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Sparks

-March 11, 2013

An antenna for the 40-meter ham radio band is a pretty large thing. A half-wave dipole antenna is around 66 feet long from end to end. Mine was center fed with RG-11/U coaxial cable terminated with a PL-259 type of UHF connector at the transmitter end of the coaxial cable feed line.

One day, I had disconnected that cable from my transmitter for some reason or other and just left the open PL-259 sitting there. Thunderstorms started rolling through.

Suddenly I noticed a sound. It was "snap..........snap...........snap........................snap....snap.." and so on at a varying rate. I couldn't imagine what it was until I saw the open PL-259. There were quite energetic sparks jumping across the gap between the connector's center pin and its outer shell. It wasn't even raining at that moment, but there was enough charge buildup via that dipole antenna for electrostatic discharge (ESD) activity to be going on and to make me very nervous.

 

 

 

 

I just left the cable totally alone and let it spark to its heart's content until the thunderstorms had gone.

Lessons learned:

ESD events don't require direct hits from lightning

Never design anything that's going to be connected to an antenna without providing an intentional discharge path as protection from electrostatic charge build-ups. 

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