Hi Gary,
K9AY:
>This is where I found the reference to 5" (5.25" actually) as the equivalent
radius of Rohn 25 tower:
>William F. Cummings (K6MYH), "Tower Equivalent Radius," Conference
Proceedings, 14th Annual Review of Progress in Applied Computational
Electromagnetics ("ACES" Conference), Monterey, CA 1998.
I've found a reference for the formula I gave and John W1FV
said it originally came from IEEE Transactions on Broadcasting, but
I don't have the exact chapter and verse. You might ask W1FV.
The model I gave apparently only works if there is no top-
loading. To follow the discussion, got to the following link and
then click Thread>Next at the upper right of the page:
http://lists.contesting.com/archives//html/Topband/2004-03/msg00205.html
After my first post here I later computed the result for Rohn 25 and
it came up a little less than 9". Why this model would so well for
Rohn 45 and not Rohn 25 seems odd. Anyway it worked well for me and
allowed me to model, construct and install a 3 element parasitic
array in one day using my existing shunt-fed tower as the driven element.
I was astounded when I moved my tap from ~66' (actual tap for my stand-
alone tower) to ~86' (per the parasitic array model) and reflected power
was only 5W out of 1.5kW forward. I was delighted not to make multiple
trips up the 180' tower! Maybe I was just lucky but I was a very happy
camper.
73, Bill W4ZV
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