Jeff and Jim,
I do understand that the ends of the antenna and radials are high voltage
points, and as such the potential exists for arcing and fire, but I have not
had that experience in 23 years at my qth running high power with more than a
dozen different wire antennas of all types. This includes the tops of Inv L’s,
element ends of dipoles and wire beams, phased vertical arrays, 4-squares, ends
of radials, etc. But after your posts I realized two things:
1) Differences in climate matter. It is definitely wetter and more humid in CT
than in other locations in the US where the air has much less humidity and the
temperatures are hotter and there is far less rainfall. That can make a big
difference!
2) The ends of my antennas are usually are terminated in porcelain insulators
not touching trees or branches although the elements certainly go through the
trees and branches and in some cases actually rest on them. I do use only pvc
coated wire so there is generally little or no direct contact between the wire
and the tree/branch, except at the very tip of the antenna at the insulator.
In the case of my radials, only the tip of the radial has no insulation and it
generally terminates in a soldered loop with a piece of #32 poly twine attached
to the loop. The rest of the pvc coated radial may go through trees or rest on
branches but there is no direct wire contact per se unless the pvc coating has
been rubbed off but this has never happened The twine loops have never burned
or charred.
So if you are concerned about fire hazards, then I would suggest that you buy
and use pvc coated wire as I do. Although I never bought it for potential
protection against fire, it seems as though it would be a good precaution at
your qth. It also is quieter than bare wire – which is noticeable during rain
and snow events – even more so with hail or sleet. At desert qth’s, I would
imagine that it would also be quieter than bare wire when sand particles are
blowing through the air.
At the bottom of the last sunspot cycle – which happened to coincide with the
end of the stock market crash, the price of copper fell dramatically and I was
able to make a deal with the local Lowe’s to buy 12 500’ spools of their #14
THHN at the incredible price of ~$0.03/ft (I had to special order it and wait a
few weeks and then had some issues with them and getting it – but it was worth
the headaches!.) This solved my wire problem for a lot less than Home Depot
which was not able to sell their THHN rolls for more than a year @ $0.12/ft.
(And then they complained that they couldn’t sell them but refused to lower the
price!) Lowe’s will occasionally make deals if you talk with the store manager
– Home Depot could care less.
73
Bob KQ2M
From: Tom WA9WSJ via TowerTalk
Sent: Monday, September 04, 2017 12:48 PM
To: Jeff Draughn ; TowerTalk@contesting.com
Subject: Re: [TowerTalk] Fire hazard with inverted L ??
Hello Jeff,
Permit me to pass along my experience. Not to be opposite to others
knowledgeable information but to only add information in which to make a well
informed decision.
I was tuning up a hamstick, (yes I realize not the same as your antenna but
you'll get the idea), on my camper with only about 50 watts and the swr was
real good when all of a sudden the bridge needle jumped erratically high. Then
it settled good again, then it randomly jumped again. It did this a few times
and then I just happened to look up at the antenna and seen that it was
intermittently touching a branch with the end of the whip. As it made contact,
it arced and visually smoked the branch. Obviously when this happened, the
bridge reading jumped, thus showing a high swr. I moved the camper and all
tuned correctly. Apparently the wind was moving the offending branch into the
antenna, which wasn't close when I started my testing.
The point of this is that the end of the antenna is the high voltage point, as
described by many online articles. As one approaches the end, the voltage
increase and current decreases.
I was curious about this when you mentioned your antenna type and found this
article: Ham Radio Site - { 80m Inv.-L on 12m Pole }
Might be worth check out.
73 GL,
Tom
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Ham Radio Site - { 80m Inv.-L on 12m Pole }
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From: Jeff Draughn <n0ost99@gmail.com>
To: TowerTalk@contesting.com
Sent: Monday, September 4, 2017 9:38 AM
Subject: [TowerTalk] Fire hazard with inverted L ??
I am considering putting up an inverted L for 80 or 160 possibly both .
My concern is the antenna will invariably touch some limbs or limbs will
touch the antenna with the wind and rain storms, ice etc. how much of a
fire hazard is there with this at the 1500 watt power level?
Also have the same concern at the feed point any information or experience
with this would be appreciated.
73, Jeff
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