Just a brief note on two towers I had installed for over 35 years. I used
three of the Radio Shack mast base mounts in the ground to support the tower
with Rhon house brackets. These units consisted of a square metal plate, about
six inches, with an 18 inch piece of sharpened angle welded to the bottom and a
piece of round tubing about six inches long welded to the top. Over the years
I had to loosen the U bolts holding the house bracket to the tower and move
them up the tower to compensate for the tower settling into the ground. The
towers were 40 and 60 ft, and the 60 ft supported an tri band beam and vertical
antenna while the 40 ft tower supported a DB-224 and a tri band beam.
I started with American tower but lost both towers due to sheer in a tornado
at about the level of the house bracket. The towers did not come down but were
tilted about 30 degrees off vertical. I replaced them with Rhon 25G and had no
more problems. The American tower did not have any diagonal bracing.
73 - Jim W5ZIT
Al Wolfe <[EMAIL PROTECTED]> wrote:
Normally, putting ANY concrete under a properly house bracketed tower
is
a mistake. There used to be a Rohn letter out about it. Had to do with two
immovable objects, that is, the house and the concrete base and the motion
of the tower between them. Towers do flex in the wind and change dimensions
with temperature. Rohn said that house bracketing any tower on a concrete
base compromised it's strength. This is not an issue with guyed towers not
using a house bracket.
Back in the 1960's as a poor college student one of my part time jobs
was with a company who did TV towers installs. (This was when we sold Rohn
25 straight sections for $7.50 each.) The company did literally hundreds of
Rohn 25 installs to typically thirty to fifty feet. The rule was to go
twenty feet above the house bracket. None were guyed.
We never used any concrete. The house bracket did the work and was
installed first into something substantial, usually a backing board or plate
in the attic. A plumb line was dropped from the house bracket and a hole was
dug about two feet deep. We then put in a couple of inches of pea gravel for
drainage and two bricks for the tower to set on. The tower up to the house
bracket was then installed and plumbed. The hole was filled and tamped. Then
the tower sections above the house bracket and the antenna, rotor, twinlead,
etc. were installed.
We never had a house bracket or tower failure using these methods. Some
of these towers from forty years ago are still around although most are gone
because of cable or rust, but none ever failed because of the installation
method.
I have two towers installed this way here at my home, one 50 feet and
one 40 feet, that have been up since 1979. Other than needing a little
paint, they are still perfect.
Al, K9SI
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