Time and Frequency Radio Stations WWV WWVH WWVB

1 Page 1 NATLINST.OFSTAND&TECH NIST PUBUCATtONS Nisr NationalInstituteofStandardsandTechnology TechnologyAdministration, U.S.DepartmentofCommerce NISTSpecialPublication250-67 NISTTimeandFrequencyRadioStations WWV,WWVH,andWWVB Gle... Open at page → 2 Page 2 rhe NationalInstituteofStandardsandTechnologywasestablished in1988byCongressto"assistindustryinthe developmentoftechnology ...neededtoimproveproductquality,tomodernizemanufacturingprocesses,toensure productreliability ..... Open at page → 3 Page 3 NISTSpecialPublication250-67 NISTTimeandFrequencyRadioStations: WWV,WWVH,andWWVB GlennK.Nelson MichaelA.Lombardi DeanT.Okayama TimeandFrequencyDivision PhysicsLaboratory NationalInstituteofStandardsandTechnology 325Broad... Open at page → 4 Page 4 Certaincommercialentities,equipment,ormaterialsmaybeidentifiedinthis documentinordertodescribeaprocedureorconceptadequately.Suchidentification isnotintendedtoimplyrecommendation orendorsementbytheNationalInstituteof Stan... Open at page → 5 Page 5 Contents Contents Introduction vii Acknowledgements viii Chapter 1.HistoryandPhysicalDescription 1 A.HistoryofNISTRadioStations 1 1.HistoryofWWV 1 2.HistoryofWWVH 6 3.HistoryofWWVB 8 B.PhysicalDescriptionofNISTRadioStati... Open at page → 6 Page 6 RemoteFrequencyCalibrations: TheNISTFrequencyMeasurementandAnalysisService a)StandardCarrierFrequencies 43 b)VoiceTimeAnnouncements 43 c)StandardTimeIntervals 44 d)StandardAudioFrequencies 45 e)UTlCorrections 46 f)100HzT... Open at page → 7 Page 7 Contents E.TelephoneTime-of-DayService 81 1.WWVTelephoneTime-of-DayService 81 2.WWVHTelephoneTime-of-DayService 82 Chapter3.OperationalProcedures 83 A.HardwareMaintenance 83 1.TransmittersandBroadcastEquipment 83 2.Timin... Open at page → 8 Page 8 RemoteFrequencyCalibrations:TheNISTFrequencyMeasurementandAnalysisService 2.EstimatedNumberofCustomersforWWVB 104 3.EstimatedNum.ofCustomersfortheTelephoneTime-of-DayService105 B.CoverageAreaforRadioBroadcasts 105 1.Cove... Open at page → 9 Page 9 Introduction Introduction TheNational InstituteofStandardsandTechnology(NIST)providesstandardtimeand frequencyinformationthroughthreeradiobroadcaststationsthatareroutinelyusedby millionsofcustomers.Thestations,WWVandWWVB... Open at page → 10 Page 10 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Acknowledgements Theauthorsthankandacknowledgetheradiostationstaffmemberswhohelpperformthetasks describedinthesepages,andwhocontributedtotheinformationcontainedinthisdoc... Open at page → 11 Page 11 Chapter1-HistoryandPhysicalDescription Chapter1 HistoryandPhysicalDescription ThischapterincludesthehistoryofNISTradiostationsWWV,WWVB,andWWVB,and thenprovidesacompletephysicaldescriptionofeachstation'sfacilities. Italso... Open at page → 12 Page 12 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB telegraphiccodewasusedtobroadcast500-wordreports,calledtheDailyMarketMarketgram, on750kHz.Theoperatingradiuswasabout300kmoutofWashington. Thesebroadcasts continueduntilA... Open at page → 13 Page 13 ChapterI-HistoryandPhysicalDescription reachtheareawestoftheMississippi.Toaddressthisproblem,aHstofotherbroadcaststations foundtobesuitableasfrequencyreferenceswasmaintained.Thefi-equenciesofthesestations weremeasuredbyN... Open at page → 14 Page 14 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Figure1.1.StationWWVinBeltsville,Maryland. Bynowwellestablishedasareferencesourceforfrequencyandtimeinterval,WWVwasstill notusedasatimesynchronization source.Thestandard... Open at page → 15 Page 15 Chapter1-HistoryandPhysicalDescription frequencycontrolofthebroadcast.By1958,thetransmittedfrequencywasroutinelykeptwithin 2partsinlO'^ofthenationalstandard. From1955to1958,WWVplayedakeyroleinthedefinitionoftheatomicseco... Open at page → 16 Page 16 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB WWVwhenannouncementsoftimebeganin1950[18].HisvoicewasuseduntilAugust13, 1991,whenthevoiceequipmentwaschanged.Forashorttime,thevoiceofJohnDoylewas usedforthetimeannouncem... Open at page → 17 Page 17 Chapter1-HistoryandPhysicalDescription Figure1.2.TheoriginalWWVHstationsiteinMaui. Acongressionalappropriation inJune1968wasusedtofundthenewstation.OnJuly1,1971, thestationbeganbroadcastingfromitscurrentlocation,a30acre(... Open at page → 18 Page 18 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB HurricaneshaveharmedWWVHonatleasttwooccasions. In1982,Kauaiwasstruckby HurricaneIwaandthestationremainedonemergencypowerforsevendays.In1992,Hurricane Inikipassedoverthes... Open at page → 19 Page 19 Chapter1-HistoryandPhysicalDescription ThetimecodeformathaschangedonlysHghtlysince1965;itusesaschemeknownasbinary codeddecimal(BCD),whichusesfourbinarydigits(bits)tosendonedecimalnumber. TheWWVBbroadcastcontinuedoperatio... Open at page → 20 Page 20 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB B.PhysicalDescriptionofNISTRadioStationFacilities ThissectioncontainsaphysicaldescriptionoftheNISTradiostationfacilities,includingthe buildingsandequipmentlocatedateachs... Open at page → 21 Page 21 Chapter1-HistoryandPhysicalDescription N.W.COR. SEC.7 S.W.COR. SEC.7 