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

Your lSk+ Votre nllénmce

Our file Nolre rdldrence

The author has granted a non- L'auteur a accordé une licence non exclusive licence allowing the exclusive permettant à la National Libréuy of Canada to Bibliothèque nationale du Canada de reproduce, loan, distribute or sel1 reproduire, prêter, distribuer ou copies of this thesis in microform, vendre des copies de cette thèse sous paper or electronic formats. la fome de microfiche/nlm, de

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The author retains ownership of the L'auteur conserve la propriété du copyright in this thesis. Neither the droit d'auteur qui protège cette thèse. thesis nor substantial extracts fkom it Ni la Wse ni des extraits substantiels may be printed or otherwise de celle-ci ne doivent être imprimés reproduced without the author's ou autrement reproduits sans son permission. autorisation.

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

3H, U I W LiULN a1 lu Ur UiauuaPi -pl KJII IWI ia u a r a ai = II iui I ~ ~ ~ I W . W ~ ... ..-. . . ---.-- .. .

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.

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[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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