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Topband: relay-switched inverted L for 40/80/160

Subject: Topband: relay-switched inverted L for 40/80/160
From: Jim Meehan <>
Date: Mon, 28 Sep 2009 12:22:53 -0700
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I've mulling over a tree-supported wire inverted L for 40/80/160 meters.
The vertical section would be supported by a high branch on a ~55' Monterey
pine not too far from my house, and the horizontal section from there to
another tree.  Lots of radials of various lengths should be no problem.

Originally I had thought to use traps to achieve multi-band operation, but
then I started wondering about using relays to simply switch out the various
segments.  If I used two-conductor speaker wire or something similar as the
radiator, I think the same wire could also carry DC to operate the relays.
I'd use SPDT normally-closed relays.  For operation on 160, no DC is applied
-- both relays are closed, and the entire length of the inverted L is
active.  For operation on 80, +12V is applied, opening the "far" relay,
cutting off both conductors of the 160 segment.  For operation on 40, -12V
is a applied, opening the "near" relay.  This would be for 100 watts only,
so I don't think I'd need anything too exotic for components.

My hope is that it would have wider bandwidth than traps would allow, and be
easier to construct and tune.

Am I missing anything obvious?  I did a little Googling and didn't find any
designs like this.

Also wondering about the bandwidth/hassle/cost tradeoff of using copper pipe
or aluminum tubing for the vertical section.  In this case, I'd run a wire
up the center of the pipe to use as the 2nd conductor for the relay
switching.  I would put the pipe next to the tree, supporting it with some
kind of standoffs attached to the trunk of the Monterey pine.  Can I get the
pipe far enough from the tree trunk to minimize interaction, but still close
enough for standoffs to be practical?  Is the bandwidth gain of pipe over
wire enough to make this worthwhile?

Thanks for your consideration,

Jim Meehan, W6XE
Oakland, CA
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