k0wa@southwind.net wrote:
>
>I ask for a "cookbook" method raising large antennas.
>
Lee,
here is the antenna lifting arrangement we use at
NK7U to lift monster beams. This arrangement has been used
to lift 20M6's (60ft booms), 20M5's, 40M4's, etc. 2 towers
are needed to do this however.
1. A large pulleys is needed at the top and bottom of both towers.
2. One rope is run from the ground, through the bottom pulley, up
through the tower, to the top pulley and then back down to the
ground at a point between the 2 towers
3. The same is done with second rope on the other tower.
The ropes will then form a "M" shape (see drawing below).
|\ <--pulley pulley--> /|
| \ / |
| \ / |
| \ / |
T | \ / | T
O | \ / | O
W | \ / | W
E | \ <- rope -> / | E
R | \ / | R
| \ / |
| \ / |
| \ / |
| \ / |
| \/ |
pulley --> |-->rope |-|-|-|-| rope<--| <-- pulley
-------------------------------------------------------- ground
^
|
beam
4. The top of our boom to mast plates have 2 holes drilled into
the corners to accept a yoke. The yoke is attached to the
plate with 2 snap links. The top side of the yoke is attached
to the ends of the 2 ropes. A photo of this setup can be found
on our home page at:
http://netnow.micron.net/~jcullum/image/joe20.jpg
5. A tag line may be used to keep the antenna from rotating.
6. At this point you are ready to lift. Actually it is more of
a pull since you are pulling horizontally against the bottom of
the tower. We use a 4-wheeler on the side that the antenna is
going to. And the other rope has 2 people on it. The antenna
can be lifted straight into the air, past the guys and then swung
into the tower at the appropriate spot. Multiple beams can be
installed up and down the tower without ever having to move the
pulleys.
A benefit of this arrangement is that the antenna can be lifted quite
a way off the ground and swr measurements can be taken. Getting the
antenna back onto the ground is only a matter of releasing the ropes
(carefully). You can also pull the antenna up 50 ft or so and use a
tag line on the reflector to point the antenna straight up for more
accurate (?) swr measurements.
Other photos of the antenna installations can be found on our home
page at: http://netnow.micron.net/~jcullum/html/nk7u.htm
I hope this helps. Let me know if you have any questions.
Also, as K1KP pointed out, there are some large forces associated
with lifting these big beams. So make sure your setup is thought
out and beefed up.
Jim K7MK
jcullum@micron.com
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: K7LXC@contesting.com
Sponsored by Akorn Access, Inc & KM9P
|
