In a message dated 97-05-13 12:11:25 EDT, firstname.lastname@example.org (Ken Freedman)
> I have been offered a 20 year old HBX-70, that looks to be in pretty
> good shape, for free. The owner is moving, and will take it down. All I
> have to do is pick it up.
> My questions are:
> 1. Are there any bear traps here? What kind of a record does this design
Well, actually the WHOLE thing is a bear trap. It is pretty rare to find
one that old in "good" shape. The Rohn BX-series has a pretty thin coat of
galvanizing on it and they age pretty rapidly, especially compared to 25G and
45G which is hot dipped.
Personally, I'm really hesitant about climbing a 20 year old BX let alone
removing it. Dismantling a tower is about the most dangerous activity you can
do around towers. Be absolutely positive that the tower is structurally sound
before you attempt anything. If there's ANY DOUBT in your mind - walk away
from it. I've done this several times and have never regretted it. There's
plenty more free BX out there.
> 2. Is installation/engineering data available on something this old?
The Rohn catalog (TOWER TECH - five bucks) has the specs but it doesn't
come with directions. It takes a special ginpole as well.
> 3. The owner tells me that he had a tri-bander on it, but right now there
> are a couple of UHF/VHF yagis up there. (BIG ones) Would a tri-bander with
> a 20 ft boom cause too much of a twisting moment at 8 sq ft?
Most emphatically, yes. The BX consists of a series of eight 8-foot
sections. If you have a 70 footer, you've got an older one or another section
(probably straight) has been added. The Rohn spec says it'll take 6 sq.st. at
64 feet of tower but recommends maximum boom length of 10 feet.
> Many thanks to anyone who can shed some light on this subject.
> respond directly if (as I suspect) this is the kind of beginner's stuff
> that has already been answered a zillion times on the reflector.
I am currently in the middle of a 4-part series on towers in my Up The
Tower column in CQ Contest magazine. Pick up the last couple of issues and
it'll get you started. It'll be available as a reprint at the conclusion of
Rohn BX is TV tower and has its limitations for ham use.
73, Steve K7LXC
TOWER TECH -- professional tower supplies for amateurs
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