40°40'55,2"N 2.5MHzDIPOLE 105'0231.3"W \\ -\ 40"40'50,5"N 5MHzSTBYDIPOLE 105° 02'26.6"W \\ I 40°40'47.6"N olOMHzDIPOLE105^02'25.1"W 40"40'45.0"N^ 5MHzD... Open at page → 22 Page 22 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Figure1.5.AerialviewoftheWWVandWWVBsitefromthesouth. Open at page → 23 Page 23 ChapterI-HistoryandPhysicalDescription property.Waterusedforagriculturalirrigationdownstreamflowsthroughtheditchesduring thelocalgrowingseason,usuallyMaytoSeptember.Tworeservoirs,NorthPoudreReservoir 6andGreenwaltLake,bo... Open at page → 24 Page 24 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Theareacontainingthetransmitters iscooledbyalargeevaporativecoolermountedonthe roof.Insummer,outsideairistakeninandpassedthroughmoistenedpads,thenfilteredtwice beforebei... Open at page → 25 Page 25 Chapter1-HistoryandPhysicalDescription broadbandantennasthatwerecapableofoperatingatanyWWVfrequency.Whenthe25MHz servicewasdiscontinued inthemid-1970's,T6andthe25MHzantennawereconvertedfor useasastandbytransmitterandante... Open at page → 26 Page 26 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB d)WWVAntennasandTransmissionLines SixWWVantennasarelocatedalongthetopofaridgetothenorthandeastofthetransmitter building.Theterraininallbutthesoutherlydirectionofpropagat... Open at page → 27 Page 27 Chapter1-HistoryandPhysicalDescription BROADBAND #1 Tl 20MHz (STBY) T2 (OFFLINE) BROADBAND #2 T3 2.5MHz (STBY) T2-A 15MHz T4 2.5MHz T5 20MHz S2 T7 10MHz (STBY) T615MHz (STBY) ANTENNA FIELD TRANSMITTER BUILDING T7-A 10MHz... Open at page → 28 Page 28 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Table1.1.WWVbroadcastequipmentconfiguration. Transmitter Frea(MHz) Configuration Power(kW)Switch 1WIIIiCI T1 AnvWWVr\i 1yVVVVV 20MHzStandby 2.5 Rrnadhand#1 NotinService... Open at page → 29 Page 29 Chapter1-HistoryandPhysicalDescription 13mmmylarguyssupportthe10,15,20MHz and15MHzstandbyantennas -8mmsteelcables Precasttransmission linesupportpost Additionalsetsofguysandanadditional setofthreeguyanchorsareusedto supp... Open at page → 30 Page 30 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB RadioCompanyandinstalledwhen thestationwasbuilt.Theyconsist ofacentraltowersection88ft(27 m)tallthatrestsonaceramicbase insulator,surroundedbyawire array(Figure 1.12).Ag... Open at page → 31 Page 31 Chapter1-HistoryandPhysicalDescription Figure1.13.TransmittertoantennatransmissionlinesatWWV. e)WWVBack-UpGenerator TheWWVemergencystandbygenerator islocatedinthegeneratorroomonthenorthwest endofthetransmitterbuilding. I... Open at page → 32 Page 32 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB f)WWVTimeandFrequencyEquipment TimeandfrequencyequipmentatWWVisinstalledinthetemperature-controlled mainscreen room.The"heart"ofthesystemisthreecommerciallymanufacturedc... Open at page → 33 Page 33 Chapter1-HistoryandPhysicalDescription 2.WWVBFacilities a)WWVBLand WWVBwasfirsttooccupythesiteitnowshareswithWWV(Seel.a.). b)WWVBBuildings ConstructionofWWVBbeganin1962.Thesingle-storyWWVBtransmitterbuilding(Figure 1.14)... Open at page → 34 Page 34 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Figure1.15.WWVBhelixhouse. Theuninterruptible powersupply(UPS) at WWVBwasmadebyBestPower,modelUT- 310. Ithasa208Vthree-phaseoutput,andis ratedat10kVA.Theestimatedruntime... Open at page → 35 Page 35 ChapterI-HistoryandPhysicalDescription Figure1.16.WWVBtransmitter. Currently,threeAN/FRT-72 transmitters areinstalled atWWVB,anddesignated aslow frequencytransmittersLFT-1,LFT-2,andLFT-3.Allhaveallbeenoverhauledaspartoft... Open at page → 36 Page 36 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB SOUTH ANTENNA NORTH ANTBWA lEGEND: 60kHzT»£SIGNAL - THBlCTRY eMHzREFERENCE \/ House \/ HBJ( HOUSE SaECTHJ TineCODS GENERATOR (10F4) SITEULSTER CLOCK ATWWV LA LF TRANSI*e... Open at page → 37 Page 37 ChapterI-HistoryandPhysicalDescription NorthAntenna " 573m Figure1.19.WWVBantennas. beingatalowerelevationthanthebasesoftheothertowers.Thetowersaremadeofweldedsteel rodin30ft(9.1m)sections.Eachsectionhasthreesidesthatmea... Open at page → 38 Page 38 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Figure1.20.Antennatotowerconnectiondetail. ringform6in(152mm)indiameter. Itextendsdownwardsfromthecenterofthetophattoa pointabout93ft(28.4m)offtheground,where itisconnec... Open at page → 39 Page 39 Chapter1-HistoryandPhysicalDescription e)WWVB Back-Up Generator Theemergency standby generatorwasinstalled in 2000 in thenewly constructed generatorroom atthenorthwestendofthe WWVB building. It replacedasmallerunitthat w... Open at page → 40 Page 40 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB f)WWVBTimeandFrequencyEquipment WWVBtimeandfrequencyequipmentconsistsoffourtimecodegenerators(TCGs)locatedin theWWVBmainscreenroom.Theseunits(Model9110)weremanufactured... Open at page → 41 Page 41 Chapter1-HistoryandPhysicalDescription ^ MOiOKA! PACIFIC OCEAN 5^, THENAPALI COAST , , PUIJKA ^ PUi * fORfST ^ PACIFIC OCEAN WWVH barking Sands ^Mana C550 WAIM(A ' CANYON STATCPARK (-jKekaha (so; \ -oWaimea K/la/ika/ti C... Open at page → 42 Page 42 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Figure1.24.ViewofWWVHsitefromthetopofthe5MHzantenna. b)WWVHBuildings TheWWVHtransmitterbuilding(Figure1.24)isasinglestoryconcreteblockstructurelocated attheeasternedgeof... Open at page → 43 Page 43 Chapter1-HistoryandPhysicalDescription c)WWVHTransmitters WWVHoperatesonfourfrequencies: 2.5,5,10, and15MHz,withaprimarytransmitterand standbytransmitterforeachfrequency.Thefirst transmitters installed atthecurrentWWVH s... Open at page → 44 Page 44 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Table1.3.WWVHtransmitterconfiguration. 