I doubt you would have much success devising some kind of "brush assembly"
to ground those top sections. I would ground the coax shield to the tower
at the top and bottom and use the Polyphasers as you suggest. I would still
ground the bottom section well, and have a good ground where the cables
enter the shack. Does the tower manufacturer say anything here?
On the guying I would say that unless the tower is specifically designed to
be guyed, in which case follow the manufacturer recommendations, be VERY
careful. A crank up tower under guying tension is like a giant loaded
crossbow, and if it fires some bad things are likely to happen. Do not even
consider this if there is no locking mechanism that takes the load off of
the crank up cable when the tower is fully extended. Even then, the guy
tensions projected into downward force can easily overload the locking
mechanism or the tower sections themselves
73 John N5CQ
.
-----Original Message-----
From: owner-towertalk@contesting.com
[mailto:owner-towertalk@contesting.com]On Behalf Of Richard Spindler
Sent: Thursday, October 21, 1999 6:54 AM
To: towertalk@contesting.com
Subject: [TowerTalk] Crankup Aluminum Tower
I am in the process of erecting a nice AlumaTower crank-up 75 footer.
This reflector has been a help in several respects, but some of the most
important issues discussed reveal that I am tower-savvy-impaired despite
reading what I can get my hands on.
First, the issue of lightning protection. It looks to me as if the
three sections of the tower are essentially insulated from each other
with plastic pads which prevent them from rubbing against each other
when the tower is cranked up. So it seems to me as if, even though I
ground the legs to kingdom come with radials and multiple rods, the
major lightning path is going to be right down the old coax. I'll have
PolyPhasers at the tower base and again at the entrance to the house,
but that whole ground-at-the-tower-base issue seems moot. Am I missing
something here? Is there a custom of bonding the sections electrically
somehow? Looks like a real problem to me.
Secondly, the issue of guy tension. I have read several treatises on
properly installing and tensioning guys. It seems to me that if I try
to tension my (PhillyStrand) guys to 10% of breaking strength, I am
going to have a tough time cranking the tower up all the way in the
first place, and have a pretty good chance of breaking the cable which
cranks the tower up in the second place. I plan to guy each section,
since we have a 100mph wind speed figure here in this county (Highlands,
Florida), so I would have nine guys tensioned. I don't see any
information on this issue in the stuff I got from the manufacturer, but
I have written for it.
There must be fellows (I hesitate to say "guys") here who have faced
these issues. Any advice?
Doc Spindler, N9AM
Sebring, FL
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
--
FAQ on WWW: http://www.contesting.com/towertalkfaq.html
Submissions: towertalk@contesting.com
Administrative requests: towertalk-REQUEST@contesting.com
Problems: owner-towertalk@contesting.com
Search: http://www.contesting.com/km9p/search.htm
|