US Navy Training Course - Electronics Technician - Volume 05 - Navigation Systems

8/11/2019 US Navy Training Course - Electronics Technician - Volume 05 - Navigation Systems

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DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.

NONRESIDENTTRAINING

COURSE

April 1994

Electronics Technician

Volume 5Navigation Systems

NAVEDTRA 14090


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DISTRIBUTION STATEMENT A: Approved for public release; distribution is unlimited.

Although the words he, him, andhis are used sparingly in this course toenhance communication, they are notintended to be gender driven or to affront ordiscriminate against anyone.


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i

PREFACE

By enrolling in this self-study course, you have demonstrated a desire to improve yourself and the Navy.

Remember, however, this self-study course is only one part of the total Navy training program. Practical

experience, schools, selected reading, and your desire to succeed are also necessary to successfully round

out a fully meaningful training program.

COURSE OVERVIEW: In completing this nonresident training course, you should be able to: Identifythe primary navigation systems used by Navy surface vessels;identifythe basic components of andexplain

the basic operation of the Ships Inertial Navigation System (SINS); identifythe basic components of and

explainthe operation of the U.S. Navy Navigation Satellite System (NNSS);identifythe basic components

of andexplainthe operation of the NAVSTAR Global Positioning System (GPS); andidentifythe basic

components of andexplainthe operation of the Tactical Air Navigation (TACAN) system.

THE COURSE: This self-study course is organized into subject matter areas, each containing learning

objectives to help you determine what you should learn along with text and illustrations to help you

understand the information. The subject matter reflects day-to-day requirements and experiences of

personnel in the rating or skill area. It also reflects guidance provided by Enlisted Community Managers

(ECMs) and other senior personnel, technical references, instructions, etc., and either the occupational or

naval standards, which are listed in the Manual of Navy Enlisted Manpower Personnel Classifications

and Occupational Standards, NAVPERS 18068.

THE QUESTIONS: The questions that appear in this course are designed to help you understand the

material in the text.

VALUE: In completing this course, you will improve your military and professional knowledge.

Importantly, it can also help you study for the Navy-wide advancement in rate examination. If you arestudying and discover a reference in the text to another publication for further information, look it up.

1994 Edition Prepared by

ETC(SW/AW) James R. Branch

Published by

NAVAL EDUCATION AND TRAINING

PROFESSIONAL DEVELOPMENT

AND TECHNOLOGY CENTER

NAVSUP Logistics Tracking Number

0504-LP-026-7560


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Sailors Creed

I am a United States Sailor.

I will support and defend theConstitution of the United States of

America and I will obey the ordersof those appointed over me.

I represent the fighting spirit of theNavy and those who have gonebefore me to defend freedom anddemocracy around the world.

I proudly serve my countrys Navycombat team with honor, courageand commitment.

I am committed to excellence andthe fair treatment of all.


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CONTENTS

C H A P T E R P a g e

1. SU RFACE NAVIG ATION SYS TEM S . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1

2. TACTICAL AIR NAVIGATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1

A P P E N D I X

I. Lis t of Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AI-1

II. References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AII-l

INDEX . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Index-1

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SUMMARY OF THE ELECTRONICS TECHNICIANTRAINING SERIES

This series of training manuals was developed to replace the Elec t ron ics

Techni cian 3 & 2 TRAMAN. The content is directed toward personnel working

toward advancement to Electronics Technician Second Class.

The nine volumes in the series are based on major topic areas with which the

ET2 should be fa miliar , Volume 1, Safety, provides an introduction to general safety

as i t relates to the ET rating. It also provides both general and specif ic information

on electronic tag-out procedures, man-aloft procedures, hazardous materials (i.e.,

s ol ve nt s , ba t t e r ie s, a n d v a cu u m t u be s), a n d r a d i a t i on h a z a r d s . Vo lu m e 2 ,

Administ rat ion, discusses COSAL updates, 3-M documentation, supply paperwork,

and other associated administrative topics. Volume 3, Communicat ions Systems,

provides a basic introduction to shipboard and shore-based communication systems.

Systems covered include man-pat radios (i.e., PRC-104, PSC-3) in the hf, vhf, uhf,SATCOM, and shf ranges. Also provided is an introduction to the Communications

Link Interoperabi l i ty System (CLIPS) . Volume 4, Radar Systems, is a basic

introduction to air search, surface search, ground controlled approach, and carrier

con t rol led approach radar systems. Volume 5, N avigat i on Systems, is a basic

introduct ion to navigat ion systems, such as OMEGA, SATNAV, TACAN, and

man-pat systems. Volume 6, Di gital Dat a Systems, is a basic introduction to digital

da ta systems a nd includes discussions a bout SNAP I I, la ptop computers, a nd desktop

computers. Volume 7, Ant enn as and Wave Propagation, is an introduction to wave

propagation, as it pertains to Electronics Technicians, and shipboard and shore-based

antennas. Volume 8, System Concept s, discusses system interfaces, troubleshooting,

sub-systems, dry air, cooling, and power systems. Volume 9, Electro-Optics, i s anintroduction to night vision equipment, lasers, thermal imaging, and fiber optics.

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INSTRUCTIONS FOR TAKING THE COURSE

ASSIGNMENTS

The text pages that you are to study are listed atthe beginning of each assignment. Study these

pages carefully before attempting to answer the

questions. Pay close attention to tables and

illustrations and read the learning objectives.

The learning objectives state what you should be

able to do after studying the material. Answering

the questions correctly helps you accomplish the

objectives.

SELECTING YOUR ANSWERS

Read each question carefully, then select the

BEST answer. You may refer freely to the text.

The answers must be the result of your own

work and decisions. You are prohibited from

referring to or copying the answers of others and

from giving answers to anyone else taking the

course.

SUBMITTING YOUR ASSIGNMENTS

To have your assignments graded, you must be

enrolled in the course with the Nonresident

Training Course Administration Branch at the

Naval Education and Training Professional

Development and Technology Center

(NETPDTC). Following enrollment, there are

two ways of having your assignments graded:

(1) use the Internet to submit your assignments

as you complete them, or (2) send all the

assignments at one time by mail to NETPDTC.

Grading on the Internet: Advantages to

Internet grading are:

you may submit your answers as soon as

you complete an assignment, and

you get your results faster; usually by the

next working day (approximately 24 hours).

In addition to receiving grade results for each

assignment, you will receive course completion

confirmation once you have completed all the

assignments. To submit your assignment

answers via the Internet, go to:

http://courses.cnet.navy.mil

Grading by Mail: When you submit answer

sheets by mail, send all of your assignments at

one time. Do NOT submit individual answer

sheets for grading. Mail all of your assignments

in an envelope, which you either provide

yourself or obtain from your nearest Educational

Services Officer (ESO). Submit answer sheets

to:

COMMANDING OFFICER

NETPDTC N331

6490 SAUFLEY FIELD ROAD

PENSACOLA FL 32559-5000

Answer Sheets: All courses include one

scannable answer sheet for each assignment.

These answer sheets are preprinted with your

SSN, name, assignment number, and course

number. Explanations for completing the answersheets are on the answer sheet.

Do not use answer sheet reproductions: Use

only the original answer sheets that we

providereproductions will not work with ourscanning equipment and cannot be processed.

Follow the instructions for marking your

answers on the answer sheet. Be sure that blocks

1, 2, and 3 are filled in correctly. Thisinformation is necessary for your course to be

properly processed and for you to receive credit

for your work.

COMPLETION TIME

Courses must be completed within 12 months

from the date of enrollment. This includes time

required to resubmit failed assignments.


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PASS/FAIL ASSIGNMENT PROCEDURES

If your overall course score is 3.2 or higher, you

will pass the course and will not be required to

resubmit assignments. Once your assignmentshave been graded you will receive course

completion confirmation.

If you receive less than a 3.2 on any assignment

and your overall course score is below 3.2, youwill be given the opportunity to resubmit failed

assignments. You may resubmit failed

assignments only once. Internet students will

receive notification when they have failed an

assignment--they may then resubmit failedassignments on the web site. Internet students

may view and print results for failed

assignments from the web site. Students who

submit by mail will receive a failing result letterand a new answer sheet for resubmission of each

failed assignment.

COMPLETION CONFIRMATION

After successfully completing this course, you

will receive a letter of completion.

ERRATA

Errata are used to correct minor errors or delete

obsolete information in a course. Errata mayalso be used to provide instructions to the

student. If a course has an errata, it will be

included as the first page(s) after the front cover.

Errata for all courses can be accessed and

viewed/downloaded at:

http://www.advancement.cnet.navy.mil

STUDENT FEEDBACK QUESTIONS

We value your suggestions, questions, and

criticisms on our courses. If you would like tocommunicate with us regarding this course, we

encourage you, if possible, to use e-mail. If you

write or fax, please use a copy of the Student

Comment form that follows this page.

