[Antennas] Help needed in EZNEC model for trap dipole driven element

[fkamp at comcast.net]

john wrote:
> 
> In my quest to modify a set of Cushcraft 15m traps to serve 12m duty (for a
> rotary 12m/17m dipole to place above my tribander), I've veered off into
> EZNEC land.  Some study shows that I don't have enough information to model
> the existing trap.
> 
> I suspect I can measure the inductance of the coil accurately (have an TEK
> 130 LC bridge) and can therefore calculate what the parallel capacitance
> must be, since I've measured the resonant freq with my Grid Dip meter. I
> don't know what figure to put in for the  parallel resistance,
> however.  Any rules of thumb?
> 
> Alternately, does someone have a decent model of a driven element of a
> cushcraft type driven element, that I could hack up?
> 

I have a couple of traps that came off a tribander beam.  I dont recall
if they came off a Mosley or Cushcraft beam, or even if they came off
the driven element.  I have used them in the past to build a 20,15,10
meter rotatable dipole using aluminum tubing.  It worked well.

If you want, I can remove the aluminum cover from one of them and
describe what is beneath it.  I recall there are two coil windings in
there on opposite ends.  Nothing I can Identify as capacitors.  I dont
remember what the turns on the coils were.

The land of EZNEC is a wonderous world of comparisons.  I find it useful
when comparing performance of different antenna designs.  I am not sure
how useful it is modeling real antennas.  There are many location and
installation quirks it may not consider.  EZNEC is wonderful in making
comparisons and getting close to a final design, but I have never
implemented an EZNEC design that did not require some tweaking of wire
or tubing during construction.

Regards,
Frank Kamp
K5DKZ