[TowerTalk] aluminum mast again

[N6CW at aol.com]

In a message dated 9/4/2003 6:45:04 AM Pacific Standard Time, K7LXC at 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