For subject matter questions:

E-mail: [email protected]

Phone: Comm: (850) 452-1001, Ext. 1713

DSN: 922-1001, Ext. 1713

FAX: (850) 452-1370

(Do not fax answer sheets.)Address: COMMANDING OFFICER

NETPDTC N315



For enrollment, shipping, grading, or

completion letter questions

E-mail: [email protected]

Phone: Toll Free: 877-264-8583

Comm: (850) 452-1511/1181/1859

DSN: 922-1511/1181/1859FAX: (850) 452-1370

(Do not fax answer sheets.)

Address: COMMANDING OFFICER

NETPDTC N331



NAVAL RESERVE RETIREMENT CREDIT

If you are a member of the Naval Reserve, you

may earn retirement points for successfully

completing this course, if authorized undercurrent directives governing retirement of NavalReserve personnel. For Naval Reserve retire-

ment, this course is evaluated at 2 points. (Refer

to Administrative Procedures for Naval

Reservists on Inactive Duty, BUPERSINST

1001.39, for more information about retirementpoints.)


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Student Comments

Course Title: Electronics Technician, Volume 5Navigation Systems

NAVEDTRA: 14090 Date:

We need some information about you:

Rate/Rank and Name: SSN: Command/Unit

Street Address: City: State/FPO: Zip

Your comments, suggestions, etc.:

Privacy Act Statement: Under authority of Title 5, USC 301, information regarding your military status is

requested in processing your comments and in preparing a reply. This information will not be divulged without

written authorization to anyone other than those within DOD for official use in determining performance.

NETPDTC 1550/41 (Rev 4-00


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CHAPTER 1

SURFACE NAVIGATION SYSTEMS

INTRODUCTION

Todays Navy uses various navigational systems

in the fleet. As an ET, you will be responsible for

maintaining these systems.

I n t h i s v o l u m e , w e w i l l c o v e r n a v i g a t i o n

fundamentals, the Ships Inertial Navigation System,

Navy Satel l i te Navigation System, NAVSTAR Global

Positioning System, fathometers, and TACAN. Lets

sta r t wi th na viga t ion fundamenta ls .

NAVIGATION FUNDAMENTALS

In simple terms, navigation is a method of gett ing

from one known point to some distant point . Pi loting,

celestial navigation, and radio navigation are the

commonly used methods. In this chapter , we wil l

discuss radio navigation and i ts components: dead

reckoning, electronic navigation, a n d t a c t i c a l

navigation. The tactical use of NTDS data (tactical

na viga t ion) w a s cover ed in v o l u m e 3 ,

Communications Systems. However, we will review

i t briefly here to help you see how i t fi ts into radio

navigation. We wil l then discuss dead reckoning and

electronic navigation in more detail.

TACTICAL NAVIGATION

Y ou must unde r s t a nd the d i f fe r e nce be twe e n

na v ig a t i on in the t r a d i t i ona l se nse a nd t a c t i ca l

navigation. Tradit ional navigation and piloting are

concerned primarily with safe maneuvering of the

ship with respect to hazards such as shoals, reefs, and

so forth. Tactical navigation is not directly concernedwit h maneuvering the ship in navigable waters. For

the purposes of tactical navigation, absolute posit ion

is unimportant except to the extent that i t supports

determining the relative posit ion of hosti le targets an d

friendly cooperating platforms.

Re me mbe r , t a c t i ca l na v ig a t i on de a l s pr ima r i l y

with fixing the location of the platform to (1) enable

instal led weapon systems to function against intended

targets, (2) prevent ownship loss to or interference

wi th fr iendly weapon systems, and (3) coordina te

o w n s h i p w e a p o n s s y s t e m s w i t h t h o s e o f o t h e r

platforms to achieve maximum effect.

In tactical navigation, navigation data is used by

combat systems, including NTDS, to ensure accuracy

i n t a r g e t t r a ck in g. S h ip s m ov e m en t s a r e

automat ica l ly recorded by computer programs for

applications such as gun laying calculations and Link

11 position reporting. Ships attitudes (pitch, roll, and

heading) are transmitted to various display and user

points , and e lectronic or mathemat ica l computer

s t a b i l i z a t i o n i s a c c o m p l i s h e d , d e p e n d i n g o n t h e

system. For example , pi tch and rol l a re used by

NTDS, missile, sonar, gun, and TACAN systems for

stabil ization data and reference. Heading is used by

the E W direction finding, sonar, a nd ra dar systems for

true and relative bearing display. Ships navigation

and att i tude data are provided by various equipment,

depending on ship class.

DEAD RECKONING

Dead reckoning is the estimating of the ships

posit ion between known navigational points or fixes.

Radio navigation, consisting of terrestr ial systems

s u c h a s O M E G A a n d L O R A N , a n d s p a c e - b a s e d

s y s t e m s , s u c h a s S A TN A V, TR A N S I T, a n d

N A V S T A R G P S , p r o v i d e s a c c u r a t e p o s i t i o n s a t

specific fixes. However, with the exception of some

gunfire support systems that provide nearly constant

posit ional updates with respect to a fixed beacon orprominent landmark, there is a l imit to how often

fixes can be obtained. This requires us to dead reckon

(DR) between the f ixes. Dead reckoning can be as

basic as a DR l ine for course and speed on a plott ing

sheet or as sophisticated as an estimate made by an

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inertia l navigation system that measures the ships

motion in several planes and integrates the results

w i t h a h i g h d e g r e e o f a c c u r a c y . Al though the

methods of dead reckoning may vary, they al l share

the following characteristics: (1) the accuracy of the

est imated posi t ion never exceeds the naviga t ion

method used to obta in the last f ix , and (2) the

accuracy of the estimated posit ion deteriorates over

time.

ELECTRONIC NAVIGATION

Simply put , e lectronic naviga t ion i s a form of

piloting. Pi loting is the branch of navigation in which

a s h i p s p o s i t i o n i s d e t e r m i n e d b y r e f e r r i n g t o

landmarks with known posit ions on the earth. These

reference points may be bearing and distance to a

single object, cross bearings on two or more objects,

or two be a r ing s on the sa me ob je c t w i th a t ime

interval in between.

Position in electronic navigation is determined in

practical ly the same way as piloting, though there is

one important differencethe landmarks from which

the ships position is determined do not have to be

v is ib le f rom the sh ip . Ins tea d , the ir bea r ings a nd

ranges are obtained by electronic means.

T h e a d v a n t a g e s o f e l e c t r o n i c n a v i g a t i o n a r e

obvious. A ships position maybe fixed electronically

in fog or heavy weather that makes i t impossible to

take visual fixes. Also, an electronic fix can be based

on stations far beyond the range of any local bad

w e a t h e r .

Since electronic navigation is the primary form of

navigation in todays Navy, the rest of this chapter

wil l deal with electronic navigation and the roles

played by the fol lowing systems:

1. Long Range Aid to Navigation (LORAN)

2. VLF Radio Navigation (OMEGA)

3. Ships Inertial Navigation System (SINS)

4. Navy Navigation Satel l i te System (NNSS)

5. NAVSTAR Global Positioning System (GPS)

We wi l l a l so br ie f ly d iscuss naviga t ion radar ,

surface search radar , and fathometers.

We will cover TACAN in chapter 2.

LORAN/OMEGATRANSITION AND

BASIC OPERATION

LORAN and OMEGA have been the workhorse

systems for many years. However, they are being

pha se d out . Ba se d on the DO D pol i cy s t a te me nt

reprinted below and because you may see a civi l ian

version aboard your ship from time to t ime, we wil l

simply give you an overview of the two systems. I n

accordance with the 1992 Federal Radio navigation

P lan (FRP) , NAVSTAR wi l l become the pr imaryre f e rence nav iga t i on sys t em fo r su r f ace sh ips ,

submar in es, and air craf t . T he DOD requi rement for

LORAN -C and OM EGA w il l end 31 December 1994

and TRAN S IT w i l l be t erm ina t ed in DECEM BER

1996. Land-based T ACAN and VOR/ DM E ar e to be

phased out by th e year 2000.

LORAN BASICS

L O R A N i s a l o n g - d i s t a n c e r a d i o n a v i g a t i o n

system used by ships at sea to obtain a posit ion fix,

The system is based on the difference in the transit

t ime required for pulsed radio signals to arrive at the

L O R A N r e c e i v e r f r o m m u l t i p l e , s y n c h r o n i z e d ,

om n id ir ect i on a l a s h or e t ra n s m it t er s . L O R A N a l s o

takes advantage of the constant velocity of radio

signals to use the t ime lapse between the arrival of

two signals to measure the differences in distance

f r o m t h e t r a n s m i t t i n g s t a t i o n s t o t h e p o i n t o f

reception. The receiving set provides a direct reading,

in microseconds, of the time difference in the arrival

of the signals. (Some sets automatical ly convert the

readings into lat i tude and longitude.) When the t ime

difference is measured between signals received from

any two LORAN transmitter stat ions, a ships l ine-of-

position (LOP) can be determined.

