Richard wrote:

Are these points true?

The following is the simplest way of obtaining a practical yagi design using
an antenna modeling program:

1 If you use a non conducting boom then you can build a practical model
using the element lengths in the model.

I don't think it matters much what boom you use. Being at right angles
to the elements, the boom should be nearly "invisible" to the antenna.
Even if it's metal, Even if the elements are directly connected to the
boom.
Sure, there will be minor differences, but for your task, I don't think
it's worth worrying about. I sure don't. I'm not *that* picky.

2 For a VHF yagi in the clear you can assume freespace.

Yes. For all practical purposes...

3 A simple straight wire in your model that is made source is DE and
is treated as a simple hertz dipole by the program. So the values given for
R and J are the values you would measure having a hertz dipole as DE.

Yes. Normally will end up a fairly low impedance, unless you space the
elements for a appx 50 ohm feed. NBS yagi's will have a fairly low
feedpoint impedance. Thats why I prefer just to use a boom grounded DE,
and use a matching device. I almost never use a split driven element
unless the yagi plans call for a 50 ohm feed due to the element spacing.
My cushcraft A4S is of this ilk...

This is true for the model and would be fairly accurate if the boom was
non conducting and reasonably in the clear in the practical design.

Again, even if the boom is conducting, I don't think it's worth worrying
about..It doesn't make that much difference. Or to me anyway...



4 It is easy to scale for frequency in antenna programs.

Yes.

5 It is fairly easy to alter element diameters in antenna programs and to
obtain a redesign that maintains the original performance characteristics.*

If you simply rescale, the results should be the same. All dimensions
are rescaled. Of course, you can doodle with the program and redesign..

It seems to me that if one is prepared to use a non conducting boom, a
hertz dipole as DE, then the model is pretty much the practical design.

I think it is good enough, no matter what the boom is...

Not sure about impact of a balun or the feedline.

If you use a split driven element with a 50 ohm feed, you need a 1:1
balun, or equal choke, or whatever...


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