementation is necessary.
Because of the shortcomings of currently available navigation systems,
there is an identiied niche of users which needs to be satisfied. The proposed
AM broadcasting based navigation system would eliminate the need for multiple
beacons in the Agtrak 2020 system while still achieving an acceptable accuracy
of less than 0.2 m. With the high power of AM broadcasting signals, the system
range would also increase to well above 20 km. High speed DSP and software
techniques will provide the system with real time updates and a potential for
higher vehicle velocity.
Chapter 3
AM BROADCASTING BASED NAVIGATION SYSTEM
3.1. Distance measurement using phase difference
Navigation systems using phase rneasurement in CW transmission yield
the highest accuracy [28]. Figure 3.1 shows an example of an activa navigation ,
system with a transceiver Iocated on a mobile vehicle. A stationary reference
station is the antenna tower of a transceiver. This system utilizes two-way
transmissions to determine the distance between two stations.
Mobile Station
Figure 3.1 : Distance measurement
Signals transmitted by the reference to the mobile (or vice versa) are time
deiayed. This time delay is determined by the speed of the signals in the
X medium and the traveling distance t, = - .
C
where fd = time delay between stations
c = signal speed in the transmission medium
x = distance between stations
l D D D Y * O I D I Y -O a w u Yvi .ru. .-ri m. m.- .r rri m.. .-. .=.. ., r. -..--- ....---..------ --
available conceming the velocity of propagation of the signal over the path
length. Figure 3.2 below illustrates the relationship between signal wavelength
(L) and distance (x). A CW signal of frequency f (f=c/X) is radiated from a
reference station in an isotropic medium (e.g., air) and is picked up ai a mobile
station. Wavefronts of the radiated wave are indicated by the line joining points
of zero phase angle represented by phase shifts of 2n, 474 6x,.., nx, where n has
even integer values. These wavefronts travel away from the source with a
unifon velocity in al1 directions.
Mobile Staüon
Figure 3.2: Phase and distance of a single frequency CW [29]
At a mobile station, sorne distance x from the stationary source, the
transmitted signal can be detected and analyzed. Assuming no Doppler effect
(Le. the mobile station is not moving toward or away from the source), the
detected signal must have the same frequency as the transmitted CW [29].
I I u w = v = I , k I IUIU 1- Y piII IUYY UYlUJ II I b I IY YIYI IUi uuv r v ri m u .mi..- ri-.- J ----- ----
introduced by the finite time taken for the signal to travel. Therefore, there will
be a constant phase difference at any instant of cornparison between the signal
at a reference station and the signal at a mobile station.
If the signal velocity c is known, then the wavelength can be calculated
as:
velocity in medium c a = = - signal frequency f (3.1
For a sinusoidal continuous waveform, the instantaneous voltage of the
signal radiated at the reference station (assuming a specific reference phase
relative to t=O) is expressed as:
vR(t) = VRsin ((ùt) (3.2)
Where o = 27d is the signal angular velocity. The detected signal at the
mobile station can be found as:
X in which At is the time lag equal to - and its equivalent phase lag is:
C
If this signal is in phase with the source signal then its phase lag is an
integer of 2z : A+ = n2.n (3-6)
The time lag can be expressed using the above relationship (equation 3.4
and 3.6):
7 where T = - is the signal period.
f
Given signal propagation velocity c, distance x becomes:
x = CA^ (3.8)
or x = nh (3.1 O)
It is realized that the measurement of phase difference of the CW
between two points will provide their distance apart. Phase measurements only
indicate part of the phase A4' between O and 2 x or 360 degrees. The actual
total phase difference is given by:
A+ = n2x + A#
where A# = oAt'
hence x = nh + Ah
The phase difference is now due solely to the path length - provided no
unwanted phase changes have been introduced in the process. The
measurement of the phase difference is fundamental in using CWs for distance
determination. The degree of precision in the navigation systems depends on
this phase measurement accuracy. For example, using a 1300 kHz AM radio
carrier signal as a CW, an accuracy of H.1 meters requires a phase
measurement error of M. 16 degrees. Frorn Figure 3.2 and equation 3.1 1 above,
there is a problem in using a single ftequency phase measurernent to detemine
the distance between the mobile station and the reference station. This distance
corresponds to the total phase delay which is given by an integer and a fraction
of the wavelength of the frequency transmitted. Since only a fraction of the
r. .--- .- . . .----. -- W . - -. ., r . .-- - . . . ----. -. . . -. .- -- -. .. ..-,--> -..- " "- 3-- r-- ---- - --
the wavelength can not be uniquely determined. This ambiguity of the correct
integer portion of the phase delay has to be solved. Some method of
detemining the integer n must be incorporated into any navigation instrument
~ 9 1 .
Any frequency in the RF spectrurn can be used as a CW signal. Low
frequencies are limited by the requirement for massive antenna systems but the
transmitted signals are less affected by atmospheric conditions [6,30]. Long
wavelengths provide navigation instrument capable of operation over the longest
range. This long range is possible because of the ground wave mode of
propagation of low frequency radio signals [30]. Frequencies in the GigaHertr
range are limited by terrain and environmental factors; however, navigation
systems using short wavelength signals are generally more accurate [31,32].
3.2. Position determination using triangulation technique
By making distance measurements to multiple reference stations, the
location of a moving vehicle can be detemined in a two-dimensional plane.
Figure 3.3 illustrates a Time Of Arrival (TOA) measurement using a triangulation
technique. By noting the time of arriva1 of a signal from the first beacon, a user
can locate its position somewhere on a circle of radius di . Distance d l is
calculated using a phase difference measurement. If a measurement is
simultaneously made using the ranging signal to a second beacon, the user will
be located somewhere on the circle of radius d2. Relative position of the user is
now at the intersections of the two cirûles. There is an ambiguity of multiple
Intê~Se~ions a1 poinrs n ana 15. nepearing rne rneasurernenc pruwss usir iy CJ
third beacon wllocates the user on the perimeter of circle of radius d3. This
third circle interseds the other two at point A which is the exact user location.
Figure 3.3: Tirne Of Arrlval measurement
3.3. Software radio
Rapid advances in Digital Signal Processing (DSP) tedinology and high-
performance Analog to Digital (ND) converters are enabling a new class of
wideband digital receivers that are altering the course of wireless
communications. These receivers are replacing traditional narrowband
receivers designed around the superheterodyne approach. Wideband receivers
are known as " software radiosn because they make demodulation and fine-
tuning a function of software. Unlike mnventional receivers, the new scherne
uses a single high performance wideband receiver for the entire band of interest.
A broad band of frequencies is captured and digitized for digital mixing and
filtering to select and receive individual channels. A single front-end RF stage is
shared among al1 channels Mi le in conventional receivers, each Channel has a
example of wideband receiver used in a cellular base station.
Figure 3.4: Software Radio
-)
This universal base station approach is the key to getting the wst of
cellular services dom. Aflowing a radio to reconfigure its bandwidth on the fly,
Digtal fiiter (seiect uniqrn channel)
depending on the type of data being transmitted, would require more powerhil
DSP Channel 1
Antenna Cornmon
portable terminals. New services wn be added or broadcast standards c m be
C
changed with a simple software upgrade. The ability of dynamic channel
allocation permits increased overall traffic throughput and trunking efFiciency.
data
The overall result is the increase in frequency muse and in such advanced
features as "bandwidth-ondemand" [33].
Requirements for software radio are the availability of powerful digital
DlA - Digtal filter - (da u n i q ~
signal processors and fast N D converters. However, digital signal processing
OutPa -L
DSP Channel 2
and down Digtal fiiter
(sdact unique chnnei) Channel 3
nas nigner power wrisur I I ~ L I U I I wIripaleu LU 115 al lawy WU ILWI pal L. UGI 1-1 airy, IL
takes more power to perform the receiver function digitally than using analog
techniques. The system can not take advantage of the Q-rise phenornenon as in
the superhet receiver in which signal voltages increase due to the tuning action.
This limitation places a burden on the antenna and the receiver's front end. In
addition, DSP chips require sufficient processing power to perfom necessary .
functions in real time. Fast N D and DIA converters must have good linearity
and wide dynamic range. Quantum leaps in DSP technology, development of
smart antennas, and substantial improvements in data conversion in recent
years have made wideband digital radio receivers practical in many wireless-
communications applications [33].
3.4. AM broadcasting radio navigation system
The AM radio navigation system being developed is based on wideband
sohare radio techniques. Figure 3.5 shows a block diagram for the system.
