[time-nuts] Improving performance of a GPS antenna...?

[Bill Hawkins]

My first job was in a blasting cap plant in 1960. Raw materials and
finished product were kept in earthen bunkers separated by a distance
that would prevent an explosion in one from propagating (the distances
were found by experience).

Tall, grounded masts were spaced among the bunkers to prevent strikes
by lightning. There is a 45 degree cone of protection from the top of
the mast to the ground. This is based on British Navy experience with
sail masts of warships between 1793 and 1847. There were 220 strikes
reported in that time. 2/3 of them struck the top masts. Only 1 in 50
struck the hull below the masts. See the report at
http://www.lightningsafety.com/nlsi_lhm/conventionalLPT.pdf
and search the PDF for "cone of protection"

Then again, this outfit says the cone is a myth
http://www.lightningsafety.com/index.html

All I know is that we never lost a bunker in the 5 years I was there.
We did have thunderstorms near Kingston, NY, 90 miles above NYC. The
safety department tested the mast grounds with an instrument like a
megger that used two probes driven in the ground (IIRC) to measure
less than a tenth of an ohm resistance to ground.

Looking back on it, I don't think anything would survive a direct hit
on the mast. It was more a matter of the mast misdirecting the leader
of the strike to look elsewhere for ground. Or, given the small numbers,
maybe it was probability that saved us, like snapping your fingers to
keep the tigers away in North America.

Lightning arrestors for lead-ins are still a very good investment.

Bill Hawkins

PS- The worst explosion I remember there was the day a new technician
took a few pounds of scrap powder to the burning grounds. It was
supposed to be mixed with ten times as much sawdust to make it burn
instead of detonate. He got the proportions backwards. The explosion
got the attention of everybody in the plant.



-----Original Message-----
From: Chris Albertson
Sent: Wednesday, April 04, 2012 12:53 PM

People will argue that if you ground the pole it then will become a
"lightning magnet"   That thinking is 180 degrees backward.  A pole
becomes a lightning magnet if it is allowed to charge above ground
potential.  So for most of us who don't live in Florida a #10 wire
clamped to the mast and run off to a ground rod is good enough.