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Old November 12th 07, 04:58 PM posted to rec.radio.amateur.antenna
Mike Kaliski Mike Kaliski is offline
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First recorded activity by RadioBanter: May 2007
Posts: 182
Default Open Loop aka Dipole bent into a square


"Priz" wrote in message
ups.com...
I'm pressed for space outdoors so right now, I'm working with attic
antennas and need some help.

I was able to put a 60 foot loop of wire into my attic and am not
having much luck getting it to load up. I configured the loop as an
open loop, aka a dipole bent into a rectangle which is open at one
corner and fed with 300 ohm twinlead at the other. I'm using an MFJ
911H 4:1 and 1:1 balun to tranform the twinlead to coax and a homebrew
antenna tuner.

Using an SWR analyzer, I find the only place I can get low SWR is near
the 15 meter band and some frequency ranges above it, like 6meters and
2 meters. I was hoping the 60 foot length would help me get down to
the lower bands with some compromise, but at least I was hoping to get
there. The transmatch, which consists of 2 capacitors and 2 inductors
isn't any help at all. I've used it in the past to load up random
wires and such, but this project doesn't seem to be working.

Anyone have any experience with this sort of antenna? Let me know
what it is I'm doing wrong.

Any advice is appreciated.

Try routing the wire around the attic so that the opposite ends are as far
apart as possible, rather than in a loop. If you have the height, mount the
feedpoint at the apex of the roof and take the wires towards the ends of the
attic. Then bend them around to follow the roof and floor line. I found this
worked more reliably for me than a loop. An ATU feeding a twinline feeder
through a 4:1 balun should be able to load this up on all bands. You could
even try feeding it via an ATU and coax directly provided that you wind a
few turns of the coax feeder around a ferrite rod or ring by the feedpoint
to reduce pickup and RF current on the coax outer. Make sure the ends of the
antenna are well insulated, they will be at high voltage.

Mike G0ULI