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OMEGA BASICS ADVANTAGES

O M E G A i s a h y p e r b o l i c p h a s e - d i f f e r e n c e

measurement system. Hyperbolic navigation involves

comparing the phase angles of two or more radio

signals that are synchronized to a common time base.

B y m o v i n g t h e O M E G A r e c e i v e r ( b y s h i p s

movement) and keeping the transmitter stat ions on

f r e que ncy w i th a cons t a n t d i f fe r e nce in t ime a nd

phase, the system can measure the relative phase

relationship between two stations to determine a l ine

of position (LOP) for the ship. The relative phase

angle measured between paired transmitt ing stat ions

depends upon the distance of the receiver from each

t r a n s m i t t e r .

I t i s impor tant to understand tha t a minimum of

tw o tran smitters a re required to obta in a ba sic posit ion

fix. Three or four are necessary to obtain an accurate

fix. Unfortunately, there are many t imes in which

only two t ransmit ters a re ava i lable but three are

desired. One way around this problem is to use the

r e c e i v e r o s c i l l a t o r a s a t h i r d , o r p h a n t o m ,

transmitter . By sett ing the receiver osci l la tor to the

frequency transmitted by each of the two OMEGA

transmitters, the operator can compare the actual

transmitted frequencies to the frequencies of the two

received signals. This compar ison provides two

phase angles. The operator can then compare the two

phase angles to determine a third phase angle. The

three phase angles wil l yield a fix as accurate as a fix

determined from three actual transmitters.

SHIPS INERTIAL

NAVIGATION SYSTEM

The Ships Inertial Navigation System (SINS) is

a na v ig a t i on sys te m tha t ( a f t e r in i t i a l l a t i tude ,

longitude, heading, and orientation conditions are set

into the system) continuously computes the lat i tude

and longitude of the ship by sensing acceleration.

This is in contrast to OMEGA and LORAN, which fix

the ships position by measuring position relative to

some known object . SINS is a highly accurate and

sophisticated dead reckoning device. Lets look at

some of the advantages of using the SINS.

SINS has a major security advantage over other

types of navigation systems because i t is completely

independent of celestial , sight , and radio navigation

a ids. In a ddi t ion, SINS ha s the following a dvanta ges:

1. It is self-contained.

2. It requires minimal outside

information.

3. It cannot be jammed.

4. It is not affected by adverse weather

conditions.

5. It does not radiate energy.

6. It is not detectable by enemy sensors.

Now tha t we have seen the advantages of this

system, lets look at its basic components.

BASIC COMPONENTS

Look at figure 1-1. The basic components of an

i n e r t i a l n a v i g a t i o n s y s t e m a r e a c c e l e r o m e t e r s ,

gyroscopes, servo systems, and the computers (not

shown). Accelerometers measure changes in speed or

direct ion a long the axis in which they l ie . Their

output i s a vol tage , or ser ies of pulses (d ig i ta l ) ,

proportional to whatever acceleration is experienced.

Figure 1-1.Stable platform with inertial components.

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Figure 1-2 shows an E-transformer accelerometer,

while figure 1-3 shows a pulse counting

accelerometer. Two accelerometers (orientated North-

South and East-West, respectively) are mounted on a

gyro-stabilized platform to keep them in a horizontal

position despite changes in ships movement. The

accelerometers are attached to the platform by an

equator ia l mount (gimbal) whose vert ica l axis is

misaligned parallel to the earths polar axis. Thispermits the N-S accelerometer to be aligned along a

longitude meridian and the E-W accelerometer to be

aligned along a lati tude meridian.

Figure 1-2.E-transformer accelerometer.

A three-gyro stabilized platform is maintained in

the horizontal position regardless of the pitch, roll, or

yaw of the ship. Figure 1-4 shows a gimbal-mounted

gyro. Ships heading changes cause the gyro signals

to operate servo system motors, which in turn keep

the platform stabilized. High-performance servo

systems keep the platform stabilized to the desired

accuracy. (You will f ind in-depth information on

accelerometers, gyros, and servo systems in NEETS

Module 15, Pr inc ip les of Synchros , Servos , and

Gyros.).

Maintaining this accuracy over long periods of

time requires tha t the system be upda ted periodically.

This is done by resetting the system using information

from some other navigation means; i.e., electronic,

celestial, or dead reckoning.

Figure 1-3.Pulse counting accelerometer.

Several models of SINS are in use. In general ,

AN/WSN -2 system s ar e insta lled on a uxilia ry sh ips,

AN/WSN -2A syst ems a re inst a lled on subma rines,

a nd AN/WSN-5 sys tems a re ins t a l l ed or be ing

insta l led on surface combatants . In the fo l lowing

pa ra gra phs, you will be int roduced to th e AN/WSN -5

SINS and its advantages over these earlier systems.

Figure 1-4. Gimbal-mounted rate gyro.

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AN/WSN-5 SINS S h i p s n o r t h , e a s t , a n d v e r t i c a l v e l o c i t y

components

The AN/WSN -5 is a st a nd -a lone set t ha t r eplaces

the MK 19 MOD 3 gyrocompass in the fol lowing

class ships: CG 16, CG 26, CGN 9, CGN 25, CGN

35, CGN 36, CGN 38 (except for CGN 41), DDG 37,

DD 963, a nd L H A 1. It a lso repla ces th e AN/WSN -2

stabil ized gyrocompass set in DDG 993, DD 997, and

CGN 41 class ships.

Functional Description

The AN/WSN -5 ha s th e sa me out put capa bilities

a s t he AN/WSN-2. I t uses an acce lerometer-

control led , three axis , gyro-stabi l i zed pla t form to

provide precise output of ships heading, roll, and

pitch data in analog, dual-speed synchro format to

support ships navigation and fire control systems.

Ships heading and a t t i tude da ta a re cont inua l ly and

aut omatical ly derived w hile the equipment senses and

processes physical and electrical inputs of sensedmotion (inertial), gravity, earths rotation, and ships

speed. The equipment has an uninterruptible backup

power supply for use during power losses, and built-

in test equipment (BITE) to provide fault isolation to

th e module/a ssem bly level.

Characteristics

In addition to the common functions described

a bove, th e AN/WSN -5 ad ds a n in creas ed level of

performance to serve as an inertial navigator andp r o v i d e s a d d i t i o n a l a n a l o g a n d d i g i t a l o u t p u t s .

Additional data provided includes position, velocity,

at t i tude, at t i tude rates, and t ime data in both serial and

p a r a l l e l d i g i t a l f o r m a t s , p r o v i d i n g a v a r i e t y o f

int erfa ces. The AN/WS N-5 common ly exis ts in a

dua l-system configura t ion on sur face combatants .

Some exa mples of AN/WSN-5 digita l da ta output s

a r e :

1 . T w o N a v a l T a c t i c a l D a t a S y s t e m ( N T D S )

serial channels transmitt ing:

Ships heading, roll, and pitch

Ships heading rate, rol l rate , and pitch rate

Ships la t i tude, longitude, and GMT

2. Two MIL-STD-1397 NTDS type D high-level

channels to an external computer

3. One MIL-STD-1397 NTDS type A slow, 16-

bit, para llel input/output cha nn el to a Na vigat ionSa telli te (NAVS AT) receiver AN/WRN -5A, G loba l

P osit ioning Sy st em (G P S) receiver AN/WRN-6, or

I/O con sole .

4. On e ser ia l AN/WSN -5 t o AN/WS N-5 digit a l

l ink that provides al ignment data , Navigation Satel l i te

(NAVSAT) fix data , cal ibration constant data , and

other n a vigat ion dat a to th e remote AN/WSN-5.

5, An a dditiona l va riety of input /output NTDS

channels , depending on which f ie ld changes areinstalled.

SATELLITE NAVIGATION SYSTEMS

Sc ie nt i s t s r e a l i ze d tha t na v ig a t i on ba se d on

satel l i te signals was possible after l istening to the

beep generated by Russia s first art i ficial satel l i te ,

Sputnik I. They noticed a shift in the received radio

frequency signals as the satel l i te passed by. This

shift , known as the Doppler effect , is an apparent

change in a received frequency caused by relativemotion between a transmitter and a receiver. As the

distance between the transmitter and the receiver

decreases, the received frequency appears to increase.

As the d istance increases, the rece ived frequency

appears to decrease.

With this discovery, scientists were able to show

tha t by a ccura tely measuring a sat ell i te s Doppler shift

pattern, they could determine the satel l i te s orbit .

They then determined tha t by u sing a known sa tel li te s

orbit, a listener could determine his own position on

the earths surface by observing the satellites Doppler

pa t tern .

Following the first successful satellite launch in

A p r i l 1 9 6 0 , t h e U . S . N a v y N a v i g a t i o n S a t e l l i t e

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System (NNSS) became operational . This system is anall-weather, highly accurate navigation aid, enablingnavigators to obtain accurate navigation fixes from thedata collected during a single pass of an orbitingsatell i te.

The following paragraphs describe the NNSS, i tssat ell ites, Doppler principles, system a ccura cy , an d t wocommon shipboard equipmentsthe AN-WRN-5( V) and

the AN/S RN -19(V)2.

