[TowerTalk] Binomial feed for three stacked 40M Yagis

[Thomas Cathey]

Hi,

I wonder if someone can help me out.

I'm finishing up a homebrew project of three, full-size, 2 element 40M Yagis
that will be stacked at 60', 125' and 190' on a free standing tower.
Modeling shows the front-back and higher angle frontal lobes to be tighter
and smaller when feeding the center Yagi at twice the current, or binomially
fed. 

 In AO, (Beezley's 'Antenna Optimizer') I have the sources set as:

Wire 1 center  7    0
Wire 3 center  10  0
Wire 5 center  7    0

Hope that's the correct source coding for binomial.  Anyway, it produces a
tremendous pattern compared to making all three sources as '10.'


If done this way in the real world, I will match the center Yagi with a 25
ohm input impedance and feed the outer and lower Yagis with 50 ohm
impedances.  Ie, the triple feed parallel connection will see a matched 25
ohm load and two matched 50 ohm loads, all equal length.

Binominal feeds are used with three verticals, etc all the time, but I've
not seen information doing it with stacked Yagis.  I understand it's done
because the middle antenna is interacting with two outer antennas, so needs
twice the current.

Is this the right approach to feed a triple Yagi stack or should I feed them
conventionally as three 50 ohm Yagis with equal feedlines, etc?

Thanks.

Tom Cathey, K1JJ