1ransminer designation rrequency (IVIHz) ^oniiguraiion ^)AiAfAr rower (kW) AntAnno Mnienna T1 5 Primary 10 5MHzPrimary T2 AnyWWVH... Open at page → 45 Page 45 Chapter1-HistoryandPhysicalDescription insulatorsnearthemid-pointofthetower.A drawingshowinganoverheadandsideviewof aphasedarraycanbeseeninFigure 1.28.The antennasarecenter-fed,thatis,theconnection fromthetransmissionhne... Open at page → 46 Page 46 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Figure1.28.Phased-arrayantennaatWWVH. 36 Open at page → 47 Page 47 Chapter1-HistoryandPhysicalDescription Figure1.29.15MHzantennaatWWVH. f)WWVHTimeandFrequencyEquipment Thetimeandfrequencyequipmentinstallation atWWVH isverysimilartothatatWWV. Equipment isinstalledinthetemperature-contro... Open at page → 48 Page 48 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB C.OrganizationalControlofNISTRadioStations EachNISTRadioStationismanaged,controlled,andmaintainedbytheServicesGroupofthe NISTTimeandFrequencyDivision.Theengineer-in-char... Open at page → 49 Page 49 Chapter2-TechnicalDescription Chapter2 TechnicalDescription ThischapterprovidesatechnicaldescriptionofhowtheNISTradiostationswork. Itdescribes theequipmentusedateachstationtobroadcaststandardtimeandfrequencysignalstothe... Open at page → 50 Page 50 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB FrequencyData NISTPRIMARY FREQUENCY \ STANDARD INTERNATIONAL ATOMICTIME SCALES(TAI,UTC) i TimeData PeriodicICalibrations NISTENSEMBLEOF ATOMICOSCILLATORS T NISTFREQUENCY... Open at page → 51 Page 51 Chapter2-TechnicalDescription Figure2.2showsasimplifiedblockdiagramofaWWVbroadcastequipmentrackandits interconnections withmonitoringandcontrolequipment. Eachsystem ismadeupofa commercialcesiumfrequencystandard,afrequenc... Open at page → 52 Page 52 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB codeddecimal(BCD)timecode,andofficialannouncements. Allelementsexceptthestandard carrierfrequenciesareintheaudiofrequencyrange.WWVandWWVHbroadcastanidentical BCDtimecode... Open at page → 53 Page 53 Chapter2-TechnicalDescription a)StandardCarrierFrequencies TheWWVstandardcarrierfrequenciesarederiveddirectlyfromthesitemasterclock.Figure 2.4showsasimplifiedblockdiagramofthestandardcarrierfrequencygenerationsystem.A 1... Open at page → 54 Page 54 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB "Atthetone:sevenhours,twentyfiveminutes,coordinateduniversaltime. " Thisannouncement isfollowedbyashort1000Hztone.Thetimeannouncement is concatenated,orassembledfromavar... Open at page → 55 Page 55 Chapter2-TechnicalDescription d)StandardAudioFrequencies Inadditiontotheinaudiblestandardcarrierfrequencies,WWValsobroadcastsstandardaudio frequenciesduringmostminutesofeveryhour.Figure2.5isanillustrationoftheWWVaudio si... Open at page → 56 Page 56 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB voicemessage.AsshowninFigure2.5,thesilentperiodsforWWVarefrom43to52minutes afterthehour,aswellasminutes29and59. TONE- 10ms 5ms 25ms •TONE Figure2.6.WWVandWWVHsecondpulse... Open at page → 57 Page 57 Chapter2-TechnicalDescription Table2.1.BCDweightingschemeusedbyWWVandWWVHtimecode. Decimal niiTTiHpr 1ILllllL/tt.'L Bit1 2° Bit2 z. Bits z. Bit4 0 0 0 0 0 1 1 0 0 0 2 0 1 0 0 3 1 1 0 0 4 0 0 1 0 5 1 0 1 0 6 0 1 1 0 7 1 1... Open at page → 58 Page 58 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB requiresthreeBCDsets.Secondscanbedeterminedbycountingthepulseswithintheframe. AllinformationinthetimecodeframeisreferencedtoUTCatthebeginningoftheframe. Figure2.7showsth... Open at page → 59 Page 59 Chapter2-TechnicalDescription onbits4-7.Likewise,thehoursaretransmittedonbits20-23and25,26,andtheminuteson bits10-13and15-17.Sincethedayofyearfunctioninvolvesthreedecimaldigits,threeBCD setsarerequired:bits30-33,35-38,an... Open at page → 60 Page 60 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Table2.2.WWVofficialannouncements. Minute Message Sponsor Website 8,9 NorthAtlanticHigh SeasStormWarnings NationalWeatherService www.nws.noaa.gov 10 EasternNorthPacificH... Open at page → 61 Page 61 Chapter2-TechnicalDescription i)WWVSignalMonitoring TheWWVsignal iscomparedandmonitoredforaccuracyatseveralpointsusingseveral methods,includingcomparatorandcontrollersystems,manualtimingcomparisons,andthe NISTFrequencyMe... Open at page → 62 Page 62 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB TheWWVtimecodeisrecordedasitisbeinggenerated.Adecodingcircuitanddatalogging computerprogramareconnectedtothedesignatedsitemasterclock.Thisarrangementallows eachbitofthet... Open at page → 63 Page 63 Chapter2-TechnicalDescription Allofthestandbytransmitters atWWVareTMCunits,aswellastheprimarytransmitterson 2.5MHzand20MHz.TheWWVsignalforthesetransmitters,whichoriginatesinthetime codegenerators, ismodulatedwiththecarri... Open at page → 64 Page 64 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB classAEimodeoftheTMCtransmitters.TheCCAtransmittersprovide10kWoutputpower, andareabout54%efficient. AsimplifiedblockdiagramofaCCAtransmitter isshowninFigure2.9.Thecarrie... Open at page → 65 Page 65 Chapter2-TechnicalDescription 0° Figure2.10.Theoreticalradiationpatternofidealverticalhalf-wavedipoleantenna. 