Newspapercartoonfromtheearly60s

NVISforEmergencyNVISforEmergencyCommunicationsCommunications

RossMazzolaMonroeCounty(NY)ARES

RossMazzolaMonroeCounty(NY)ARES

WhyNVIS?

DamagetoInfrastructureDamagetoInfrastructure

Inoperative Towers &Inoperative Towers &InoperativeTowers&RepeaterSites

InoperativeTowers&RepeaterSites

LossofBackupPowerLossofBackupPower

DifficultTerrainDifficultTerrain

ValleysValleysCanyonsMountainsForestsForestsJungles

WhatisNVIS?

LowAngleofRadiation

DXDX

Note:Antennaishigh abovetheground

NVISDefinitionNote:AttenuationonNVISpathislessthanDXpathbecausetheRFtakestheshortestpossibletripthroughtheionosphere'shighlyb bi D labsorbingDlayer

NearVerticalIncidentSkywave ("NVIS")isamodeofradiopropagationusingFLayeratmosphericrefractionaround65 to90 (nearvertical)

HighAngleofRadiation65 Degrees

NVIS

Note:Antennaislow totheground

300400mileCoverageisTypical

Note:Signalsabove10megahertz(approx.)cannotbereflectedbythef2layer They pass right through intolayer.Theypassrightthroughintospace.

NVISCoverstheSkipZone

200MILES

NVISCoverageinNYS

HistoryofNVIS PioneeredbytheGermansinWWII Known as "rail" or "cage" antenna Knownas"rail"or"cage"antenna WidelyusedbytheUSforcesinVietnam Stillinuseforcommunicationsinroughmountainousterrain

NVISisaSystem LicensetooperateonHF

LowBandFrequencies,typically40mand80m E i t Equipment

HFRadio(100Wissufficient) Tuner(onlyifnecessary)

EmergencyPower Battery GeneratorGenerator Charging

Frequency C t F i U d CorrectFrequenciesareUsed FrequencyCoordinationPlan

Antenna DirectRFupwards(cloudwarmers)

What FrequenciesWhatFrequenciesShould I Use?ShouldIUse?

CriticalFrequency ThehighestfrequencywhichtheionospherewillreflectverticallyiscalledfoF2 I d f NVIS i l t b t d t th th InorderforNVISsignalstobereturnedtotheearthssurface,itsfrequencymustbelessthanthecriticalfrequencyoftheFlayer Duringdaylight,thecriticalfrequencyisapprox5to10MHz. AfterSunset,thecriticalfrequencydropsthroughoutthe night reaching a low of 2 to 5 MHz just before dawnthenightreachingalowof2to5MHzjustbeforedawn

10 MHz

CriticalFrequency

NightDay

ThesefoF2measurementsfromvarioussitesareusedtocreateamapoffoF2.ThemapsbelowcanbeusedasaguidetoNVISionospheric frequencysupport.

Night(9pmlocal)

Day(12noonlocal)

FrequencySelection GeneralopinionisthatNVIStechniqueworksfromroughly2to10MHz Ti f d ti f t ti it t f t Timeofday,timeofyear,sunspotactivity,typeofantennaused,atmosphericnoise,andatmosphericabsorptionaffectthefrequencyselection

Highsunspotactivity 60,40,30mbestdaytimebands; 80 m nightbands;80mnight Lowsunspotactivity 80,60,40bestdaytimebands;80or160mnight

FrequencySelection TheCriticalFrequencyisthekeytosuccessfulNVISworking AgoodworkingfrequencyforNVISwilloftenbebetween10 15% b l i 85% f th F F2 C iti l F10 15%below,i.e.85%oftheFoF2CriticalFrequency

foF2 CriticalClosest

Amateur Band10% below

foF2 Critical Frequency

15% below foF2 Critical Frequency

foF2 Critical Frequency (Mhz) from USA Map

Amateur Band Working NVIS

frequency (Mhz)

0.9 0.9 11.7 1.8 2 1.8 - 2.02.6 2.7 33 4 3 6 4 3 8 3 93.4 3.6 4 3.8 - 3.94.3 4.5 5 4.05.1 5.4 66.0 6.3 76.0 6.3 76.8 7.2 8 7.1 - 7.3

FrequencyPlanning Netmustbepreparedtochangefrequencyasconditionschangechange Proceduresforfrequencyhoppingshouldbeagreedonbeforehand M k h d d i ht ti ti t ll Makesureyouhavedayand nighttimeoptionstoallowroundtheclockoperation ConsiderbandCongestion

