WHOA ! Let's not go overboard here.
Did you perform a stress analysis for the proposed system?
He wants to put a TH3 and a 17M dipole on a 7 ft mast.
Put the TH3 a few inches above and the 17M dipole on top.
NO PROBLEM.
Even if it bends, with that small top load, all he would need
to do is put up a gin pole, tie the rope to the bent mast
and hacksaw it off. But I seriously doubt that will ever
happen with such a small load. One of my 3L20's has
a 24 ft 2 inch OD 1/8 inch wall thickness 6061-T6
ALUMINUM Boom supporting the 20M parasistic elements
12 ft out with NO truss support. It has NEVER bent.
Against K7LXC's sage advice, I have a 5L10 and 4L15
stacked 7 ft apart on a galvanized waterpipe. It survived
the tornado that took out dozens of trees in my woods.
(I pretested the waterpipe by placing it on a couple of
supports with 7 ft sticking out and stood on the end
without it bending so I knew it could handle a 200 lb load.)
Tom N4KG
On Fri, 11 Jan 2002 Jerry Kincade <w5kp@swbell.net> writes:
>
> Tom, I wish you the best of luck, but be sure to plan for access
> around the
> tower for the $300 boom truck you'll need to safely lift that rig
> out the
> top after it's bent. At that point, the galvanized steel mast you'll
> buy as
> a replacement should have a cumulative cost of about $500 to $700,
> depending
> on how much damage the antenna suffered. :-)
> 73, Jerry W5KP
>
> ----- Original Message -----
> From: "Thomas Beltran" <tbeltran@earthlink.net>
> To: "Bill Coleman" <aa4lr@arrl.net>; <towertalk@contesting.com>
> Sent: Friday, January 11, 2002 12:00 AM
> Subject: Re: [TowerTalk] Alum Masts
>
> >
> > Bill:
> >
> > I plan on using a 10" mast, three with the rotator mounted about
> three feet
> > below the top of the tower, so 7 feet would stick out above the
> top of the
> > tower. The guy at the industrial metal supply told me that that
> pipe-wall
> > thickness would be 0.120", OD is 2". So I guess according to your
> > statement, that should be fine. Tom W6EIJ.
> >
> > ----- Original Message -----
> > From: "Bill Coleman" <aa4lr@arrl.net>
> > To: "Thomas Beltran" <tbeltran@earthlink.net>;
> <towertalk@contesting.com>
> > Sent: Thursday, January 10, 2002 1:02 PM
> > Subject: Re: [TowerTalk] Alum Masts
> >
> >
> > >
> > > On 1/10/02 1:03 PM, Thomas Beltran at tbeltran@earthlink.net
> wrote:
> > >
> > > >This discussion of Masts is quite timely for me. I was
> planning on using
> > > >schedule 80 Aluminum pipe for a TH-3MKIII and perhaps a
> rotatable dipole for 17. Should I consider one of HRO's steel masts?
> > >
> > > Tom,
> > >
> > > What you left out is how high above the tower top you planned to
> have the antenna(s). That makes all the difference.
> > >
> > > In general, I'd avoid the use of "pipe" of any kind for a
> structural component, but if the antenna is right at the top
> of the tower, the
> > > bending moments are small enough that even "pipe" would work.
> > >
> > > I've got an A3S mounted 6 feet above the top of the tower on a
> 2" Al tube with a 3/32" wall. Plenty strong enough.
> > >
> > > Bill Coleman, AA4LR, PP-ASEL Mail: aa4lr@arrl.net
>
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