NAVY NAVIGATION SATELLITE SYSTEM

This highly a ccura te, world-wide, a l l wea ther system

enables na vigat ors to obta in fixes a pproximat ely every 2

hours, day or night. Looking at figure 1-5, you can see

that i t consists of earth-orbiting satell i tes, tracking

stations, injection stations, the U.S. Naval Observatory,

a computing center, and shipboard navigation

equipment.

System Satellites

Satell i tes are placed in a circular polar orbit ,

illustrated in figure 1-6, at an altitude of 500 to

(nominally 600) nautical miles. Each satellite orbit

approximately 107 minutes, continually transmit

phase-modulated data every 2 minutes on two

carriers. This data includes time synchronizat

signals, a 400-Hz tone, and fixed and varia

para meters tha t describe the sa tell i tes orbit .

The fixed parameters describe the nominal orbi

the satell i te. Variable parameters (small correction

the fixed parameters) are transmitted at two-min

intervals and describe the fine structure of the satel

orbit. The satellite memory stores sufficient varia

parameters to provide the two-minute orbit correcti

for 16 hours following injection of fresh data into

memory. Since data injections occur about every

hours, the sa tell i te memory w il l not

Figure 1-5.Navy Navigation Satellite System.

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Figure 1-6.Satellite orbits.

run out. Each two-minute long satel l i te message is

t imed so tha t t he end of the 78th bit , wh ich is th e lastbit of the second synchronization signal, coincides

with even 2 minutes of Greenwich mean t ime (GMT).

Thus the satel l i tes can also be used as an accurate

t ime re ference by a l l naviga tors equipped wi th a

sat ell i te na vigation set .

Each satellite is designed to receive, sort, and

s t o r e d a t a t r a n s m i t t e d f r o m t h e g r o u n d a n d t o

retran smit this da ta at scheduled interva ls as i t circles

the earth. Each satel l i te tel ls users which satel l i te i t

is, the time according to the satellite clock, and itspresent loca t ion. With this informat ion, the user s

na v ig a t i on se t ca n de te r mine e xa c t l y whe r e the

s a t e l l i t e i s , o n e o f t h e n e c e s s a r y s t e p s t o w a r d

determining a precise navigational posit ion.

Tracking Stations

Tracking s t a t i o n s a r e l oc a t e d i n M a i n e ,

Minnesota , Cali fornia , and Hawaii . As each satel l i te

passes within radio line-of-sight (los) of each of these

tracking stat ions, i t is tracked to accurately determine

its present a nd fut ure orbits. J ust before predicted

satel l i te acquisi t ion, the tracking stat ions antenna is

pointed toward the satel l i te to acquire i ts signals. As

the satel l i te r ises above the horizon, the tracking

antenna continues to fol low the satel l i te s predicted

path unti l the radio receiver in the tracking stat ion

locks on to the satellites transmitted signal. The

receiver processor and data processing equipment

decode and record the satellite message. The Doppler

tracking signal is digi t ized and sent with the satel l i te

time measurements to the computing center , via a

control center, where a refined orbit is calculated.

The tra cking st at ions ma inta in highly sta ble oscil-

lators that are continually compared against a WWVtransmit ted frequency standard . In addi t ion, the

Naval Observatory sends dai ly messages that give the

e r r or in the t r a nsmi t te d s t a nda r d . The Na va l

observatory error is then added to the data obtained

f r om the f r e que ncy s t a nda r d , a nd cor r e c t i ons a r e

made to the station oscillators. The station oscillators

are used to drive station clocks, which are compared

with the time marks received from the satellite. This

t ime da ta i s t ransmit ted by the t racking sta t ions to the

control center , where the sa te l l i te c lock error i s

calculated and the necessary t ime correction bits areadded or deleted in the next injection message to the

satellite.

Computing Center

The central computing center continually accepts

sa te l li te da ta inputs from the t racking sta t ions a nd the

N a v a l O b ser va t or y . P e r i od i ca l l y , t o o bt a i n f ix ed

or b i t a l pa r a me te r s f o r a s a t e l l i t e , t h e c e n t r a l

computing center computes an orbit for each satellite

that best fi ts the Doppler curves obtained from al ltracking stat ions. Using this computed orbital shape,

the centr al computing center extrapolates t he posit ion

of the satel l i te at each even 2-minutes in universal

t ime for the 12 to 16 hours subsequent to da ta

injection. These various data inputs are supplied to

the injection sta t ions via t he control center , a s is da ta

on the nomina l space of the orbi ts of the other

satel l i tes, commands and t ime correction data for the

sat ell i te , an d an tenna pointing orders for the injection

s ta t ion an tennas .

Injection Station

T h e i n j e c t i o n s t a t i o n s , a f t e r r e c e i v i n g a n d

ver i fying the incoming message from the control

center , s tore the message unt i l i t i s needed for

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transmission to the sa tel l ite . J ust before sat el li te t ime-

of-rise, the injection stations antenna is pointed to

acquire, lock on, and track the satel l i te through the

pass. The receive equipment receives and locks on to

the sa tel li te signa ls and t he injection stat ion tra nsmits

the orbi ta l da ta and appropr ia te commands to the

satel l i te . Transmission to the satel l i te is a t a high bit

rate, so injection is completed in about 15 seconds.

T h e m e s s a g e t r a n s m i t t e d b y t h e s a t e l l i t e

immediately after an injection contains a mix of old

and new da ta . The inject ion sta t ion compares a

readback of the newly injected da ta wi th da ta the

satel l i te should be transmitt ing as a check for errors.

If no errors are detected, injection is complete, If one

or more errors are detected, injection is repeated at

t w o-m in ut e i n t er v a ls (u pd a t i n g t h e v a r i a bl e

para meters as necessar y) unti l sat ell i te transm ission is

verified as being correct.

DOPPLER PRINCIPLES

Look at figure 1-7. Stable oscillator frequencies

radiating from a satel l i te coming toward the receiver

are first received (T1) at a higher frequency than

t r a n s m i t t e d , be ca u s e of t h e v e l oc i t y o f t h e

approaching satellite. The satellites velocity produces

accordion-like compression effects that squeeze the

radio signals as the intervening distance shortens. As

the satel l i te nears i ts closest point of approach, these

compression e f fects lessen rapid ly , unt i l , a t the

moment of closest approach (T2), the cycle count ofthe received frequencies exactly matches those which

are generated. As the satel l i te passes beyond this

p o i n t a n d t r a v e l s a w a y f r o m t h e r e c e i v e r ( T 3 ) ,

expansion effects cause the received frequencies to

drop below the generated frequencies proportionally

to the w idening distance an d th e speed of th e receding

satel l i te .

FACTORS AFFECTING ACCURACY

Measurement of Doppler shift is complicated bythe fact that satel l i te transmissions must pass through

the earths upper atmosphere on their way from space

to the receiver. Electrical ly charged particals in the

i o n o s p h e r i c l a y e r c a u s e r e f r a c t i o n o f t h e s e

transmissions. To solve this problem, the satellites are

designed to broadcast on two frequencies (150 and

400 MHz). The receiver measures the difference in

refraction between the two signals and supplies this

measurement to the computer. The computer uses this

refraction measurement as part of i ts computation to

obta in accura te f ixes. The most ser ious problem

affecting accuracy is the effect of uncertainty in the

vessels velocity on the determination of position.

Velocity computation problems are inherent in the

system. Posi t ion error resul t ing from an error in

velocity measurement is somewhat dependent on the

geometry of the satellite pass. You can expect about

a 0 .2 mi le error for every one-knot error in the

vesse l s ve loci ty . Knowing this , you can see tha t

precision navigation of a moving vessel requires an

accurate measurement of the velocity of the moving

v e s s e l , s u c h a s i s p r o v i d e d b y a g o o d i n e r t i a l

navigation system (See the section on Ships Inertial

N a v i g a t i o n S y s t e m . ) . I n g e n e r a l , i n t e r m i t t e n t

precision navigation fixes would not be of extreme

value for a m oving vessel unless i t h ad some mean s of

interpolating between these precision fixes. A good

inertial navigation system provides such a means, and

simul taneously provides t h e a c c u r a t e v e l o c i t y

measurements required to permit posit ion fixes with

the NNSS.

In summary, precision naviga t ion for moving

vessels cant be provided by the Navy Navigation

Sa tel l ite Syst em alone, but can be provided by the use

of this system in conjunction with a good inertial

system. G iven th e orbital para meters of a sa tel l ite , theDoppler shift of the signal transmitted from that

satellite, and the velocity of the vessel, it is possible

to obta in a na vigational fix i f the satel l i te is w ithin los

of the na viga t ion se t a nd ha s a maximum eleva t ion a t

the time of closest approach (TCA) of between 10

and 70 degrees. Satellite passes suitable for use in

obtaining a navigational fix wil l usually occur at no

m o r e t h a n 2 - h o u r i n t e r v a l s ( d e p e n d i n g o n u s e r

la t i tude and configura t ion of the sa te l l i te cons-

tel lat ion). I t is a ma tter of your viewpoint w hether you

c o n s i d e r t h e i n e r t i a l s y s t e m a s a m e a n s o finterpolating between the satel l i te navigation fixes or

consider the satellite fixes as a means for correcting

the inevitable long term dri l ls (see the paragraphs on

basic components of an inertial navigation system) of

even th e best inertia l na vigation systems.

