Jesse,
A radio engineer in Atlanta years ago told me a neat trick he said allows
confirming a strike, and estimating the current it produced. It involves
rexcording an audio tone on a piece of magnetic tape several feet long, sealing
it in a weatherproof, non-conductive tube, and positioning it perpendicular to
a tower leg.
If lightning strikes, the magnetic flux produced around the conductor will vary
proportionate to the current, and playing back the tape will reveal an erased
portion which can be measured for its physical length.
I have no idea how well that would actually work, or how to calculate the
current based on how many inches of tape are erased. These days the only
magnetic tape machines left in common use are old cassette decks, but it might
be worth a piece of PVC pipe and some glue to try it.
If you just want to know if it's hit, set up a vertical conductor some distance
from the tower, but well within its "cone of protection," connected through a
fuse to an independent ground. If the tower gets smacked, you can bet some
serious current will be induced in a 10-foot vertical wire.
Years ago, an engineer for WBEN radio in Buffalo told me that on summer days
when thunderstorms would hit the Toronto area across Lake Erie to the north, a
hit on a radio tower up there would produce a spark across the ball gaps on the
towers in Buffalo. That's 90 miles!
73,
Paul, AE4KR
----- Original Message -----
From: Jesse Lloyd
To: Repeater-Builder@yahoogroups.com
Sent: Monday, April 26, 2010 11:32 PM
Subject: [Repeater-Builder] Direct Strike Lightning Detector
Hey All,
I am trying to think of a way to detect if a tower at one of our sites
gets a direct hit. I was thinking of paralleling a ground strap with
a 10mA amp glass fuse. Maybe make the two connections to the ground
stap 2 ft apart and use a fuse holder for fuse testing and
replacement. I suspect the fuse would blow if any significant current
went down the ground strap (or would the whole thing melt? I suppose
either way I'd know!). Ideas?
I live in an area that doesn't see a lot of lightning, I'm curious if
the tower gets hit.
Jesse
