This link shows the base of a typical AM broadcast tower, with two hard steel balls used as lightning protection. At kilowatt power levels its not unusual to use a credit card to set the gap.
http://www.thebdr.net/articles/steel/twrs/LimitingStatic.pdf 73 Frank W3LPL ---- Original message ---- >Date: Fri, 27 Jul 2012 16:29:15 -0400 >From: "Tom W8JI" <[email protected]> >Subject: Re: Topband: Spark gaps >To: "Mike Waters" <[email protected]>, "topband" <[email protected]> > >> Man, I don't know, Dave. How long have they been selling those carbon >> balls >> for that purpose? > >I've never seen a carbon ball in a lightning gap application. I'd have to >see a few after being in action a long time before trusting them. > >Broadcast stations use hard metallic balls, as do electrical substations and >other applications where the peak voltage is near gap voltage. Polished >round gaps have more consistent breakdown. > >If there is a great deal of headroom between operating and breakover >threshold, a pointed gap works OK. > >_______________________________________________ >UR RST IS ... ... ..9 QSB QSB - hw? BK _______________________________________________ UR RST IS ... ... ..9 QSB QSB - hw? BK
