Specifications

Maxiva UAX
October 17, 2013
2‐5
888‐2693‐004 WARNING:Disconnectprimarypower priortoservicing.
Copyright©2013,HarrisBroadcast
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.