5.WWVandWWVBBroadcastMonitoringandAlarmSystems SeveralindependentalarmandmonitoringsystemsareinuseatWWVandWWVB... Open at page → 66 Page 66 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB The status of the telephone and data connections totheNIST Boulderlabsismonitored bya linemonitoring device thatdetects an outageordiscontinuityof theservice. Whenan out... Open at page → 67 Page 67 Chapter2-TechnicalDescription alarmcontactsismadeandthe alarmsequence started.The sequence includes an approximate 120sdelayto allowfortransmitteroverload recycling or standby transmitter activation. Ifthe signalhasnotbe... Open at page → 68 Page 68 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB 6.CommercialElectricalPowerMonitoring ThecommercialpowercomingintotheWWVBbuildingismonitoredbyapowermonitoring systemmadebyDranetz/BMI Inc.Thissystemconstantlymonitorsth... Open at page → 69 Page 69 Chapter2-TechnicalDescription C.TechnicalDescriptionofWWVB TheWWVBsignalisderivedfromthesitemasterclock,locatedintheWWVscreenroom.A 5MHzsinewaveoutputfromtheselectedrackissentviaburiedcablestotheWWVBscreen room,adistance... Open at page → 70 Page 70 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB WNSIBPhaseSignature CoordinatedUniversalTime(UTC),5minutesegments Figure2.14.WWVBphasesignature. scheme isshowninTable2.4.UnhketheWWVA^Htimecode,theWWVBtimecode includes... Open at page → 71 Page 71 Chapter2-TechnicalDescription Table2.4.BCDweightingschemeusedbyWWVBtimecode. Decimal number Bit1 Bit2 Bit3 2' Bit4 2° U (J 0 0 0 1 1 U A U A U 1 z A u A U 1 1 A U -5 J A u A U 1 1 1 1 A n u 1 1 A U A U 5 0 1 0 1 6 0 1 1... Open at page → 72 Page 72 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB WWVBTIMECODEFORMAT —ONTIMEPOINTA TIMEFRAME 1MINUTE (indexcount1second) 20 30 40 1 IllIIIIIIIM 1 1 1 1 1M 1 1II IIIIIIIMIIMIMII P1 |<-0.8SECOND ^2 -*-\*- 0.2SECOND--|w|<-... Open at page → 73 Page 73 Chapter2-TechnicalDescription WWVB isnormallyoperatedindualantennamode(seeFigure1.19). Inthismode,two transmittersareontheair,simultaneously broadcastingthesameWWVBinputsignal.One transmitterfeedsthenorthantenna,andanoth... Open at page → 74 Page 74 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB switchesandconnectsthetransmittertotheload.Interlockswitchesarealsoconfiguredtotrack theswitchconfigurations; thisinformation issenttothecontrolconsole. 7.ControlConsole... Open at page → 75 Page 75 Chapter2-TechnicalDescription UNEIN: TOkVt eOkHi WVW8 SH3NAL FROM CONSOLE HKW/7DR AND CONmOLBUS TOCONSOLE UNEIN: 4S0v 70kVi POWER DISTRIBUTION PLATE POWER SUPPLY TRANSMITTER LOCAL CONTROL lOkVDC PLATE XFMR J I OUTPUT '~... Open at page → 76 Page 76 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Figure2.18.Interiorviewofhelixhouse. Thehelixhousesarenamedforthelargehehcalcoilthatwasinstalledthereaspartofthe originalWWVBandWWVLantennamatchingequipment.Whenthestati... Open at page → 77 Page 77 Chapter2-TechnicalDescription ROOF BUSHING SOOHM COAXIAL CABLE TKANSUITTER BUILDING TEE- NETWORK J. VARIOMETER <:::> FIBEROPTIC ANDCOPPER TELEMETRY ANDCOmPOL CABLES < SINGLE/DUAL \ RELAY HEUXHOUSEANDANTENNA TQEMETRYANDCO... Open at page → 78 Page 78 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB motornearthefloor.Whenthegroundcommand isgiven,themotorisswitchedon,unspooling thecableandallowingthespringtodrivethetwospherestogether. Intheungroundedposition, thedist... Open at page → 79 Page 79 Chapter2-TechnicalDescription Table2.5.ResistanceandefficiencyofWWVBantennas. Single Dual North South North South Mutual Grossresistance 0.859 0.825 1.264 1.151 0.366 Rg(ohms) Radiation 0.464 0.464 0.104 0.104 0.360 resi... Open at page → 80 Page 80 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB D.TechnicalDescriptionofWWVH ThedesignandconfigurationofRadioStationWWVHinHawaiibearsmanysimilaritiestothat ofWWV.Themaindifferences arefoundinthebroadcastequipment,whic... Open at page → 81 Page 81 Chapter2-TechnicalDescription generationsystemanditsinterconnectionwithmonitoringandcontrolequipment.The5MHz outputfromthefrequencystandardissenttoadivider/distribution ampUfier,whichdistributes thesignaltotheTCG,theFMAS... Open at page → 82 Page 82 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB a)StandardCarrierFrequencies WWVHstandardcarrierfrequenciesarederivedfromthesitemasterclock.Figure2.22shows asimpHfieddiagramofthecarrierfrequencygenerationsystem.A5MHzs... Open at page → 83 Page 83 Chapter2-TechnicalDescription Theannouncement isfollowedbyabout8secondsoftickswithoutatone,thenashort1200Hz