On 9/22/11 8:02 AM, Rick Stealey wrote:
>
> I got a few requests for the file. Here it is. This is the 3 element
> SteppIR with an added reflector closer to the driven element. It would be
> easy to add a director similarly. If you want to see the effect of such an
> element on the other bands you would take the original dimentions for the
> other band and stick this reflector in and see if it affects the pattern or
> swr. That's what modeling is all about.
> The file is easy to use because all variables are defined. You can change
> any of the SY lines to suit your own needs.
> It should not be necessary to change the GW lines.
> The values in this file were determined by using the optimizer feature in
> 4NEC2 to get best f/b.
> I used the latest release of 4NEC2 (5.8.7)
>
> Rick K2XT
>
This is a great example of what modeling can do for you. A simple
model, you can quickly fool with it to get a semi-quantitative
understanding of whether a change is worth trying.
>
> CM 3-element Yagi, ten meters, SteppIR elements, the 28.2 setting
> CM 'The antenna will actually appear to be higher in freq. than in reality
> due to loading of the elements by the fiberglass
> CM 'This is the 28.2 configuration, but designed for 28.8 MHz
> CM 'The fiberglass supports load the 28.8 lengths so they work at 28.2
> MHz. ok ?
> CM
I wonder if we could come up with a suitable LD card that represents the
effect of the fiberglass. I generically dislike schemes that wind up
tuning the antenna (in the model) somewhere different, because the
spacings really need to scale too.
Maybe a distributed L/C/R loading? In NEC4 you might be able to get
there with "insulated wires", but it would be nice to come up with a
rule of thumb technique for NEC2.
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