Topband: Spark gaps

[donovanf at starpower.net]

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" <w8ji at w8ji.com>  
>Subject: Re: Topband: Spark gaps  
>To: "Mike Waters" <mikewate at gmail.com>, "topband" <topband at contesting.com>
>
>> 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