Paul,
I have used the same basic set-up here with very good results. There were
two changes however which I found necessary. First, winding RG-58 on a
small diameter core will work for a few days but after a short time, the
center conductor will distort the poly insulation and change both impedence
and capacitance of the coax. It would be better to use a few turns on a
poly form of about 4 inch diameter. Actually, for multiband use, ladder
line of either 300 or 450 ohm impedence would be much better and easier to
match. Try WWW.cebik.com for more info.
73,
Frank, K4VMO
----- Original Message -----
From: "Paul" <gw7lhi@hotmail.com>
To: "Ten-Tec List" <tentec@contesting.com>
Sent: Sunday, January 04, 2004 4:39 PM
Subject: [TenTec] Not TT - Wire antenna question.
Hello all, thanks for looking
As folk were discussing wire antennas, please forgive another non T-T
specific post!
I have a fair amount of experience with beam antennas on HF / VHF, and
colinears on VHF but very little practical experience and know how with wire
antennas.
I finally got round to putting up a horizontal loop for HF use.
It is a slightly distorted rectangle at about 23ft AGL, and is supported by
4 fibreglass telescopic fishing rods.
The total length of wire in the loop is 48m or 156ft, the rectangle has 17m
sides and 7m ends
The wire is 1mm diameter with 19 strands.. it's very thin and fireproof,
also tough.. I cannot break it with bare hands. Made by RayChem.
The feed arrangements ( don't laugh now! ) are an 8ft long piece of RG58 and
terminal block to the middle of a 7m end. I did consider using some 300 ohm
twin feeder, but thought that as it is such a short run to the shack that
co-ax would do for a test. I have wound 12 turns of the RG58 around a 3/8
inch ferrite rod as an RF choke, this is located right at the feedpoint.
The choke was an afterthought to cure the excess RF in the shack on 80m.
My shack is upstairs, the nearest dirt is 20ft of wire away at least. I have
no RF problems with the vertical, but that antenna is about 30ft away from
the shack.
The antenna loads up on all HF bands using an MFJ 949e tuner, although it is
harder to achieve a good match on 80m.. it seems particularly reactive on
80.
To my surprise, it happily loads up on 160m.. haven't tried calling anyone
yet.
Good results on 40m daytime UK signals, most reports said the loop was 10 or
more dB better than my Butternut HF6 vertical which is ground mounted with
buried radials.
I can see a good dip on a GDO at around 6.8MHz, which agrees with an SWR of
2.5:1 at 7.0MHz as indicated on the ATU metering.
Now for the questions..
Is there anything I can do about the reactivity on 80m?
Should I swap the co-ax for 300 ohm twin feeder?
Would it be worth shortening the loop slightly to bring the natural
resonance up to 40m?
Or is there another "magic number" to multiband the loop better?
I like to talk local and work DX, would it be worth adding vertical segments
at each corner, running down the 6m long fishing rods?
Or maybe I should consider another form of wire antenna altogether? I picked
the loop because I know a few others using them to good effect. I can only
really have 1 wire antenna installed at a time.
Any other good ideas welcome, the main bands I want the antenna to be
useable on are 160 / 80 / 40m, although 40 and higher are a bonus really.
Any good websites also welcome.
My email address is valid.
A very happy 2004 to all!
Paul MW0CDO.
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