NAVEDTRA 12415Naval Education and April 1994 Training ManualTraining Command 0502-LP-479-3800 (TRAMAN)
Electronics Technician
Volume 5—Navigation Systems
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ELECTRONICS TECHNICIAN
VOLUME 5NAVIGATION SYSTEMS
NAVEDTRA 12415
1994 Edition Prepared byETC(SW/AW) James R. Branch
PREFACE
This training manual (TRAMAN), Electronics Technician, Volume 5,Navigation Systems, NAVEDTRA 12415, and its companion nonresident trainingcourse (NRTC), NAVEDTRA 82415, are part of a planned 9-part series ofTRAMANs intended to provide Navy enlisted personnel with information pertinentto their assignments and necessary for advancement to the Electronics TechnicianSecond Class rate. The nine volumes planned for the series are as follows: Volume1, Safety; Volume 2, Administration; Volume 3, Communications Systems; Volume4, Radar Systems; Volume 5, Navigation Systems; Volume 6, Digital Data Systems;Volume 7, Antennas and Wave Propagation; Volume 8, System Concepts; Volume9, Electro-Optics.
Designed for individual study instead of formal classroom instruction, theTRAMANs provide subject matter that relates directly to the Occupational Standardsfor the Electronics Technician Second Class. The Navy Electricity and ElectronicsTraining Series (NEETS) modules provide information that is basic to yourunderstanding of the material presented in these volumes. To avoid repeating suchbasic information, these volumes refer you to the appropriate NEETS modules andEIMB handbook. You may also be directed to review or study additional referencescommonly found in ET workspaces or used by Electronics Technicians. You shouldstudy the referenced publications as thoroughly as you would if they were repeatedas part of the ET2 TRAMAN. The NRTCs, printed under separate cover, consist ofsupporting questions designed to help you study the associated TRAMAN andreferenced publications and to satisfy part of the requirements for advancement.
This training manual and the nonresident training course were prepared by theNaval Education and Training Program Management Support Activity for the Chiefof Naval Education and Training.
1994 Edition
Stock Ordering No.0502-LP-479-3800
Published byNAVAL EDUCATION AND TRAINING PROGRAM
MANAGEMENT SUPPORT ACTIVITY
UNITED STATESGOVERNMENT PRINTING OFFICE
WASHINGTON, D.C,: 1993
i
THE UNITED STATES NAVY
GUARDIAN OF OUR COUNTRY
The United States Navy is responsible for maintaining control of the sea and is a readyforce on watch at home and overseas, capable of strong action to preserve the peace orof instant offensive action to win in war.
It is upon the maintenance of this control that our country’s glorious future depends;the United States Navy exists to make it so.
WE SERVE WITH HONOR
Tradition, valor, and victory are the Navy’s heritage from the past. To these maybeadded dedication, discipline, and vigilance as the watchwords of the present and thefuture.
At home or on distant stations we serve with pride, confident in the respect of ourcountry, our shipmates, and our families.
Our responsibilities sober us; our adversities strengthen us.
Service to God and County is our special privilege. We serve with honor.
THE FUTURE OF THE NAVY
The Navy will always employ new weapons, new techniques, and greater power toprotect and defend the United States on the sea, under the sea, and in the air.
Now and in the future, control of the sea gives the United States her greatest advantagefor the maintenance of peace and for victory in war.
Mobility, surprise, dispersal, and offensive power are the keynotes of the new Navy.The roots of the Navy lie in a strong belief in the future, in continued dedication to ourtasks, and in reflection on our heritage from the past.
Never have our opportunities and our responsibilities been greater.
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CONTENTS
CHAPTER Page
1. SURFACE NAVIGATION SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1-1
2. TACTICAL AIR NAVIGATION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2-1
APPENDIX
I. List of Acronyms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . AI-1II. 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 ElectronicsTechnician 3 & 2 TRAMAN. The content is directed toward personnel workingtoward advancement to Electronics Technician Second Class.
The nine volumes in the series are based on major topic areas with which theET2 should be familiar, Volume 1, Safety, provides an introduction to general safetyas it relates to the ET rating. It also provides both general and specific informationon electronic tag-out procedures, man-aloft procedures, hazardous materials (i.e.,solvents, batteries, and vacuum tubes), and radiation hazards. Volume 2,Administration, discusses COSAL updates, 3-M documentation, supply paperwork,and other associated administrative topics. Volume 3, Communications 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 CommunicationsLink Interoperability System (CLIPS). Volume 4, Radar Systems, is a basicintroduction to air search, surface search, ground controlled approach, and carriercontrolled approach radar systems. Volume 5, Navigation Systems, is a basicintroduction to navigation systems, such as OMEGA, SATNAV, TACAN, andman-pat systems. Volume 6, Digital Data Systems, is a basic introduction to digitaldata systems and includes discussions about SNAP II, laptop computers, and desktopcomputers. Volume 7, Antennas and Wave Propagation, is an introduction to wavepropagation, as it pertains to Electronics Technicians, and shipboard and shore-basedantennas. Volume 8, System Concepts, discusses system interfaces, troubleshooting,sub-systems, dry air, cooling, and power systems. Volume 9, Electro-Optics, is anintroduction to night vision equipment, lasers, thermal imaging, and fiber optics.
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CHAPTER 1
SURFACE NAVIGATION SYSTEMS
INTRODUCTION
Today’s Navy uses various navigational systemsin the fleet. As an ET, you will be responsible formaintaining these systems.
In this volume, we will cover navigationfundamentals, the Ship’s Inertial Navigation System,Navy Satellite Navigation System, NAVSTAR GlobalPositioning System, fathometers, and TACAN. Let’sstart with navigation fundamentals.
NAVIGATION FUNDAMENTALS
In simple terms, navigation is a method of gettingfrom one known point to some distant point. Piloting,celestial navigation, and radio navigation are thecommonly used methods. In this chapter, we willdiscuss radio navigation and its components: deadreckoning, electronic navigation, and tacticalnavigation. The tactical use of NTDS data (tacticalnavigation) was covered in v o l u m e 3 ,Communications Systems. However, we will reviewit briefly here to help you see how it fits into radionavigation. We will then discuss dead reckoning andelectronic navigation in more detail.
TACTICAL NAVIGATION
You must understand the difference betweennavigation in the traditional sense and tacticalnavigation. Traditional navigation and piloting areconcerned primarily with safe maneuvering of theship with respect to hazards such as shoals, reefs, andso forth. Tactical navigation is not directly concernedwit h maneuvering the ship in navigable waters. Forthe purposes of tactical navigation, absolute positionis unimportant except to the extent that it supportsdetermining the relative position of hostile targets andfriendly cooperating platforms.
Remember, tactical navigation deals primarilywith fixing the location of the platform to (1) enableinstalled weapon systems to function against intendedtargets, (2) prevent ownship loss to or interferencewith friendly weapon systems, and (3) coordinateownship weapons systems with those of otherplatforms to achieve maximum effect.
