Hi, David,
"Official" models that include the traps are essentially non-existent. It
is the traps that are the wild-card instead of the aluminum tubing size and
length. To create an accurate model, the traps would need to be put on an
analyzer, and the R, C, L elements calculated from the response. That would
give you the values to put in EZNEC "load" elements to provide the trap
function. Also the trap physical length that is exposed between the regular
aluminum tubing would have to be added as another tubing length that
contains the load in the center.
Simply taking the trap apart and measuring the value of coils, etc will NOT
work because these designs have already incorporated the significant amount
of miscellaneous capacitance added AFTER the construction due to physical
proximity, coils inside tubes, etc.
The process of providing the actual L, R, C values of the trap from a 10-30
MHz impedance (R + Jx) sweep of the traps is not something that is provided
by available, affordable software that I know of. This may account for the
lack of such models out in ham-internet-space.
Nothing you do with the elements will change the trap values, which is why
using these elements any way except as designed is doomed to failure.
Running a 10 to 30 Mhz sweep on a trap tribander with an AIM4170 analyzer or
equivalent will show you why you can't use those elements on the WARC bands.
The problem with 18 MHz is that the 10 and 15 traps in there have
unaccounted for impedance in between. You MIGHT get it to work, but the
derived information to lay it out with EZNEC is not there without a lot of
work.
Since elements can be set to useable gain and f/b length settings over a
wide range of element spacings it is not surprising that the WARC version
has the same element spacing as the 10-15-20m version. Use the same boom,
and save on manufacturing.
73, Guy.
On Tue, Sep 13, 2011 at 9:23 AM, David Gould <dave@g3ueg.co.uk> wrote:
> I wonder if anyone has an EZNEC model of the cushcraft element for
> the D3 dipole or an element of the A3S beam.
>
> I would like to investigate a couple of ideas..
>
> I have noticed that the element spacing on the A3S is identical to
> the WARC A3WS.. So I wonder if I could get 18MHz on the A3S
> (loosing the 14MHz) by just shortening the outer tips?
>
> Secondly as I am very tight for space I was thinking of bending the
> tips at 90degs (up or down) to shorten the wingspan.
>
> 73,
> Dave, G3UEG
>
>
>
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