I can't offer much in the way of suggestions for the tower, other than
I'd give it a good visual inspection, including cables and pulleys. I'd
also check the pulley rotation for rough spots, but remember that few
bearings can set long without developing rough spots, or "bumps". I can
offer a few notes on lightning.
I'd not expect lightning to cause much in the way of dissimilar metal
problems. It's both too quick and too powerful to respect something like
that.
However there is lighting and then there is lightning. The power in
lighting bolts varies tremendously by several orders of magnitude.
There there are the so called "super strikes" that are many times more
powerful than most lightning. They are not only more powerful than
regular lightning, the main power is down instead of up and they are
usually associated with "sprites", which are seen well above the tops of
the clouds and extending into space. These are the ones that blow holes
in big airplanes and are very destructive. A well laid out ground system
that would eliminate damage from garden variety lightning may lessen the
damage, but there is little that will protect from these.
The induced voltages and currents from the stronger near by strikes can
be quite damaging them selves. Where it will go is difficult to predict.
I've seen it strike tall towers and get off half way down getting off
the tower horizontally and curving down to the ground a few hundred
yards out and yes, it can crack, split, or even blow apart basement
walls some distance from the strike, some times with no apparent reason,
or direction.
My tower has been struck 17 times that I know of since it went up, yet
I've had no damage and the equipment was all connected most of the
times. I have a network of over 600' of bare #2, cad welded(TM) to 32
or 33 8' ground rods.
My antennas are connected to two separate stations that are on different
electrical feeds (The shop and house have different addresses) although
the ground systems are all tied together.
73
Roger (K8RI)
Jim McDonald wrote:
> My US Tower HDX-589MDPL, which is motorized with the remote control option,
> recently took a very large, direct lightning hit. The antennas on it at the
> time were (and still are) a Diamond 2M/450 vertical at the top, a 2L M2 40,
> a Force-12 Delta 130 30M rotatable dipole, and a 4L (+26M directors) SteppIR
> at the bottom.
>
> There are ICE lightning arrestors on the coax cables at the bottom of the
> tower and a large grounding panel with arrestors on every coax and control
> line at the house entrance. I also have lightning radials with ground rods
> every 16' going out from the base of the tower and the tower/radial ground
> connected to the entrance panel, the telephone, and the electric ground
> rods. With one exception, all ground rods with connected to #4 wire with
> Cadwelds, and the #4 wires were connected to each face of the tower with ICE
> ground clamps on the cross bracings.
>
> The lightning apparently struck the tip of the 40M reflector, which is bent
> into a curl, and that element had the Phillystran linear-loading wire
> support break off. The large box of relays for the tower remote control
> exploded. Inside, the Yaesu rotor control, the SteppIR controller, and my
> K3 were damaged. The condition of my Alpha 87A is unknown, though the power
> supply turns on, but the RS-232 doesn't work. I don't have another radio to
> test it. The 2M and 450 radios are fine; I would have preferred them to be
> sacrificed.
>
> I haven't climbed the tower yet, but measurements from the ground indicate
> the remote switch, rotor, and SteppIR are damaged.
>
> My question concerns the US Tower repairs. US Tower says the cable and all
> pulleys need to be replaced and the tower inspected - all necessary to
> ensure structural integrity. The cables look to me to be undamaged, and the
> pulleys seemed to turn, as I didn't have any difficulty lowering the tower
> with a US Tower emergency hand crank. BTW, anyone with a motorized tower
> should consider getting the emergency hand crank in case the tower has to be
> lowered when the power if off.
>
> Obviously the relay box has to be replaced. US Tower's price to travel from
> Kansas to the Chicago area and do the work is unreasonably high, in my
> opinion, and they haven't given me a technical explanation on why the cables
> and pulley need to be replaced to "ensure structural integrity." They said
> that the inspection could be performed by another AWS-certified welder, but
> I don't know of any locals with cable or pulley replacement experience.
>
> Any thoughts on the need to replace the pulleys and cables would be
> appreciated. Yes, I have homeowners' insurance, but they also are going to
> ask why.
>
> Oh yes, one more question. After the strike, my unfinished basement walls
> have several cracks that we never noticed before. The house is five years
> old and is about 50' from the tower at the closest point. Has anyone
> experienced that? I haven't been able to find any literature on the
> subject.
>
> Probably related, the water well is about 100' from the tower, and the water
> was cloudy for two weeks afterwards. The well guys said that the aquifer
> can get disturbed in a lightning strike, causing cloudy water.
>
> I have pictures at
> http://picasaweb.google.com/jim.n7us/LightningStrike100405 . (The crawdad
> was magically transported to our drive; the nearest pond is several hundred
> feet away.)
>
> It's a safe assumption that my wife isn't enthused about ham antennas these
> days.
>
> Thanks for any information!
>
> Jim N7US
>
>
>
>
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