[TowerTalk] Need modeling help: Tower and yagi(s) in centre of Four Square

[Barry Kirkwood]

Hello again,
Thanks to all who have replied with advice on effect of tower in centre of
160m four square array.
Very helpful and have learned a lot.
Looks like things could become critical if the tower and yagi structure
resonate somewhere close to 1825.

Do not have EZNEC loaded (bought it years back) and am low on skills to use
it.

Would be very grateful if anyone could do a very approximate model of the
tower and 80 m beam on top.
The full system will have stacked yagis for the higher bands but think we
could ignore these for a first cut at modeling the system.

What we have:

60 m steel tower (guys broken with insulators so will ignore them),
triangular section 66cm each side.
On top of tower Optibeam OB-80: Boom 20m long, 3 elements 20m approx,
Turning radius 15.6m.
Base of tower earthed, presumably tied to radial system of 4 square.

Question: To an approximation, what is the primary resonant frequency of the
tower and beam combination visualised as a vertical antenna?

Am sure Santa Claus will be kind to anyone who is good enough to do this bit
of work.

73 es tnx

Barry ZL1DD


-- 
Barry Kirkwood PhD ZL1DD
barry.kirkwood at gmail.com
NZ: 021 160 8999
Thailand 081 235 1556