Bill,
I, too, have been following the discussion. Some of it was right, and
some
was not so right. I'm not going to give a lesson on antenna and transmission
theory, so let me just make a few comments. First, wire antennas can be very
effective. In fact, wire antennas can sometimes seriously outperform beams
at average ham heights.
The real trick is to keep your system losses low. You appear to be doing
that by using open wire feeders. Open wire feeders have low loss even at
high SWR's. So, you need not be overly concerned by SWR. You just have to
worry about your antenna tuner's range. I suspect that the AH3 will handle
your SWR without problem.
There is only one issue that you need to look to, the transition from
the
ladder line to the AH3. The AH3 is an unbalanced tuner and your ladder line
is balanced. I usually transition to coax at the point I come into the house
using a balun. This addresses several issues at once, and painlessly. Coming
into your house with coax allows you freedom to run the cable however you
need without having to worry about bends, metal in window frames, wiring in
the walls, etc. The balun takes care of the balanced to unbalanced
transition.
For coax I would use a short run of LM-400 or 9913. This will help keep
losses due to SWR low even if you don't have a flat line. Some might think
this particular variant of RG-8 might be overkill, but you really need to
keep losses low. If you do this, SWR is not a problem.
Lastly, the choice of a 4:1 or a 1:1 balun is a function of what
impedances
you expect. It you feel that you are going to be seeing high impedances us
the 4:1. However, I would start with a 1:1 balun made up of 10-12 turns of
coax on a piece of PVC pipe at the transition point. If all works as you
like, leave it. You can always spend the additional money later if needed.
I have two delta loops and a Windom. The loops are each fed with ladder
line and coax as I suggested above. I wouldn't have any other combination.
They have been very effective over the years. Best of luck.
Vy 73,
Barry
K3NDM
-----Original Message-----
From: tentec-bounces@contesting.com
[mailto:tentec-bounces@contesting.com]On Behalf Of William
Sent: Wednesday, February 01, 2006 6:42 PM
To: tentec@contesting.com
Subject: [TenTec] Loop/open wire/AH3?
I have been following the discussions re open wire feeders and invite
comment on my planned new antenna. I will be installing a loop around my
residential yard thanks to a fortunate arrangement of fir and cedar trees
here on the West (Wet) coast of Vancouver Island.
I will feed this with ladder line-when it arrives---and feed it with my Icom
AH3 tuner by connecting the main output of this tuner (generally used for
long wires and whips) to one side of the ladder line and then connecting the
ground terminal of the tuner to the other side.
Coax should then run through the wall of my shack to the Argonaut V.
Suggestions/comments/improvements?
Bill
VE7BER
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