In tactical navigation, navigation data is used bycombat systems, including NTDS, to ensure accuracyin target tracking. Ship’s movements areautomatically recorded by computer programs forapplications such as gun laying calculations and Link11 position reporting. Ship’s attitudes (pitch, roll, andheading) are transmitted to various display and userpoints, and electronic or mathematical computerstabilization is accomplished, depending on thesystem. For example, pitch and roll are used byNTDS, missile, sonar, gun, and TACAN systems forstabilization data and reference. Heading is used bythe EW direction finding, sonar, and radar systems fortrue and relative bearing display. Ship’s navigationand attitude data are provided by various equipment,depending on ship class.
DEAD RECKONING
Dead reckoning is the estimating of the ship’sposition between known navigational points or fixes.Radio navigation, consisting of terrestrial systemssuch as OMEGA and LORAN, and space-basedsystems, such as SATNAV, TRANSIT, andNAVSTAR GPS, provides accurate positions atspecific fixes. However, with the exception of somegunfire support systems that provide nearly constantpositional updates with respect to a fixed beacon orprominent landmark, there is a limit to how oftenfixes can be obtained. This requires us to dead reckon(DR) between the fixes. Dead reckoning can be asbasic as a DR line for course and speed on a plottingsheet or as sophisticated as an estimate made by an
l-l
inertial navigation system that measures the ship’smotion in several planes and integrates the resultswith a high degree of accuracy. Although themethods of dead reckoning may vary, they all sharethe following characteristics: (1) the accuracy of theestimated position never exceeds the navigationmethod used to obtain the last fix, and (2) theaccuracy of the estimated position deteriorates overtime.
ELECTRONIC NAVIGATION
Simply put, electronic navigation is a form ofpiloting. Piloting is the branch of navigation in whicha ship’s position is determined by referring tolandmarks with known positions on the earth. Thesereference points may be bearing and distance to asingle object, cross bearings on two or more objects,or two bearings on the same object with a timeinterval in between.
Position in electronic navigation is determined inpractically the same way as piloting, though there isone important difference—the landmarks from whichthe ship’s position is determined do not have to bevisible from the ship. Instead, their bearings andranges are obtained by electronic means.
The advantages of electronic navigation areobvious. A ship’s position maybe fixed electronicallyin fog or heavy weather that makes it impossible totake visual fixes. Also, an electronic fix can be basedon stations far beyond the range of any local badweather.
Since electronic navigation is the primary form ofnavigation in today’s Navy, the rest of this chapterwill deal with electronic navigation and the rolesplayed by the following systems:
1. Long Range Aid to Navigation (LORAN)
2. VLF Radio Navigation (OMEGA)
3. Ship’s Inertial Navigation System (SINS)
4. Navy Navigation Satellite System (NNSS)
5. NAVSTAR Global Positioning System (GPS)
We will also briefly discuss navigation radar,surface search radar, and fathometers.
We will cover TACAN in chapter 2.
LORAN/OMEGA—TRANSITION ANDBASIC OPERATION
LORAN and OMEGA have been the “workhorse”systems for many years. However, they are beingphased out. Based on the DOD policy statementreprinted below and because you may see a civilianversion aboard your ship from time to time, we willsimply give you an overview of the two systems. Inaccordance with the 1992 Federal Radio navigationPlan (FRP), NAVSTAR will become the primaryreference navigation system for surface ships,submarines, and aircraft. The DOD requirement forLORAN-C and OMEGA will end 31 December 1994and TRANSIT will be terminated in DECEMBER1996. Land-based TACAN and VOR/DME are to bephased out by the year 2000.
LORAN BASICS
LORAN is a long-distance radio navigationsystem used by ships at sea to obtain a position fix,The system is based on the difference in the transittime required for pulsed radio signals to arrive at theLORAN receiver from multiple, synchronized,omnidirectional ashore transmitters. LORAN alsotakes advantage of the constant velocity of radiosignals to use the time lapse between the arrival oftwo signals to measure the differences in distancefrom the transmitting stations to the point ofreception. The receiving set provides a direct reading,in microseconds, of the time difference in the arrivalof the signals. (Some sets automatically convert thereadings into latitude and longitude.) When the timedifference is measured between signals received fromany two LORAN transmitter stations, a ship’s line-of-position (LOP) can be determined.
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OMEGA BASICS ADVANTAGES
OMEGA is a hyperbolic phase-differencemeasurement system. Hyperbolic navigation involvescomparing the phase angles of two or more radiosignals that are synchronized to a common time base.By moving the OMEGA receiver (by ship’smovement) and keeping the transmitter stations onfrequency with a constant difference in time andphase, the system can measure the relative phaserelationship between two stations to determine a lineof position (LOP) for the ship. The relative phaseangle measured between paired transmitting stationsdepends upon the distance of the receiver from eacht r a n s m i t t e r .
It is important to understand that a minimum oftwo transmitters are required to obtain a basic positionfix. Three or four are necessary to obtain an accuratefix. Unfortunately, there are many times in whichonly two transmitters are available but three aredesired. One way around this problem is to use thereceiver oscillator as a third, or “phantom,”transmitter. By setting the receiver oscillator to thefrequency transmitted by each of the two OMEGAtransmitters, the operator can compare the actualtransmitted frequencies to the frequencies of the tworeceived signals. This comparison provides twophase angles. The operator can then compare the twophase angles to determine a third phase angle. Thethree phase angles will yield a fix as accurate as a fixdetermined from three actual transmitters.
SHIP’S INERTIALNAVIGATION SYSTEM
The Ship’s Inertial Navigation System (SINS) isa navigation system that (after initial latitude,longitude, heading, and orientation conditions are setinto the system) continuously computes the latitudeand longitude of the ship by sensing acceleration.This is in contrast to OMEGA and LORAN, which fixthe ship’s position by measuring position relative tosome known object. SINS is a highly accurate andsophisticated dead reckoning device. Let’s look atsome of the advantages of using the SINS.
SINS has a major security advantage over othertypes of navigation systems because it is completelyindependent of celestial, sight, and radio navigationaids. In addition, SINS has the following advantages:
1. It is self-contained.
2. It requires minimal outsideinformation.
3. It cannot be jammed.
4. It is not affected by adverse weatherconditions.
5. It does not radiate energy.
6. It is not detectable by enemy sensors.
Now that we have seen the advantages of thissystem, let’s look at its basic components.
BASIC COMPONENTS
Look at figure 1-1. The basic components of aninertial navigation system are accelerometers,gyroscopes, servo systems, and the computers (notshown). Accelerometers measure changes in speed ordirection along the axis in which they lie. Theiroutput is a voltage, or series of pulses (digital),proportional to whatever acceleration is experienced.
Figure 1-1.—Stable platform with inertial components.
1-3
Figure 1-2 shows an E-transformer accelerometer,while figure 1-3 shows a pulse countingaccelerometer. Two accelerometers (orientated North-South and East-West, respectively) are mounted on agyro-stabilized platform to keep them in a horizontalposition despite changes in ship’s movement. Theaccelerometers are attached to the platform by anequatorial mount (gimbal) whose vertical axis ismisaligned parallel to the earth’s polar axis. Thispermits the N-S accelerometer to be aligned along alongitude meridian and the E-W accelerometer to bealigned along a latitude meridian.
Figure 1-2.—E-transformer accelerometer.
