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
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