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Figure 1-7.Doppler shift relative to satellite transmitted frequency.

The tw o m os t c om m on s a te l l i t e nav i g a t i on AN/WRN-5(V) RADIO NAVIGATION SET

syst ems used by t he Na vy a re th e AN/WRN-5 an d t he

AN/SR N-19. The fo l lowing pa ra gra phs prov ideThe AN/WRN-5 Ra dio Na viga t ion Set , show n

descriptions of these navigation sets.figure 1-8, is a receiver-data processor-display s

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d e s i g n e d t o r e c i e v e a n d p h a s e t r a c k s i g n a l s

transmitted by satellites of the NNSS. These signals

are processed to obtain navigation information that is

monitored on video displays and used elsewhere for

ship navigation.

The AN/WRN-5 is design ed t o be used in va rious

configurations as described below. Each of these

configurations is def ined by options in external

equipment used or variations in inputs and outputs.

The options available for alternative configurations

a r e :

1.

2.

3.

4.

5.

6.

Teleprinter, ASR-33

Additional remote video displays, IP-

1154(U )

Fr equen cy s ta nda rd, AN/U RQ-10/23

(external reference)

Dual antennas (separate 400-MHz and

150-MHz antennas)

Input /output bus

External lock indicator

7. 100-KHz output

The fu nct iona l e lement s of t he AN/WRN

include the following components:

1.

2.

3.

4.

5.

6.

7.

8.

Preamplifier unit

Built-in two channel receiver

Built-in expanded data processor unit

(XPDU) with 16K word memory

Front panel keyboard for operator-to-

system interface

Front panel magnetic tape cassette transpo

w i t h r e a d /w r i t e c a p a b i l it y f or O P N A

program loading or data recording

F r on t pane l v i d e o d i s p l ay f o r s y s te m

opera tor input /outpu t

Remote video monitor

Bui l t - in synchro- to-d ig i ta l conver tor fo

interface with the ships speed and heading

sensors to provide dead reckoning capabili

Figure 1-8.AN/WRN-5 front panel.

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and accurate satellite position fixes during

ship ma neuvers

6. Displays inputted speed and heading.

7. Displays inputted set and drif t .

9. Optional addition of a teleprinter

8. Displays data on a tracked satell i te.

The combination of f ictional elements in the

AN/WRN-5 provides ma ny capa bili t ies including

automatic s torage of sa tel l i te information, t ime-

ordered alerts for up to eight satellites, and built-inself test. The front panel video display provides

current t ime, la ti t ude/longitud e, dea d reckoning

position (automatically updated by satellite fixes), and

satell i te tracking information such as f ix merit and

satellite alerts. You will find specific information on

th e capabilities of th is na vigat ion set in t he AN/WRN-

5 operation and maint enance technical ma nual.

9. Performs a self-test of computer functions

[limited t o verificat ion of t he digita l circuitry ).

The AN/S RN -19(V)2 consis t s of t he m a jor

components shown in figure 1-9.

Figure 1-10 shows a simplified block diagram of

this system. The following paragraphs describe these

components.

ANTENNA GROUP OE-284/SRN-19(V)

AN/SRN-19(V)2 RADIO NAVIGATION SET

The AN/SR N-19(V)2 is a n a ut oma tic s hipboa rd

navigation set that provides a continuous display of

the ships position. The ships position, which is

o b t a i n e d b y d e a d r e c k o n i n g o n t r u e s p e e d a n d

heading, is periodically corrected by satellite fixes.

Speci f ica l ly , the navigat ion set can perform the

following functions:

1. After each successful satellite pass, computes

and displays the present location of the ship to a

nominal at-sea accuracy of 0.25 nautical mile.

The a nt enna group consist s of th e AS-3330/SR N-

19(V) a nt enn a a nd AM-7010/S RN -19(V) rf a mplif ier

Antenna

The antenna is a linear, vertically-polarized type

tha t receives rf signals tra nsmitted by th e satell i te. Its

horizonta l pat tern is omnidirect ional ; i ts ver t ica l

pattern varies approximately 11 dB from 10 to 70

degrees above the horizontal plane.

Rf Amplifier

Note: Accuracy of the fix is affected by high The rf amplifier provides initial amplification of

s un spot a c t iv it y . D ur in g t h es e p er iod s, n om in a l t h e 400-M H z s a t el lit e si gn a ls fr om t h e a n t en n a a n d

at-sea accuracy may degrade to approximately then sends them, via rf coaxial cable, to the receiver

0.5 na ut ica l mile. for fur t her a m plif ica t ion a n d pr ocessing. The r f

amplifier consists of a bandpass filter module, a 400-

2. Dead reckons between satellite fixes MHz amplifier, and a dc block module.

3. Computes and displays the range and bearing RECEIVER-PROCESSOR R-2135/SRN-19(V)

from t he present position t o any destinat ion using t he

great circle program. The receiver-processor consis ts of a s ingle

channel (400-MHz) receiver, a 5-MHz reference

4. Computes and displays the next expected rise oscillator, a da ta processor w ith a program ma ble read-

t im e a n d eleva t ion a t clos es t a p pr oa ch of t he only memory (PROM) program, a keyboard, display,

previously t ra cked sa t ellit e, ca s s et t e r ecor d er , t w o s y n ch r o-t o-d ig i t a l (S/D)

converters, and a power supply. It processes inputs

5. Displays GMT accurate to 1 second. from the rf amplifier, ships EM log, gyrocompass,

and receiver-processor keyboard.

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Figure 1-9.AN/SRN-19(V)2 major components.

Receiver

The receiver extracts, amplifies, and formats

message information from the rf signal transmitted

by the sat elli te, and mea sures the Doppler shift of the

signal . The message da ta obtained by demodulat ion of

the rf carrier describes the satell i tes position at the

time of tra nsmission.

Data Processor

This un it pr ocesses input s from t he receiver, ship

EM log, an d gyrocompa ss th rough t he S/D convertors

an d the keyboar d. It th en performs computa tions and

provides the desired outputs to the front pane

display, readout indicator, teleprinter, and cassette

recorder.

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READOUT INDICATOR

AND TELEPRINTER

The readout indicator provides an identical visual

readout of the dat a display ed on th e front pa nel of the

receiver-processor. The readout indicator is usually

located at a site some distance from the receiver-

processor.

The teleprinter provides a permanent record of

displayed data. The printouts for modes 01 and 03

occur every 15 minutes or as selected by the operator.

A printout also occurs each time a display mode is

elected and when satellite fix data is received.

One fin a l note on th e AN/SR N-19 syst em. You

must te l l the equipment where i t i s when i t i s

ini t ia l ized. You must a lso enter information on

antenna height before the system can provide an

accurate fix.

Y o u c a n f i n d s p e c i f i c i n f o r m a t i o n o n t h e

AN/SR N-19(V)2 in th e sh ipboard opera tions a nd

maintenance manual for this navigation set.

NAVSTAR GLOBAL

POSITIONING SYSTEM

N A V S T A R G P S i s a s p a c e - b a s e d , r a d i o

navigation system t h a t p r o v i d e s continuous,

extremely accura te th ree-d imens iona l pos i t ion ,

velocity, and timing signals to users world-wide. It

consists basically of ground control, satellites, and

user equipment, as shown in figure 1-11.

Figure 1-10.AN/SRN-19(V)2 simplified block diagram.

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NOTE

G P S w i l l b e c o m e t h e p r i m a r y r e f e r e n c e

navigation system for surface ships, submarines,

and aircraft . Refer to the DOD policy statement

under the LORAN and OMEGA section of this

chapter for specif ic details on this important

transit ion.

GROUND CONTROL

The ground control segment tra cks t he sa tell ites,

monitors and controls satell i te orbits , and updates the

satell i te navigation data message. The ground control

system consists of unmanned monitor stations and a

manned control center . Monitor s ta t ions , located

throughout the world, use GPS receivers to track each

satellite. Tracking in format ion ga thered by the

monitor stations is sent to the control center, where a

precise position and a clock error for each satellite ar

calculated. The control center also calculates satellit

positioning for the group of satellites. Positionin

data for a single satell i te is called ephemeris data

data for a group of sa tel l i tes is ca l led a lmanac data

Once each 24 hours, the control center transmits th

ephemeris and a lmana c data to each sa t ell ite to updat

the navigat ion data message.

SATELLITES

There ar e 21 a ctive operationa l an d 3 a ctive spar

s a t e l l i t e s i n c i r c u l a r o r b i t s , w i t h a 5 5 - d e g r e

incl inat ion to the ear th . These sa tel l i tes provid

navigation data to the navigation sets. The satell i te

are arranged in six concentric rings that allow them t

orbit the earth twice a day and provide world-wid

continuous coverage. Each satell i te broadcasts tw

Figure 1-11.NAVSTAR GPS major elements.