A three-gyro stabilized platform is maintained inthe horizontal position regardless of the pitch, roll, oryaw of the ship. Figure 1-4 shows a gimbal-mountedgyro. Ship’s heading changes cause the gyro signalsto operate servo system motors, which in turn keepthe platform stabilized. High-performance servosystems keep the platform stabilized to the desiredaccuracy. (You will find in-depth information onaccelerometers, gyros, and servo systems in NEETSModule 15, Principles of Synchros, Servos, andGyros.).
Maintaining this accuracy over long periods oftime requires that the system be updated periodically.This is done by resetting the system using informationfrom 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 systems are installed on auxiliary ships,AN/WSN-2A systems are installed on submarines,and AN/WSN-5 systems are installed or beinginstalled on surface combatants. In the followingparagraphs, you will be introduced to the AN/WSN-5SINS and its advantages over these earlier systems.
Figure 1-4.— Gimbal-mounted rate gyro.
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AN/WSN-5 SINS l Ship’s north, east, and vertical velocitycomponents
The AN/WSN-5 is a stand-alone set that replacesthe MK 19 MOD 3 gyrocompass in the followingclass ships: CG 16, CG 26, CGN 9, CGN 25, CGN35, CGN 36, CGN 38 (except for CGN 41), DDG 37,DD 963, and LHA 1. It also replaces the AN/WSN-2stabilized gyrocompass set in DDG 993, DD 997, andCGN 41 class ships.
Functional Description
The AN/WSN-5 has the same output capabilitiesas the AN/WSN-2. It uses an accelerometer-controlled, three axis, gyro-stabilized platform toprovide precise output of ship’s heading, roll, andpitch data in analog, dual-speed synchro format tosupport ship’s navigation and fire control systems.Ship’s heading and attitude data are continually andautomatically derived while the equipment senses andprocesses physical and electrical inputs of sensedmotion (inertial), gravity, earth’s rotation, and ship’sspeed. The equipment has an uninterruptible backuppower supply for use during power losses, and built-in test equipment (BITE) to provide fault isolation tothe module/assembly level.
Characteristics
In addition to the common functions describedabove, the AN/WSN-5 adds an increased level ofperformance to serve as an inertial navigator andprovides additional analog and digital outputs.Additional data provided includes position, velocity,attitude, attitude rates, and time data in both serial andparallel digital formats, providing a variety ofinterfaces. The AN/WSN-5 commonly exists in adual-system configuration on surface combatants.Some examples of AN/WSN-5 digital data outputsare :
1. Two Naval Tactical Data System (NTDS)serial channels transmitting:
l Ship’s heading, roll, and pitch
l Ship’s heading rate, roll rate, and pitch rate
. Ship’s latitude, longitude, and GMT
2. Two MIL-STD-1397 NTDS type D high-levelchannels to an external computer
3. One MIL-STD-1397 NTDS type A slow, 16-bit, parallel input/output channel to a NavigationSatellite (NAVSAT) receiver AN/WRN-5A, GlobalPositioning System (GPS) receiver AN/WRN-6, orI/O console.
4. One serial AN/WSN-5 to AN/WSN-5 digitallink that provides alignment data, Navigation Satellite(NAVSAT) fix data, calibration constant data, andother navigation data to the remote AN/WSN-5.
5, An additional variety of input/output NTDSchannels, depending on which field changes areinstalled.
SATELLITE NAVIGATION SYSTEMS
Scientists realized that navigation based onsatellite signals was possible after listening to thebeep generated by Russia’s first artificial satellite,Sputnik I. They noticed a shift in the received radiofrequency signals as the satellite passed by. Thisshift, known as the Doppler effect, is an apparentchange in a received frequency caused by relativemotion between a transmitter and a receiver. As thedistance between the transmitter and the receiverdecreases, the received frequency appears to increase.As the distance increases, the received frequencyappears to decrease.
With this discovery, scientists were able to showthat by accurately measuring a satellite’s Doppler shiftpattern, they could determine the satellite’s orbit.They then determined that by using a known satellite’sorbit, a listener could determine his own position onthe earth’s surface by observing the satellite’s Dopplerpattern.
Following the first successful satellite launch inApril 1960, the U.S. Navy Navigation Satellite
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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 orbitingsatellite.
The following paragraphs describe the NNSS, itssatellites, Doppler principles, system accuracy , and twocommon shipboard equipments—the AN-WRN-5( V) andthe AN/SRN-19(V)2.
NAVY NAVIGATION SATELLITE SYSTEM
This highly accurate, world-wide, all weather systemenables navigators to obtain fixes approximately every 2hours, day or night. Looking at figure 1-5, you can seethat it consists of earth-orbiting satellites, trackingstations, injection stations, the U.S. Naval Observatory,a computing center, and shipboard navigationequipment.
System Satellites
Satellites are placed in a circular polar orbit, asillustrated in figure 1-6, at an altitude of 500 to 700(nominally 600) nautical miles. Each satellite orbits inapproximately 107 minutes, continually transmittingphase-modulated data every 2 minutes on two rfcarriers. This data includes time synchronizationsignals, a 400-Hz tone, and fixed and variableparameters that describe the satellite’s orbit.
The fixed parameters describe the nominal orbit ofthe satellite. Variable parameters (small corrections tothe fixed parameters) are transmitted at two-minuteintervals and describe the fine structure of the satelliteorbit. The satellite memory stores sufficient variableparameters to provide the two-minute orbit correctionsfor 16 hours following injection of fresh data into thememory. Since data injections occur about every 12hours, the satellite memory will not
Figure 1-5.—Navy Navigation Satellite System.
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Figure 1-6.—Satellite orbits.
run out. Each two-minute long satellite message istimed so that the end of the 78th bit, which is the lastbit of the second synchronization signal, coincideswith even 2 minutes of Greenwich mean time (GMT).Thus the satellites can also be used as an accuratetime reference by all navigators equipped with asatellite navigation set.
Each satellite is designed to receive, sort, andstore data transmitted from the ground and toretransmit this data at scheduled intervals as it circlesthe earth. Each satellite tells users which satellite itis, the time according to the satellite clock, and itspresent location. With this information, the user’snavigation set can determine exactly where thesatellite is, one of the necessary steps towarddetermining a precise navigational position.
Tracking Stations
Tracking stations are located in Maine,Minnesota, California, and Hawaii. As each satellitepasses within radio line-of-sight (los) of each of thesetracking stations, it is tracked to accurately determineits present and future orbits. Just before predictedsatellite acquisition, the tracking station’s antenna ispointed toward the satellite to acquire its signals. Asthe satellite rises above the horizon, the trackingantenna continues to follow the satellite’s predicted
path until the radio receiver in the tracking stationlocks on to the satellite’s transmitted signal. Thereceiver processor and data processing equipmentdecode and record the satellite message. The Dopplertracking signal is digitized and sent with the satellitetime measurements to the computing center, via acontrol center, where a refined orbit is calculated.
The tracking stations maintain highly stable oscil-lators that are continually compared against a WWVtransmitted frequency standard. In addition, theNaval Observatory sends daily messages that give theerror in the transmitted standard. The Navalobservatory error is then added to the data obtainedfrom the frequency standard, and corrections aremade to the station oscillators. The station oscillatorsare used to drive station clocks, which are comparedwith the time marks received from the satellite. Thistime data is transmitted by the tracking stations to thecontrol center, where the satellite clock error iscalculated and the necessary time correction bits areadded or deleted in the next injection message to thesatellite.
