Gents:
I saw an elegant solution to how to get a 20-24 foot piece of chrome moly
inside a tower. I do it a different way, and have had no problems up to this
point in my strategy. I mention it as a point of comparison.
I have used several large stacks above my Rohn 45s. I build my towers in the
standard way, and then put the mast in through the top of the tower. I
always set the rotal at the bottom of the top section so about 8 feet of the
mast is inside the tower with about 12 feet out the top. That gives me space
for a top guy for the top antenna.
The way I get the long mast above the tower and down into the thrust bearing
is that I use the standard size ginpole to raise a very long ginpole made
out of 1.5 or 2" black pipe used only for this operation. I went to the
scrap yard and purchased to sections of channel iron and drilled holes for
u-bolts to bolt the two sections to the tower. I also had them burn out two
"U" shaped indentations in the middle of the channel iron. The two pieces of
channel iron are spaced about 5 feet apart at the top of the tower,
horizonatally of course, and I mount the long gin pole in the center of each
of these. The "U" indentations hold the long gin pole firmly vertical so
that it can not slip when the weight goes on it. The long ginpole simply has
an appropriately large and heavy duty pully inserted in the top.
Using this top raising position, I have had no problem lifting the main most
up over the top of the tower. Things you have to consider are:
1. Make sure that the channel iron is going to space the long gin
pole out away from the tower enough to clear the mounting plate at the top
of the tower.
2. Measure the chrome moly mast so that the weight is distributed
on the raising line so that it is bottom heavy, but the lifting point is low
enough to let the mast clearly pass over the top of the tower.
3. I use a removable knot around the top of the chrome moly mast to
keep it vertical as it comes up and remove the know when it gets to my
position. I then make sure that the bottom stays down where it is supposed
to be if there is any tendency to want to top.
The problems that I have had coming up through the center are with
excessive binding of the raising rope or line going through to thrust
bearing or through the tower. Either way, there will be problems with being
other than totally vertical coming through the thrust bearing and there is a
tendency to want to scrape all the galvanizing or anti-rust outer surface
due to lifting torque producing a bind. I have found that the over the top
process seems to be a little less destructive to my mast. I have found less
binding and scraping when I am using the over the top system than the pull
it up through the center system... I have found the pulling it up through
the center from the bottom system to be incredibly tedious to get the mast
worked up through the thrust bearing and then raised with the antennas on it
using only a bottom raising point. That was tough. I wonder how the ops
coming up from the bottom find that they get leverage and stability to move
the mast up through the bearing with no rotor or bottom stabilitization
point as the mast plus one or two big yagis are slowly elevated. Piece of
cake from the top.
Gary W5FI Ex-W5VSZ
Now, the professional engineers may have problems with my strategy,
I don't know, but I have built quite a few stacked arrays this way and have
been happy with the system.
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With Warm Regards, Gary E. Jones, Ph.D.
Office Phone: (601) 266-4588 Laboratory: (601) 266-4855
E-mail: gary.jones@usm.edu
URL: http://ocean.st.usm.edu/~gejones/psyphylab.html
URL: http://ocean.st.usm.edu/~gejones
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