For many years, the JSC Amateur Radio Club station at NASA's Johnson Space
Center in Houston, used an un-guyed Rohn 45G tower consisting of one
straight section and a pointy-top section as it's satellite antenna tower.
The tower straight section had steel 'tabs' welded to the mounting sleeves
at the leg bottoms. The tabs mated with corresponding tabs on a base plate
bolted to bolts imbedded in a concrete base and served as a tilt-over
mechanism--only used when we installed and removed the tower.
With the demolition of the building housing W5RRR, the SCUBA club room, and
the employee's recreation center grounds maintenance building/garage, the
tower had to be removed. A new building will go up in that space and will
again house W5RRR, Lunarfins, and the grounds maintenance staff & equipment.
A new tower base will be put in place next to the building for the satellite
tower/antennas.
However, the building will be taller, necessitating adding at least one more
section to the old satellite tower--I don't know the new roof elevation. We
cannot attach the tower to the building. With the tower concrete base next
to, but not contacting, the building slab, there is no room for proper
guying.
I've done some looking around to find windloading for the antennas we are
using (I don't have the doc's -- they are in storage during the construction
period), but they are a 2m 24-element and a 70cm 36-element (both circular
polarized) antennas. I didn't find the same antennas (24- and 36-el's)
listed in the three or four antenna manufacturer webpages, but from the
specs for the biggest 2m/70cm satellite antennas, it looks like windloading
won't be more than four or five square feet. How much should I add for the
AZ/EL rotator?
With the added height requirement, I'm considering changing the base to an
imbedded base section with two straight and one pointy-top sections.
Is it safe to freestand a 28' Rohn 45g with 4-5 sq.ft. of antennas on top?
With real beams (C4, TH6DXX, A4, 204ba, etc.), I woldn't consider it. But,
for these two 'lightweight' antennas?
Thanks in advance for any info, guidance...
73,
Dale, kg5u
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