Hi Mike,
Based on my W6SAI yagi handbook (the bible) the greatest forward gain occurs
right around .11 wavelength between the driven element and the director. This
also seems to give you the best F/B ratio. I "THINK" that this also applies if
you have a 2-element yagi with a driven and a reflector, not a director, but
I've not read anything about that.
As you increase the distance between the driven element and the parasitic
element, you decrease the maximum forward gain somewhat, but since there's less
interaction between the elements, you gain bandwidth. So longer-spaced
elements give you average gain over a larger bandwidth. Narrow-spaced elements
give higher gain but sacrifice bandwidth.
As you add elements, anything over a 3el yagi will not gain anything from
having close-spaced directors. In other words, when adding the 4th, 5th, 6th
director, you can increase the spacing between the director elements.
Good luck!
Scott - KI5DR
--- Mike Urich <ka5cvh@ka5cvh.com> wrote:
> Yes, I posting to three reflectors so please don't flame me.
>
> I'm going to try to build a new 6 meter yagi for the contest next week end.
> I'm only going with two elements for space considerations. I'm also
> considering a driven / director configuration as opposed to reflector /
> driven in as much as I'm not concerned about F/B ratios and being able to
> hear off the back side may be advantages.
>
> I went and looked at some different designs and have seen spacing from as
> little as .17 wave to .30 wave. I'm leaning towards somewhere around .22 -
> .25 wave. So I'm polling y'all to see what you have to say.
>
> Mike Urich
> www.ka5cvh.com
> www.ka5cvh.com/vhf/vhfindex.htm
>
>
>
>
>
>
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