A n t e n n a
w
R F P r o c e s s i n g
Figure 3.5: AM broadcasting radio navigation system
This system uses AM radio stations as primary beacons. The AM signals
are captured by an antenna placed on a vehicle to be navigated. The AM
moaacasring speanim covers a rrequency range rrom aaa Knr iu I uua nnL. I I ia
RF stage includes an AM wideband receiver which has the ability to detect,
select, and amplify only AM radio signals. This un-tuned receiver offers a
number of advantages over the superheterodyne counterpart. (1) It does not
require high performance analog wmponents such as high Q inducton and
capaciton. (2) The undesired phase distortion due to high Q tuning of the
superhet receiver can be avoided. (3) One receiver c m be used to capture al1
AM signals. However, the receiver requires high gain to provide smcient
voltage output ta the N D converter. The receiver also requires gain control to
adjust the gain accarding to the available input signal levels and the output level
requirements.
The AM spedrum is directly digitized using a fast A/D converter. Fast
conversion is required due to the highest AM broadcasting frequency of 1605
kHz. The A.D converter requires a high aliasing frequency rejedion to minimize
spurious effect. High dynarnic range and a high degree of reliability of the
converter are also important. System precision requires a high number of output
bits to achieve the desired phase measurement accuracy. Unfortunately, this
requirement places a heavy demand on the memory required for data storage
and the speed of the DSP to obtain real time updates. The number of bits
required has been determined to be 12 1451. A low cost, off-the-shelf, 12-bit, 40
Mega Sample Per Second (MSPS) N D converter (ADS800 made by Burr-
~rown@--see Appendix 1 for specificationç) has b e n used. The sarnpling
speed of this converter is sufficient to digitize the AM spectnim directly without
siyr lai uuwr i wr iver aiur 1. ni I GALGI i id1 uu\;n 13 avaiiauiG iu r i tan- ii IG wi i v ~ i LGI
more flexible for future use. The sarnpling frequency can be changed
accordingly to provide ovenampling or undersampling if necessary [45]. Low
power consumption and a simple interfacing make the converter very attractive.
The ADS800 employs digital error correction to provide excellent Nyquyst
differential linearity performance. Low distortion, high Signal to Noise Ratio
(SNR) and a high ovenampling rate capacity give it the entire margin needed for
this application.
Reœiving data from a common bus of the AID converter, one or more
DSP processon perfom the required functions of phase measurements and
channel selection. Basic DSP operations include digital filtering, error correction,
Fast Fourier Transform (FFI), Discrete Fourier Transform (DFT), data handling,
and reœiver gain control. High speed DSP's are required to allow the system
update in real tirne. Positioning and navigating sections receive phase
measurement information from the digital signal processors to carry out
positioning and navigating tasks.
The research is an ongoing project, this thesis addresses the first phase
of the project which includes: (1 ) building a wideband front end receiver, (2)
digitizing AM radio signal for testing, (3) evaluating signal strength and stability,
(4) determining phase measurement accuracy by using local broadcasting AM
radio stations.
uiiapwi .+
BROADCASTING WIDEBAND RECEIVER
4.1. Amplitude modulation signals
AM signals are amplitude modulated carrier waves. The amplitude of the
carrier wavefonn is caused to Vary directly with a modulating voltage [Ml. An
AM radio carrier could be wnsidered a pure sine wave and its instantaneous
voltage is of the fom Ec(t) = E 4 i n ( o c t), in which Ec- is the peak voltage and
oc is the signal angular velocity. This angular velocity wnveys the phase
characteristic of the waveform.
Assume the modulating signal is a sinusoidal wave which has a time
variation voltage of:
e,(t) = E,-sin(amt) (4.1
Then the instantaneous modulated voltage of an AM signal can be expressed in
l
the fom: AM signal = (E- +em(t) )sin(@, t)
A useful measure of the degree of modulation is called
~~ (m) which is defined as: m = - E,,
This index has a value between O and 1 depending on
(4.2)
modulation index
(4.3)
the ratio of peak
modulating voltage and peak carrier voltage at an instant in time.
The AM signal can be written in terms of the modulation index as follow:
AM signal = E-[1+ m sin(cù,t)J sin(a,t) (4.4)
In order to describe an AM signal in the frequency domain, the signal will
be expressed in sine and cosine terms using trigonometric functions.
or:
AM signal = E l + m(sin(o,t))] sin(oct)
AM signal = sin(oct)+0.5m [ ws(o,-w,)t - ~ s ( o ~ + ~ ~ ) t ] (4.5)
The first term on the right hand side of the above equation is the carrier
wave of frequency f.. The second term is a wsine wave having a frequency of
(fc-fm). This component is known as the lower side band frequency. The third
temi is the upper side band of frequency (f.+fm). Both sidebands have the same
amplitude of 0.5m of the carrier.
Figure 4.1(a) illustrates the time variation of a modulated signal. Figure
4.1 (b) shows the frequency spectnim of an AM signal with a carrier frequency of
1 kHz being modulated by a 100 Hz sine wave.
Am plitude Am ~ l i t u d e
tima 300 5 0 0 kqucncy 1500 1000 (Hz)
Io(
lad -
- 1. a
Figure 4.1: Time variation of an AM signal and its spectrum
For AM broadcast signals, the modulating signals are in a band of audio
I
Carrier
frequencies ranging from 20 Hz to 5 kHz. The spectrum of a double side band
- Lower Side band
1300 kHz AM radio with its carrier and sideband frequencies is shown in Figure
-
U P P ~ ~ Side band
7.6. n \ I1# YY.I IYIY YI- YY".~..Y.YY m. I .,,Y ,.Y.,YY..VJ .-.mg- --.ri--., --- ... i- -i. .-
1605 kHz according to Federal Communications Commission (FCC) regulation.
Station frequency assignments are spaced at 10 kHz intervals to prevent
overlapping.
Amplitude
Lower side band
Carrier
Upper side band
13OOkHz Frequency
Figure 4.2: Spectrum of 1300 kHz double sideband AM radio signal
After modulation, an AM signal is amplified and transmitted through an
antenna system in the form of radio waves. A propagated radio wave wntains
both electrostatic and electromagnetic fields of energy. Electromagnetic energy
is propagated through space and guided along transmission lines in the forn of
a transverse electromagnetic wave (TEM wave). The electromagnetic
component of the wave traveling horizontally to the earth's surface will indue a
small voltage termed e.m.f. (electmrnofive force) into any vertical wndudor in its
path. If the wnductor is an antenna, a small cuvent will be caused to flow along
its length under the influence of the induced 0.rn.f. The frequency of this
induced e.m.f. will be the same as the transmitted frequency. An AM receiver
captures radio waves and extracts the desired signals from al1 other radio
amplifies and passes the modulating signals from the radio carrier to the user.
4.2. AM broadcasting wideband receiver design approach
A vertical dipole antenna of one meter in length is used in the system to
pi& up radio waves. The antenna is mounted vartically on a flat metal plate of
.6m x .6m. The plate is used to simulate the top of a vehicle to be navigated and
to provide a ground plane. The antenna can pick up al1 RF frequencies in the
AM radio band. A 50-Ohm coax cable is connected to the antenna and feeds
RF signals to the receiver. For practical purposes, the antenna does not match
for the 50-Ohm cable. Carrier signal strengths of various local AM radio stations
at a field testing site appear in Table 4.1 below.
Table 4.1 : Local camer signal levels
For a 50-Ohm system, an output level of -10dBm is required at the input
of the AID converter. A minimum gain of 65dB is required to amplify four local
AM carriers. This power gain can not be attained with a single stage amplifier.
A multistage amplifier is required for the wideband receiver to achieve the
essential gain requirement. One of the problems of a high gain amplifier is the
PutUr Illa! UI US~lIldllUI 1. I 1 !G bII WII 1 143 &U UO Wi W I U I I Y UWVIYI I W U k W Ili Ili i 1 8 6 -
feedback to the input stage of the amplifier.
Since the received input power depends on transmitted power of the radio
stations, gain control is required in order to adjust the output level for the AID
conversion process. This feature is necessary because the received radio
signal strength, which depends on transmitter power and on the distance from
the antenna to the transmitting towers, could vaiy over a wide range.
lmpedance matching is required to prevent power loss between stages.
The noise Roor has to be kep! as low as possible to provide an adequate Signal
to Noise Ratio (SNR) for precision phase measurements. Finally, the receiver
has to be able to simultaneously capture al1 the AM signals available for
navigation purposes. A minimum of three channels is required ta determine the
location of the vehicle through triangulation.
A number of options were investigated for the receiver and are discussed
below:
1. Multichannel receivers tuned to specific stations. ~otorola@ MC3362
integrated circuit receivers were used. The benefits of using these superhet
receivers are their low cost and their easy implementation. The drawback is that
each channel has to be tuned using separate hardware wmponents. This is not
convenient as the available AM stations have carrier frequencies which Vary
from area to area.
2. Multistage RF amplifier and filtering. This approach used commercial
RF low noise amplifier modules Mich were cascaded to obtain the required
J"." . . "" r-" ""-' " -' " ---. --- - ------. . -- -- --- u-- -- - - -
signals above the AM band. A number of RF amplifiers have been tested
including MAN and MAR modules made by ~inicircuits" and RF amplifiers made
by phi lipsa. These modules have excellent matching characteristics and a
complete receiver can be realized with only a few extemal components.
