[TowerTalk] Army MARS antenna tower strucutural Analysis

[Pat Barthelow]

At the N6IJ club station, a converted Army MARS station from the 60's,  there
is a Military Log Periodic Antenna  (They call it a small LP, but for Hams, it is
definitely BIG... 17 elements, 40 ft dual tube boom, about 350 lbs, with a 
monster HY gain 3501 Rotator. Good  40 meters throgh 10 meters.

Now made for the military, and Embassy use,  by US antenna,  it is the LP 1017-C.
Moves are a foot to determine a future for the LP which is currently in need of 
a clamp for  the antenna king post of the rotor output.  The current clamp 
is obviously broken.  It is/has been difficult to get a team of qualified climbers to inspect
and repair the clamp, and to inspect the tower platform.  

The clamp  can be fixed, but the antenna is tilted in an ugly way, 
and the local hams are thinking of scrapping the antenna, merely on that basis of the 
broken clamp, and an assumption that the tower is also not safe.

The tower is standard fare for 60s vintage Army MARS stations.  3 ea McFarland brand,
class one poles, 70 ft long, buried about 10 ft.  The poles are healthy, wrt 
underground rot, etc.  They were treated, and had injection ports about 1 ft up from the ground,
for periodic pressure preservative treatments.  The question, and groundless assumptions made, by some, are the platform on the top of the power poles is of questionable health, simply due to age.

The platform is made of the pressure treated timbers, the kind that are green from the treatment solution and checked all over with slight perforations at the time of soaking with the treatment chemical.  When I last serviced the LP, (10 years ago) the pressure treated timbers were in excellent shape, at least to an untrained observer.   If I recall correctly, they are about 4" x 8" or 4" x 12" timbers.spanning the complete triangular "floor".

Underneath these timbers is a support framework of multiple timbers in a cris cross pattern, and bolted to 3 perimeter timbers, in a 21 ft triangle.  These structural members that hold the whole platform to the tops of the poles, are BIG timbers, about 21 ft forming the equilateral perimeter triangle.  they are Pinned with large diameter, galvanized steel bolts,  that actually are the heavy guy anchors seen in Utility pole guy anchors with the big forged guy "eye hole" in a forging that is about the size and shape of one's fist.  These pins go completely throgh the pole, through  a drilled hole, about 3 ft from the top of the pole.  It appears that the whole loading of the antenna platform is on these steel through pins, two to each corner of the triangle, for a total of 6 heavy pins anchoring the platforms to the poles.

Question:  Is there anyone on the reflector with experience in analyzing such a wooden structure for health and safety that would be willing for a fee to analyze this structure?  My gut level feeling is, that if there is any aging that has weakened the struture, is in the timber framework that underlies the platform. The perimeter timbers, and the platform timbers, looked very sound and solid,  as did their steel pins.
The structure was probably built in the Mid 60s.  I remember it when I visited the Ft Ord Army MARS station as a Novice ham.  Its MARS call was AAA6WAE.  I would hate to see it and the LP die a premature death when it may actually have more years yet in store.  Instant low swr band changes, and no traps anywhere 40 throgh 10 sure are nice.

All the Best, Pat Barthelow,
 AA6EG   aa6eg at k6bj.org   Skype: sparky599
Jamesburg Moon Bounce Team
http://www.jamesburgdish.org

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