Hello Top Banders,
We've been using a top loaded 100 ft vertical wire over 45 quarter radials
on the ground with quite good success. We're looking to improve things and
after doing quite a bit of research have an idea as to what we may do, but
have some questions as well.
First, we 190 feet of AB-105 in place with no beams on it and no plans for
any at least for a few years. It's in place primarily to support one end
of an 80 meter quad.
We'd like to get something in place with decent gain, but after putting
the 80 meter 4SQ in place with the four radial fields, I was kind of
looking for something that might perform close to the 4SQ with a single
set of radials.
First look was a K8UR array. I think we could easily achieve that and
believe that while it has half wave elements, performance would be better
with a good field of radials under it.
As I was doing my research I was intrigued by the W1FV/K1VR spitfire
array. It's essentially a quarter wave vertical with 4 sets of folded
switchable half wave parasitic elements. Gain looks to be within .2 db of
a 4SQ.
My first thoughts were to match the ground 190 tower as the driven
element. It's insulated with fiber rod. As I've read comments on the
reflector regarding matching towers exceeding a quarter wave electrical,
I'm getting the feeling that it may not be the way to go. Convential
theory seemed to indicate that a half wave or five eights wave vertical
would be better than a quarter wave. What we'd end up with is 3/8 wave.
SO MY FIRST QUESTION IS WHETHER ANYONE HAS MATCH A 3/8 WAVE ROUNDED TOWER
ON TOP BAND AND HOW WELL DID IT PERFORM?
So taking a second look at things and seeing a reflector entry by KK9A
regarding a 1/4 wave vertical supported by a 140 foot tower, I started
thinking we could build the spitfire using a quarter wave wire (or wire
cage) vertical supported by our 190 footer. The thought was essentially to
build it the same as the original spitfire with 60 feet of tower extending
above it.
Then I started thinking about using a quarter wave wire vertical, but not
folding the 1/2 wave relectors as was done with the Spitfire. The idea is
to run the half wave parasitic elements from the top of the tower. I
realize that in doing so the spacing between the parasitic elements and
the driven element would be wider than for the original spitfire. I'll
have to start looking at the spitfire spacing in terms of a wavelength as
well as what I'm proposing. Then I'll have to look at what the that
difference in spacing means in terms of gain and f/b.
I'm thinking of approaching this in phases. We start with the quarter wave
vertical over 60 quarter wave radials to keep us on that band as we
progress. Next we'll put a single director towards Europe and evaluate
things (including possible interaction with the 80M quad). From there we
put a parasitic reflector sw of the driven element to give us a 3 el array
to evaluate (again considering the 80 quad)(oh yeah we need to consider
interaction with the 80m 4sq as well). If this all works out well, we can
then add the other two parasitic elements and switching.
SO MY SECOND QUESTION IS - WHAT DO THE RESIDENT EXPERTS THINK OF THE IDEA?
ANY DRAWBACKS I'M NOT CONSIDERING?
By putting halyards in the right places at the top of the tower, I think
it should be pretty easy to emperically develop this thing.
73 from the NR4M crew
Larry K7SV
_______________________________________________
Topband mailing list
Topband@contesting.com
http://lists.contesting.com/mailman/listinfo/topband
|