Specifications

Appendix-d Lightning Protection Recommendation
November 11, 2013
d‐6
Copyright©2013,HarrisBroadcast
WARNING:Disconnectprimarypowerpriortoservicing. 888‐2628‐300
Figure d-7 Basic Elements of a Properly Designed Antenna System
d.4 AC Service Protection
Allincomingaclinesshouldhaveachokeconnectedinseriestolimitthehighfrequencysurgesonthelinesfollowed
byasurgeprotector.Thesurgeprotectormustbeconnectedtothebuildinggroundsystembyshortdirect
connections,see
Figured‐6.
Asurgeprotectorisasolidstatedevicethathasahighimpedanceuntilthevoltageacrossitreachesitsrated
clampingvoltage,atwhichtimeitsim pedancesuddenlydecreases.Theprotectorwillthenconducthundredsto
thousandsofamperestoground.Allprotectorsareratedformaximumvoltageandmaximum
surgeenergy.Ifthe
surgeenergyexceedsratingofthedeviceitwillnormallyshortandforthisreasonmustbefusedsoitwill
disconnectitselffromthelinebeingprotected.Whenthishappensallprotectionislostsosomewarningsystem
mustbeusedtotelltheoperators
thatanewprotectorshouldbeinstalled.
Speedisessentialtoprotectequipmentfromcurrentsurgeswithratesofriseexceeding10,000ampsper
microsecondandpulsesthatlastnolongerthan100microseconds.Veryshort,lowinductancegroundstrapsare
requiredtopasssurgesofthistype.
Thesurgeprotectorsmustbeselectedforthelinetogroundvoltageandthemaximumenergytobediverted.Bigger
isalwaysbetterinthiscase.Thereareseveralmanufacturersofsurgeprotectors:
• LightningEliminationAssociates.,Inc.
• CurrentTechnolo gy
• ControlConcept
• MCGElectronics,Inc.
• EFICorp.
• GeneralElectric
Allofthesevendorsprovidepartsandsystemstoprotectbroadcasttransmitters.
Allaudioandcontrollinesshouldbeprotectedthesameasdescribedforaclineswithcomponentssized
accordingly.
Allcoaxiallinesshouldhavetheshieldconnectedtothesystemgroundatthepointofentranceandinadditionhave
aferritechokearounditlocatedbetweentheentrancepointandtheequipmentrack.Thiswillprovideahigh
impedanceforcurrentflowingintheshieldbutdoesnotaffect
thesignalcurrents.
d.5 Conclusion
The1%chanceofamajorlightningstrikeprobablycannotbeprotectedagainstbuttheother99%canbecontrolled
anddamageprevented.Installsurgeprotectiononallincomingandoutgoinglinesatthewallofthebuilding
connectedtoawelldesignedgroundsystem.Properlyinstalltheantennaground
systemwithsparkgapadjusted
correctlyandmaintained.Withthisdoneyoucansleeppeacefullyatnightifyourbedisn’tunderthefeedline.