However, their noise performance (NF=3dB typical [44]) did not meet receiver
requirements and due to their low gain (1 OdB to 15dB per stage), four or more
cascaded stages were required. They are also expensive modules and they
have high power requirement to operate. In addition, it is difFiwlt to implement
gain control using these modules.
3. Multistage wideband receiver and filtering. Three commercial
integrated circuit wideband amplifiers were investigated. Using this approach,
the required gain was obtained using two cascaded stages of the Analog
~ e v i c e s ~ AD603AR amplifien. As with the previous example, a low pass filter
was inserted between stages. This approach gave the best results and will be
described in detail below.
4.3 AM broadcasting wideband receiver
A block diagram for the wideband receiver c m be seen in Figure 4.3. The
circuit wnsists of two gain stage amplifiers and a low pass filter to select AM
radio frequencies. The gain of the cascaded amplifier can be adjusted between
IOdB and 8066 as required. The Mo-stage amplifier operates in sequential
mode for a maximum SNR with low signal distortion. The receiver accepts a 50-
an output voltage swing of 3 Volts peak-to-peak. This driving capacity is
sufficient for the input requirements of the N D converter.
Antenna
converter
Figure 4.3: AM broadcasting wideband receiver
A low pass filter is inserted between the amplification stages with a corner
frequency of 1.8MHz to select the AM radio spectrum. The filter also provides
impedance matching for the two amplifier stages and prevents the circuit from
oscillating under high gain conditions.
4.3.1 AM broadcasting wideband receiver circuit
Three main sections have been designed for the receiver circuit: a power
supply, an amplifier and a fow pass filter. Each part has a different function and
they are const~ded on one Printed Circuit Board (PCB).
4.3.1.1 Power su~ply
A single 12V DC-û.2A supply is required to operate the receiver (see
Figure 4.4). An onboard voltage regulator (LM7805CV) converts this supply into
stages. The supply V, can be adjusted from 9.5V to 1 O.N via VRI .
Feed-through capacitor and ferrite bead
LM7805CV 3 VCC (9.5V-10.7V) - voltage v - -
regulator - 2 .oluF .OluF .OluF
VR 1 (1 .SK)
Figure 4.4: Power Supply
Feed-through capacitors and ferrite beads are used for decoupling
purposes. These components also serve as EMVRF filters and provide noise
suppression.
4.3.1.2 Amplifier
A schematic diagram for the wideband receiver is given in Figure 4.5.
The receiver uses RF lntegrated Circuit (IC) amplifiers (AD603AR) made by
Analog Devices (see Appendix 1 for specifications). These IC's are low noise,
high sensitivity, variable gain operational amplifiers used in RFIIF applications.
The two-stage cascadeci amplifier provides an adjustable gain from 10dB to
8066. Gain variation is achieved by adjusting potentiorneter VR2 manually or by
applying a voltage at the V, terminal after apening solder switch Ri2.
- C I , C ~ , C ~ , C ~ , C ~ , C ~ ~ , C ~ ~ = O . ~ U F - C3, Cl0 = 3ûuF Tantalm - Cage = 0.1 UF -RI,R5=100Ohm - B, R3, R6, R7 = 5.0 KOhm - R4, Rl1= 2.4 KOhm - R8 5.5 Kûhm - RO = 1.05 K o h m - R I 0 = 3.48 KOhm
- Ri2 = 1 KOhm - R l 3 = 5 0 O h t ~ ~ - W?2 = f 5 KOhms poterrtiometer - Al, A2 = Aü6û3AR, Analog Devices - L l , L 2 = 1 2 ~ H - 06, C9 = 1.2nF - C7 = 1.7nF -J I , J2 = M m BNC Recemde
Figure 4.5: AM broadcasting wideband receiver schematic diagram
The operational amplifiers have an impedance of 100 Ohms between their
input terminais (pin 3 and pin 4). Resistor RI of 100 Ohms is placed in parallel
with the first stage input impedance. This combination provides a 50 Ohm match
between the antenna and transmission line (50-Ohm characteristic impedance).
The two cascaded amplifiers require impedance matching to ensure maximum
power transfer. Output resistor R5 has a value of i00 Ohms to match with the
input irnpedance of the second stage. This matching is provided by the
component values of the ladder network low pass filter (see section 4.3.1 -3).
IOW impWUanct3 vb uiur;nir I&J l;a)lar;iiui b~ I ~ V I Q L U ~ IW III ai a i a y w ai IU ri IG
antenna. Capacitors C5 and C9 btock any DC offset voltage at the output of the
first stage which may overload the second stage under high gain condition.
These two capacitors also eliminate low frequency noise since they introduce
high-pass filtering to the circuit.
Both negative inputs of the op-amps (pin 4) are biased at a DC level of
0.5V,. This bias voltage provides a maximum voltage swing at the output of the
op-amps. Two 30pF tantalum capaciton C3 and CIO provide low impedance
paths for ac signals to ground at the op-amp's negative input terminais.
Resistors R4 and R I 1 which are wnnected from the outputs (pin 7) to pin
5 perfon feedback functions. This feedback configuration, combined with the
X-AMPW structure (Analog Devices) of the op-amps, a m p l i s h e s reœiver gain
control. Resistance values of R4 and RI1 detemine maximum gain of the
circuit, for the given resistances, each stage can acquire a maximum power gain
ûf 40dB.
Voltage divider network (R8, R9 and R i O) sets up gain control input "LOU
at pin 2 of the two op-amps. The voltages are offset about 1.1V betwwn two
stages which is equivalent to 40dB differential gain. As the cascaded amplifier
operates in sequential mode, the gain of the second stage increases only when
the first stage reaches its maximum gain.
Gain control is accomplished simply by applying a voltage to the gain
control input 'HI" at pin 1 of the op-amps. Gain increases with the rise of Vw.
The opamp only yields gain when this voltage is greater than the voltage set at
the gain control input "LO" at pin 2 ot the op-amps. Gapacitor G , inrroauces a
time constant for the automatic gain control (AGC) feature. This property is
useful in some applications and rninirnizes distortion due to ripple of Vw
Receiver output can be connected directly to the 50-Ohm input of an N D
converter without impedance rnatching components.
4.3.1.3 Low Pass Filter
The receiver is used as an AM wideband receiver which has a frequency
range of 535 kHz to 1605 kHz. The function of the low pass filter (LPF) in the
circuit is to select the AM spectnim and to prevent unwanted oscillations caused
by the high gain amplifier. The designed filter uses a ffih order Chebyshev
response low pass filter prototype with a ripple of 0.168 in the passband. It is
implemented by using a 6dB insertion loss passive ladder network as show in
Figure 4.6. Components' values were obtained by using norrnatized R, L, and C
with appropriate magnitude and frequency scaling factors to achieve the
required response and impedance matching.
+ - - - A 5th order Chebyshev raspans. Low Pas8 Filtor (normalized at CO -1 radls)
Corn ponent scaling: Cut off frequency: f,, = 1.8 MHz
- R = Km. RN Km = 100 Ohms L1 = L2 = 1.2 uH K
- t = # . L N KI = 2. r . f,, Ra = RL = 100 Ohms
Figure 4.6: Low pass filter (see frequency response in Appendix 2)
4.3.2 Circuit construction
Circuit la yout and construction are critical as stray capacitances and lead
inductances can forrn resonant circuits and are a potential source of circuit
peaking, oscillation, or both. The receiver is constnicted in a double sided
printed circuit board to provide good ground planes for the circuit. Component
leads and wires are made as short as possible to minimize EMllRF interference.
All resistors, capacitors, and inductors are chip components to minimize leads
and to reduce the size of the receiver. The AD603AR op-amps are &pin SOC
package integrated circuit.
Patterns were drawn on both sides of a copper cladded board using an
etching resistant pen. Etchant was applied to removed unwanted mpper on the
printed circuit board . The finished board was cleaned up and populated with
wmponents. A shielded box was used to house the receiver. Required
connedors were brought out and mounted on the box.
Figure 4.7 shows a photograph of two receivers housed in an aluminum
enclosure. BNC mnn8Cfors are used to connect antenna cables and RF outputs
of the receivers. Feed-through capacitors are mounted on the case to maintain
the shield box at ground potential.
Figure 4.7: Two AM Wideband Receiver Housed in an Aluminum Enclosure
4.4. Test result
4.4.1. Bench tests
Various tests have been carried out in the laboratory to verii the receiver
performance. Some charaderistics of the designed AM wideband receiver are
given in Table 4.2. Appendix 3 provides testing procedures and the plot of the
receiver frequency response.
Table 4.2: Receiver performance
Parameter
Frequency range Power Gain Input Noise THD (i MHz input) 1 dB compression lmpedance Power Supply
Receiver
DC-1.8MHz 10-80 dB i r n ~ / J F i ; -58 dBc +9.3 dBm 50 Ohm 12V, 200 mA
Field tests were carried out in a residential area in which strong AM radio
signals could be detected. Two tests were carried out to measure the
performance of the receiver in the field: (1) using a spect~m analyzer, (2) using
an AiD converter and a logic analyzer.
