I've put up 30' of R25 for about 10 field days with an A4S (or similar)
and rotator. I use a welded "H" frame base plate, square tube (eg 3" x
3/16) is best for strength and ease of welding. The cross of the H is
about 4' long and the verticals 3', so 10' of tube makes one or 2 from
a standard 20' length. Most suppliers will saw to length for a buck a
cut or so and don't require taking the full 20' since a 10' rem is
readily salable..
Then the hinged base plate (I make my own) goes at one cross to vertical
point and three R25 leg stubs get welded on the other for a 10' section
of R25 as the hoist derrick. I don't use a pivoting derrick. Usually
there is a length of mast so the antenna ends up at 37' or so, sometimes
more if I use an 6061 mast. For a few days use a year, painting works
fine and I am partial to the Rustoleum spray cans, one coat of red
primer, one of grey primer and one of a contrasting color last a LONG
time out in the weather. The color contrast makes it easy to see where
there isn't enough paint to do the job. btw welded tube has no mill
scale so painting is easy once the mill oils are cleaned off with a few
paint thinner soaked rags.
I weld 4" long 3/4" black iron pipe sections angled outwards at all 4
corners so 36" long concrete form stakes can be driven thru them as a
basic and under construction base restraint. The derrick is back guyed
and side guyed and the tower has 4 guys to the top, the two side ones in
tension from the start. I use 2x2 x 3/16 angle 24" long as the guy
anchors with a pad eye welded on them below a top 1/4" thick 2" square
plate so a sledge hammer miss doesn't damage the eye. Four are used so
derrick and tower share 3. The guys are low stretch 7/16" braided
dacron, that size for ease of handling, way more than enough strength.
The hoist line is a 3:1 advantage ball bearing block and tackle set with
the same 7/16 low stretch. There is enough leverage and low enough
friction that I can lift the tower plus antenna/mast/rotator alone once
it is walked off the ground a bit by some helpers.
IMO, this is a super safe, always under control way to do a temp tower.
I wouldn't bet on wind survival much past 60 mph, but that is more a
function of the temporary anchors rather than the tower and guys. It
all fits in the back of a pickup. The base is best handled by 2 people,
more due to shape than weight. I've made several of these and left them
behind for the club when I've moved.
Scaling this to 40' of R25 tower probably requires up sizing the base
tube to 4x4x 3/16 which gets pretty heavy and should have upsized guy
anchors. The first implementation of this design used 4" channel, and
that bowed a surprising amount during hoisting until I boxed the web
with a welded on 3/16" plate.
Have fun, be safe,
Grant KZ1W
On 8/16/2016 8:43 AM, Ken Fritz wrote:
Hi all,
I'm looking to erect a temporary tower for CQ WW SSB. I have 40ft of Rohn
25G and an A3S that I'd like to put up. I've seen a number of ways to do
it but I'd like to hear from those who have some experience. What's the
easiest and safest way to do something like this?
I've looked into plenty of options so far but I'd like to keep the question
open-ended to see what you all think.
Thanks!
Ken
N3WAX
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