[TowerTalk] Modeling a Yagi in EZNec

[Wes]

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