To: <towertalk@contesting.com>
> Date: Tue, 14 Apr 1998 22:06:43 -0300
> From: LU5CW Ernesto Grueneberg <lu5cw@qsl.net>
Hi Ernesto,
> My idea is to build a big wire antenna for ten meters (about 6 WL boom) so I
> was concerned about the sag in the elemtents because of the weight, si I
> figured that if the elements were verticals, I could build it easier.
>
> Now I see it's not a good idea. So, any help with my project will be vy much
> appreciated.
I certainly don't know why it would not be a good idea Ernesto. I'd
try it anyway.
> BTW, anyony had built a sterba courtain?
I've used them. They are frequency and dimension sensitive because
the outer elements are series fed. Tiny errors add up and give large
phase and amplitude errors for the end elements. Everything
tries to work the wrong way in a Sterba.
Rather than a Sterba, I suggest using a USIA curtain array. It looks
like a Sterba, but has parallel feeders. It is a collinear and
broadside stack of elements, with the feeders brought to a
common point. The feed arrangement uses more feedlines, but the
advantage is the parallel feeders allow use over a very wide
frequency range with no pattern change. It is VERY much more
forgiving for construction errors or frequency shift. A USIA curtain
designed for 14 MHz will work on 28 MHz!
The highest gain SW broadcast arrays in common use are all USIA
curtains, they blow the large Rhombics away and use a tiny amount of
space in comparison.
But why not just try the simple vertical wire yagi? I think potential
disadvantages may not be as bad as suggested. Certainly the polarity
of stations on the other end of a sky-wave path makes no difference
at all, and I suspect the ground re-enforcement difference won't be
near as bad as suggested.
73, Tom W8JI
w8ji.tom@MCIONE.com
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