TopBand: Rohn 25

[Earl W Cunningham]

Hello, All,

In the thread about shunt-feeding Rohn 25, two things have been mentioned
that cause me some concern about error in my modeling of the structures:

1)  Someone mentioned that an 8" diameter "wire" should be used in models
to emulate 12" triangular Rohn 25.  After giving this some thought, I
decided to try using a wire diameter of about 8.91" because a circle that
size covers the same area as a 12" per side triangle.  In an attempt to
verify this, I'm building a more accurate (I think) model of Rohn 25
tower by defining tower legs and cross braces in EZNEC.  I did this once
for my own towers and came up with accurate results, but thought I'd
never do it again because of the complexity and pain involved in such
modeling, hi.

2) Someone also mentioned that Rohn 25 top sections come in 8' lengths. 
Are they all 8', or also 10'?  What is the net length of such Rohn 25 top
sections?  Do they taper ( the last foot or so) down to accommodate 2"
mast?

When I get the answer to 2) above and determine an accurate "wire"
diameter to substitute for triangular towers, I'll re-post the ELNEC
results again for various heights of shunt-fed Rohn 25, including 2:1 swr
bandwidth.  Also gain and angle of radiation figures for over all types
of soil, including over fresh water and salt water.

73, de Earl, K6SE

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