[TowerTalk] Tower resonant frequency

[john at kk9a.com]

I am not sure how accurate this is but I usually model the tower as a  
large diameter wire and I only include the boom of the top antenna (I  
use insulated elements).  K9RS has an interesting article on using  
bent wire verticals around a tower  
https://www.kkn.net/dayton2008/multi-element%20lowband%20verticals%206.pdf

John KK9A


k4xs wrote:

Plans are VERY slowly progressing for my new station in Belize.  Plans  
are for a 106 foot tower with lots of goodies on it.
Here's what is planned:106 ft of Rohn 55 guyed with Phillystran.   
Three swing armed  Skyhawks at 32, 64 and 96.  Two A3WS WARCs at  
around 76 and 42 ft.  I plan on running four ropes to hold a wire 4  
square surrounding the tower.  This is similar to what I had in KH6  
and the 4 square worked well although the F/B was down to around 10-12  
dB.
My question is this:  I know the tower will have some effect on the 4  
square surrounding it.  Obviously I don't want the tower to be  
anywhere near resonant on 80.  My guess is the top loading of the  
tower will lower the resonant frequency quite a bit, and the effective  
height will be around 145-150 ft, but I am not sure.  Obviously if it  
is in the range of around 130 it would be a big issue.
There is not enough room to put up a 4 square by itself so I'm stuck  
with this set up.  I do have some fiberglass poles that I could attach  
to the tower vertically to give it another 13 feet or so by running a  
wire up the pole and attaching it to the tower, but I really don't  
want to do that if I don't have to.
Thoughts on this?

73  Bill K4XS/KH7XS