Computing Center
The central computing center continually acceptssatellite data inputs from the tracking stations and theNaval Observatory. Periodically, to obtain fixedorbital parameters for a satellite, the centralcomputing center computes an orbit for each satellitethat best fits the Doppler curves obtained from alltracking stations. Using this computed orbital shape,the central computing center extrapolates the positionof the satellite at each even 2-minutes in universaltime for the 12 to 16 hours subsequent to datainjection. These various data inputs are supplied tothe injection stations via the control center, as is dataon the nominal space of the orbits of the othersatellites, commands and time correction data for thesatellite, and antenna pointing orders for the injectionstation antennas.
Injection Station
The injection stations, after receiving andverifying the incoming message from the controlcenter, store the message until it is needed for
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transmission to the satellite. Just before satellite time-of-rise, the injection station’s antenna is pointed toacquire, lock on, and track the satellite through thepass. The receive equipment receives and locks on tothe satellite signals and the injection station transmitsthe orbital data and appropriate commands to thesatellite. Transmission to the satellite is at a high bitrate, so injection is completed in about 15 seconds.
The message transmitted by the satelliteimmediately after an injection contains a mix of oldand new data. The injection station compares areadback of the newly injected data with data thesatellite should be transmitting as a check for errors.If no errors are detected, injection is complete, If oneor more errors are detected, injection is repeated attwo-minute intervals (updating the variableparameters as necessary) until satellite transmission isverified as being correct.
DOPPLER PRINCIPLES
Look at figure 1-7. Stable oscillator frequenciesradiating from a satellite coming toward the receiverare first received (T1) at a higher frequency thantransmitted, because of the velocity of theapproaching satellite. The satellite’s velocity producesaccordion-like compression effects that squeeze theradio signals as the intervening distance shortens. Asthe satellite nears its closest point of approach, thesecompression effects lessen rapidly, until, at themoment of closest approach (T2), the cycle count ofthe received frequencies exactly matches those whichare generated. As the satellite passes beyond thispoint and travels away from the receiver (T3),expansion effects cause the received frequencies todrop below the generated frequencies proportionallyto the widening distance and the speed of the recedingsatellite.
FACTORS AFFECTING ACCURACY
Measurement of Doppler shift is complicated bythe fact that satellite transmissions must pass throughthe earth’s upper atmosphere on their way from spaceto the receiver. Electrically charged particals in theionospheric layer cause refraction of thesetransmissions. To solve this problem, the satellites are
designed to broadcast on two frequencies (150 and400 MHz). The receiver measures the difference inrefraction between the two signals and supplies thismeasurement to the computer. The computer uses thisrefraction measurement as part of its computation toobtain accurate fixes. The most serious problemaffecting accuracy is the effect of uncertainty in thevessel’s velocity on the determination of position.Velocity computation problems are inherent in thesystem. Position error resulting from an error invelocity measurement is somewhat dependent on thegeometry of the satellite pass. You can expect abouta 0.2 mile error for every one-knot error in thevessel’s velocity. Knowing this, you can see thatprecision navigation of a moving vessel requires anaccurate measurement of the velocity of the movingvessel, such as is provided by a good inertialnavigation system (See the section on Ship’s InertialNavigation System.). In general, intermittentprecision navigation fixes would not be of extremevalue for a moving vessel unless it had some means ofinterpolating between these precision fixes. A goodinertial navigation system provides such a means, andsimultaneously provides the accurate velocitymeasurements required to permit position fixes withthe NNSS.
In summary, precision navigation for movingvessels can’t be provided by the Navy NavigationSatellite System alone, but can be provided by the useof this system in conjunction with a good inertialsystem. Given the orbital parameters of a satellite, theDoppler shift of the signal transmitted from thatsatellite, and the velocity of the vessel, it is possibleto obtain a navigational fix if the satellite is within losof the navigation set and has a maximum elevation atthe time of closest approach (TCA) of between 10and 70 degrees. Satellite passes suitable for use inobtaining a navigational fix will usually occur at nomore than 2-hour intervals (depending on userlatitude and configuration of the satellite cons-tellation). It is a matter of your viewpoint whether youconsider the inertial system as a means ofinterpolating between the satellite navigation fixes orconsider the satellite fixes as a means for correctingthe inevitable long term drills (see the paragraphs onbasic components of an inertial navigation system) ofeven the best inertial navigation systems.
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Figure 1-7.—Doppler shift relative to satellite transmitted frequency.
The two most common satellite navigation AN/WRN-5(V) RADIO NAVIGATION SET
systems used by the Navy are the AN/WRN-5 and theAN/SRN-19. The following paragraphs provide The AN/WRN-5 Radio Navigation Set, shown in
descriptions of these navigation sets. figure 1-8, is a receiver-data processor-display set
1-9
designed to recieve and phase track signalstransmitted by satellites of the NNSS. These signalsare processed to obtain navigation information that ismonitored on video displays and used elsewhere forship navigation.
The AN/WRN-5 is designed to be used in variousconfigurations as described below. Each of theseconfigurations is defined by options in externalequipment used or variations in inputs and outputs.The options available for alternative configurationsare:
1.
2.
3.
4.
5.
6.
Teleprinter, ASR-33
Additional remote video displays, IP-1154(U)
Frequency standard, AN/URQ-10/23(external reference)
Dual antennas (separate 400-MHz and150-MHz antennas)
Input/output bus
External lock indicator
7. 100-KHz output
The functional elements of the AN/WRN-5include 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 transportwith read/write capability for OPNAVprogram loading or data recording
Front panel video display for system tooperator input/output
Remote video monitor
Built-in synchro-to-digital convertor forinterface with the ship’s speed and headingsensors to provide dead reckoning capability
Figure 1-8.—AN/WRN-5 front panel.
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and accurate satellite position fixes duringship maneuvers
6. Displays inputted speed and heading.
7. Displays inputted set and drift.9. Optional addition of a teleprinter
8. Displays data on a tracked satellite.The combination of fictional elements in the
AN/WRN-5 provides many capabilities includingautomatic storage of satellite information, time-ordered alerts for up to eight satellites, and built-inself test. The front panel video display providescurrent time, latitude/longitude, dead reckoningposition (automatically updated by satellite fixes), andsatellite tracking information such as fix merit andsatellite alerts. You will find specific information onthe capabilities of this navigation set in the AN/WRN-5 operation and maintenance technical manual.
9. Performs a self-test of computer functions[limited to verification of the digital circuitry).
The AN/SRN-19(V)2 consists of the majorcomponents shown in figure 1-9.
Figure 1-10 shows a simplified block diagram ofthis system. The following paragraphs describe thesecomponents.
ANTENNA GROUP OE-284/SRN-19(V)AN/SRN-19(V)2 RADIO NAVIGATION SET
The AN/SRN-19(V)2 is an automatic shipboardnavigation set that provides a continuous display ofthe ship’s position. The ship’s position, which isobtained by dead reckoning on true speed andheading, is periodically corrected by satellite fixes.Specifically, the navigation set can perform thefollowing functions:
1. After each successful satellite pass, computesand displays the present location of the ship to anominal at-sea accuracy of 0.25 nautical mile.
