[TowerTalk] Antenna Survival in Severe WX
Wed, 2 Feb 2000 15:45:41 EST
In a message dated 02.02.00 07:39:17 Pacific Standard Time,
I just got power back after almost 1 week without due to two
severe back-to-back ice storms here in North Carolina. I would like to
share my experience from here and Colorado in the hopes it may save your
antennas in severe weather conditions.
Case 1 - Survival in high winds only:
Align your booms in the direction of the wind with the reflector
facing the wind direction...i.e. if the wind is from the West, point the
antennas East. I speak from personal experience with a KLM 3 el 40 and
5 el 20 at 150' with no major damage in 11 years surviving many Colorado
Chinook winds over 100 MPH and two over 140 MPH (unfortunately my house
did not survive one of those and lost a chimney which was blown into our
family room!) This case is also easiest on the rotator.
Case 2 - Survival in wind AND severe icing:
If you expect severe icing WITH wind, align your antennas
(before you lose power!) with the tips into the wind...i.e. if the wind
is from the North, point the antennas East. This will minimize ice
build-up on the elements which are smaller and probably not supported
by a truss like your boom. It will also minimize the tendency of the
elements to mechanically self-resonate if they are broadside to the
wind. In Colorado, I learned this the hard way and watched several
monobanders self-destruct because I left the booms into the wind,
mistakenly following the Case 1 scenario above, and then lost power
without the ability to turn the antennas.
A very visible demonstration of the tendency for ice to build
more severely on elements broadside to wind can be seen on Beverages.
My only Beverages to survive the latest storm were those that ran roughly
longitudinally in the wind direction. Fortunately I had no major damage
with the recent storm but thought my experience might be useful to some.
73, Bill W4ZV
This was a great Post. One advantage of the Prop-Pitch motor is that a
car battery could have been used to turn it if the AC power went out and no
damage would have occurred to it either from high wind torque loads. Find
out what DC voltage your rotator uses and perhaps with 12 or even 24 VDC, it
could be rotated also.
I just got the idea of running the 110 VA. Heat wires used on water
pipes, inside the boom and elements for the ice loading. Measure the
resistance and see what it is for checking purposes. Use one of those 12
VDC-110 AC converters off the car to power warm up the beam or the power the
rotator if the house power goes out. On Quad DE's fed with open wire line,
run a parallel insulated resistance wire taped to the feedline and quad DE.
Feed the resistance wire only with what ever voltage melts the ice. (There
is one quad literally with resistance wire already). Since the 110 VAC water
pipe heat wires don't come in resonant lengths, just run a Folded Dipole of
insulated resistance wire to length inside the DE (Plumbers Delight
Construction-T or Gamma Match) and down the mast etc to normal power lines.
Insulated resistance wire wrapped on the tower is a good ice removal
technique also inparticular around the rotator and steps. Survival and
ingenuity is the name of the game.
Beef up the center elements and further sections with telescoping tubing
from other beams (even Eagle Hardware if you have to) like Dave Leeson W6QHS
does. It's called "Survival Insurance." For those who survived ice loading
damage, you will perhaps consider the "Insurance Premiums" after and when you
do suffer ice-loading damage and had to replace it. You will be sufficiently
motivated and able to afford it then. With center beef up precautions like
this, I've never had any ice loaded Inverted Vee bends in my yagi's in S.D.
or Seattle. One ice country ham had a 25 KW Commercial Rig (on the job) used
for hamming (he normally ran at 4 KW)--a little more just for "Ice clearing
emergencies"--of course. I like that idea with which it could also be used
for other short "Pile-Up-Cleaning and Melting Emergencies". You see there are
2 kinds of "Pile Ups"--"Hot & Cold". Hmmmm! It had the disadvantage that
it melted from the center out but it was beefed-up. In FCC Court I can hear
it now. "Your Honor I was just clearing Blue/Yellow Ice from Airplanes and
Acid Rain Ice as it stinks and makes pits in the tubing---." My insulated
resistance heat wires idea inside the elements will melt from the smaller
diameter ends toward the middle due to the diameter change--not too shabby!.
The wires also stop the low wind velocity mechanical vibrations when not
enough telescoping joints are not used. That type of vibration doesn't occur
A high powered W6 had a 20M Lo-Z high gain 10 ohm yagi and long T matched,
that ended up with an Inverted Vee DE on a hot day with the speech
compression used then with the long AM transmissions of the day (and my long
sentences). "That's an absolutely true story--I just made it up." No, it's
a true story as told to me. Using around 25 KW (perhaps more-operating at a
Commercial SW station), he had about 50 amps of RF in the center of the DE
and around 20A at the 50 ohm T match points. It was OK in the winter and it
cleared the ice. He switched to a 2" center DE for the summer months. His
aluminum joints were welded also--by RF.
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