I used gray PVC for the insulator on my 160m vertical and it works fine. I
see no reason not to use the material that you have. You don't mention what
power level you intend to transmit with, but perhaps if you were QRO+ and
the material was conductive, it would melt, but I wouldn't worry about this.
Another easy way to load your antenna is to attach a wire to the top and tie
the other end on the ground someplace. I do this at P40A with good
results.
John KK9A
To: towertalk@contesting.com
Subject: [TowerTalk] Grey PVC Loading Coil
From: "Dan Zimmerman N3OX"
Date: Mon, 4 Dec 2006 11:42:18 -0500
List-post: <mailto:towertalk@contesting.com>
In the spirit of "some antenna is better than no antenna at all," I'm
going to add a base loading coil to for 160m to my 40 foot vertical
(http://www.n3ox.net/projects/lowbandvert).
I know it's a substantial compromise over other forms of loading, but
I'm willing to accept the efficiency penalty for convenience in this
particular case. What I want to know about is whether or not grey PVC
electrical conduit is suitable for coil forms at 1.8MHz. I searched
the archives and found a discussion on PVC formers for HF and that
they're not unacceptable unless you're running many close-spaced
turns, but I wonder if people have tried grey vs. white and what
they've found. I know the microwave trick is routinely used but I
don't think absorption at 2.4GHz says much about the MF properties of
the material.
I've got access to some 5" conduit and a lathe; a few minutes and I
can have a beautiful coil form like the 80m one on the page above, but
I wonder if the grey PVC is lossier than the white stuff?
There are plenty of other approaches, but if grey PVC is decent at
1.8MHz, I'm just going to cut a nice groove in it and go. It's going
to be something like 20-30 turns of #10 wire and having a grooved form
makes for a quick and solid coil.
73,
Dan
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