Nets,local,regional,national PeriodicallyAdjustforsunspots,solarcycle,etc... Consider using Region 2 IARU Emergency Center ofConsiderusingRegion2IARU EmergencyCenter ofActivityfrequencies(3985kHzand7290kHz)

NVISPlanExampleCourtesy of Marc Tarplee N4UFP

WinterPlan,SSBNets

Local Time of Net Operating Frequency (15)

CourtesyofMarcTarplee,N4UFP

LocalTimeofNet OperatingFrequency(1 5)

0001 0800 Primary:3.996MHz Alternate:1.976MHz0801 1600 Primary:7.285MHz Alternate:5.40350MHz1601 2000 Primary:5.40350MHz Alternate:3.996MHz2001 2400 Primary: 3 996 MHz Alternate: 1 976 MHz2001 2400 Primary:3.996MHz Alternate:1.976MHz

SummerPlan,SSBNets

Local Time of Net Operating Frequency (15)LocalTimeofNet OperatingFrequency( )

0001 0800 Primary:3.996MHz Alternate:1.976MHz0801 1600 Primary:5.40350MHz Alternate:3.996MHz1601 2400 Primary:3.996MHz Alternate:1.976MHz

Notes:(1)IfprimaryfrequencycannotsupportNVIS,thenetwillmovetothealternatefrequencyforthetimeperiodinwhichthenetisoperating.IfthealternatefrequencycannotsupportNVIS,thenetwillmovetothealternatefrequencyofthenextlatertimeperiod,ifitis lowerthanthecurrentalternatefrequency.Ifthealternatefrequencyofthelatertimeperiodisnotlower,usethealternatefrequencyfromtheadjacentearliertimeperiod,ifitislower.Ifaloweralternatefrequencycannotbefound,thenetmustbemovedtoVHF.(2)Bandchangeswilloccuratquarterhourintervals.(3)Alloperatingfrequencies,otherthanthoseinthe60mband,mayvaryby+/ 10KHztoavoidinterference.(4)Outputpoweron60mmustbelimitedto50WPEP.(5)OnlyUSBisallowedon60m

What AntennaWhatAntennaShould I Use?ShouldIUse?

Antennas KeyelementforNVISistheAntenna.Needstoradiateatveryhightakeoffangles Field Expedient FieldExpedient

Lightweight Easy/QuicktoErect Easytotransportwhendisassembled

Multiband avg.NVISfreq.3.5Mhz (80m)and7.3Mhz (40m)g q ( ) ( )

DirectionofRFisprimarilyupwards(nearvertical) Easytobuild InexpensiveInexpensive NVISANTENNASAREACOMPROMISE!!!!!!

AreYouNVISNow?

Horizontalantennasmountedlessthanwavelengthabovegroundhavemaximumradiationathighangles!

HeightAboveGround

Singlemostcontroversialsubject! HeightAboveGroundg

Belowwaverecommended Somehavefound10 15heightfunctionsverywell

h ffi i i b f SometestsshowNVISefficiencyisbestattento15footheightfor40mto75mfrequencyrange

Loweringtheantennatonear1/20th wavelengthlowersg gthebackgroundnoiselevel

1/4Wavelength

Gain

Ashorizontaldipolemovesclosertotheearth,thegainbeginstodecreasebecausethegroundislossy

1/4 Wavelength1/8 Wavelength 1/4Wavelength1/8Wavelength

NVISAntennasThatWork LoopAntenna

TwoWavelengthLoop Veryeffective,butnotpracticalg p FullWavelengthLoop

HalfwavelengthHorizontalDipolei l LowDipole

FanDipole Inverted VInvertedV RandomWire DualHamstickshortdipole

HorizontalDipole

Note:Heightshouldbe

LowDipole Twosupports Low=1to6 Somedesignsuse

reflectorwires

LowDipoleNote:Theshapeoftheelevationpatterndoesntchangemuchasthefrequencyisvariedovera5to1range.Thegainincreasesathigherfrequenciesg g g qbecausetheantennaisfartherfromtheground,intermsofwavelength,andthereislessgroundloss.

