[TowerTalk] Modeling a Yagi in EZNec

[Leeson]

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

On 5/29/24 2:46 PM, john at kk9a.com wrote:
> That is something I have also thought about.  I do not include the balun
> lead wires.  They are likely part of the transmission line but if not, a
> short 90° segment like that may still may not model correctly in NEC2.  I
> use OWA designs and so even if the lead wires had some effect, I adjust the
> driven element for the desired SWR pattern anyway.  Typically I see SWR
> curves very close to my EZNEC model with very little adjustment.
> 
> John KK9A
> 
> 
> Tom K0SN wrote:
> 
> Those who use NEC to model a yagi, do you include the lead lengths in the
> model for the connecting wires that go from the balun to the feed terminals
> of the driven element?
> If so, do you model them as part of the element itself or as a transmission
> line?
> My leads are 4" long. So if I model them as part of the element, I would
> just describe the center portion of the element to be an 8" piece of say,
> #12 wire, then the next portion of the element would contain the correction
> for the element to boom clamps.
> Do I have this right or am I overthinking it?
> My goal is to get the model perfected to the point that when I actually
> build the beam, I will not have to make adjustments in the lengths of the
> driven elements to bring them to resonance.
> Maybe that's an unreasonable expectation, or not?
> 
> Any input appreciated.
> 
> Tom Hellem
> K0SN
> 
> 
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