Date: Tue, 21 Sep 2010 11:01:48 -0600
From: "W4ZW" <w4zw@comcast.net>
Subject: [TowerTalk] How to support a large loop?
I?ve used my bow &arrow, spinning reel, and parachute cord to get the
supports up, and have until this past week just tied the antennas up with
enough sag to compensate for the wind. When I put up the Delta Loop I used
small sailing pulleys mainly for ease in adjusting the loop after the two
support points were fixed. I also thought that letting the #14 insulated
antenna wire ?roll? through the pulleys would help with the wind.
I just received my 1000? spool of flex-weave and a spool of 450 ohm ladder
line for my next project. It will be a loop approximately 500-550? with the
lower side about 120? long at 70?, and two spans running up at about a 60
degree angle to three support points up a ridge to Lodgepole pines that will
be about 100? higher than the low end. There will be five support points in
addition to the feedline point which will be fixed.
My question is should I firmly attach the flex-weave to each insulator point
and leave enough slack for the wind, or should I use the sailing pulleys and
let the wire run through them as the wind blows?
## whoa. Are you talking about BUILDING the loop.... or SUPPORTING
the loop in 5 x places....or BOTH ??
## The loop itself would have to handle any ice load. As far as lifting the
loop up 70-100', you could probably use either 1/8" to 5/32" galvanized
winch cable and 5 x pulleys. You could also use something like 1/4 " to
3/8" dacron rope..and 5 x pulleys.
## Is this flex weave you bought 14 ga ?? Is it insulated ?? What is the
breaking strength of 14 ga insulated flex weave ? I think I would be using
something a lot stronger than that. I have been using 10/8 ga RW-90 since
1980 and never a problem with it. RW-90 is just 10/8 ga stranded CU..with
a heavy duty black insulation on it. Standard heavy duty electrical cable,
usually
pulled through conduits, and also used as power feeders down the back ends
of equipment bays at most telco's.
## When I was 400 miles north for 10 yrs, we would get 8.5' of heavy wet snow
each winter..and 2 x ice storms in the same 10 yr period. A buddy across town
with a hb quad tried using TEFLON coated wire for making the loops on his
20-10m
quad. He thought for sure that ice would NOT stick to Teflon insulation.
Guess what,
it does stick to Teflon..and really good too. In fact, ice sticks to teflon
better than reg
plastic insulation, go figure.
## IF you apply dc/ac to try and heat the loop, it will work. Now if you use
Teflon coated wire,
or wire with 75/90/105 deg C insulation on it, the insulation will want to
hold the heat in!
Now you have a helluva time trying to generate enough heat in the copper wire,
such that you
can get enough residual heat THROUGH the insulation....to melt the ice...or
stop it from forming.
## various schemes have been tried for heating the loops. Everything from low
voltage isolation xfmr's,
to small 120 vac variacs, and also reg/unregulated DC supplies..and also
current limited dc supplies.
The trick was to recognize you have an impending ice problem, disconnect the
450 ohm
ladder line from the tuner..then feed power to the open wire line. [ not easy
to do when ur asleep
at 3 AM]. What ga is your plastic coated 450 ohm line? How much heat will it
take, b4 the insulation cooks ?
## we came up with this other elaborate plan, where series dc blocking caps
were to be used
in each leg of open wire line, then a single RF choke [ 12 ga magnet wire
wound on a torroid] wired
to each open wire line..and dc power fed to the loop..via the 2 x chokes.
The idea was you could use the
ant in normal operation..and simultaneously apply current regulated DC voltage
to the loop. This idea was
never tried, but on paper, it should work. The DC blocking caps had to have
low XC on the lowest freq in use,
and not screw up the ant tuner performance.
## with 550' loop, made from 14 ga cu wire, the DC resistance is 1.4 ohms.
14 ga wire will handle a helluva
lot of current, without any heating at all ! Heck, 12 ga cu will handle 15
A CCS..with virtually no temp rise over
ambient. My guess is, you will require 28-50 vdc to generate 20-35A of
current. Factor in the 450 ohm line..
and your dc loop resistance will be even more, so Vdc will be reduced a
little. 560-1700 watts in total power,
which sounds like a lot, but it does not have to be applied for very long. 2
x edged sword. Use small ga wire,and
it's not strong to begin with, but has higher dc resistance,[less current
required] if heat required to melt ice.
Use bigger ga wire, it's stronger, but requires a huge amount of current to
heat it up. You may require more than
5 x supports to keep it up....or use a lot of heat. If it all fails, the fix
would be 10 ga copper clad steel [copperweld], which
has no insulation, and has a higher dc resistance...[ cuz of the steel core].
It would be less prone to breaking, [1500 lb
breaking strength]...and if it required heat, way less current required..[cuz
of the high resistance steel core].
## what might work in fair weather W6 land usually doesn't... when heavy wet
snow/ice is involved.
I know that soon, there will be enough snow to perhaps seize up the pulleys
even though I coat them liberally with grease. Also does anyone have any
experience with radial ice on #14 insulated long spans?
## use quality pulley's, with low temp grease applied. Dry snow is not
and issue, wet snow is, and ditto with any ice loading. What else may
well work, is to apply WAX to the metal pulley. Wax works great on metal snow
shovel's,
doesn't stick at all.
later.. Jim VE7RF
I usually have 1 meter of snow back here, and maintenance then will be an
ordeal.
73's from 10,000'
Jon Hamlet, W4ZW/?
Breckenridge, Colorado 80424
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