ElevationRadiationpatternofan80mNVISdipole12.5ftaboveground

FanDipole

InvertedV

MaypoleStyle Singlesupport DualBand Easytoerect AS2259/GR

W7ARCLongWire

Note:HaveagoodcounterpoisetoavoidRFburnsfromyourequipment

ShortDipole(Mobilewhips)

CourtesyofWA5ZNU

OtherProvenNVISAntennas

ShirleyDipole PattersonLoop AnyhorizontallypolarizedantennawillhaveanNVIS

componentinitsradiationwhenplacedbelowwavelengthaboveground

AntennaTips Horizontalantennasseemtoworkbest Itsalwaysbettertohavethebase/nety /controlstationantennahigherabovegroundbutthatmeansthesupportsystemismorepp ycomplicated Ideally,youwantNVISantennastobey ytalkingtootherNVISantennas Lotsofhomebrewdesignsareavailableongtheinternet,tryone!

S f t Fi tSafetyFirst

Safety Alwayswatchforoverheadpowerlinesandotherelectricalhazardswhenerectingantennamastsandwires BeawareofRFradiationhazardsinthe nearfield when using low dipolesthenearfieldwhenusinglowdipoles.Keepallpeopleasafedistanceaway.For100watts,keeppeopleatleast10'away Markyourantennaandguywireswithbrightlycolored ribbonstog ypreventpeoplewalkingintothemorbetteryet,establishasafetyperimeter

SSummary

NVISHints&Tips Loweringtheantennadropsthenoiselevelandchanges

thefirstbouncedistance Lowisconvenient,butitsalsolowinefficiency.Andthere

isasafetyconcern Optimum dipole height is between 0 1 and 0 25Optimumdipoleheightisbetween0.1and0.25

wavelength14'to34'at7.15MHz26'to65'at3.75MHz

Bestsignalwillbefromstationsinthe175300milerangeusing NVIS antennasusingNVISantennas

Bepreparedwithsomesortof"PlanB"involvingcommunicatingthroughalternatechannels,orfollowingsomeprearrangedschemefortryingallavailablefrequencychoicesinascheduledpatternofsomesort

NVISHints&Tips(continued) Transmitsystemperformanceisadirectfunctionof

antennasystemefficiency Usetraplessandresistorlessantennas StriveforalowVSWRonthetransmissionline Avoid antenna coupling units (ACU at the antenna feed Avoidantennacouplingunits(ACU attheantennafeed

point)andtuningunits(ATU insidetheradio)ifpossible A30fthighdipoleis+10dBinperformancecomparedto

f h h d la10fthighdipole Thetransmittingstationmustprovidesufficientsignalto

overcomethenoiseatthereceivingstationsg

Linkswww.qsl.net/wb5ude/nvis/

www.athensarc.org/nvis.htm

th /f 2418 htwww.athensarc.org/fm2418m.htm

www.w0ipl.com/ECom/NVIS/nvis.htm

www co missoula mt us/acs/ACS/NVISpage1 htmwww.co.missoula.mt.us/acs/ACS/NVISpage1.htm

www.co.missoula.mt.us/acs/ACS/N6VNG%20AS2259.htmhttp://groups.yahoo.com/group/nvis/http://www.co.missoula.mt.us/acs/documents/TM%20NVIS%20antenna.pdfwww.arrl.org/qst/2005/12/Straw.pdfwww.arrl.org/qst/2005/12/Straw.pdfwww.tacticallink.com/field_deployed_nvis.htmwww.sedata.net/nvis.htmlwww cebik com/wire/cb htmlwww.cebik.com/wire/cb.html

Credits WhatsthedealaboutNVIS?ByDeanStraw,N6BV,QST Dec2005 NVISOperationsbyEdFarmer,AA6ZM,QST,Jan1995 TheNVIS ALowAntennaforRegionalCommunicationsbyAlbert

Pion,KK7XO,QST,Jun2002 NVISPropagationandAntennas:SomeBackgroundBasicsbyL.B.

C bik W4RNLCebik,W4RNL UnderstandingNVISAntennas&PropagationbyHaroldMelton,

KV5R,2002,2006US A fi ld l "FM 24 18" ( di M) b D Fi dl USArmyfieldmanual"FM2418"(appendixM)byDaveFiedler

Antenna PerformanceforNearVerticalIncidenceSkywaveCommunicationsbyDaveFiedlerNVIS A t F d t l b Ed d F NVISAntennaFundamentalsbyEdwardFarmer

NearVerticalIncidenceSkyWave(NVIS)PropagationbyMarcTarplee,N4UFPN V ti l I id Sk (NVIS) A t b P t L b t NearVerticalIncidenceSkywave (NVIS)AntennabyPatLambert,W0IPL

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