The antenna group consists of the AS-3330/SRN-19(V) antenna and AM-7010/SRN-19(V) rf amplifier
Antenna
The antenna is a linear, vertically-polarized typethat receives rf signals transmitted by the satellite. Itshorizontal pattern is omnidirectional; its verticalpattern varies approximately 11 dB from 10 to 70degrees above the horizontal plane.
Rf Amplifier
Note: Accuracy of the fix is affected by high The rf amplifier provides initial amplification ofsunspot activity. During these periods, nominal the 400-MHz satellite signals from the antenna andat-sea accuracy may degrade to approximately then sends them, via rf coaxial cable, to the receiver0.5 nautical mile. for further amplification and processing. The rf
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 the present position to any destination using thegreat circle program. The receiver-processor consists of a single
channel (400-MHz) receiver, a 5-MHz reference4. Computes and displays the next expected rise oscillator, a data processor with a programmable read-
time and elevation at closest approach of the only memory (PROM) program, a keyboard, display,previously tracked satellite, cassette recorder, two synchro-to-digital (S/D)
converters, and a power supply. It processes inputs5. Displays GMT accurate to 1 second. from the rf amplifier, ship’s EM log, gyrocompass,
and receiver-processor keyboard.
1-11
Figure 1-9.—AN/SRN-19(V)2 major components.
Receiver
The receiver extracts, amplifies, and formatsmessage information from the rf signal transmittedby the satellite, and measures the Doppler shift of thesignal. The message data obtained by demodulation ofthe rf carrier describes the satellite’s position at thetime of transmission.
Data Processor
This unit processes inputs from the receiver, ship’sEM log, and gyrocompass through the S/D convertorsand the keyboard. It then performs computations andprovides the desired outputs to the front paneldisplay, readout indicator, teleprinter, and cassetterecorder.
1-12
READOUT INDICATORAND TELEPRINTER
The readout indicator provides an identical visualreadout of the data displayed on the front panel of thereceiver-processor. The readout indicator is usuallylocated at a site some distance from the receiver-processor.
The teleprinter provides a permanent record ofdisplayed data. The printouts for modes 01 and 03occur every 15 minutes or as selected by the operator.A printout also occurs each time a display mode iselected and when satellite fix data is received.
One final note on the AN/SRN-19 system. Youmust “tell” the equipment where it is when it is
initialized. You must also enter information onantenna height before the system can provide anaccurate fix.
You can find specific information on theAN/SRN-19(V)2 in the shipboard operations andmaintenance manual for this navigation set.
NAVSTAR GLOBALPOSITIONING SYSTEM
NAVSTAR GPS is a space-based, radionavigation system that provides continuous,extremely accurate three-dimensional position,velocity, and timing signals to users world-wide. Itconsists basically of ground control, satellites, anduser equipment, as shown in figure 1-11.
Figure 1-10.—AN/SRN-19(V)2 simplified block diagram.
1-13
NOTEGPS will become the primary referencenavigation system for surface ships, submarines,and aircraft. Refer to the DOD policy statementunder the LORAN and OMEGA section of thischapter for specific details on this importanttransition.
GROUND CONTROL
The ground control segment tracks the satellites,monitors and controls satellite orbits, and updates thesatellite navigation data message. The ground controlsystem consists of unmanned monitor stations and amanned control center. Monitor stations, locatedthroughout the world, use GPS receivers to track eachsatellite. Tracking information gathered by themonitor stations is sent to the control center, where a
precise position and a clock error for each satellite arecalculated. The control center also calculates satellitepositioning for the group of satellites. Positioningdata for a single satellite is called ephemeris data;data for a group of satellites is called almanac data.Once each 24 hours, the control center transmits theephemeris and almanac data to each satellite to updatethe navigation data message.
SATELLITES
There are 21 active operational and 3 active sparesatellites in circular orbits, with a 55-degreeinclination to the earth. These satellites providenavigation data to the navigation sets. The satellitesare arranged in six concentric rings that allow them toorbit the earth twice a day and provide world-widecontinuous coverage. Each satellite broadcasts two
Figure 1-11.—NAVSTAR GPS major elements.
1-14
spread-spectrum rf signals, 1575.42 MHz (LI-RF)and 1227.60 MHz (L2-RF). Each signal is modulatedwith a unique code sequence and a navigation datamessage. The code sequence allows the navigationsets to identify the satellite, and the data messageprovides the navigation sets information about theoperation of the satellite.
An observer on the ground will observe the samesatellite ground track twice each day, but the satellitewill become visible 4 minutes earlier each daybecause of a 4 minute per day difference between therotation of the earth and the satellite orbit time. Thesatellites are positioned so a minimum of foursatellites are always observable to a user anywhere onearth.
Satellite Signal Structure
The satellites transmit their signals using spreadspectrum techniques. Two types of techniques areused: course acquisition (C/A) code and precise (P)code. The C/A code is available to military andcivilian GPS users. The P code is available only toU.S. military, NATO military and other users asdetermined by the DOD.
Since only the P code is on both frequencies, themilitary users can make a dual-frequency comparisonto compensate for ionospheric propagation delay.The C/A code-only users must use an ionosphericmodel, which results in lesser navigation accuracy.Superimposed on both codes is the NAVIGATION-message (NAV-msg), containing satellite ephemerisdata, atmospheric propagation correction data, andsatellite clock-bias information.
Satellite Ranging
GPS navigation is based on the principle ofsatellite ranging. Satellite ranging involves measuringthe time it takes the satellite signal to travel from thesatellite to the navigation set. By dividing the traveltime by the speed of light, the distance between thesatellite and the navigation set is known. By rangingthree satellites, a three-dimensional picture, such asthe one shown in figure 1-12, can be developed. Thedistance measurement to each satellite results in a
sphere representing the distance from the navigationset to the satellite. The point where the three spheresintersect (X) is the position of the navigation set,This explanation does not account for errors. Forsatellite ranging to provide accurate position data, thefollowing three sources of error must be compensatedfor:
l Satellite position and clock error
l Atmospheric delay of satellite signals
l Navigation set clock error
With these errors compensated for, the GPS candetermine position fixes within 50 feet or less and isaccurate to within a tenth of a meter-per-second forvelocity and 100 nanoseconds for time. This accuracy,however, requires inputs from four satellites.
USER EQUIPMENT
User equipment is installed in ships, aircraft, andmotorized vehicles. The vehicle version can also becarried by personnel (particularly SEAL teams andother special forces units) as a manpack. The mostcommon manpack version is the AN/PSN-8( ). Themost common shipboard GPS receiver is theAN/WRN-6. These GPS receivers will be describedlater in this chapter.
Signal Acquisition
During operation, navigation sets collect andstore satellite almanac data in critical memory. Thealmanac data is normally available when thenavigation set is first turned on and providesinformation on satellite locations. Operators mayinput information about the navigation set position,time, and velocity to enhance the information incritical memory. With this information, the navigationset determines which satellites are available andsearches for the code sequences that identify thoseparticular satellites. When the C/A code of anavailable satellite is identified, the navigation setswitches to the more accurate P code, collects thenavigation data message, and updates criticalmemory.