1. Spectnim analvzer
The receiver gain was set at 50dB (using an input signal of 1MHz) and its
output was wnnected directly to a spectnim analyzer (Advantest, Model
R326113361) as shown in Figure 4.8 below.
A n t e n n a
W i d e b a n d S pectrum R e c e i v e r Ana lyser
Figure 4.8: Spectrum Analyzer field test connection
Carrier signal levels were read off the output display of the analyzer using
a resolution of 300 Hz. The results are tabulated in Table 4.3 below.
Table 4.3: Typical AM camer signal output
Carrier Freq. (kHz)
Power level (dBm)
2. N D converter and loqic analvzer
A block diagrarn of the receiver field test wnnection is illustrated in Figure
4.9. Total receiver gain was set at 65 dB (using 1MHz input signal) to get an
output voltage peak of 1V across the input of the A/D converter.
Antenna
Wideband Receiver Analyser
Figure 4.9: N D converter field test connection
Figure 4.10 shows a photograph of the AM wideband receiver connected
to an N D converter and a logic analyzer. The N D converter was programmed
to sample at a rate of 4 MSPS based on the minimum Nyquist criterion referred
to approximate 2MHz input signal. This conversion provided a 12-bit parallel
digital data output. The logic analyzer (HP1662A Logic Analyzer, Hewlett
Packard) captured, displayed and stored data in a file of 8,192 points. A Fast
Fourrier Transfomi (FFT) was perforrned on the data to plot the frequency
spectrurn of the receiver output (see Appendix 4). Due to the nurnber of data
points available, the FFT yielded a minimum resolution of 488 Hz.
Figure 4.1 1 (a) presents a wideband AM radio spectnim of local AM radio
stations received. A weak AM signal (45dBm at the receiver input) of one radio
approximately 300 km from the test site. The other AM station broadcasting at
800 kHz is located about 70 km from the receiver. At the local test site, the
receiver provides at least four local AM channels for phase measurements (620
kHz, 800 kHz, 980 kHz, and 1,300 kHz). The secund plot (Figure 4.1 1 (b))
shows an AM spectrum of the 980 kHz carrier frequency and its sidebands.
Receiver AID A(D AID Antenna Output in~ut Converter
HP1662A ' Logic Anaiyzer
Figure 4.10: AM broadcasting wideband receiver field tests
O 1 620 kHz
800 kHz
i80 kHz
1300 kHz
Figure 4.1 1: Typical spectnim of an AM broadcasting wideband receiver
output
PHASE MEASUREMENT USING DIRECT CONVERSION AM RADIO
One solution to acuirately detemine the position within a localized area
is through the use of a navigation spstem where distance is detemined frorn
phase measurements of continuous wave transmissions. By using a single radio
station with both a mobile and stationary receiver, one can detemine how
accurately phases can be measured. Many facion affect the accuracy of phase
measurement which include frequency fluctuation of the CW, equiprnent error,
circuit temperature drift, stability, environment, and measuring method.
Sinœ AM carriers are used as the primary beacons in the navigation
system, precise phase measurement depends on the stability of these CWs.
The first step is to evaluate the carriers to ensure that they can be used in the
system to measure phase differences.
5.1 Evaluation of AM carrier stability
Any RF carrier can be used as a continuas wave signal to measure the
phase change and determine the position of a rnoving abject. However, frequency
of the CW shwld be constant during phase measurements. Any fluctuation in
frequency causes error in distanœ determination. For a frequency (9 of the CW,
there is a axresponding wave length (X) .)th a total phase change of 360~. If the
frequency is changed to f+6f, the total phase change over distance h will be
3 6 0 ~ ~ . This l a d s to a wmputed distance of h+5X in which 6L is the enor due to
Ine ïïeqUenGy Tluccuarlon. ror exampie, a rn nL u iar iye: II I o I ,aw nriL a11 IW w a v =
results in a position error of Qmm. Therefore the CW frequency must be stable to
limit sources of error in precision navigation systems. CWs are generated using
crystal oscillators which do not have exad nominal osdlating frequencies. The
dominant sources of errot are the inaccuracy uf the oscillator's frequency and
changes in the oscillator's frequency due to ageing, temperature fluctuations and
mechanical stress [35].
Figure 5.1 shows the connedion of a circuit k i n g used to measure the
carrier frequency of a local AM radio stations (schematic diagram of the mixer
MC1496 can be found in Appendix 5 [36]). The wideband receiver deteds and
amplifies the AM signais. The local oscillator (LO) and mixer provide a low
intermediate frequency (IF) to a frequency wunter. The LO is a wavefom generator
(HP53120A) which has a stable frequency output The munter (HP53132A) is a
precision frequency cainter. It has an accuracy of m.2 rnilitiertz when measwing
a 15MHz square wave signal [37l. The LPF diminates high image frequencies Mer
mixing. Changing the frequency of the LO seleds a specific station. The circuit
functions as a superheterodyne radio receiver.
Readings were made at different times of the day to check for the variation of
the camers. Every measurernent of each station was averaged with 1,000 readings
from the frequency counter. The triggering level of the counter was set accordingly
to eliminate the eff8d of modulation in the signal which might cause reading error.
n Waveform Generator (HP53120A)
Figure 5.1 : AM radio carrier frequency rneasurement
The maximum variation of the camers over a period of 24 hours appears in
Table 5.1. The wave length ermr is the distance difference due to this change of
camer frequency.
Table 5.1: Local AM radio stations camer frequencies
Measured 1 Max. freq. 1 Wavelength carrier freq. variation (Hz) error (mm)
Radio station
CKCK CKRM CJME
* Averaged in a pend of 24 hours
Nominal canier ftequency (Hz)
620,000 m,m
t3ocwQo
The stability of the camers has k e n verifid by using a second technique. A
BPF and an amplifier circuit were buiit to diredly rneasure the canier frequency of
the 620 kHz AM radio (without mixing). The outcorne agreed with previous
measurement - frequency drift of the carrier was within 0.5 Hz. This variation is
m i n the frequency tolerance of 10 Hz of AM broadcasting standards. In any event,
a 10 Hz variation wwld m i d e acceptable positional precision.
r r quwriLy var iaiiui I ui rr ic: r;ai r iei 1s ver y 31 11~111 u IQI I v.ii r - t ~ II I aveu agw)
which presents a negligible distance error. The results indicate that AM camer
broadcasts can be used as CWs for positioning in precision navigation. The
accuracy of phase measurement mn be evaluated using these carriers.
5.2 Phase measurement system overview
A block diagram of the phase measurement system can be seen in Figure
5.2. Signals from AM radio stations are picked up by the mobile antenna and
the stationary antenna. These signals are then passed to the wideband direct
conversion receivers which can produce up to 80 dB of gain using two amplifier
gain stages and a fifth order low pass filter (see AM wideband receiver in
Chapter 4).
Mobile Antenna
Phase Phase Oetedor Difference
I
Figure 5.2: Phase
The broadband AM signals
measurernent block diagram
are fed to a phase detector which filters out a
single station from each of the antennas. Note that the two signals will be
aimosr me sarne, excepr rnar rnere wiii ue a pr i a s w si r i i l uucz lu LI 1- UIIIGI -1 I&
signal propagation times from the transmitter. The phase detector output is
directly proportional to the phase difference between the two signals.
A 1,300 kHz AM radio broadcast was chosen for phase measurernents
since this carrier had the shortest wavelength in the band and better accuracy
wuld be achieved using a high frequency CW. A phase measurement error of
k0.16~ is desired in order to achieve a position accuracy of IO.1 m (see
calwlation in Appendix 6). Six different approaches were used to measure phase
shift at the wideband receiver outputs. These included:
1. Measuring directly with phase meter
2. Mixing ta DC
3. Mixing to low intermediate frequency and rneasurement with phase
meter
4. Mixing to 455 kHz IF, high Q bandpass filtering and measurement with
phase meter
5. Mixing to a low frequency, local carrier generation with Phase Lock
Loop (PLL) and mixing to DC
6. Mixing to a low frequency, local carrier generation with PLL and
measurement with phase meter
Phase measurements were made by changing the mobile antenna position a
known distance (up to 5 meters) and recording the resulting phase shifts. The
antenna was moved in 15cm (six inches) increments and then returned to the
original position to verify the phase error. Five hundred readings of the phase meter
shift was calculatecl at each position based on precise distance measurements. The
rewrded measurement was compareci to the theoretical values to calculate the
phase measurement emr at a given position. Ail the mors for al1 positions were
then averaged and recorded as the result accuracy.