toneindicatesthetopoftheminute.Astationidentificationmessage isbroadcasttwiceeach hour.ThestationIDreadsasfollow... Open at page → 84 Page 84 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB WWV,andminute 1onWWVH.Thetonesareinsertedinthebroadcastforthefirst45seconds oftheirallocatedminutes,andarefollowedbythevoiceannouncementindicatingthetime,and asilentperi... Open at page → 85 Page 85 Chapter2-TechnicalDescription g)OfficialAnnouncements WWVH alsocarries officialannouncements byU.S.Government agencies. The announcements areofapublicservicenatureandarelimitedto45secondspersegment.More thanonesegmentmay... Open at page → 86 Page 86 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB i)WWVHSignalMonitoring AswithWWV,theWWVHsignalismonitored atseveralpoints:comparatorandcontrol circuits,manualtimingcomparisons,andFMAS.TheWWVHsystemincludesatimecodeand... Open at page → 87 Page 87 Chapter2-TechnicalDescription MODULATED WWVH - SIGNAL 20SV 3PHASE */-180VDC DRIVER AMP FINAL PA 3000V DC MAIN MAIN POWER PLATE DIST. SUPPLY 7500V DC 5MV TO ANTENNA TheElcom-Bauer transmittershavea final ampUfier stageope... Open at page → 88 Page 88 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Table2.7.WWVHantennadata. Frequency (MHz) Use Height (m) Type Latitude Longitude r1llllaly 70Q Z.-7. " quarter-wavebase- fedmonopole 1SQ"4S'S94"W 2.5 Standby 22.9 base-f... Open at page → 89 Page 89 Chapter2-TechnicalDescription 0 180 Figure2.26.Approximationofradiationpatternfrom5MHzphasedarrayantenna. 5.WWVHBroadcastMonitoringandAlarmSystems WWVHismannedduringnormalworkinghours.Automatedsystemsareinstalledtomonito... Open at page → 90 Page 90 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB statusoftheincomingelectricalpower,andthefUellevelinthestandbygeneratordaytank.Ifa majoralarmisnotresolvedin5minutes,signalsaresenttotheautomaticdialingsystem,naval base... Open at page → 91 Page 91 Chapter2-TechnicalDescription 7.UPSMonitors ThePowerware(9170+)uninterruptiblepowersupply(UPS)isadoubleconversionunitwith nearzeroswitchingtime. Itisatrueon-lineunitusedtoprotectthesensitiveelectronic equipmentinbothscre... Open at page → 92 Page 92 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB servicebetweenBoulderandthestation.ThePBXattheBoulderlabsisaNortelMeridian system,asisthePBXatWWV/WWVB. ThecallscreeningunitsaremadebyInteralia,Inc, andarelocatednexttot... Open at page → 93 Page 93 Chapter3-OperationalProcedures Chapter3 OperationalProcedures ThissectiondescribestheoperationalproceduresoftheNISTradiostations.Theseprocedures mustbeperformedtokeepthestationrunningsmoothly,andtocontrolthequalityofthe... Open at page → 94 Page 94 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB mechanicalinspectionsofhardwareandconnections,usuallyfromtheground.Lightbulbs mustbechangedannuallyintheWWVBtowersandthe2.5MHzantenna;thisisperformedby contractors.WWVBa... Open at page → 95 Page 95 Chapter3-OperationalProcedures C.ScheduledTasks Schedulesofthevarioustasksperformedbypersonnelattheradiostationsareshownbelow. Allaspectsofstationoperationsandproceduresincludingmaintenance, repairs,service,etc. areinclu... Open at page → 96 Page 96 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Semi-annualTasks • InsertorremoveDaylightSavingTimeinformationfromthebroadcast.AtWWVthisisa programentrythatcanbeperformeddaysorweeksaheadoftheactualevent,whichoccurs th... Open at page → 97 Page 97 Chapter3-OperationalProcedures 2.WWVBTaskLists DailyTasks •Checkbroadcaststatus.Observemonitoringprogramsandnoteanyovernightaberrations (sHghtchangesinphaseorpowerlevels). •Checktransmitter statusatconsole;logtransmitter... Open at page → 98 Page 98 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB •Performpreventivemaintenanceonthehelixhouseequipment.Thisinvolvesplacingthe WWVBbroadcastinsinglemode,andgroundingtheantennaatthehelixhousetobe inspected. Thevariometer... Open at page → 99 Page 99 Chapter3-OperationalProcedures • InsertDUTlcorrectionintothebroadcastwhennecessary.Mustbeprogrammedmanually thedaybeforetheinsertion. • Insertleapsecondcorrection intothebroadcastwhenleapsecondsoccur.Mustbe programmedman... Open at page → 100 Page 100 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB •CheckoperationofIRIG-Hdatalogger,stripchartrecorder,ACTS,FMAS, and2kHzalarm. •Timeandfrequencylogbook •Logcommon-viewGPSdataandresultsbetweenWWVHandBoulder. •Logandanal... Open at page → 101 Page 101 Chapter3-OperationalProcedures •Testandlog(clamp-onampmeter)high/lowreadingsoftowerbeacons,climband replaceasnecessary. •GeneratorRoom •ExerciseKohlergeneratorfor30minuteswithnoload. •Logengine/generatormeterreadingswhil... Open at page → 102 Page 102 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB •StandbyGenerator •Checkallfluidlevels. •Checkconditionoffanbelt,strobelightandbatteryelectrolytelevels. •Cleanoutdebrisfromsecondarycontainmenttank. •Testdaytankfuelala... Open at page → 103 Page 103 Chapter3-OperationalProcedures Bi-annualTasks •Climbandpaintantennasorangeandwhite. OtherTasks(performedasrequired) • Insertleapyear,leapsecond,andDUTlinformationasdescribedinWWVtasklist. D.RepairsandServiceofEquipment R... Open at