1-15
Figure 1-12.—Satellite ranging.
Navigation Set Clock Error
GPS navigation sets determine distance to asatellite by accurately measuring the time differencebetween satellite signal transmission and when thenavigation set receives this signal. This difference intime is directly proportional to the distance betweenthe satellite and the receiver. Therefore, the sametime reference must be used by both the receiver andthe satellite.
The clock in the GPS receiver in not nearly asaccurate as the atomic clock in the satellite. Thiscauses the receiver and satellite clocks to be slightlyout of sync, which in turn causes the timemeasurements to be inaccurate. The error is furthercompounded by the distance calculation, so theposition of the navigation set cannot be accuratelydetermined.
The navigation set compensates for these errorsby using the distance measurement from a fourthsatellite to calculate the clock error common to allfour satellites. The navigation set then removes theclock error from the distance measurements, and then
determines the correct navigation set position.
Signal Delay and Multipath Reception
Two types of atmospheric delay can affect theaccuracy of navigation set signal measurements. Thefirst is tropospheric delay. Tropospheric delay can beaccurately predicted; the prediction is included in thealmanac data.
The second type of delay is caused when thesatellite signal passes through the ionosphere. Thistype of signal delay is caused by the ionosphere beingthicker in some areas and by satellite signals receivedfrom nearer the horizon having to pass through moreof the ionosphere than those received from directlyoverhead. Ionospheric delay will phase shift thelower satellite transmission frequency, L2-RF, morethan the higher frequency, L1-RF. The navigation setmeasures ionospheric delay by measuring the phaseshift between these two signals and then uses thiscomputation to compensate for the ionospheric delay.
Multipath reception is caused by a satellite signalreflecting off of one or more objects. This causes the
1-16
reflected signals to reach the navigation set at differenttimes than the original signal. The reception of multipathsignals may cause errors in the navigation setcalculations. The AN/WRN-6 navigation set makesoperators aware of multipath errors by a “fail” or “warn”message and/or fluctuations in the carrier-to-noise ratio.Multipath reception may be corrected by changing theship’s position.
AN/WRN-6(V) Satellite Signals Navigation Set
The Satellite Signals Navigation Set AN/WRN-6(V)computes accurate position coordinates, elevation,speed, and time information from signals transmitted byNAVSTAR Global Positioning System (GPS) satellites. Inthe P mode, it has an accuracy of 16 meters. In the C/A
C/A mode. it has an accuracy of 100 meters, thoughbetter results have been obtained by individual users.
The AN/WRN-6(V), shown in figure 1-13, operates inthree modes.
The “Initialization” mode is part of the set start-up.During initialization, the operator tests current position,date, and time data, either manually or from otherequipment. The data entered is used to speed up satelliteacquisition.
“Navigation” is the normal operating mode. Duringthe navigation mode, the set receives satellite data,calculates
Figure 1-13.—Satellite Navigation Set AN/WRN-6(V).
1-17
navigation data, exchanges data with other interconnectedsystems, and monitors the set’s performance. Thenavigation mode allows the operator to enter mission data;view position, velocity, and time data; and control the set’sconfiguration.
The “self-test’’ mode allows the operator to perform acomplete test of the navigation set at any time. When theset is in “test,” it will not track satellites.
The two major components of the AN/WRN-6(V) arethe R-2331/URN receiver and the indicator control C-11702/UR. The other units (antenna, antenna amplifier,and mounting base) perform functions similar to those ofsimilar units in other systems. For more detailed
operation and maintenance technical manual.
AN/PSN-8( ) Manpack Navigation Set
The AN/PSN-8( ) operates similarly to the AN/WRN-6(V), though obviously it is not interfaced with otherequipment. Shown in figure 1-14, each manpack containsa receiver section and a computer section. The receiverprocesses the rf signals from the satellites and sends thesatellite’s positions and times to the computer. Thecomputer uses the positions and times to find the satelliteset’s position coordinates, elevation, and changes in theposition of the manpack set. The time it takes for the setto change position is used to compute speed. For moredetailed information on this navigation set. refer to the
information on this system, refer to the AN/WRN-6(V) operator’s manual for the AN/PSN-8( ) Manpack
Figure 1-14.—Manpack Navigation Set AN/PSN-8( ).
1-18
Navigation Set. The AN/VSN-8( ) VehicularNavigation Set is also included in this manual.
NAVIGATIONAL AIDS
Other equipment used for navigation that ETs areresponsible for includes: navigation radars, surfacesearch radars (sometimes used as navigation radars)and fathometers. Information on surface search andnavigation radars is contained in NAVEDTA 12414,Radar Systems.
The following paragraphs will discuss
fathometers.
FATHOMETERS
Fathometers are used for taking depth soundings.They are particularly useful when the vessel istransitioning shallow, unfamiliar waters. A blockdiagram of the Sonar Sounding Set AN/UQN-4A isshown in figure 1-15,
On many ships the Sonar Technicians will beresponsible for this equipment, but there are ships
(mostly noncombatants) on which ETs are responsiblefor the fathometers. For more detailed information onfathometers, refer to the appropriate equipmenttechnical manual.
Figure 1-15.—AN/UQN-4A functional diagram.
1-19
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 systemused to locate points on a plane. In electronics, it isusually used for plotting antenna directional patterns.
TACAN is a polar-coordinate type radio air-navigation system that provides an aircrew withdistance information, from distance measuringe q u i p m e n t (DME) , and bear ing (az imuth)information. This information, as shown in figure 2-1, is usually provided by two meters. One meterindicates, in nautical miles, the distance of the aircraftfrom the surface beacon. The other meter indicatesthe direction of flight, in degrees-of-bearing, to thegeographic location of the surface beacon. By usingthe TACAN equipment installed in the aircraft andTACAN ground equipment installed aboard aparticular surface ship or shore station, a pilot canobtain bearing to and distance from that location. Heor 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 specificbeacon to fix his or her geographic location.
TACAN PRINCIPLES
The distance measuring concept used in TACANequipment is an outgrowth of radar-rangingtechniques. Radar-ranging determines distance bymeasuring the round-trip travel time of pulsed rfenergy. The return signal (echo) of the radiatedenergy depends on the natural reflection of the radiowaves. However, TACAN beacon-transpondersgenerate artificial replies instead of depending onnatural reflection.
Now look at figure 2-2. The airborne equipmentgenerates timed interrogation pulse pairs that thesurface TACAN system receives and decodes. Aftera 50-µsec delay, the transponder responds with areply. The airborne DME then converts the round-trip time to distance from the TACAN facility. Thefrequency and identification code provide thegeographic location of the transmitting beacon.
TACAN PULSE PAIRS
TACAN transponders use twin-pulse decoders topass only those pulse pairs with the proper spacing.The purpose of this twin-pulse technique is toincrease the average power radiated and to reduce thepossibility of false signal interference.
After the receiver decodes an interrogation, theencoder generates the necessary pulse pair requiredfor the transponder’s reply. A TACAN pulse pairgenerated by airborne or ground equipment is shownin figure 2-3.