5.3 Phase measurements
5.3.1 Direct measurement
The first approach was to diredly measure the phase shift using a HP
53132A Universal countertphase meter as shown in Figure 5.3. The band pass
filters were designed using a sixth order Chebyshev response. The filters had a
œnter frequency of 1,300 kHz, a 3dB bandwidth of 10 kHz and a passband ripple of
IdB. These LC bandpass filters selected the 1,300 kHz carrier from the AM
wideband receivers. Two CWs of the same frequency w r e then fed into the phase
rneter to measure phase diirenœ. The resulting phase shift acairacy was k3O
which translated into a range accuracy of 11 92m.
Mobile Antenna
Wideband Receiver
(HP531 3ZA) Stationary
4-~] Wideband - Receiver
Figure 5.3: Phase measurement using direct measurement
1 1 1 8 3 Up)iII UPW I UUpYI Iuu VI 8 CI IY PI IYYY v a a u u w u i v i a ivi m. ri-, ri-J \ri ri i-
HP53132A phase rneter. The poor accuracy is prirnarily due to the triggering
performance of the meter for high frequency sinusoidal signals. Modulation of
the carrier is also a signifiant source of error as the sideband signals also
trigger the phase meter.
5.3.2 Mixing to DC
When two signals of the same frequency are mixed, they produce a DC
component given by the following expression:
sin(a) sin(a+cp) = 0.5 [ cos(cp) - cos(2a) ] (5.1
The tem cos(<p) in equaüon 5.1 is the magnitude of a DC wmponent which
represents the phase diierenœ between the two signals. The voltage level of the
mixer's output depends on the phase relationship between the two inputs.
The approach of mixing the two input signals to DC is shown in Figure 5.4. A
LPF was addd to the output of the mixer to reject unwanted image frequencies. A
Precision DC voltmeter was essential ta masure aie srnall changes in DC voltage
due to the input signals phase differenœ (5ûpVldegree). The HP34401A multimeter
pmvided the necessary acarracy. When measuring a 100.000 mV DC signal, the
meter has an acwracy of I5pV p]. Using #is technique, a phase shift accuracy of
e0 was obtained which is equivalent to a range aaxiracy of k1.2ûr-n.
This is a simple rnethod to measure the phase dierence between two
signals. One of the limiMions of this approach is temperature drifts in the circuit.
These temperature drifts significantly reduœ the acairacy of the system.
Temperature stabilizaaon can be very complicated and expensive. The detedor
UUWUL VUiUyG V a l Ica 3 1 1 iu3uluaiiy wiu 1 pi iaaw ai i y i ~ ~ a i v - I I LVTW U U Y Y I ~ - . .. mrY.V.
The nonlinearity of the output voltage gives signifimnt emxs in phase measurement
if the phase differenœ is not close to 90? In addition. the detectots phase voltage
charaderistic repeats every 180O instead of 360' which makes phase shïft
calculations more complicated as two possible input phase dierences can produce
the same output voltage [39]. The advantage of this technique is that the mmer
modulation has l e s effect on the phase measurements since both signals have the
same frequencies, including their sidebands.
Mobile Antenna
Mdeband Receiver 4
Stationary Antenna
v Mixer CI (MC1 4i
Figure 5.4: Phase measurement using DC mixing
5.3.3 Low IF measurement
When hm signals are mixed, they produce low intemediate and high image
frequencies. This mixing process will not alter phase charaderistics of the signals.
In the case of an AM signal, the low IF still has the same phase as the AM camer as
shown in equation 5.2
hl carrier LO lob IF high image frequency
Sinœ the phase charaderistic of the original signal is preserved after rnixing. The
IFS c m be used to measure phase differenœ between two AM carriers.
The third approach was to mix the two signals to a lbwer IF and to use the
phase meter to measure phase differences (Figure 5.5). The two CWs were mixed
to 1 kHz IF wing a 10 of 1,301 kHz. The unwanted image frequencies resulting
fmm mixing were rejeded by a LPF wiih a corner frequency of 10 kHz. The two
input signals were identical in frequency. The 1 kHz IFS were fed diredly into the
HP531 32A phase meter to measure their phase differenœs. This technique took
advantage of the improved phase meter acairacy for lower frequency input signals.
Using this approach a phase shift acairacy of k1° was adiieved.
Mobile Antenna
-, Mixer and LPF A
Phase Phase Meter Difierence
Mixer and LPF
Figure 5.5: Direct phase measurement using low IF
LPF cm not rejed al1 the modulating signals. These sideband frequencies can be
as close as 20 Hz to the carrier and they may trigger the phase meter causing phase
errors. In addition, the phase rneter is less accurate when measuring a sine wave
signal compare to a square wave input. The approach can be improved by: (1)
building a very high order LPF with an ideal cut off to reject al! modulation and (2)
mnverting the signals into square waves More feeding hem into the phase meter.
5.3.4 High IF and band pass filter phase measuriement
The fourth approach relied on a high Q bandpass crystal filter as depicted in
Figure 5.6. The filter had a œnter frequency of 455 kHz and a bandwidth of 200 Hz.
The two AM signals were rnixed down using a LO of 1,745 kHz to provide a 455 kHz
IF to the aystal filters. The high Q filter with sharp cut off selected only the 1,300
kHz carrier which had been wnverted down to 455 kHz The phase dierenœ
between the IF signals was then measured using the phase meter. The resulting
phase acairacy was il0.
Mobile Antenna
- Mixer -, Wideband BPF 455 kHz Receiver
(HP531 3îA) I Stationary l ' n -
9 A E:; v h a s e 1755 kHz ~0
Difference (Cry-0
Receiver 455 kHz
Mixer (MC1496)
Figure 5.6: Direct phase measurement using high Q BPF on IF
m ..V Yrr. --W. . --i ---- -. .- --. - .-- -- - -- -
in the phase meter. Hawever, the overall accuracy is not improved due to the higher
IF input to the phase meter. Camer modulation is not totally eliminated because the
modulating frequencies are t m dose (20 Hz -5 kHz) to the mmer. The filters can
not reject al1 the sideband frequencies. In addition, high Q filters tend to have phase
shifts in their pass bands and the two filters may not have identical phase shifts.
This difference contributes to range measurement errors.
5.3.5 Low IF, PLL, and DC phase measurement
The fffth approach was more complicated than previous approaches and
relied on two making stages and one phase lock bop. This circuit was adapted from
the original design of P. Shakkottai [4q. First, AM signals were mixed d m to low
IF signals of 1 kHz using a LO as shown in Figure 5.7.
Mobile Antenna
h ,-.--- . -* -.
Loop . . DC mking
!Stationary Antenna Difference
meter m
Mdeband
Mixer ,, , .: . - : - .: -
$ . . . . . . . . . . . . .
Figure 5.7: DC mixing phase measunment using low IF and PPL
The two low IF signals were
converted hem into square waves
then passed through phase lock loops which
(A schematic diagram of this PLL circuit is
v a II I I U A 1 . i I lm yuai u *.au= uuyiuw WI u I= I LLU WYI Y IVH-UY II 1
frequency and phase to the IF signals and were amplified by operational amplifiers.
The two square waves were then fed to a mixer which produced a DC voltage. This
voltage represented the phase difference between two signais as describecl in the
second approach above (section 5.3.2). This technique also required a precision
DC voltmeter to measure small phase differences. A phase shft acairacy of a.8'
was obtained. This approach has many of the advantages and disadvantages of the
previous DC mixing method (section 5.2.2).
5.3.6 Low IF, PLL, and phase meter measurement
The last appmach was to mix the signals ta a low IF and then use a PLL to
canvet them into square waves as shown in Figure 5.8. The hm square wave
outputs of the PLL were fed directly to the HP531 32. phase meter. This technique
taak advantage of the improved accuracy of the phase meter when measuring
square waves at low frequency. The phase meter has a trigger emr inversely
proportional to the stew rate of the input signal at the trigger point [3q. An accuracy
of kO.9 was obtained using this appmach.
Mobile Antenna
Wdeband Receiver
Stationary Antenna
Wdeband Receiver
Mixer ' . , , , .. . . . . .
Figure 5.8: Direct phase measuremerlts wing PLLs
This cimit is superior in phase rneasuring of noisy input signals where
typical signal to noise ratios are near 4 [40]. The result is not as amrate as desired
because the SNR of the measured signals is much less than 4. For navigation
purposes, the noise indudes circuit noise and AM signal noise which is large due to
the modulation of the carrier. The spedral densrty of the modulating signal
dominates the ottier sources of noise. As discussed in chapter 4, the modulation
index (m) of an AM signal is the raüo of maximum modulating voltage (E-) and
maximum camer voltage (L).
and the SNR of the carier with respect to modulating is given by equation 5.4.
