On 12 jan 2009, at 23.19, Brad KV5V wrote:
> I've just finished an Inverted-L for topband, using four 135 ft.
> elevated radials. The radials are made from 17 Ga. fence wire, and
> they're each about 9 feet above ground. The ends are supported by 12
> ft. T-posts.
>
> I was pleased to find the feed impedance is 20 j9 Ohms. This suggests
> that losses in the radial system are very low, and the antenna was
> easily matched with a 2.25:1 balun taken right out of Sevik.
A few weeks ago I raised my topband inverted L which have an 62 feet
vertical section and uses two elevated radials that are bent almost 90
degrees 10 meters out from the base. My location is on the coast and
although the salinity of the Baltic Sea is very low, I feel that I
benefit from it. The antenna measures about 22 Ohm and very little J,
similar to what is being described by Brad above. An un-un is used to
transform the impedance to 50 Ohm
One thing I have noticed is that resonance is very dependent of the
weather and it drops 30 kHz during rain or in moist air. This
surprised me a little as my previous antenna, av vertical 49 feet high
with three top load wires only dropped around 10 kHz in wet WX. My
guess is that the change of resonance is a product of the elevated
radials and the one loading wire used now, am I right?
I would like to learn how I can improve this situation as a 30 kHz
drop in rain is a huge change and the antenna almost every night will
have a different resonance frequency dependent on the current
conditions. Using radials on ground is not really an option for me,
and going back to a symmetric top hat would result in a very steep
angle of the hat wires as my guy points in two out of three directions
are only 26 feet away from the antenna base.
Any comments?
73 de Björn,
SM0MDG
SE0X
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160 meters is a serious band, it should be treated with respect. - TF4M
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