[Antennaware] Fwd: Modelling yagi split DE

[Charlie Ocker via Antennaware]

Hi Guy -

Thanks for the thoughtful response.  What I was trying to do is model 
the effect of the actual split DE and it being fed by #12 wire balun 
leads.  Maybe this is overkill.  It does make sense that the NEC engine 
might have a problem with the abrupt taper difference.

I'll try your suggestions regarding wire segment length.  Right now, I 
am using the EZNEC automatic "conservative" wire segmentation feature.

Thanks again for the reply - really appreciate having this reflector as 
a technical resource.  There is no one in my immediate ham radio circle 
of friends who dabble in antenna design and modelling.  And, I am a self 
admitted hack, having had some success with it.  But, I do find it 
fascinating!

Vy 73,
Charlie  N9CO

On 7/9/2014 3:17 PM, Guy Olinger wrote:
> Hi Charlie,
>
> You are modeling in an area of segment size where the segment center
> (node) space can affect the results.
>
> Reduce the segment size in the model to the region of six, five or four
> inches, and apply that to the entire antenna. Start with segment counts
> for wires which give the region of four inchs and only lengthen if the
> segment count is too high for your program version. This should be done
> in YO as well, though it uses a different mechanism for establishing
> what amounts to segment size.
>
> On 160m I use fine grain one foot segments until the design is set. For
> passing along the design to others, I reduce the number of segments
> until the results start to change, and then back off a bit to get the
> fewest segments that **still get the same results as the 1 foot
> segments**. While I am using EZNEC Pro which supports gobs of segments,
> even the early EZNEC will support much finer segments than you are using.
>
> On your second method, what was the rationale for dropping from inch
> diameter tubing to number 12? That what actually happens?
>
> There is a modeling gotcha advisory to not place a source in a segment
> adjacent to a junction of more than two wires or adjacent to a wire with
> a widely divergent diameter, or widely divergent segment length. While
> this does not effect all models, it clearly poxes enough to stay away
> from it.
>
> Remember that models are creatures of algorithms and math. Most of these
> strange issues have to do with the need to do many things with the same
> math, just to have a program which is affordable to code. There are just
> places where the math can't deal with an issue, without the expense of
> writing exception code to handle it.
>
> 73, Guy K2AV