VYI I lUl1 III IV W~UULIUI I Y W . V YI IV V.7 l W W U I b W m i i ui i y, ri. m i i . u r i i i rri i i i-riri.i..rri i i. .-W.. -i-
follows: 1
SNR = - m2
For example, an AM signal with a modulation index of 0.75 yields a SNR of
1.78. The worst case happens when the canier is fully modulated or' over
modulated. In sorne instant in time, the PLL locks on to the sideband signals
instead of the camer. This low SNR prevents the PLL from l d n g on to the desired
carrier precisely for phase measurement The major source of emxs in this
approach is still the camer modulation. The other enw mmes from the phase rneter
itsetf sinœ very small phase differences are being measured but this error can be
neglected Much more precise measurements can be made if the sidebands are
removed completely.
5.3.7 Phase measumment surnrnary
As shovm in Table 5.2, the acairacy of phase measurernents depends on the
methoâ used. The PLL using low IF has the best result. This is due to the accuracy
of the phase meter when measuring lav frequency square waves. ln general, the
camer modulation is the main source of errors. The modulating signals tngger the
phase meter which makes incorred carrier phase diffmœs. The primary problem
can be reduω by isolating the camer from noise (mostly the AM modulating
signals) More camet phases can be measured accurately.
i . Direct measurement 2. DC mixing 3. Low IF, phase rneter 4. High IF, BPF, phase meter 5. Low IF, PLL, DC mixing 6. Low IF,PLL, phase meter
Phase measurement Phase shift approach accuracy (O)
Accuracy (meter)*
* See distance calculation in Appendix 6 for 1 -3MHz carrier
u r i a p r c i u
CONCLUSIONS AND FUTURE WORK
6.1 Conclusions
The research presented in this thesis indicates that AM radio caniers can be
used as continuous waves in precision navigation systems. nie stability of the
carriers demonstrates that these signals can be used to measure phase with
negligible error due to their frequency fluctuation. One drawback in using these
signals is the phase measurement accuracy required for these low frequency RF
signals. For precision distance measurements, a smaller phase error is required
compareci with the use of higher frequency radio waves. The use of high pouver AM
broadcasts inmeases operation range and reduces hardware structure of the system
campared to the curent AGTRAK 2020.
The wideband receiver greatly simplifies the RF. front end of the new
navigation system. This receiver a l l m the system ta process multiple channels
concurrently using digital signal processing techniques. Channel setedion is much
easier and more accurate sin- tuning is a fundion of software. Careful design of
the receivw helps improve the SNR and minirnize phase distortion of the received
signals. The receiver is very flexible in itç use. It can be adapted to receive other
wideband frequencies by simply changing the passband of the low pass filter. This
wideband reoeiving technique can be applied in future reœivers as radio stations
move to al1 digital signals (AM&FM will gradually disappear and al1 stations will be
on one band transrnitting digitally).
I I I ICI= -1 I JI IUWl I LI l C l L pl IU3G Il IQCIUUl W l l l G 1 l L U UUll lu a1 6511- L Q H II I I L I U W Y V 1 D NII
frequencies will not provide the accuracy of the current Agtrak 2020 system. The
precision obtained is comparable with other commercial real time navigation
systems such as Differential GPS. To improve the acairacy, Digital Signal
Pracessing techniques are being investigated. Signal processed using digital
technique offers higher seledivity, reduœs system cost and decreases variations
due to wmponent tolerances and drift.
6.2 Future work
The first a m of further stuây would be the implementation of DSP into
phase measurernent techniques. By using digital filten, the modulation in the signal
could be further reduœd in order to isolate the carriers and measure their phase
changes more accurately. The parallel output of an AID converter has to be
interfaced with the serial input of a DSP pracessor. This could be done by using a
tri-state bufier to dock the data into the prooessors' bus. DSP fundions could be
testeci using a simple DSP test txlarû. An FFT would require the highest molution
possible to isolate the camer h m the sidebands to measure its phase. This would
require that a large number of samples be used in the FFT'. An alternative would be
the use of a DFT to measue phases of the carriers. This technique would speed up
proceçsing time because undersampling wuld be deployed sinœ the carrier
frequencies are known. The phase measurernent emrs caused by modulation
would be minimized by the high seladivity of the DFT.
h U - 1 U b V I J b U Y C Y W Y I W Y u W Y I IY YI I WI I-II I U Y Y V V I V I Y Y I V I - L - Y m.-... Y
simulation station. If modulation is introduœd into the signal, the effects on phase
measurernents could be detemined. Field tests could be carried out using the
wideband receivers to measure phase differences as shown in Figure 6.1. The basic
measurement procedures described in Chapter 5 could be used.
Wideband A/D Receiver converter - DSP -
Stationnary Antenna m
Figure 6.1 : Digital Signal Pracessing phase measurement
v
-L
Further study could al- be conduded on increasing the mal time update
PC or Display
rate of the system. This waild accommodate increased vehide speed and reduce
data storage requirement. Higher processing speed could also increase resolution
-
which in tum would improve the phase measurement awracy. This researdi
would involve the investigation of digital signal proœssing time. Faster DSP
pr0~8ssors and optimized processing codes could be investigated. Another
- Wideband Receiver .
apptoach would be consider the use FPGAs as DSP processor. New advanœs in
Dsp
FPGA C s and their applications have made possible the use of FPGAs to perfom
DSP functions [41]. The speed of digital processirtg increases tremendously as
- - - m I I I
DSP processors [41,42,43].
Further research could also be conducted in the area of multipath and signal
interruption. The error introduced by multipath h m several sources could be
evaluated to detemined the accuracy of the system in extreme conditions of
multipath. Multipath and signal intemption are enmuntered when the navigation .
system operates within a forest or an u b n area. In the event of signal interruption,
dead reckoning navigation could be deployed to ensure mntinuous navigation for a
moving vehide. In addition, studies could be dom ta determine the effects of
atrnospheric conditions on the phases of the AM carriers.
[ l ] Elliot D. Kaplan, "Understanding GPS- Principles and Applications, Mobile Communications Series," Boston: Artech House Publishers, 1996, pp. 1-13
[2] Myron Kayton, Navigation Land, Sea, Air 8 Space, New York, New York: IEEE Press, 1990, page 102
[3] Gin Liu, 'Cornpufer Generation of Efiiciency Field Coursen, Regina, Saskatchewan: M.Sc. Thesis, University of Regina, 1988, pp. 1-1 0
[4] Paul Welsh, KAccutrak Hits Mark in Wyoming",askatchewan Business, May-June 1992, pp. 15-16
[5] D. Wells, Guide to GPS Positioning, Fredericton, New Brunswick: University of New Bninswick Graphic Services, 1987, pp. 12.0-1 2.19
[6] Joseph Mervin Toth, 'The Application of Adaptive Fiitem to Navigation", Regina, Saskatchewan: M.Sc. Thesis, University of Regina, 1994, pp. 1-10
m Lawrence A Whitcomb, " Using b w oost magnetic sensors on magneücalïy hostile land veh~es",osition Location and Navigation Symposium, IEEE 1988, pp 34-35.
[8] Pierce J., 'An Introduc2ion to LORAK, IEEE AES Magazine, October 1990, pp. 16-33
[9] Getting I., "The Global Positioning System", IEEE Spectrum, December 1993, pp. 35-47
[ I O Scott Feairheller, Jay Pervis, and Richard Clark, " The Russian GLONASS System, Understanding GPS," Boston: Artech House Publishers, 1 996, pp. 439-465
[il] D.Last, Y.Bian, Tamer Wave lnterfrrrence and LORAN-C receiver pedbmanœ," IEE Proceedings-F, Vol. 140, No. 5, October 1993, pp. 273-283
[12] Toth J., Maçon R., Runtz K., "Precise Navigation Using Adaptive FIR Filtering and Time Damain Spectral Estimation," IEEE Trans. On Aerospace and Electronic Sys., Vot.30, No.4, 1994, pp. 1071 -1 075
[13] Palmer R., Mason R., Runtz K., Morris R., 'VHF Navigation System Based on XILINX FPGA, " 1 994 Canadian Workshop on Field-Programmable Devices, June 1994.
[AS] Brown A., Wolt B., "Digital L-Band Receiver Architecture with Direct RF Sampling," lEEE Position Location and Navigation Symposium, April 1994, pp. 209-2 t 6
[16] Baines R., Russell J., "nie sofi approach," Telephony, July 1994, V01.227, pp. 20-22
[17] Brown Chappell, "RF Research takes Mo paths, " Electronic Engineering Times, Sept. 4, 1995, Issue 864, pp. 35-38
[18] US Coast Guard, Radio Navigation Division, "LORAN-C Users Handbookw, 1992 Edition, Chapter 1.
