All,
Thought I would jump in and tell you my tale of woe about using THHN
insulated wire.
I bought a 1000 ft roll of #12 copper from Home Depot to make some 160
meter radials. After about 2 years, the insulation had turned hard and was
cracking. When I peeled back some of the insulation from one of the wire
ends, the wire had a greenish sticky substance all over it. I asked N7IR
who is fairly knowledgable in chemistry and he said the insulation
outgasses a substance that attacks the copper. Wish I could remember
exactly what he said it was.
With that info, I immediately took down all the radials and stripped off
all the insulation. They were a real mess. The wire cleaned up nicely using
a soapy type of brillo pad and a garden hose.
Out here in AZ practically nothing lasts in the heat and ultra violet we
have. I was happy to catch the problem before it got worse. Of course, YMMV.
73 N7RT
At 10:27 PM 10/22/2007 -0700, Jim Brown wrote:
>On Mon, 22 Oct 2007 19:06:40 -0400 (EDT), n8cc@mei.net wrote:
>
>>Faced with this question several years ago, I made a 15 meter dipole
>>out of #14 solid copper 600V THHN wire. I strung it up between a
>>tree and a wooden pole, about 20 feet off the ground. I checked
>>the resonant frequency. I then lowered the antenna, stripped the
>>insulation off the wire, and repeated the exercise. The difference
>>in resonant frequency was almost exactly 3 percent. Since then,
>>I've observed that THHN wire always makes a difference of between
>>2-3 percent from formula, depending on wire size,manufacturer, and
>>whether solid or stranded.
>
>>Not the most scientific approach,
>
>I'd call that VERY scientific -- you set up a controlled experiment and
>carefully measured it! The only way to improve your science would be to
>measure a lot of antennas and a lot of wire types and wire sizes. But
>what you've done was right on, and quite helpful! Thanks.
>
>73,
>
>Jim K9YC
>
>
>
>_______________________________________________
>Topband mailing list
>Topband@contesting.com
>http://lists.contesting.com/mailman/listinfo/topband
>
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|