On 9/9/12 4:00 PM, K7LXC@aol.com wrote:
I would like to put up 40-50 feet of 25. It would be behind my single
story ranch house. One guy would go towards the rear. The other 2 would head
toward the front left and right. The easiest would be to guy to the roof.
This tower will be for some vhf and uhf antennas. Your thoughts.
I've seen roofs that have been pulled loose by attached guy wires. You
can do it but I'd be very careful about the engineering. A fellow
TowerTalkian, Tony, K1KP, wrote a QST article some years ago about this topic.
ahold of a copy of it and you'll be much wiser.
Please note that 25G uses 3/16" EHS with a ultimate breaking strength
of 4000#. Could your homebrew roof guy anchor take that kind of stress? I
didn't think so.
Obviously your proposed installation will be on the small side so you
won't have much risk but I'd still be careful.
This falls in the "is it ok if it fails" category. Maybe you're willing
to have the tower collapse, as long as it happens in a safe way. Maybe
it's like folks putting up 40 feet of thin wall pipe to hold up a TV
antenna, and guying it with 1/8" solid steel wire. The wire fails
before the anchor pulls out of the roof. If you're not going to climb
the tower (i.e. you'll rig pulleys at the top or bolt everything on and
tilt it up assembled), it's not much different than the TV antenna scenario.
The thing to worry about would be that the r25 is heavier than the 2"
push up mast, so when it comes down, it might break more stuff (like
your roof or car)
Think of it as a field day installation? I'm sure more than one person
on this list has pushed up 40 feet of Rohn 25 with something like rope
guys to iffy T-stakes or Bull Pins hammered in the ground. Likewise,
I'm sure all those people have had an exciting time when it came down
unexpectedly, but hopefully with no damage to people or expensive
things (bent yagi elements don't count).
The thing to watch out for is starting small, and then forgetting your
original design compromises. A 3 element 6 meter Yagi to start, guys
made of fence wire so it doesn't wiggle too much. Then, 5-6 years
later, Oh, I'll just add another couple sections on (and the guys you DO
have make it seem sturdy enough when you climb it) and throw a 40 meter
Yagi on, oh, and a microwave dish, and a bigger 2m Yagi array for
moonbounce with an Az El positioner, etc.
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