page → 104 Page 104 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB supportpersonnel.MajorprojectandupgradesareusuallyfundedbyEMSS,andperformedby localcontractors. Still,logisticsrequireagreaterlevelofinvolvementforstationstaffevenin the... Open at page → 105 Page 105 Chapter3-OperationalProcedures Interactingwithusersofthebroadcasts isanotherongoingtask.Allstationstaffmembersare requiredtohandleinquiriesaboutthebroadcastsfromusers,bytelephone,emailorpostalmail. E.FailureModes 1.WWV/W... Open at page → 106 Page 106 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Whenabroadcastortransmitteroutageoccurs,anautomaticbackupsystem(described in Chapter2)isenabled.Amicroprocessor circuitmonitorsRPcurrentsamplesfromeachmain transmitter.W... Open at page → 107 Page 107 Chapter3-OperationalProcedures 2.WWVBFailureModes TheWWVBbroadcastconsistsofonefrequency,60kHz,normallycarriedbytwotransmitters operatingsimultaneously intoseparateantennas. a)TimingFailures WWVBtimingusestwoofthecesiumf... Open at page → 108 Page 108 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB c)OtherEquipmentFailureModes Intheeventofacommercialpoweroutage,theemergencystandbygenerator startsand transfersthebuildingloadwithinoneminute.Restartcircuitryineachacti... Open at page → 109 Page 109 Chapter3-OperationalProcedures 2.FrequencyControl Thefrequenciesbroadcastbytheradiostationsarederivedfromthefrequencystandards at eachsite.Theoutputsofthethreestandardsareeachmonitoredbycomparingtheiroutputs witheachothe... Open at page → 110 Page 110 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB He EditViewOptionsDataJooisWindow Help DOIOOPOOOIOIOIOPOOOOOOOOOPIOOOOOOOIPIOC :0100P100101010POOOOOOOOOP100000001P1GC 5010OP0D0OO000OP10GO000O0P10O000OO1P1OC 50100P1000... Open at page → 111 Page 111 Chapter3-OperationalProcedures Thepurchaseofpoweramplifiertubesisasignificantpartofthestation'sbudget.Thesetubes areexpendableitems.Aspartoftheequipmentlogs,extensivedocumentation iskeptonthe poweramplifierandmodulatortu... Open at page → 112 Page 112 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB H.PhysicalSecurity Thissectiondescribesafewofthekeyfeaturesofthephysicalsecuritysystemfortheradio stations.However,theactualsecurityproceduresfollowedbyNISTpersonnelarep... Open at page → 113 Page 113 Chapter4-Customers Chapter4 Customers ThissectionprovidesadetailedlookatthecustomersoftheNISTtimeandfrequency broadcaststations. Itdiscussesthenumberandtypeofcustomers,thesignalcoveragearea, andhowNISTinteractswithandsup... Open at page → 114 Page 114 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB broadcasts. AccordingtoFederalCommunicationsCommission(FCC)licensingdata,there wereabout685,000licensedradioamateursintheUnitedStatesasofOctober2002(afive- yearhigh).Whi... Open at page → 115 Page 115 Chapter4-Customers 3.EstimatedNumberofCustomersfortheTelephoneTime-of-DayService Thetelephonetime-of-dayserviceprovidesanaudiosimulcastoftheWWVbroadcasttocallers whodial303-499-7111, alongdistance calloutsidethe303areaco... Open at page → 116 Page 116 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB 1.CoverageAreaforWWV PriortoWWV'smovetoColoradoin1966,apropagationstudywasconductedtopredictthe coverageareaofthesignalatboth100kWand10kWofradiatedpower[34]. Itwas deter... Open at page → 117 Page 117 Chapter4-Customers AnothervariableaffectingWWVcoverageisinterferencefromotherstations.BothWWVand WWVHusefrequenciesinternationally allocatedforstandardtimeandfrequencybroadcasts, andthesesamefrequenciesareusedbystationsi... Open at page → 118 Page 118 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Frequency=20MHz 2/25 2/26 2/26 2/26 2/27 2/27 2/27 2/28 2/28 2/28 3/10:00 16:00 0:00 8:00 16:00 0:00 8:00 16:00 0:00 8:00 16:00 Date/Time(UTC) Figure4.2.SamplegraphsofWW... Open at page → 119 Page 119 Chapter4-Customers 19300km.About22,000QSLcardshavebeensentsincethestationwentontheairinKauai in1971throughtheendof2002.AlthoughthepracticeofrequestingQSLcardshas diminishedinrecentyears,thestationstillreceivesanumberofre... Open at page → 120 Page 120 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB IN I 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 I 1 I I I 1 1 1 1 I 1 1 r . . I . . I . . I . I . . I . I I 1 I I I 1 I I 1 1 1 1 1 i 1 1 1 L 180E ISOW l^OW 90W 60W .30... Open at page → 121 Page 121 Chapter4-Customers JapanonOctober 1,2001.Atthiswriting,theJJYbroadcastshavecreatednoreported problemswiththeWWVBsignalcoverage,althoughJJYreceptionhasbeenreported in Hawaiiatboth40and60kHz,andinCaliforniaat40kHz. Figure4... Open at page → 122 Page 122 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB decoded,aquartzclockissetontime.Atypicalquartzcrystalfoundinaradiocontrolled clockcankeeptimetowithin 1sforafewdaysorlonger.Therefore,thecustomerwon't noticeanyvisibleer... Open at page → 123 Page 123 Chapter4-Customers Figure4.5.Fieldstrengthradialmapreproducedfrom1967study. b)FieldStrengthReadings(RadialMeasurements) Inthelate1960's,NBSconductedastudyalongwiththeFederalOfficeofCivilDefensethat attemptedtomeasurethef... Open at page → 124 Page 124 