CONSTANT TRANSPONDERDUTY-CYCLE
In principle,reply to aircraft
2-1
the TACAN transponder need onlyinterrogations at 30 pulse pairs-per-
Figure 2-2.—Distance measuring round-trip travel time.
second, per airborne equipment, to supply thenecessary distance data. However, the total pulseout put of the transmitter constantly varies, accordingto the number of interrogating aircraft. In addition,random noise may trigger the transmitter.
Figure 2-3.—TACAN pulse train.
For the transponder to provide azimuthinformation, the average power supplied to theantenna must be relatively uniform over time. Toaccomplish this, the transponder is operated on theconstant-duty-cycle principle.
In this method of operation, the receiver usesautomatic gain and squitter (noise generated output)controls to maintain a constant pulse output to the
transmitter, as shown in figure 2-4. If fewinterrogations are being received, the gain and squitterof the receiver increase and add noise-generated pulsesto the pulse train. If more interrogating aircraft comeinto range, the gain and squitter decrease and reducethe number of noise-generated pulses.
The relationship between the gain and the numberof pulses is such that only a 2-dBm change insensitivity occurs between reception from 1 aircraftand those from 100 aircraft. An added advantage ofusing a constant duty cycle is that overall transmitterpower drain remains constant.
BEACON-TRANSPONDERIDENTIFICATION CODE
Before an aircrew can use TACAN informationthat its equipment receives, it must positively identifythe transmitting TACAN station. To meet this need,the ground station transmits an identification code atapproximately one-half minute intervals. It does thisby momentarily interrupting the transponder distancedata and squitter-generated output with pulse groupsspaced at a 1350-pps rate. Each pulse group containstwo sets of 12-µsec pulse pairs spaced 100 µsec apart.The duration of the identification pulse groups varies,to represent Morse-coded characters. The durationfor a dot is 100 to 125 ms, and for a dash 300 to 375ms. An identification group is shown in figure 2-4.
2-2
Figure 2-4.—Transponder output pulse train.
15-HZ-BEARING INFORMATION The rf energy from the TACAN transmitter is fedto the antenna central element, which has no
The timing of the transmitted pulses supplies the directivity in the horizontal plane. Parasitic elementsactual distance information to the aircraft. This leaves positioned around the central element areamplitude modulation as another medium for the electronically rotated (switched on and off) at 15transponder to convey other information to the revolutions per minute. (See the section below on theaircraft. The TACAN beacon-transponder modulates OE-273(V)/URN antenna group). The distancethe strength of the pulse to convey bearing information between the central element and the parasitic elementsby producing a specific directional-radiating pattern is selected to obtain a cardioid radiation pattern. Torotated around a vertical axis. This signal, when an aircraft at a specific location, the distance dataproperly referenced, indicates the aircraft’s direction pulses appear to contain a 15-Hz amplitude-modulatedfrom the TACAN facility. This signal and distance signal because of the rotation of the cardioid radiationdata give a two-piece fix (distance and direction) for pattern. This pattern is showndetermining specific aircraft location. and view B.
in figure 2-5, view A
2-3
Figure 2-5.—TACAN radiation pattern: A. cardioidpattern; B. Ampltitude-modulated pulse pairs.
The aircraft TACAN equipment obtains bearinginformation by comparing the 15-Hz modulated signalwith a 15-Hz reference burst signal it receives from theground facility. The phase relationship between the15-Hz modulated signal and the 15-Hz reference burstsignal depends on the location of the aircraft in thecardioid pattern. The 15-Hz reference burst signalsare transmitted when the maximum signal of thecardioid pattern aims due East. This group of 12 pulsepairs is commonly referred to as the North or mainreference burst. You can see the relationship betweenthe reference pulses and the cardioid pattern bycomparing view A and view B of figure 2-5.
135-HZ BEARING INFORMATION
Errors arising from imperfections in the phasemeasuring circuits and radio propagation effects areknown as site error. These errors are significantlyreduced by the addition of 32 outer parasitic elementsadded to the electronically scanned antenna. (See the
section on the OE-273(V)/URN antenna group).Electronically switching these elements modifies theantenna cardioid pattern. Though the cardioid patternis still predominant, it is altered by superimposedripples. The aircraft now receives the 15-Hz signalwith a 135-Hz ripple amplitude modulated on thedistance data pulses (figure 2-6).
To furnish a suitable reference for measuring thephase 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-Hz reference. The 135-Hz reference group iscommonly referred to as the auxiliary or aux referenceb u r s t .
The composite TACAN signal is composed of2700 interrogation replies and noise pulsepairs-per-second, plus 180 North burst pulsepairs-per-second, 720 auxiliary burst pulse pairs-per-second, for a total of 3600 pulse pairs-per-second, or7200 pulses-per-second.
TACAN SIGNAL PRIORITIES
Priorities have been established for transmission ofthe various types of TACAN signals. These prioritiesare as
1.
2.
3.
4.
follows:
Reference bursts (North and auxiliary)
Identification group
Replies to interrogations
Squitter
Therefore, the identification group, replies, orsquitter will be momentarily interrupted for thetransmission of either the main or auxiliary referencegroup. The transmission of replies or squitter will beinterrupted every 37.5 seconds during the transmissionof an identification code dot or dash.
CHARACTERISTICS OFRADIO BEACON SIGNALS
Depending on what channel (X or Y) the TACANis on, the number of pulses-per-second and the pulse
2-4
Figure 2-6.—TACAN modulation envelope
spacing are a characteristic of that particular TACANsignal element. However, it is important to understandthat proper spacing between pulses and pulse pairs iswhat actually provides the aircraft with the means todistinguish between the TACAN pulses and any otherpulses that might be present on the received radiofrequency. Check the reference data in the appropriatetechnical manual for specific pulse characteristics andspacing.
TACAN EQUIPMENT
Many different types of TACAN equipment havebeen used for air navigation. Today, the AN/URN-25is taking over the task of tactical air navigation fromthe older AN/URN-20 on new construction ships andas ships complete overhaul. Two types of antennasare used with the AN/URN-25. They are the OE-273(V)/URN, used primarily in shipboard installations,and the OE-258/URN, which is used primarily ashore.Because both antenna systems are similar in theory of
operation, we will discuss only the OE-273/URN. Inthe following paragraphs, we will discuss theAN/URN-25 and the antenna group 0E-273(V)/URN,and then we will briefly discuss the AN/URN-20.
TACAN SET AN/URN-25
The AN/URN-25 TACAN is used as a ground-based or shipborne beacon transponder to providerange and bearing information to aircraft equippedwith TACAN equipment. It consists of two majorunits: the Transponder Group OX-52/URN-25,commonly referred to as unit 1, and the Control-Indicator C-10363/URN-25, commonly referred to asunit 2. These units are shown in figure 2-7. Eachtransponder is housed in a cabinet with two verticaldrawers, one containing a coder keyer and the othercontaining a receiver-transmitter.
The control-indicator displays the status of thetransponder(s) and failure alarms, and allows limitedcontrol of the transponder(s) from a remote location.
2-5
Figure 2-7.
2-6
It may be mounted in its own cabinet or in a standard19-inch rack.