[19] Bill Schuster, a LORAN-C updates", April 1997, The Technology Team Inc., http:Ihnw. fglsen.wm1boatinglbjll-s/LORANCC htm
[20] Peter H. Dana, "Global Positioning System Overview", The Geographer's Craft Project, Department of Geography, University of Texas et Austin, 1995, pp. 34. (http:llwww.utexas.edu/depts/g~g~~aft/noteslgps/gps.html)
[21] Sam Highley, "Announcements & GPS resources", August 1996, NAVSTAR Global Positioning Systems. (http:lhvww. laafb. af. mi VSMClCZ/homepage/)
[Z] Office of Science and Tedinology Policy National Security Council, "Fact sheet U.S. Global Posifioning System Polic~f, the White House. (http:lhvww. nvacen. uscg. mil/gps/factsgps. pdf)
1231 Scott Lewis, " GPS Markets and Applications, Understanding GPS", Boston: Artech House Publishers, 1996, pp. 47-54 7
[24] Michael Foss, G. Jeffrey Geier, "lnfegration GPS with other sensors, Understanding GPS", Artech House Publishers, 1996, pp. 386-387.
[25] Gary Smith and John Kates, "GPS pmise time for the VMEbusi VMEbus Systems, AprilMay 1996, pp. 29.
[26] Michael Beamish, P.Eng., and Randolph Hartman, "Diffierential GPS lmplementation: The Professional Edge, Association of Professional Engineers and Geoscientists of Saskatchewan, issue no. 49, 1997, pp. 1 8
[27] Ron Palmer, a PosMoning Aspects of Sl'teSpccif Applicaoions: Site- Specific Management for Agriculture Systems, ASA-CSSA-SSSA, 677 South Segae Road Madison, WI, 5371 1, USA, 1995, pp. 613-61 7
66
[28] Joseph Mervin Toth, " The application of Adaptive FIR Filtets to IVavigationn, (Regina, Saskatchewan, M.Sc. Thesis, University of Regina, 1994), pp. 11
[29] C. D. Bumside, "Electronic Distance Measurement," London: Crosby Lockwood & Son Ltd., 1971, pp. 3247
[30] C.D.Bumside, "Electronic Distance Measurement," London: Crosby Lockwood & Son Ltd., 1971, pp. 34
[31] C. D. Bumside, "Electronic Distance Measurement," London: Crosby Lockwood & Son Ltd., 1971, pp. 35
[32] Elliot D. Kaplan, 'Understanding GPS- Principles and Applications, #obi le Communications Series," Boston: Artech House Publishers, 1 996, pp. 2
1331 Ashok Bindra, "DSPs fuel wideband temiver revolution"', Eledron ic Engineering Times, September 1 995, pp. 41 4 2
[34] O. Roddy, J. Coolen, "Electronic Communicationsn, 3rd Edition, Virginia: Reston Publishing Company lnc., - 1 984, pp. 256
[35] Gary Smith and John Kates, 'GPS precjse time for the VMEbus", VMEbus Systems, April/May 1996, pp. 37.
[36] The American Radio Relay League, "The ARRL Handbook for Amateurs, 72nd Edition, USA: The Arnerican Radio Relay League Inc., 1994, pp. 17.47
1371 Hewlett Packard, WP 53 13 IN1 32A Universal Counter, Operafing Guide", Hewlett Packard Company, 1995, pp. 3-8
[38] Hewlett Packard, "HP 34401A Mufimeter, User's Guide", Hewlett Packard Company, 1992, pp. 21 0
[39] The American Radio Relay League, "The ARRL Handbook for Amateurs," 72nd Edition, USA: The American Radio Relay League Inc., 1994, pp. 1 4.37-1 4.39
[40] P. Shakkottai, E.Y. Kwack, and L.H. Back, Analog cimit for the masurement of phase dMeence between two noisy sine-wave signais," American lnstitute of Physics, Review of Scientific Instruments, Vol. 60, No. 9, September 1989, pp. 3081 -3083
141 j L ~ S nnrnrzer, -WK rrlrers wrrn rre~a-rrograrnmaore uare nrrays , mur ai ur VLSl Signal Processing, 6,1993 Kluwer Academic Publishers, Boston, pp. 119- 127
[42] Altera Corp., "Digital P~rocessing with F E X Devices': Produd Information Bulletin 23, January 1996, Ver. 1, A-PIB-02341, pp. 1-5
[43] Altera Corp., "Technology Update: Canada: Electronic Products and Technology, May 1 996, pp.30
1441 Mini-Circuits, "RFIIF Designer's Handbook", 92/92 Edition, Brooklyn, New York: The Mini-Circuits Division of Scientific Components, pp. 3-1 2
1451 Ron Palmer, 'P-se Positioning Using AM Radio Stationsn , Winnipeg, Manitoba: Ph.D. Thesis, University of Manitoba, 1997
Appenaix 1
lntegrated Circuit Specifications
1. ADS800U: 1 2-Bit, 40MHz Sampling, Analog-to-Digital Converter ( ~ u r r - ~ r o w n ~ )
At TA +2S°C. Vs = +SV. Sampling Rate = 40MHz. with a 50% duty cyde clock having a 2ns riseflall time. unless othemise noted
PARAMETER
ADSaOOE (SSOP)
TEMP
Resolution S p e u f i Temperatus Range Operating Temperature Range
ANALOG INPUT D N m l i a l Full Scale lnput Ra+ 00th Inputs.
180" OUI 01 Phase CmrnorrMode Vo4tage Analog lnput B m d l h (-3dB)
Small Signal Full Powu
Input lmpcdancs
DIGITAL INPUT Logic Famity Convert Command
ACCURACYt') Gatn E m
-2WBFSI21 Input WBFS lnput
ITUHCT Compalibk CMOS rrUHCT Compatible CMOS
+2S°C Full
*2S0C Full
+2S°C
+2SeC Full
+2SoC Full
+2S°C Full
+29C Full
+25% Full
+25'C Full
*2PC Full
+2S°C Full
+2S°C Full
+2S°C Full
+2S°C +2S°C +2PC +2S°C +2S°C
Gain Ternpco Power Supply Rqeclm d Gam Inpit Offset E m Powu Supply Rqection ai Offset
CONVERSION CHARACTERISTKS Sarnpla Rate Data Lat-
DYNAMIC CHARACTERISTICS Di i fmt ial Lineanty Emr
I=500kHr LSB LSB LSB LSB LSB CS0
dBFS dBFS dBFS dBFS
dBc dBc
dB dB dB dB
dB dB dB dB %
degrees ns
ps mis ns
No Miuing Codes Integral Lincmty Enw at f = SOMtHz S p v r i w s i m Dynamr Range (SFDR)
f = MOknz (-ldBFS vtpnl
f = 12MHz (-ldBFS input)
Two-Tone Intemodulation Oistortion (IMD)i51 1 = 4 4MHz and 4.5MHz 1-7dBFS each tom)
Sqnal-tMoisa Ratia (SNR) 1 = 5QOkHz (-ldBFS i n w )
f = t2MHz (-ldBFS input)
Signal-te(Noise + Disiartion) (SINAD) f = 500kHz (-ldBFS input)
Diirentiai Gain Erroi Ddiereniial Phase Emr Aperture Delay Time Aperture JRtw Ovemoltaga Recovery TirndBl
NTSC or PAL NTSC or PAL
.5x Full Scala Input
NOTE: (1) An asterisk ( t : ) indicales same speUfications as the ADSEWU. (2) dBFS raters Io dB balow Full Scala. (3) Percentage acwracies are referred to the internai N D Full Scale Range of 4Vpp. (4) Rater to Timing Diagram fodnotes for the guarantead differential lineanty parlofmance end no missing codes condition for the SOlC and SSOP packages. (5) IMD is referred Io the larger of the two inpu! signais. If refened to the peak enwlope signal ( =WB). the intermodulation produas will be 7dB lwer . (6) No 'rotlovef ai bits.
SPEClFlCATlONS (CONT) At TA = +2S°C. V, = +SV. Sampling Rate = 2SMl-t~. wilh e 50% duly cycle clock hwing a 2ns riselfail lime. unless olherwise noted.
PARAMETER
OUTPUTS Logic Famtly Lagic Coding Logic Lcvels
3Stale Enable Timc 3 S t e DisaMe Time
POWER SUPPLY REQUIREMENTS Supply Vdteg~: +Vs supply C m t : +l,
CONDITIONS
Logic Selszable Lopic 'LO'.
CL = 15pF max Lqtc 'HI'.
CL = 15pF max
TEMP
Full
Full
Full
Full +2S'C Full
+2S°C Full
ABSOLUTE MAXIMUM RATlNGS r i
....................................................................................................... +V, +6V .............................................................. Analog Input OV to (+V, + 3Mknv)
................................................................ Logic Input OV to (+V, + 300mV) ......................................................................... Case Temperature + 1 KI 'C
.................................................................... Jurmion Temperaturc + l a OC .............................. ..................................... Storage Tempeahrre .. +125 OC
.................................. Extemal Top Rsiemnca Voltage (REFT) +3.4V Max .............................. Exlemal Bottom Referenw Voltage (REFB) +l. I V Min
VOTE: (1) Stresses above these ratingr may pemgnenîly damage the davicu.