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26/56

Figure 1-12.Satellite ranging.

Navigation Set Clock Error

GPS nav iga t ion se ts de termine d i s t ance to a

satell i te by accurately measuring the time dif ference

between satell i te signal transmission and when the

navigation set receives this signal. This difference in

time is directly proportional to the distance between

the satellite and the receiver. Therefore, the same

time reference must be used by both the receiver and

the satellite.

The clock in the GPS receiver in not nearly as

accurate as the atomic clock in the satellite. This

causes the receiver and satellite clocks to be slightly

o u t o f s y n c , w h i ch in t u r n ca u s es t h e t i m e

measurements to be inaccurate. The error is further

compounded by the dis tance calcula t ion, so the

position of the navigation set cannot be accurately

determined.

The navigation set compensates for these errors

by using the distance measurement from a fourth

satellite to calculate the clock error common to all

four satell i tes. The navigation set then removes the

clock error from t he dista nce measurements, an d t hen

determines the correct navigation set position.

Signal Delay and Multipath Reception

Two types of atmospheric delay can affect the

accuracy of navigation set signal measurements. The

first is tropospheric delay. Tropospheric delay can be

accurately predicted; the prediction is included in the

a lmanac da t a .

The second type of delay is caused when the

satellite signal passes through the ionosphere. This

type of signal delay is caused by the ionosphere being

thicker in some ar eas a nd by sat elli te signals received

from nearer the horizon having to pass through more

of the ionosphere than those received from directly

overhead. Ionospheric delay wi l l phase shi f t the

lower satellite transmission frequency, L2-RF, more

than the higher frequency, L1-RF. The navigation set

measures ionospheric delay by measuring the phase

shif t between these two signals and then uses this

computation to compensate for the ionospheric delay.

Multipath reception is caused by a sat elli te signal

reflecting off of one or more objects. This causes the

1-16


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eflected signals to reach the navigation set at differentimes th an the original signa l . The reception of mult ipathignals may cause errors in the navigation setalcula tion s. The AN/WRN -6 na viga tion set ma kesperators aware of multipath errors by a fai l or warn

messa ge an d/or fluctua tions in t he car rier-to-noise ra tio.Multipath reception may be corrected by changing thehips position.

AN/WRN-6(V) Satellite Signals Navigation Set

The Sa tellite S igna ls Na viga tion S et AN/WRN-(V)computes accurate position coordinates, elevation,

peed, and time information from signals transmitted by

NAVSTAR G lobal P ositioning Syst em (GP S) sat elli tes. In

he P mode, it h as an accuracy of 16 meters. In the C/A

C/A mode. it ha s a n a ccura cy of 100 meters , th o

better results ha ve been obta ined by individual users.

The AN/WRN -6(V), show n in fig ur e 1-13, opera t e

three modes.

The Initial ization mode is part of the set start

During initial iza tion, the operat or tests current posi

date , and t ime data , ei ther manual ly or from o

equipment. The da ta entered is used to speed up sat e

acquisit ion.

Navigation is the normal operating mode. Du

the navigation mode, the set receives satell i te d

calculates

Figure 1-13.Satellite Navigation Set AN/WRN-6(V).

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navigation data, exchanges data with other interconnected

systems, and monitors the sets performance. The

navigation mode allows the operator to enter mission data;

view position, velocity, and time data; and control the sets

configurat ion.

The self-test mode allows the operator to perform a

complete test of the navigation set at any time. When the

set is in test, it will not track satellites.

The t w o ma jor component s of t he AN/WRN -6(V) a re

th e R-2331/U RN receiver a nd t he indica tor cont rol C-

11702/U R. The other units (an tenna , a ntenna am plifier,

and mounting base) perform functions similar to those of

similar units in other systems. For more detai led

operation and m aintena nce technical manua l.

AN/PSN-8( ) Manpack Navigation Set

The AN/P SN -8( ) opera tes sim ila rly to t he AN/WRN -

6(V), though obviously it is not interfaced with other

equipment. Shown in figure 1-14, each manpack contains

a receiver section an d a comput er section. The receiver

processes the rf signals from the satellites and sends the

satellites positions and times to the computer. The

computer uses t he positions a nd t imes to find the sat ellite

sets position coordina tes, eleva tion, an d chan ges in the

position of the manpack set. The time it takes for the set

to change position is used to compute speed. For more

detai led informat ion on th is na vigation set . refer to th e

inform a tion on t his s yst em, refer t o the AN/WRN-6(V) operators ma nua l for th e AN/P SN -8( ) Manpa ck

Figure 1-14.Manpack Navigation Set AN/PSN-8( ).

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Na viga t ion S e t . Th e AN /V S N - 8( ) V e h i c u l a r

Navigation Set is also included in this manual.

NAVIGATIONAL AIDS

Other equipment used for navigation that ETs are

responsible for includes: navigation radars, surface

search radars (sometimes used as navigation radars)

and fathometers. Information on surface search andnavigation radars is contained in NAVEDTA 12414,

Rada r Systems.

The following p arag rap h s w i l l discuss

fathometers.

FATHOMETERS

Fathometers are used for taking depth soundings.

They are part icularly useful when the vessel is

t rans i t ioning sha l low, unfami l i ar wate rs . A b lock

dia gra m of th e Sona r S ounding S et AN/U QN-4A is

shown in figure 1-15,

On many ships the Sonar Technicians will be

responsible for this equipment, but there are ships

(mostly noncombatants) on which ETs are responsible

for the fathometers. For more detailed information on

fa thometers , re fe r to the appropr ia te equipment

technical manual.

Figure 1-15.AN/UQN-4A functional diagram.

1-19


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TACTICAL AIR

INTRODUCTION

Before we begin discussing TACAN, you need torecall the definition of the polar-coordinate system.

The polar-coordinate system is a geometric system

used to locate points on a plane. In electronics, it is

usually used for plott ing antenna directional patterns.

TACAN is a polar-coordina te type radio a i r-

na v ig a t i on sys te m tha t pr ov ide s a n a i r c r e w w i th

d i s t a n c e i n f o r m a t i o n , f r o m d i s t a n c e m e a s u r i n g

e q u i p m e n t (DME), a n d b e a r i n g ( a z i m u t h )

information. This information, as shown in figure 2-

1, is usually provided by two meters. One meter

indicat es, in na utical miles, the dista nce of the a ircraft

from the surface beacon. The other meter indicates

the direction of flight, in degrees-of-bearing, to the

geographic location of the surface beacon. By using

the TACAN equipment instal led in the aircraft and

T A C A N g r o u n d e q u i p m e n t i n s t a l l e d a b o a r d a

particular surface ship or shore stat ion, a pi lot can

obtain bearing to and distance from that location. He

or she can then either:

(1) fly directly to that particular location, or

CHAPTER 2

NAVIGATION (TACAN)

Figure 2-1.TACAN aircraft indication.

(2) use the bearing and distance from a specific

beacon to fix his or her geographic location.

TACAN PRINCIPLES

The distance measuring concept used in TACAN

e q u i p m e n t i s a n o u t g r o w t h o f r a d a r - r a n g i n g

te chnique s . Ra da r - r a ng ing de te r mine s d i s t a nce by

measuring the round-trip travel t ime of pulsed rf

ene rg y . The r etur n s ig na l (echo) of the r a d ia te d

energy depends on the natural reflection of the radio

waves. H owe ve r , TACAN be a con- t r a nsponde r s

generate art i ficial replies instead of depending on

natural reflection.

Now look at figure 2-2. The airborne equipment

generates t imed interrogation pulse pairs that the

surface TACAN system receives and decodes. After

a 50-sec delay, the transponder responds with a

reply. The airborne DME then converts the round-

trip time to distance from the TACAN facility. The

f r e q u e n c y a n d i d e n t i f i c a t i o n c o d e p r o v i d e t h e

geographic location of the transmitt ing beacon.

TACAN PULSE PAIRS

TACAN transponders use twin-pulse decoders to

pass only those pulse pairs with the proper spacing.

The pur pose o f th i s tw in-pul se t e chnique i s t o

increase the average power radiated and to reduce the

possibility of false signal interference.

After the receiver decodes an interrogation, the

encoder generates the necessary pulse pair required

for the transponders reply. A TACAN pulse pair

generated by airborne or ground equipment is shown

in figure 2-3.

CONSTANT TRANSPONDER

DUTY-CYCLE

In principle,

reply to aircraft

2-1

the TACAN transponder need only

interrogations at 30 pulse pairs-per-


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Figure 2-2.Distance measuring round-trip travel time.

s e c o n d , p e r a i r b o r n e e q u i p m e n t , t o s u p p l y t h e

necessary distance data . However, the total pulse

out put of the transmitter constantly varies, according

to the number of interrogating aircraft . In addit ion,

random noise may tr igger the transmitter .

