Rob you asked:
"" What is your vendor source for H50s? ""
I just had 2 delivered yesterday from TESSCO. I'm going
to replace 2 that have been up for almost 20 years.....
73
MAL
N7MAL
BULLHEAD CITY, AZ
http://www.n7mal.com
Everyone in the world is
entitled to be burdened
by my opinion
----- Original Message -----
From: Rob Atkinson
To: towertalk@contesting.com
Sent: Thursday, November 17, 2011 19:34
Subject: Re: [TowerTalk] How To Avoid Telescoping Mast Colapse
I use a pair of Tesso 50 footers at my station along with a tree and a
50 foot aluminum tube guyed at 33'. I have a 1/2 wave dipole for 80
m. fed with ladder line, a second 1/2 w. dipole for 20 m. fed with
ladder line and an Inverted L for 160. The aluminum mast also serves
as a 1/4 w. vertical on 80 m.
I don't know about the Rohn H50s but the Tessos have a threaded L
shaped screw clamp on each section with a support bolt that passes all
the way through the mast under each section to prevent collapse. I.e,
it is _not_ relying on friction only, to stay extended.
What is your vendor source for H50s? I am surprised they are
available as I thought they were getting hard to find. Also, I think
they give a true 50 foot height as each section is a little longer
than 10 feet to account for the nesting in the next lower section. On
one of mine, I removed the top section to get a stronger 40 foot mast.
Wire does not present much wind load (unless you use something huge
like AWG 8 or unless it ices up and then all bets are off). You can
take liberties therefore.
You will find that working with telescoping masts is kind of nasty.
After I got mine up I said never again. You may have an easier
go--you might have some help, or have more strength than I have. Wear
work gloves and extend them on the ground first, just to make sure
they pull out and there are no problems. have a tub of axle grease in
case the sections need some more lubrication. _Never_ work with them
with bare hands. you will be surprised at how fast a section can free
up and shoot inward catching your hand. I found it helpful to drive
in a metal fence post and clamp the unextended mast to it where I
planned to put it, with s.s. hose clamps to hold it while I guyed off
the bottom section. Once that is done you can lean a ladder on on it
and get up high enough to start pushing it up but make sure it is a
calm day. have your anchors in and guys on the mast and visegrips at
the anchors ready to use to clamp the guys. Leave the fence post
there as a safety anchor with the bottom of the mast on a brick or
metal plate. When you extend a mast the guy rings may ride up with
the sections. Be ready to work them back down by pulling on the guy
ropes.
You should use earth screw anchors but you can get by in most cases
with the hardware store variety and not the large more expensive
version from Glen Martin or Rohn. Just check them after a couple of
years below grade to see how they are holding up. Be prepared to
replace them. This is never the case with a tower but a push up mast
is okay. a pipe in the ground at a right angle to the guy will work
toward the guy through the earth when under tension and will never
prevent slack in the line. It might be okay if in concrete but an
earth screw in line wtih the guy is so much easier. Have some rebar
or crow bar to use to turn them through rocks.
I started out guying my masts with clips and thimbles but they are a
PITA when it comes to retensioning the guys. I now simply use Dacron
3/16" diameter. It holds up perfectly fine and has the advantage of
being RF transparent. I tie it to the guy rings on the masts with a
bowline knot.
( http://www.radioworks.com/ninstallant.html has a drawing of it, or
used to). It will stretch at first so it has to be retensioned. I
loop it through the earth screw eye with no thimble or clips. Instead
I tension it and clamp it with a cheap lightweight visegrip. You can
get clamping pliers knockoffs that are okay for this at big box
discount stores like Menards. Eventually they rust so you have to
oil them up before releasing them if you need to. I have read all
sorts of over-engineered comments frowning on this practice but I have
been doing it for 10 years with no problems.
You can also get away with an anchor distance that is as little as 1/2
the height of the guy level for the feedpoint support mast. The
reason is that it has no unilateral pulling force on it. All it has
to do is hold up wire and feedline dead weight. The secret is to
tension the guys so they keep it vertical without making them so tight
they are like a violin E string. That much tension is not necessary.
Also 3 way guying is okay. I would avoid if possible using an
inverted V unless you can get the feedpoint up at 70 feet on 40 and
the ends up 20 feet or more. The reason is a V has an average height
of 1/2 way up between the ends and the feedpoint. If the apex is at
40 feet and the ends are on the ground, the working height is equal to
a dipole flat top at 20 feet. That is why they perform more poorly
than a flat dipole at 40 feet.
If you have winds up to 100 mph it makes sense to engineer a easy to
fix break point. With a wire antenna it is probably best to set up a
system of marine pulleys to facilitate raising and lowering the
antenna and feedline and using wire that will snap under icing because
it is a lot easier to drop a wire and solder it than it is to put up
another mast.
73
Rob
K5UJ
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