To increase the channels available, the TACAN setcan be operated in either the X or Y mode. The Ymode changes the pulse pair spacing and the auxiliaryburst count and spacing, and increases system delay.
ANTENNA GROUP OE-273(V)/URN
Shown in figure 2-8, the Antenna Group OE-273/URN is a solid-state, high-performance,electronically-scanned, all-band TACAN antennasystem, complete with integral monitoring system andbuilt-in fault isolation capability. The antenna groupdevelops the coarse and fine bearing modulationselectronically.
Rather than forming the TACAN radiation patternby the old mechanical rotation method, the AS-3240achieves the same effect by digital switching of
parasitic elements arranged in concentric arraysaround the central radiator. Twelve inner elementsprovide the 15-Hz modulation (replacing the single-phase rotating parasitic element in the mechanicallyrotated antenna), and 32 outer elements provide the135-Hz modulation (replacing the nine outer elementsof the rotated antenna). The 15- and 135-Hzmodulation pattern is provided by electronicallyswitching the diodes in each of the parasitic elementsin prescribed time sequence, which is repeated once ineach 15-Hz interval.
In effect, the elements are rotated electrically,rather than mechanically. An advantage this providesis the elimination of the bandwidth limitations inherentin the old mechanically-rotated antennas. In theelectronically-scanned antenna, the appropriate ringfor a given frequency segment is activated by a fastelectronic switch, based on information from theTACAN frequency synthesizer. This allowsinstantaneous band switching and all-band operation.
Figure 2-8.—Antenna Group OE-273(V)/URN.
2-7
Figure 2-9.—TACAN Set AN/URN-20(V)1.
2-8
TACAN SET AN/URN-20
Though not modern by any standard, theAN/URN-20 TACAN set is reliable and operatessimilarly to the AN/URN-25. Shown in figure 2-9, ituses the same electronically-scanned antenna andcontrol-indicator as the AN/URN-25. The AN/URN-20 is being replaced by the AN/URN-25.
CAPABILITIES AND LIMITATIONS
In the X mode of operation, the TACAN settransmits on one of 126 discrete channel frequencies(which are 1-MHz apart) from 962 to 1024 MHz andfrom 1151 to 1213 MHz. In the Y mode of operation,the set transmits on one of 126 discrete channelfrequencies (which are 1-MHz apart) within the rangeof 1025 to 1150 MHz. The navigation set receiver,operating in the 1025- to 1150-MHz range for boththe X and Y modes, is always displaced 63 MHz fromthe transmitter frequency.
The TACAN set can simultaneously provideindividual distance measuring service for up to 100interrogating aircraft. Of the 3 ,600 pulsepairs-per-second transmitted by the TACAN, 900pulse pairs (MAIN and AUXILIARY bursts) containthe bearing information; the remaining 2,700 pulsepairs are either random noise pulses, identity pulses, orreplies to interrogating aircraft. Once every 30seconds, the interrogation replies and random noisepulses are interrupted for the transmission of identitypulses.
The navigation set has a receiver sensitivity of -92dBm or better and a nominal peak power output of 3kilowatts at the transponder cabinet output. (Poweroutput may limited to less than peak by directives).Since the bearing and identification signals aredelivered spontaneously and not in response tointerrogations, an unlimited number of properlyequipped aircraft can derive this information from theTACAN set over a line-of-sight (los) range up to 200nautical miles.
2-9
APPENDIX I
LIST OF ACRONYMSAUX- auxiliary.
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 Radio Navigation Plan.
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-- milliwatt.
NAV-MSG- NAVIGATION-message.
NAVSAT- navigation satellite.
NAVSTAR GPS- satellite Global PositioningSystem.
NNSS- Navy Navigation Satellite System.
NTDS- Naval Tactical Data System.
OMEGA- VLF radio navigation.
P CODE- precise code.
PPS- pulses per second.
PROM- programmable read-only memory
RF- radio frequency.
SATNAV-- satellite navigation
S/D- synchro to digital.
SINS- Ship’s Inertial Navigation System.
TACAN- Tactical Air Navigation.
TCA- time of closest approach.
UT-- Universal Time.
VOR- VHF--omnidirectional range.
XPDU- expanded data processor unit.
AI-1
APPENDIX II
REFERENCES USED TO DEVELOP THE TRAMAN
NOTE: Although the following references were current when thisTRAMAN was published, their continued currency cannot be assured. You,therefore, need to ensure that you are studying the latest revision.
Electronics Technician 3 & 2, NAVEDTRA 10197, Naval Education andTraining Programs Management Support Activity, Pensacola, FL, 1987.
Inertial Navigation Set AN/WSN-5, NTP S-30-7519E, Naval Sea SystemsCommand, Washington, DC, 1991.
Manpack Navigation Set AN/PSN-8( ), Operator’s Manual EE170-AA-OPI-010/MV, Space and Naval Warfare Systems Command, Washington, DC,1990.
Naval Aeronautical Facilities, Naval Shore Electronics Criteria, NAVELEX0101,107, Naval Electronic System Command, Washington, DC, 1971.
NAVSTAR Global Positioning System (GPS) User Equipment, NTP E-70-8215E,Space and Naval Warfare Systems Command, Washington, DC, 1993.
Satellite Signals Navigation Set AN/WRN-6(V), Technical Manual EE-170-AA-OMI-010/WRN6, Space and Naval Warfare Systems Command,Washington, DC, 1990.
Shipboard Electronics Material Officer, NAVEDTRA 12969, Naval Educationand Training Programs Management Support Activity, Pensacola, FL, 1992
TACAN, Navigation Set AN/URN-25, Technical Manual EE172-AB-OMI-010,Space and Naval Warfare Systems Command, Washington, DC, 1990.
AII-1
INDEXD
Doppler principlesrefraction measurement, 1-8velocity computation, 1-8
GO
NNSScomputer center, 1-7injection station, 1-7naval observatory, 1-7satellites, 1-6tracking stations, 1-7
GPS navigation setsAN/PSN-8 manpack, 1-18AN/WRN-6, 1-17
L
LORANline-of-position, 1-2
N
Navigation aidsfathometers, 1-19radar, 1-19
Navigation fundamentalsdead reckoning, 1-1electronic navigation, 1-2piloting, 1-2tactical, 1-1
Navigation setsAN/SRN-19, 1-11AN/WRN-5, 1-9
NAVSTAR Global Positioning Systemclock error, 1-16ground control, 1-14ionospheric delay, 1-16multipath reception, 1-16satellite ranging, 1-15satellite signal structure, 1-15satellites, 1-14signal acquisition, 1-15tropospheric delay, 1-16
Omegahyperbolic navigation, 1-3
s
SINSaccelerometers, 1-4advantages, 1-3AN/WSN-5, 1-5gyros, 1-4servo systems, 1-4
T
TACANaircraft indications, 2-1aux reference burst, 2-4bearing information (15 Hz), 2-3bearing information (135 Hz), 2-4cardioid, 2-3constant transponder duty-cycle, 2-1identification code, 2-2north reference burst, 2-4principles, 2-1pulse pairs, 2-1signal priorities, 2-4squitter, 2-2
TACAN equipmentantenna group OE-273(V)/URN, 2-7AN/URN-20, 2-9AN/URN-25, 2-5
INDEX-1
