[TowerTalk] Fire hazard with inverted L ??

[Bob Shohet, KQ2M]

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 at 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
  
|  
|   
|   
|   |    |

   |

  |
|  
|   |  
Ham Radio Site - { 80m Inv.-L on 12m Pole }
Neue Seite  |   |

  |

  |

 


      From: Jeff Draughn <n0ost99 at gmail.com>
To: TowerTalk at 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