[Top] [All Lists]

[Towertalk] side mounting on an AB-577/GRC

To: <>
Subject: [Towertalk] side mounting on an AB-577/GRC
From: (Dick Green)
Date: Fri, 19 Jul 2002 00:25:44 -0400
I know the AB-577/GRC portable military tower (mast) isn't designed to
accommodate a side mounted antenna, and one should never violate the LXC
prime directive, but I'm wondering if it can be done and if anyone has ever
done it.

What I want to do is mount a 40-2CD and rotor at the top of an AB-577/GRC
that's been extended to 75' with the standard extension kit. Then I want to
side mount a Force-12 EF-610 6-el 24' boom 10m monobander at the 50' level,
just above the second set of guys from the top. The 40-2CD has a windload of
about 6.4 sq ft and the EF-610 windload is 4.1 sq ft. I'm aware of several
successful AB-577/GRC installations with TH-7s at the top, which is about
9.5 sq ft of windload.

It seems to me that the biggest issue is the guy anchors. This tower uses
3-foot screw-in anchors and that's the biggest potential weak point in the
system. However, I believe the soil in which the anchors are screwed is
well-suited for the task. In fact, the tower in question (in the 50-foot
version) has been up for three years supporting a C3E with a windload of
about 5-6 sq ft and the anchors haven't budged at all. The 50-foot version
has three sets of guys going to three guy anchors 30 feet from the base. The
75' version has four sets of guys: the bottom two sets go to guy anchors at
30 feet from the base and the top two sets go to a second set of guy anchors
at 52 feet from the base. I certainly could put the anchors in cement, but
would prefer to avoid that if possible.

The second concern is that the tower tubes are connected together only with
steel spring clips. Normally, this is only an issue when raising the
tower -- if the tubing leans too far to one side (it's like a wet noodle),
the spring clips can fail. For this reason, it's wise to have a man on each
guy wire when raising the tower on a windy day (or when raising the 75-foot
version in any conditions.) Once the tower is plumb and guyed, the downward
pressure keeps the sections together and the spring clips aren't a point of
failure anymore. I'm wondering if having the EF-610 just above one of these
spring clip joints is going to put any additional bending moment on the
joint (thus putting pressure on the spring) or whether the guys will keep
the joint from flexing. Seems like they would, but I don't know.

Comments from knowledgeable people would be most appreciated.

73, Dick WC1M

<Prev in Thread] Current Thread [Next in Thread>
  • [Towertalk] side mounting on an AB-577/GRC, Dick Green <=