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Itwasdeterminedthatdatashouldbetakenalongthesameradialpathsusedduringtheoriginal study,sothatthenewdatacouldbecomparedtotheold.Althoughthedetailsoftheactual measurementt... Open at page → 125 Page 125 Chapter4-Customers discussed inthenextsection),theseradialmeasurementsseemtovahdatethecomputer- generatedestimates,andmoreradialmeasurementsareplannedforthefuture.Oneinteresting findingoftheradialmeasurementswasthedaytim... Open at page → 126 Page 126 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB a)TimeCustomers Notsurprisingly, allthreesurveysidentifiedthevoicetime-of-dayannouncements asthemost widelyusedfeatureonWWV,andthatnearlyallusersofthebroadcastsusethisfe... Open at page → 127 Page 127 Chapter4-Customers moreexpensive(boththeantennaandreceiver),andperhapslessreliablethantheirWWVB counterparts.Howeveratthiswriting,atleastthreeU.S.companies(listedalphabetically) still produceandsellWWVtimecodereceivers:C... Open at page → 128 Page 128 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB substantialnumberofpeoplestillindirectlygetthetimefromWWVwhentheycalltheirlocal phonecompany'stimenumber. Astronomers-The2001CustomerSurvey[51]containedanumberofcomments... Open at page → 129 Page 129 Chapter4 -Customers importantroleinsolvingthisproblem. Itquicklybecameareferenceforthecalibrationofboth radiotransmittersandreceivers[3]. Asoscillatortechnologyimproved,beginningwiththeappearanceofthefirstquartzoscillato... Open at page → 130 Page 130 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Radioamateursandshortwavelisteners-SinceWWVandWWVHarewidelyusedbythe amateurradiocommunity, itisprobablynosurprisethatthegeophysical alertsprovidedby NOAAarethestation's... Open at page → 131 Page 131 Chapter4 -Customers AnotherlargegroupofWWVBtimingcustomersusethesignalstosatisfytherequirementsof theOrderAuditTrailSystem(OATS)prescribedbytheNationalAssociationofSecurities Dealers(NASD)SecuritiesandExchangeCommission.... Open at page → 132 Page 132 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB frequencyusers,NISTpublishesphasemonitoringdatathatiscollectedbyaveragingthe signalsreceivedinBoulderagainsttheUTC(NIST)timescaleforoneday.Thisinformation isavailableont... Open at page → 133 Page 133 Chapter4-Customers Table4.6.WeblinkstoNISTradiostationinformation. WWVHomePage http://tfnist.gov/stations/wwv.html InformationbroadcastbyWWV http://tfnist.gov/stations/iform.html WWVtimecode http://tfnist.gov/stations/ww... Open at page → 134 Page 134 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB c)TechnicalSupport(E-mail,Phone,andPostalMail) NISTpersonnelquicklyrespondtoqueriesmadebycustomersabouttheradiostations,and offertechnicalsupportwhenevernecessary,asdesc... Open at page → 135 Page 135 Chapter5-MeasurementUncertainties Chapter5 MeasurementUncertainties Thissectiondiscussesthemeasurement uncertaintiesofthesignalstransmittedbytheNIST radiostations,andofthesignalsreceivedbycustomers. Italsodiscussesestabl... Open at page → 136 Page 136 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB a)TheMethodUsedtoControltheStationClockFrequency SincethetransmittersoperatedbyNISThavealwaysbeenlocated"off-site",farawayfromthe laboratorywherethenationalstandardsarem... Open at page → 137 Page 137 Chapter5-MeasurementUncertainties Insteadofafirewhistle,common-viewGPS comparisons(Figure5.1)employasatellite(S) andtworeceivers(AandB).Thesatellite transmitsatimesignalthatissimultaneously receivedbybothreceivers. Bothr... Open at page → 138 Page 138 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB 1,7,November:2002) DailyAveragedCommon-vrewDifference tvtJD.days M.JD52709 2003-03-112351.27 (ScheduledCVDiff.Time125000) Figure5.2.AgraphdisplayedusingtheRadioStationTi... Open at page → 139 Page 139 Chapter5 -MeasurementUncertainties -4.50 WWV/WWVBStationClock DN10_WWVB.005 80 120 160 200 240 280 320 360 Days(May2003toMay2004) Figure5.3.DailyfrequencyoffsetestimatesforWWV/WWVBstationclock. orerrorinGPStimewouldnotch... Open at page → 140 Page 140 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB FrequencyStability l^WV/WWVBstationClock AveragingTime,x.Seconds Figure5.4.EstimatedfrequencystabilityofWWV/WWVBstationclock. 2.TransmittedFrequencyUncertaintyofWWVH WWV... Open at page → 141 Page 141 Chapter5-MeasurementUncertainties fromMay10,2003toMay16,2004.Somedailyvalues(about60days)werelostsincethe GPSreceiverscanstoreonlyafewdaysofdatainmemory,anddataarelostifaphonecallis notsuccessfullycompletedwithinseverald... Open at page → 142 Page 142 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB FrequencyStability ^A/WVHstationClock AveragingTime,x.Seconds Figure5.6.EstimatedfrequencystabilityofWWVHstationclock. Toassurequalitycontrolofthebroadcasts,theWWVHstaff... Open at page → 143 Page 143 Chapter5-MeasurementUncertainties However, relatively largedelaysareintroducedbythetransmissionequipmentandthe antennas,sotheuncertaintyofthetransmittedOTMismuchlargerthantheuncertaintyofthe OTMproducedbythestationclock.... Open at page → 144 Page 144 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB