# [Antennaware] Equivalent Diameter of Triangular Tower

Warren Robinson warren at rakon.co.nz
Mon Feb 23 18:14:03 EST 2009

Hello All,
Can anyone give references for shunt feeding lattice towers,
75'self supporting with a good radial system for 80m.
THANKS
WARREN
ZL1AIX

On 24/02/09 4:29 AM, "K9AY" <k9ay at k9ay.com> wrote:

> 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.
>
> Gary
> K9AY
> _________
>
>> 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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