Sharp SD-AT1000W Spécifications télécharger pdf (Page 47)

Maxiva UAX

October 17, 2013

2‐5

888‐2693‐004 WARNING:Disconnectprimarypower priortoservicing.

2.7.1 OverviewofRFGroundingPractices

TheimportanceofagoodRFgroundingsystemandlightningprotectioncannotbeoveremphasizedforreasonsof

personnelsafety,protectionoftheequipment,andequipmentperformance.Thefollowingisabriefoverview.

Ligh

tningandtransientenergyviathepowerlineortowerconnectionscanimposeseriousthreatstopersonnel

safety,aswellasdamagetheequipment.Forthesereasons,a goodprotectivegroundingsystemtodivertthese

formsofenergytoearthgroundisimperative.Theenergyin alightningstrikehasave

ryfastrisetimeandcanhave

frequencycomponentsuptothemegahertzrange.Forthisreason,itisalwayspreferredtousestraight,directruns

oflarge,flatconductorssoastominimizeinductanceandallowthefreepassageoftransientenergytoearth.Note

thatthesmallcross‐sec

tionandnon‐directpathtogroundofthegreen/yellowwireoftheACsafetygroundmakeit

anunsuitablemeansforsafelydivertingthetransientenergypresentduringalightningstrike.

Ag

oodgroundingsystemshouldincludesubstantialgroundingatthetowerbaseusingcoppergroundrodsand/ora

buriedcoppergroundscreen,withcopperstrapusedtoconnectthetowerbasetoearthground.Coaxialcable

shield(s)shouldbeelectricallyconnectedtoandexitthetowerasneartothebottomaspr

acticaltominimizethe

lightningvoltagepotentialcarriedbythecablebacktothetransmitterbuilding.

Ideally,acomm

ongroundingplate(bulkheadpanel)withalowimpedanceconnectiontobuildingearthground

shouldbetheentrypointforallsignallines,includingACmains.Itshouldserveasa single‐pointgroundforall

coaxialandmainssurgeprotectiondevices.Widecopperstrapsshouldbeusedforma

kingtheconnectionfromthe

commongroundingplatetoearthground.

Agoodgr

oundsystemshouldincludeperimetergroundingofthetransmitterbuildingusingcoppergroundrodsand

copperstrap.Thereshouldalsobeacopperstraprunningfromtowergroundtothe buildingperimeterground.

Goodgr

oundingandshieldingwillhelpkeepstrayRFcurrenttoaminimum.Thisisespeciallytrueinthepresenceof

stronginterferencefromlocalmediumorlongwavestations.RFinterferenceusuallyshowsupasintermittent

problemswithdigital/controlcircuits,spuriousradiatedemissions,oraudio/videonoiseonanalogsignals.

2.8 CoolingSystemRequirements

UAXtransmittersuseforcedaircoolingprovidedbyinternalblowerstoremovetheheatgeneratedbytheRF

amplificationprocess.Toavoidoperationalproblemsduetoexcessivetemperature,thebloweropeningsmustnot

beblocked.Thetransmitteroutlinedrawingprovidesanindicationoftherelativelocationofthetransmitter

blowersandth

enecessaryclearancestorespect.

Airisin

putthroughthetransmitterfrontwithhotairexhaustattherearofthePABandLPUchassis.Whenfactory

rackintegrationhasbeenprovided,theUAXrackallowstheexhaustairtoexitthroughaventatthetopoftherack.

Thisventhasprovisionsforconnectiontoanex

ternalductedairexhaustsystem,ifdesired.Anoptionalductedair

inputoptionprovidesanairplenumatthefrontoftheracktopermittoporbottom,airinput.

Inge

neral,transmittercoolingsystemsfallintotwocategories:

Anop

ensystem,inwhichtheheatedtransmitterexhaustpassesthroughadedicatedducttotheoutsideofthe

transmitterbuilding.Thetransmittermayreceivefreshoutsideairdirectlythroughaseparateductormayreceive

ambientairfromthetransmitterhall,withthetransmitterhallbeingsuppliedmake‐upairfr

omoutsideviaafiltered

inletvent.Withanopensystem,itisimperativetocorrectlybalan cetheinputandoutput airflowvolumes,paying

particularattentiontothepressuredropsinexternalductsandprovidingexternalblowersasnecessarytoensure

correctairflow.

Acl

osedsystem,inwhichthetransmitterexhaustsandinputsairdirectlytoandfromthetransmitterroom.The

transmitterroomisclosedtooutsideairandmakesuseofairconditioningunitstoremovetheresultingheat

buildup.Thistypeofsystemisrecommendedingeographicareaswithespeciallysalty,sulfuric,orot

herwise

pollutedair.Withaclosedsystem,itisimperativetocorrectlybalancetheheatload.Thatis,tosizeandpositionthe

airconditioningunitsproperlytohandletheheatgeneratedbythetransmitter,ancillaryequipment,building

lighting,and evensolarradiationenteringthroughwindows.

Figuresfo

rboththetransmitterheatloadandairflowvolumeareprovidedindrawing843‐5602‐148Outline

Drawing,UAXTransmitters.Consultaprofessionalheatingandventilationexpertforhelpindesigningthebuilding

coolingsystem.

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