View Full Version : It's Only (was) an Antenna!

08-11-2019, 11:35 AM
I couldn't decide which thread to post this in - I'm calling it "Good News" only because it obviously could have been a lot worse.

My through-the-glass 2 meter antenna on the RV, mounted on the driver side window, never was a great antenna anyway. But it looks like it served well as a lightning arrestor. The RV is parked in a storage area here in central FL, surrounded by metal buildings. A neighboring truck cab has a big CB antenna waving far above the height of what was my 2M antenna and didn't draw a spark.

I'm hoping the scorched area on the new RV paint job will rub out. Nothing inside the RV was torched - even the old Radio Shack 2 meter rig still is receiving - haven't put it on a dummy load yet to see if it transmits.

Pictures of before and after...

08-11-2019, 02:31 PM
I conjecture that the whip was missing a little round ball on the end, or the ball was too tiny, or scratched. The photo seems to confirm this. Charge density on a metal surface will be much greater if the surface is highly curved, like a sharp point at the end of a whip, or a gouged place on the ball. A corona discharge on the sharp end is very common (because the charge density is so high), and it has two major effects:

(1) It serves to dissipate the charge into the air, ionizing the air. This is very useful on, say, "lightning rods" because the rod, connected to a good ground and surrounded by conductive, ionized air, provides an easy, nominally safe path for the lightning to reach ground. Usually it also reduces the voltage gradient in the surrounding volume so that lightning won't strike there anyhow (which is how lightning rods are supposed to work); and

(2) If the rod isn't grounded at the bottom, it still ionizes the surrounding air, providing a nice path for the lightning, which hits and vaporizes the rod and (usually) whatever it's connected to. You perhaps got lucky.

The ball also makes it less likely that you'll lose an eye by stabbing it with the end of the whip when working around it. Being stabbed in the eye can ruin your whole afternoon.

I'll bet that nearby CB antenna has a half-inch (or bigger) ball.

And here I once thought that little ball was mere decoration.

08-12-2019, 11:17 AM
Hi Carl,

Wow, so you're guessing I may have "invited" this lightening bolt? HI

The "before" picture shows the antenna had a ball at the end. Whether too small or whatever; I didn't design or build it.

It was a thru-the-glass antenna, so yep, no ground.


Tired Old Man

08-12-2019, 12:14 PM
Well, lightning is kind of cussed anyway -- there's really no sure way to control it. Best anyone can do is try to improve the odds.