Correction... >>this greatly reduces the moment loading on the anchors
which increases pull-put strength and minimizes tensile bending (not shear)
stress in the metal. -MF
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Matt
Sent: Tuesday, June 04, 2013 11:34 PM
To: towertalk@contesting.com
Subject: [TowerTalk] FW: Mast recommendations?
I recommend a 4-section, 36' TV-type push-up pole extended to a height of
about 32 feet. Radio Shack used to sell these for about $80. I have used
one for more than a decade of field operations with a 25 lb triband yagi. I
can erect this mast and mount the antenna by myself in about a half hour. I
only extend the mast to 32 feet - the section heights I use are marked on
the mast sections with a "sharpie". I use three sets of three guy ropes
each (3x3=9 guys). I use three "screw in" type dog leash hooks to anchor
the guys (expensive a pet shop, cheap at hardware stores or Walmart) Be sure
to screw these all the way into the ground to the point where the loop
starts to dig into the ground - this greatly reduces the moment loading on
the anchors which increases pull-put strength and minimized shear stress in
the metal. Erection of the mast only requires a step ladder to reach the
top of the first section. Screw the anchors in the ground in an appropriate
sized triangle. Tie off all the sets of guys to the appropriate mast
sections and anchors - approximate the tension only on the lowest section.
Leave the upper sections loose (these are precut long enough to stay loose
initially but still prevent a crash if the wind kicks up unexpectedly
before the installation is complete. Tilt up the mast and just adjust the
1st set of guys rather taught then readjust the bottom location of the mast
to get perfectly vertical. Put a small board under the bottom of the mast
(learned after heavy rain and high wind while operating portable in North
Dakota - pushed my mast over three feet into the ground!) Mount the antenna
and coax and push up the mast - one section at a time. Tension the upper
guy ropes just enough to keep things stable in the wind. You are set to go.
Take down in reverse order but use a leather glove around the mast to act as
a friction brake (also prevents pinched fingers). A pry bar is useful to
unscrew the guy anchors. Appropriate lengths of #8 rebar with a "Shepard's
Crook" end and a mallet sledge will also work for anchors when driven at an
angle away from the direction of tension. You will find that rebar anchors
usually have to be set deeper to prevent pullout) A 14" pipe wrench will
pull rebar out of the ground with little effort on takedown.
PS - this combo will also work fine with a TV type rotor but have found
"Armstrong" rotor is usually good enough.
73
Matt
KM5VI
-----Original Message-----
From: TowerTalk [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim
Lux
Sent: Tuesday, June 04, 2013 10:54 PM
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Mast recommendations?
On 6/4/13 5:19 PM, Robert Fanfant wrote:
> Our field day team is planning to put up a SteppIR 2 element yagi (~25
pounds). We'd like to mount the yagi ~20-30 feet high and would like mast
recommendations. This is only a field day (i.e. once a year) event so cost
is a factor, yet the mast should be strong enough so that we aren't out the
price of a replacement antenna. Our field day location will be in eastern WA
where we at times tend to get moderate winds (~10-20mph) coming through our
campsite. Thoughts?
>
A couple lengths of pipe with a coupler or lots of duct tape might work.
Armstrong rotator?
A 30 foot extension ladder (you can rent them pretty cheap) is another good
way. You can lash a rotator to it, it walks up pretty easily as long as you
have 3 or 4 people, and guy it with ropes and stakes.
Check your local rental yard.. they have all kinds of stuff that might work
out real well for you.
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