In a message dated 9/4/2003 6:45:04 AM Pacific Standard Time, K7LXC@aol.com
writes:
> put a piece of steel inside the
> bottom of the mast to strengthen up the place where it's going to bend -
> right
> at the thrust bearing.
>
I am using a MA770 with a 10 foot aluminum mast (1/4 inch wall) out the top.
I have done a lot of experimenting with various antennas and the mast has been
tightened down in many different places along its length. For about 3 years I
had a CC X7 tribander mounted 8 feet above the top of the tower, a CC D40
dipole mounted at the top of the tower, bottom of the mast, and a 2 meter
vertical mounted at the very top of the mast. I had no problems with this
arrangement.
I recently installed a M2 5 element 50 Mhz antenna at the top of the mast and
moved the X7 to the bottom of the mast keeping about an 8 foot separation. I
added a 50 foot element to the X7 which is a combination 30/40 dipole and got
rid of the D40.
Imagine my surprise when I noticed one day, shortly thereafter, that the X7
was not horizontal but was leaning to one side. The mast bent right at the
bottom and bent to one side and not in line with the boom as I would have
expected. I was not aware of any wind storms that were severe enough to cause
this
action. I was able to drop the mast down about 1 foot inside the tower and all
is
well again.
Speculation is that the aluminum mast weakened or stretched over time and
finally had enough when I added the extra element to the X7 even though it was
at
the bottom of the mast by then. Could the strength have been compromised by
all the indentations from tightening the mast bolts into it?
Needless to say, I am keeping a close watch on the mast but I think I will
change out the mast, or at least install a steel insert the next time I have
the
tower down.
Terry/N6CW
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Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
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