[VHFcontesting] 6 meter yagi

[Zack Widup]

Something that seems to be a not so well known fact is that the possible
gain of an antenna is more dependent on the boom length than the number of
elements.  I've discovered this and a few other things after years of
playing with yagi designs on MININEC and Yagi Optimizer and experimenting
with antennas (actually building and trying them).

The number of elements affects the beam width, number of sidelobes and F/B
ratio.  When you're planning on doing portable operations and assembling
the antennas at the site, the number of elements also becomes a weight and
time factor.  I've come up with a few antenna designs for 144, 222 and 432
that have decent performance with wide-spaced elements on a given boom
length (lighter and faster to assemble).

There was a good 3-element 50 MHz yagi design in Comm Quarterly a few
years ago (I forget the date/year) that used a 3 ft boom length.  It's not
a perfect antenna but it's a decent performer, simple to build and is
well suited for portable assembly and setup.

73, Zack W9SZ


On Thu, 10 Jul 2003, Scott Pederson wrote:

> 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
>