Figure 2-3.TACAN pulse train.

F o r t h e t r a n s p o n d er t o p r o v id e a z i m u t h

in for ma t ion , the a ve r a g e powe r suppl i e d to the

antenna must be relatively uniform over t ime. To

accomplish this, the transponder is operated on the

constant-duty-cycle principle.

In this method of operation, the receiver uses

automatic gain and squitter (noise generated output)

controls to maintain a constant pulse output to the

t r a n s m i t t e r , a s s h o w n i n f i g u r e 2 - 4 . I f f e w

interrogations are being received, the gain a nd sq uitter

of the receiver increase and add noise-generated pulse

to the pulse train. If more interrogating aircraft come

into range, the gain and squitter decrease and reduce

the number of noise-generated pulses.

The relationship betw een t he gain a nd t he numbe

of pulses i s such tha t only a 2-dBm change in

sensitivity occurs between reception from 1 aircraft

and those from 100 aircraft . An added advantage o

using a constant duty cycle is that overal l transmitter

power drain remains constant .

BEACON-TRANSPONDER

IDENTIFICATION CODE

Before an aircrew can use TACAN information

tha t i ts equipment receives, i t must posit ively identi fy

the transmitting TACAN station. To meet this need,

the ground station transmits an identi fication code at

approximately one-half minute intervals. I t does this

by momentari ly interrupting the transponder distance

data and squitter-generated output with pulse groups

spaced at a 1350-pps ra te. Ea ch pulse group conta ins

tw o sets of 12-sec pulse pairs spa ced 100 sec apa rt .

The duration of the identification pulse groups varies,

to represent Morse-coded characters. The duration

for a dot is 100 to 125 ms, and for a dash 300 to 375

ms. An identification group is shown in figure 2-4.

2-2


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Figure 2-4.Transponder output pulse train.

15-HZ-BEARING INFORMATION The rf energy from the TACAN transmitter is fed

t o t h e a n t e n n a c e n t r a l e l e m e n t , w h i c h h a s n o

The timing of the transmitted pulses supplies the directivi ty in the horizontal plane. Parasi t ic elements

actua l distan ce informa tion to the a ircraft . This leaves pos it ion ed a r o u n d t h e c en t r a l el em e n t a re

amplitude modulation as another medium for the electronically rotated (switched on and off) at 15

t r a n s p o n d e r t o c o n v e y o t h e r i n f o r m a t i o n t o t h e revolutions per minute. (See the section below on the

aircraft. The TACAN beacon-transponder modulates O E -2 7 3( V)/U R N a n t e n n a g r o u p ) . Th e d i s t a n c e

the st rength of the pulse to convey bearing informa tion between the central element and the parasitic elements

by producing a specific directional-radiating pattern is selected to obtain a cardioid radiation pattern. To

r o t a te d a r ound a ve r t i ca l a x i s . Thi s s i g na l , whe n an aircraft a t a specific location, the distance data

pr oper ly r efer ence d, ind ica te s the a i r cr a f t s d ir ect i on pul se s a ppe a r to conta in a 15-H z a mpli tude-modula te d

f r om the TACAN fa ci li t y . Thi s s i gna l a nd d is t a nce s ig na l beca use of the r ot a t i on of the ca r d ioid r a d i a t ion

d a t a g iv e a t w o -p iece f ix (d is t a n ce a n d di rect i on ) f or p a t t er n . Th is pa t t e rn is sh ow n

det ermining specific a ircra ft loca t ion. a nd view B .

in figure 2-5, view A

2-3


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Figure 2-5.TACAN radiation pattern: A. cardioidpattern; B. Ampltitude-modulated pulse pairs.

The aircraft TACAN equipment obtains bearing

information by comparing the 15-Hz modulated signal

wit h a 15-Hz r eference burst sign a l it receives from t heground facility. The phase relationship between the

15-Hz m odulat ed signa l an d th e 15-Hz r eference burst

signal depends on the location of the aircraft in the

cardioid pattern. The 15-Hz reference burst signals

are transmitted when the maximum signal of the

cardioid pattern aims due East. This group of 12 pulse

pairs is commonly referred to as the North or main

reference burst. You can see the relationship between

the reference pulses and the cardioid pat tern by

comparing view A and view B of figure 2-5.

135-HZ BEARING INFORMATION

Errors arising from imperfections in the phase

measuring circuits and radio propagation effects are

known as site error. These errors are significantly

reduced by the addition of 32 outer parasitic elements

added to the electronically scanned antenna. (See the

sect ion on th e OE-273(V)/U RN a nt enn a g roup

Electronically switching these elements modifies th

an tenna cardioid patt ern. Though the cardioid pat ter

is still predominant, it is altered by superimpose

ripples. The aircraft now receives the 15-Hz sign

with a 135-Hz ripple amplitude modulated on th

distance data pulses (figure 2-6).

To furnish a suitable reference for measuring thphase of the 135-Hz component of the envelope wave

the transponder is designed to transmit a coded 135

Hz reference burst similar to that explained for the 15

H z r e fe re nce. Th e 1 35 -H z r e fe r en c e g r ou p i

commonly referred to as the auxiliary or aux referenc

b u r s t .

The composite TACAN signal is composed

2 7 0 0 i n t e r r o g a t i o n r e p l i e s a n d n o i s e p u l s

pairs-per-second, plus 1 8 0 N o r t h b u r s t p u l s

pairs-per-second, 720 auxiliary burst pulse pairs-persecond, for a total of 3600 pulse pairs-per-second, o

7200 pulses-per-second.

TACAN SIGNAL PRIORITIES

P riorities ha ve been esta blished for tra nsmission

the various types of TACAN signals. These prioritie

ar e as

1.

2.

3.

4.

follows:

Reference bursts (North and auxiliary)

Identif ication group

Replies to interrogations

Squitter

Therefore, the identif ication group, replies, o

squi t ter wi l l be momentar i ly interrupted for th

tra nsmission of either the m ain or auxiliary referenc

group. The transmission of replies or squitter will b

interrupted every 37.5 seconds during the transmissionof an identification code dot or dash.

CHARACTERISTICS OF

RADIO BEACON SIGNALS

Depending on what channel (X or Y) the TACAN

is on, the number of pulses-per-second and the puls

2-4


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Figure 2-6.TACAN modulation envelope

spacing a re a chara cteristic of th at part icular TACAN

signal element. However, i t is importa nt to understa nd

tha t proper spacing betw een pulses and pulse pairs is

wha t a ctual ly provides the a ircraf t w i th the means todistinguish between the TACAN pulses and any other

pulses that might be present on the received radio

frequency. Ch eck the r eference dat a in th e appropriat e

technical manual for specific pulse characteristics and

spacing.

TACAN EQUIPMENT

Many different types of TACAN equipment have

been used for a ir na viga tion. Toda y, th e AN/U RN-25is taking over the task of tactical air navigation from

th e older AN/U RN-20 on new const ruct ion ships a nd

as ships complete overhaul. Two types of antennas

a re used w ith th e AN/U RN-25. They a re t he OE -

273(V)/U RN, used prima rily in shipboard insta llat ions,

a nd t he OE-258/U RN, w hich is used prima rily a shore.

Because both antenna systems are similar in theory of

operat ion, we will discuss only t he OE -273/U RN. I n

t h e f o l l o w i n g p a r a g r a p h s , w e w i l l d i s c u s s t h e

AN/U RN-25 a nd th e a nt enna group 0E-273(V)/U RN,

a nd th en w e w ill briefly discuss th e AN/U RN-20.

TACAN SET AN/URN-25

The AN/U RN -25 TACAN is us ed a s a gr ound -

based or shipborne beacon transponder to provide

range and bearing information to aircraft equipped

with TACAN equipment . I t consis ts of two major

u n i t s : t h e Tr a n s p o n d e r G r o u p O X -5 2 /U R N - 25 ,

commonly referred to as unit 1, and the Control-

In dica tor C -10363/U RN-25, commonly referr ed t o as

unit 2. These units are shown in figure 2-7. Eachtransponder is housed in a cabinet with two vertical

drawers, one containing a coder keyer and the other

containing a receiver-transmitter.

The control-indicator displays the status of the

transponder(s) and failure alarms, and allows limited

control of the transponder(s) from a remote location.

2-5


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2-6


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It may be mounted in i ts own cabinet or in a standard

19-inch ra ck.

To increase th e chan nels a vaila ble, the TACAN set

can be operated in either the X or Y mode. The Y

mode cha nges the pulse pair spa cing a nd t he auxiliary

burst count and spacing, an d increases system delay.

ANTENNA GROUP OE-273(V)/URN

Shown in f igure 2-8, the Antenna Group OE-

2 7 3/U R N i s a s o l i d -s t a t e , h i g h -p e r f o r m a n c e ,

electronically-scanned, a l l -band TACAN an tenna

system, complete w ith int egral monitoring system an d

built-in fault isolation capability. The antenna group

develops the coarse and fine bearing modulations

electronically.