PACKAGUORDERING INFORMATiON PACKAGE ORAWlNG TEYPERANRE
PROOUCT
2&Pin SOC 4 "C 10 + 8 5 T ADSBOOE 2BPin SSOP -40 O C Io +BS°C
NOTE: (1) For deîailed drawing and dimsnsion table. plsase xe end of data sheet. or Appendlx C of Burr-Brcwn IC Data Book.
TLRTCT ~ o m p a t k CMOS SOB or ETC
~ U H C T ~ompatUe CMOS SOB or BfC I
ELECTROSTATIC DISCHARGE SENSlTlVlTY
This integrated circuit can be damaged by ESD. Burr-Brown recommends that al1 integrated circuits be handled with a p propriate precautions. Failure to observe proper handiing and installation procedures can cause damage.
Electrostatic discharge can cause damage ranging fiom performance degradation to complete device failure. Burr- Brown Corporationrecommends that al1 integrated circuits be handled and stored using appropriate ESD protection methods.
AD603-SPECIFICATIONS (8 Th = + 2S°C, Vs = 25 V, -500 mV < Vc I +500 mV. -10 dB to +30 dB Gain Range, R, = 500 St, and CL = 5 pF. unless otherwise noted.)
Mode1 Parameter
INPUT CHARACTERISTICS Input Resistance Input Capacitance Input Noise Spectral Densicy' Noise Figure 1 dB Compression Point Peak Input Voltage
OUTPUT CHARACTERISTICS -3 dB Bandwidth Slew Rate Peak Outpu+ Output Impedance Output Short-Circuit Current Group Delay Change vs. Gain Group Delay Change vs. Frequency Differential Gain Differential Phase Total Harrnonic Distortion 3rd Order h t e r c e ~ t
ACCURACY Gain Accuracy
Tm CO TM Output Offset Voltaga Tm tO TM
Output Offset Variation vs. VG
GAIN CONTROL INTERFACE Gain Scaiinn Factor -
TMIN t~ TM C ornmon-Mode Range Input Bias Cumnt Input Offset Cumnt DifKerential Input Resistance Response Rate
POWER SUPPLY Specified Operathg Range Quiescent Current
T M ~ to T w NOTES
Conditions
Pins 3 to 4
Input Shorc Circuited f = 10 MHz, Gain = max, Rs= IO iZ f = 10 MHz, Gain = max, & = 10 LI
Vom = 100 mV rms RL 2 500 Q RL r 500 R f s 10 MHz
f = 3 MHz; Full Gain Range VG=OVjf=l MEkto10M.H~
f = 10 MHz, Vom= 1 V rms f = 40 MHz, Gain = max, F ~ x = 50 R
Pins 1 to 2 Full 40 dB Gain Change
AD603 Min Typ Max Units
MHz V/P v R mA ns ns % Degree dBc dBm
' T y p i d open or shon-circuited input; noise is lower when sjntcm is set to maximum pin and input is short-circuited. This figure includes &c cffccts of both voltage and currcnt noise sourccs.
'Using mistive loadr of 500 f2 or p a t e r , or with the addition of a 1 kû puiidown miiror when driving lowcr londr. )The dc gain of rhe main amplilier in the AD603 ir x35.7; thus, an hput offset of 100 pV becornes a 3.57 mV output offset. Specifications shown in botdfacc arc tesrcd on aU production units nt fmd elccmcai test. Rcrults frorn those tests arc uscd to calculate outgoing quaiirp leveb. Al1 min and m u speciiïcauons arc guannrtcd, althougb only rhosc shown in boldrPcc arc ta tcd on PU production units. Specifications subject ro chrngc without notice.
ABSOLUTE MAXIMUM RAT~NGs' ............................ Supply Voltage f Vs f 7.5 V
Intemal Voltage V M P (Pin 3) ........... f 2 V Continuous .................................... fVS for 10 ms
....................... GNEG, GPOS (Pins 1,2) 2% .................... Intemal Power Dissipation2 400 mW
Operating Temperature Range ........................... AD603A -40°C to +85"C .......................... AD603S -55°C to +12S°C
Stotage Temperature Range ............ -6S°C to + 150°C Lead Temperature Range (Soldering 60 sec) ........ +300°C
NOTES 'Stmscs abovc thov Iistcd under 'Absolute Muimum hn'ngi" m y cause pemancnt damage to the device. This is a s tms n i h g oniy uid functiond operation of the device at thae o r m y othcrconditioos above those indicared in rhc openrionai sec[ion of [bis specifïcation ir mot impkd. Erpasurc to absolurc maximum nting cooditioos for artcodcd pcriads may a i k t dcvice reliaaliy.
'Theml Chancreristin: 8-Pin SOIC Package: BJ* = 155*CIPQart, = 33.UWan 8-Pin Cenmic Package: = I 40DC/Wan, gc = 15*CIWatl
ORDERïNG GUIDE
NOTES IR = SOIC; Q = Cerâip. 'Refer to AD603 Mîlirary data &cet. Alur av?ilable as 5962-9457203MPA.
. Part Number
Pin Mnemonic
Temperature Range
Pin 1
Pin 2
Pin 3 Pin 4 Pin 5 Pin 6 Pin 7 Pin 8
GPOS
GNEG
W P COMM FDBK VNEG VOUT m'os
Package ~escription'
Description
Package Option1
Gain-Conuol Inpur "HI" (Positive Voltage increases Gain) Gain-Control inpur "LO" (Negative Voltage increases Gain) Amplifier Input Amplifier Ground Connection to Feedback Network Negative Supply input Amplifier Output Positive Supply Input
1
CONNECTION DLAGRAM 8-Rn Plastic SOIC (R) Package 8-Pin Cetamic DIP (Q) Package
CAUTION ESD (electrostatic discharge) sensitive dcvicc. EIectmatic charges as high as 4000 V madiy accumulate o n the hurnaa body and test quipmenr and u n discbargc without dtrtction. Although the AD603 f t a ~ c s proprictary ESD protection circuiay, permanent damage may occur on devices subjmed to high energy clecaostltic dischuges. 'Ibcrcforc, proper ESD prccautions arc rccom- muided to avoid perfonnancc degradation or loss of fuuctionaliry.
m)rp-i IUIA L
Low Pass Filter Frequency Response Simulation
Magnitude [dB] db(V(4)) 0.0 4
frequency [Hz]
frequency [Hz]
PSPICE file: LPF V I 1 O A C I RS 12100 L1 2 3 1.2uH L2 3 4 1.2uH Cl 2 0 1.2nF C2 30 t7nF C3 4 O 1.2nF RL4O 100
Wideband Receiver Bench Tests
1. Total Harmonic Distortion (THD):
A IMHz (midband of AM frequency) sinusoidal signal was fed to the
receiver input and the h a m i c s power (dB@ were measured at the ouput. The
THD was calculated using following formula:
The THD was found to be at -58dBc.
2. IdB compression:
A plot of output vs input (dBm) was plotted to masure the linearity of the
receiver. Figure A l below depicts the definition of 1 dB compression.
P(in) - Figure A1 : Definition of 1dB compression
M. l l - y u ~ l i t v 1 \=apui IJG.
The receiver gain was adjusted to 50dB at midband of AM signal (1MHz
input signal). Gain and phase delayed were measured and recorded with
different frequency settings. Results were tabulated as show in Table A l . The
plots of frequency response are also presented in Figure A 2
Table A1 : Receiver frequency response
Gain (dB)
Phase Delayed (degree)
Gain (dB)
Phase Delayed (Degree)
Figure A2: Wideband receiver frequency msponse
~athcad' file for FFT calculation
This file (MATHCAD 4.0) reads data fite (antO4.dat) 6om the HP Logic Analyser. converts intu voltage Ievels, pzrforms a, and plots: the speclnim
Set number of simples for Et : n =0. .2" ' - 1
Enter s ampling îkequmcy: fi .=4-1o6
Read data: rn = READ ( anl04 ) +- READ ( 8nt04 ) sn =READ (d ) - READ (Mt04 )
Convert data:
Fast Fourier T r d m :
Convert amplitude into dB:
Frequericy conversion :
Plot spectnmi:
Sptnmi of' an AM radio band
9600M) R " s k (Hz) Spectnim of the 980K.H~ AM radio
MC1496 (~otorola@') MIXERS
Figue A3: Mixer schematic diagram and photograph
78
Distance calculaüon
Assuming the signal travel in air which has a velocity of c=300,000,000 mls, a
CW frequency f has a wavelength h af:
h=df
Therfore, a 1.3MHz signal has a wavelength of:
h=230.77rn
This wavelength has an quivalent of 360' phase angle. A 0.1 m distance equates
to a phase shift of:
Or one degree in phase shR has a distance of 0.64m.
PHASE LOCK LOOP
I l
, LPF
1
sine wave input 1
: Running frequency setting Square wave output I T i n g capacibor
1
1 \
1 f
lc 1 \ \ \ 7
Figure A4: Phase Lock Loop schematlc diagram and photograph
80
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