ThecalibratedreceiverwasthenusedtoreceivetheWWVHsignalofftheairateachofthe fourfrequencies.Thedistancebetweenthereceivingantennaandthetransmittingantennas rangedfrom107t... Open at page → 145 Page 145 Chapter5-MeasurementUncertainties ThetransmittedtimedelayofWWVBwasestimatedbymeasuringthedelayofallcomponents betweentheTCGandtheantennaterminals,includingamicroprocessor controlledswitch,a cablethatrunsfromtheswitchtoth... Open at page → 146 Page 146 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB exponentialdecay(Figure5.10)thatonlyvaguelyresemblestheoriginalwaveform. This decaytimeisrelatedtotheperiodoftheantennabandwidth(Chapter2).Thegroupdelay conceptlosesitsm... Open at page → 147 Page 147 Chapter5-MeasurementUncertainties C.FrequencyUncertaintyofReceivedRadioSignals NISTdoesnotcertifyormaintaintolerancesonthereceivedfrequencyuncertaintyofitsradio stations.Theactualuncertaintycanvaryconsiderabledependingup... Open at page → 148 Page 148 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB knownatanygiventimewhetherthe1ppsislockedtotheincomingsignal,orcoastingusing itsinternalquartzoscillator. Therefore,someofthephasechangesinFigure5.11aredueto thesefactor... Open at page → 149 Page 149 Chapter5-MeasurementUncertainties slips.Thequalityofthereceivingantennaandreceiveralsoimpactsthereceivedfrequency uncertainty.AreceiverselectiveenoughtofilteroutinterferencefromotherLFsources,and sensitiveenoughtostayloc... Open at page → 150 Page 150 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB Figure5.13,usingthesamesetplottedinFigure5.12.Notethesharpdropinthegraphatan averagingtimeofexactly 1h.Thisillustrates thatthefrequency stabilityimproves dramatically if... Open at page → 151 Page 151 Chapter5-MeasurementUncertainties 900 WWVBReceivedPhase (comparedtoUTC(NIST) InBoulder) 150 300 450 600 April2003(1houraverages) 750 Figure5.14.WWVBreceivedcarrierphasedataforApril2003. FrequencyStability WWVBReceivedPha... Open at page → 152 Page 152 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB D.TimeUncertaintyofReceivedRadioSignals TheNISTradiostationsareusedprimarily fortime-of-day information, sincemost applicationsrequiringprecisetimesynchronizationnowrely... Open at page → 153 Page 153 Chapter5-MeasurementUncertainties 2.ReceivedTimeUncertaintyofWWVB SinceWWVBsignalsareprimarilygroundwave,thesignalpathismuchmorestablethanthe skywavepathfollowedbyWWV/WWVH signals.ThebiggestdifficultywithusingWWVB fortim... Open at page → 154 Page 154 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB telephoneservicecanexpectasignaldelayoflessthan30ms,butcallersusingcellular telephonesmayencounteradelayofmorethan100ms. TektronicsOscilloscope WWVTTDS (303)499-7111 CHI... Open at page → 155 Page 155 Chapter5 -MeasurementUncertainties Table5.3.Summaryofmeasurementuncertainties. MeasurementQuantity TypeA( 1daverage) 1ypeB WWV/WWVBtransmittedrrequency 1 1/-V-13 1x10 <1X 10"'^ WWVHtransmittedfrequency 2x10 <1X10 wwv/vvw... Open at page → 156 Page 156 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB accuracyofthebroadcastwithrespecttoUTC(NIST),andareobtainedbynonstatistical means,suchasaddingtogetherthevariouscomponentsofstationdelays.Thecombined measurementuncertai... Open at page → 157 Page 157 References References 1]W.F.SnyderandC.L.Bragaw,Acheivement inRadio:SeventyYearsofRadioScience, Technology,StandardsandMeasurement attheNationalBureauofStandards,Natl.Inst.Stand. Technol.Spec.Publ.555,October1986,863pp.... Open at page → 158 Page 158 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB [15]ChangesinWWV/WWVH StandardsBroadcasts,Nat.Bur.Stand.(U.S.)Tech.NewsBull.45,1 1- 13,January1961.(available at:http://tf.nist.gov/general/pdf/1684.pdf) [16]NBSFrequenc... Open at page → 159 Page 159 References [31]R.Brown,FortCollinsBecomingWorld'sTimeCenter,FortCollinsColoradoan,8A,November7, 1965. [32]WWVBaddsTimeCodetoBroadcast,NBSTech.NewsBull.50,15-16,January1966.(available at:http://tf.nist.gOv/generai/pdf/l 7... Open at page → 160 Page 160 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB [45]RoughestimatesobtainedfromBBCandVoiceofAmericareportsaboutshortwaveradio listenership. [46]Datacompiledfromcorrespondence withleadingmanufacturers ofradiocontrolled... Open at page → 161 Page 161 References [60]G.KamasandM.A.Lombardi,TimeandFrequencyUser'sManual,Natl.Inst.Stand.Techno!. Spec.Publ.559,September1990,164pp.(availableat:http://tf.nist.gov/generai/pdf/461.pd0 [61]M.A.Lombardi,L.M.Nelson,A.N.Novick,and... Open at page → 162 Page 162 NISTTimeandFrequencyRadioStations:WWV,WWVH,andWWVB [75]J.J.Carr,ElementsofElectronicInstrumentationandMeasurement,PrenticeHall,NewJersey,3rd ed.,(1996),pp.439-440. [76]R.Evans,ALaboratory-Grade10-MHzFrequencyStandard,QEX... Open at page → 163 Page 163 TechnicalPublications Periodical JournalofResearchoftheNationalInstituteofStandardsandTechnology—ReportsNISTresearchand development inmetrologyandrelatedfieldsofphysicalscience,engineering,appliedmathematics, statistics,... Open at page → 164 Page 164 U.S.DepartmentofCommerce NationalBureauofStandardsandTechnology 325Broadway Boulder,CO80305-3328 OfficialBusiness PenaltyforPrivateUse$300 Open at page →