In a message dated 97-05-07 13:11:23 EDT, firstname.lastname@example.org
(Greville Balzarini) writes:
> My tower is a 60 ft. Rohn 25, guyed at the 25 and 50 ft.
> 1/4" guys anchored in cement with the twist-in anchors.
Hi, Sandy --
Welcome to TowerTalk. You are now officially a TowerTalkian.
First of all, Essex County is a 90 MPH wind speed zone plus it's within
100 miles of a hurricane oceanline so you need to build everything to that
speed or even 100 MPH.
Sixty feet of 25G at 90 MPH is rated at 10.2 sq.ft. The PRO-67B is
11.9 sq.ft. Sounds like you've got an overloading problem. And the mast
hasn't been added in yet.
> The rotor is mounted at the fifty foot level where the last guys are
Rohn specifications call for the guys at 55 feet, not 50. You'll have a
very large bending moment between the mast, antenna and the ten feet of naked
tower. Probably more than the 25G is capable of handling. The guys should
be installed at either the 55 or 60 foot level.
> A ten foot piece of galvanized pipe, 1/4" wall, is used to run through the
> top section.
> Another piece of piece of pipe has been inserted into the first ten foot
> piece and will extend above the tower by seven feet.
> The additional three feet of the second piece of pipe is used to double
> portion of the first piece of where it goes through the tower top and
> the mounting point for the Pro-67B, which will be 6 inches above the top
> the tower.
The mounting of the PRO-67 at six inches is fine and the galvanized pipe
is suitable for that ONLY. What's the rest of the seven feet of mast going
to do? Your galvanized pipe is NOT suitable for any load higher on the mast.
> Rohn has made the comments that this tower and the guying I have mentioned
> will work OK.
Did you ask them about the load?
> I have been told the best way to setup this antenna is to build and test
> on test-stands that are ten feet tall.
> Then lift and mount the antenna as a complete package. I believe the
> antenna weight is approx. 150lbs.
Do not try this at home. A 150 pound load is a HEAVY load and the
combination load of an antenna and a "test-stand" is NOT recommended as one
load to be installed on the tower. A 150 pound tower load is for experienced
tower installers ONLY. Better to break everything into smaller, bite-sized
What is a "test-stand"? The easiest thing to do is to use a tram line
for beam installation and you can run the antenna part way up the tram line
with coax attached and test it in the air.
The Mosley comes predrilled and should not require ANY changes to the
The purpose of TowerTalk is to try to help keep people out of trouble
when it comes to tower and HF antenna installations. You need to follow the
manufacturer's specs in installing EVERYTHING or you're asking for trouble.
Sandy, don't think that I'm picking on you. You are embarking on an
exciting and potentially rewarding tower and antenna project that you've
invested time and money. But MY primary concern for all TowerTalkians is
safety and reliability in all tower and antenna projects. My concern is
73, Steve K7LXC
TOWER TECH -- professional tower supplies for amateurs
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