[Antennaware] Equivalent Diameter of Triangular Tower

K9AY k9ay at k9ay.com
Mon Feb 23 10:29:29 EST 2009

Bill and all,

If I change from 5" to 8" the reactance moves the right way, but the 
resistance moves the opposite direction. The net result is that the model is 
a little closer to the measurement, but still far enough away to look for 
other issues.

The 5" number comes from a paper at one of the ACES conferences (Applied 
Computational Electromagnetics Society). I'll look it up later today and 
post the reference.


> K9AY:
> > This is easily explained by uncertainty in choosing an equivalent
> diameter "solid wire" for
> the 25G tower (I used 5 inches).
>         That sounds too small.  Here's the formula I used to model
> my 160 vertical made of Rohn 45:
> http://lists.contesting.com/archives//html/Antennaware/2002-05/msg00001.html
> Equivalent Cylindrical Diameter = 2 * CUBEROOT [(D * F^2)/2]
> where D = tube diameter and F = Face width.  For Rohn 45, D = 1.25"
> and F = 18", so cylindrical diameter equivalent = 11.7446"
> This turned out to be very accurate in predicting both the tap point
> and capacitance needed for my shunt fed tower (and later a 3-el
> parasitic array using the tower as the driven element).  I don't have
> the tube diameter for Rohn 25 handy to actually go through the
> formula but think the equivalent diameter might be closer to 8" (just
> mentally scaling the result above).
>                                         73,  Bill  W4ZV

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