Rat her tha n forming the TACAN radiat ion pat tern

by the old mechanical rotation method, the AS-3240

achieves the same ef fec t by digi ta l swi tching of

paras i t ic e lements arranged in concentr ic arrays

around the central radiator. Twelve inner elements

provide the 15-Hz modulation (replacing the single-

phase rotating parasitic element in the mechanically

rotated antenna), and 32 outer elements provide the

135-Hz modulation (replacing the nine outer elements

o f the ro ta ted an tenna) . The 15- an d 135-H z

modulat ion pat tern is provided by elec tronical ly

switching the diodes in each of the parasitic elements

in prescribed time sequence, which is repeated once in

each 15-Hz interval.

In effect, the elements are rotated electrically,

rather than mechanically. An advantage this provides

is the elimination of the bandwidth limitations inherent

in the old mechanically-rotated antennas. In the

electronically-scanned antenna, the appropriate ring

for a given frequency segment is activated by a fast

elec tronic swi tch, based on information f rom the

T A C A N f r e q u e n c y s y n t h e s i z e r . T h i s a l l o w s

instantaneous band switching and all-band operation.

Figure 2-8.Antenna Group OE-273(V)/URN.

2-7


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TACAN SET AN/URN-20

T h o u g h n o t m o d e r n b y a n y s t a n d a r d , t h e

AN/U RN-20 TACAN set is rel ia ble a nd operat es

simila rly t o the AN/U RN-25. Show n in fig ure 2-9, it

uses the same electronical ly-scanned antenna and

cont rol-indica t or a s t he AN/U RN -25. The AN/U RN -

20 is being r eplaced by th e AN/U RN-25.

CAPABILITIES AND LIMITATIONS

In the X mode of operation, the TACAN set

transmits on one of 126 discrete channel frequencies

(which are 1-MHz apart) from 962 to 1024 MHz and

from 1151 to 1213 MHz. In the Y mode of operation,

the se t t ransmits on one of 126 discre te channel

frequencies (which are 1-MHz a part ) with in th e ran ge

of 1025 to 1150 MHz. The navigation set receiver,

operating in the 1025- to 1150-MHz range for both

the X and Y modes, is a lways displaced 63 MHz from

the tra nsmitt er frequency.

The TACAN se t ca n s imul t a ne ous ly pr ov ide

individual distance measuring service for up to 100

in te r r og a t ing a i r c r a f t . O f t h e 3 , 60 0 pu l s e

pairs-per-second transmitted by the TACAN, 900

pulse pairs (MAIN and AUXILIARY bursts) contain

the bearing information; the remaining 2,700 pulse

pairs are either random noise pulses, identity pulses, or

replies to interrogating aircraft . O nce e ve r y 30

seconds, the interrogation replies and random noise

pulses a re interrupted for the t ran smission of identi ty

pulses.

The navigation set has a receiver sensitivity of -92

dBm or better and a nominal peak power output of 3

kilowatts at the transponder cabinet output. (Power

output may l imited to less than peak by directives).

S ince the be a r ing a nd ide nt i f i ca t i on s i g na l s a r e

del ivered spontaneously and not in response to

interrogations, an unl imi ted number of proper ly

equipped aircraft can derive this information from the

TACAN set over a line-of-sight (los) range up to 200

nautical miles.

2-9


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APPENDIX I

LIST OF ACRONYMS

AUX- auxil iary.

BITE- built-in test equipment.

C/A CODE- course acquisition code.

DB- decibel.

DBM- decibel with a reference zero value of 1 mW.

DME- distance measuring equipment.

DOD- Department of Defense.

DR- dead reckon.

EW- electronic warfare.

FRP- Federal Ra dio Navigat ion P lan.

GMT- Greenwich Mean Time.

HZ- Hertz .

KHZ-- kilohertz.

LOP- line-of-position.

LORAN- Long Range Aid to Navigation.

LOS- line-of-sight.

MHZ-- megahertz .

MS- millisecond.

MW-- mill iwat t .

NAV-MSG- NAVIGATION-message .

NAVSAT- navigation satell i te.

NAVSTAR GPS- satell i te Global Positioning

System.

NNSS- Navy Navigation Satell i te System.

NTDS- Naval Tact ica l D at a System.

OMEGA- VLF radio navigation.

P CODE- precise code.

PPS- pulses per second.

PROM- programmable read-only memory

RF- radio frequency.

SATNAV-- satell i te navigation

S/D- synchro to digita l .

SINS- Ships Inertial Navigation System.

TACAN- Tactical Air Navigation.

TCA- time of closest approach.

UT-- U niversa l Time.

VOR- VHF--omnidirectional range.

XPDU- expanded data processor unit .

AI-1


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APPENDIX II

REFERENCES USED TO DEVELOP THE TRAMAN

NOTE: Although the following references were current when this

TRAMAN was published, their continued currency cannot be assured. You,

therefore, need to ensure that you are studying the latest revision.

El ectr oni cs Techni cian 3 & 2, NAVEDTRA 10197, Naval Education and

Training Programs Management Support Activity, Pensacola, FL, 1987.

In er t i a l N avigat ion Set AN / WSN-5, NTP S-30-7519E, Naval Sea Systems

Command, Washington, DC, 1991.

M anpack N avigat ion Set AN / PSN-8( ), Operators Manual EE170-AA-OPI-

010/MV, Spa ce a nd Na va l Wa rfa re Syst ems Comma nd, Wa shingt on, DC,

1990.

Naval Aeronautical Facil i t ies, Naval Shore Electronics Criteria, NAVELEX0101,107, Naval Electronic System Command, Washington, DC, 1971.

NAVST AR Gl obal Posit ionin g System (GPS) User Equi pment, NTP E -70-8215E,

Space and Naval Warfare Systems Command, Washington, DC, 1993.

Satell i t e Signal s N avigat ion Set AN / WRN -6(V), Technical Manual EE-170-AA-

OMI-010/WRN6, Spa ce a nd Na va l Wa rfa re Sy stems C omman d,

Washington, DC, 1990.

Shi pboard El ectr oni cs Mat er i al Off i cer, NAVEDTRA 12969, Naval Education

and Training Programs Management Support Activity, Pensacola, FL, 1992

TACAN , Navigat ion Set AN/ URN -25, Technical Manual EE172-AB-OMI-010,

Space and Naval Warfare Systems Command, Washington, DC, 1990.

AII-1


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INDEX

D

Doppler principles

refraction measurement, 1-8

velocity computation, 1-8

GO

N N S S

computer center, 1-7

injection station, 1-7

naval observatory, 1-7

sa tellites, 1-6

tracking stations, 1-7

GPS navigation sets

AN/P S N-8 ma npa ck, 1-18

AN/WRN -6, 1-17

L

LORAN

line-of-position, 1-2

N

Navigation aids

fathometers, 1-19

radar, 1-19

Navigation fundamentals

dead reckoning, 1-1

electronic navigation, 1-2

piloting, 1-2

tactical, 1-1

Navigation sets

AN/S RN-19, 1-11

AN/WRN -5, 1-9

NAVSTAR Global Positioning System

clock error, 1-16

ground control, 1-14

ionospheric delay, 1-16

multipath reception, 1-16

satellite ranging, 1-15

satellite signal structure, 1-15satellites, 1-14

signal acquisition, 1-15

tropospheric delay, 1-16

Omega

hyperbolic navigation, 1-3

s

S I N S

accelerometers, 1-4

advantages, 1-3

AN/WSN-5, 1-5gyros, 1-4

servo systems, 1-4

T

TAC AN

aircraft indications, 2-1

aux reference burst, 2-4

bearing information (15 Hz), 2-3

bearing information (135 Hz), 2-4

cardioid, 2-3constant transponder duty-cycle, 2-1

identification code, 2-2

north reference burst, 2-4

principles, 2-1

pulse pairs, 2-1

signal priorities, 2-4

squitter, 2-2

TACAN equipment

a nt enna group OE -273(V)/U RN, 2-7

AN/U RN -20, 2-9AN/U RN-25, 2-5

INDEX-1


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Assignment Questions

Information: The text pages that you are to study are

provided at the beginning of the assignment questions.


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1-24.

1-25.

1-26.

127.

128.

129.

IN ANSWERING QUESTIONS 1-24, 125,AND 126, REFER TO FIGURE 17 IN

CHAPTER 1 OF THE TRAMAN.

At what point during the satellite

pass will expansion effects cause

the received frequencies to drop

below the generated frequencies?

1. T1

2. T23. T3

At what point will the received

frequencies exactly match the

transmitted frequencies?

1. T1

2. T2

3. T3

At what point will compression

effects cause the received

frequencies to be higher than thetransmitted frequencies?

1. T1

2. T2

3. T3

Which of the following factors

affects the measurement of Doppler

shift?

1. Refraction

2. Reflection

3. Reduction

4. Reproduction

To solve the problem of Doppler

shift accuracy, satellites are

designed to transmit on how many

frequencies?

1. One

2. Two

3. T

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