One man's experience with a wooden pole.
I "inherited" a number of Class 1 Western Red Cedar 65 ft poles from an
obsolete government site. They were approximately 8 years old when
I adopted them. Nine inches in diameter at the top and thirty inches in
diameter at the butt. Heavy duty and fully stepped.
At the 1 ft of hole per 10 ft of pole (plus 2 ft) I buried the pole 9
ft, leaving
56 ft exposed. Then I installed an 8L 15M beam on a 60 ft boom. And on
an 80 ft Rohn 55 tower with two sets of guys that was approximately 150 ft
away I installed a second, identical 15M Yagi.
Both the pole and the tower were at the same elevation with the same
exposure -- only difference was that the tower was 24 ft higher. Both
antennas worked well over the next few years and then the beam on
the wooden pole dropped a half-element from metal fatigue due to
crystalisation. Then it dropped another half-element, and then a third,
a fourth, and finally a fifth half-element. So during a period of about
8 years the beam on the wooden pole dropped five half-elements.
But the IDENTICAL beam on the guyed tower had ZERO failures.
The identical beams were very heavy duty on 3 inch booms with 1 inch
element center sections and 7/8 inch tips. Essentially the old
N0XX DX Engineering design with insulated-center (KLM-style)
element mounts.
After a lot of investigating and theorizing, it is my contention that the
beam on the pole was driven into a low amplitude, high frequency
oscillation/vibration over a long period of time from the un-guyed
(but very heavy duty) wooden pole.
Whereas the identical beam on the very well-guyed tower (5/16 inch EHS
for the lower-half and 3/8 fiberglass for the upper-half of each guy) never
had any failures.
I was disappointed with the wooden pole in this application and
installation. YMMV -- but this was MY experience.
--John W0UN
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