I think this violates some modelling guidelines.
From the EZNEC manual:
1.
The source shouldn't be placed on a wire which is shorter than about 0.02
wavelength, particularly if adjacent wires connect at an angle.
2.
The segments adjacent to the source segment should be the same length and
diameter as the source segment. If placing it on a short wire, it's good
practice to give the wire three segments to insure this condition.
3.
Segments beyond the adjacent segments shouldn't be drastically different in
length and diameter from the source segment and segments adjacent to the
source segment.
4.
Sources shouldn't be put on a wire which is part of a small loop.
5.
It's usually better to use a split source at wire junctions than to insert a
short wire containing the source."
If your DE has an inch or two gap between dipole ends, I suggest that the balun
leads should be treated as a transmission line, in which case it's so short it
doesn't matter.
Wes N7WS
On 5/29/2024 3:31 PM, Leeson wrote:
In designing some Yagis to be built without further adjustment at a DX contest
station, I experimented with calculating the shortening of the driven element
tip to compensate for balun leads. As a simplification, I modeled the leads
parallel to the element.
I just add an inner section on the DE that is 0.064" diameter and the chosen
length of the balun leads, and then adjust the tip to get back to the base
design SWR. I had thought this would show something like a 1:1 adjustment, but
instead it turns out the tip shortening ranges from 1.5-1.7x the balun lead
length.
In antennas that use the HyGain element clamps, I try to account also for the
shunt capacitance of the mounting setup.
Dave, W6NL/HC8L
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