A few of you may remember that I was soliciting advice on lightning
protection at my QTH, where I have essentially zero ground conductivity.
I have most of the parts on-hand for a minimal protection system,
consisting of copper straps running radially from the base of the tower.
Of course, my installation delay didn't have any effect on mother
nature's plans. On September 6, I had a (near) direct hit, although I
can't be sure exactly where the strike was. At the time of the hit, I
was in the house, saw the flash, and a sound like a shotgun going off
inside the house. The most obvious visible damage was that the
telephone protector block was blown off the side of the house, another
protector block was blown from a pole about 300 feet from the house
(most parts of that block were never found), and the power line fusible
switch on the pole 60 feet from the house was blown off. Those problems
were quickly and easily fixed by the utilities.
Inside the house, there was no damage to any consumer electronics or
appliances. The ham shack was a different story. At the time of the
strike, all of the shack equipment was plugged into AC outlets, and were
all protected with MOV's. The coax lines and control lines (rotators,
antennas switches) were connected to equipment inside the shack, but
were completely disconnected from the outdoor bulkhead (with a 6 foot
air gap). The outdoor ends of the coax and control lines were sitting
in a covered, water-resistant plastic bucket. Now, here's where it gets
interesting - 95% of the damage came into the shack on the disconnected
control lines. 4 out of 5 rotator controllers were damaged, and both
antenna switches. Both TS-950SDX's has exactly the same (minor) damage
- The quad inverter on the TTL-level computer interface was blown.
Strangely, the TTL/RS-232 converters that were connected to the 950's
were not damaged, nor were the serial boards on the computer. The only
damage to the shack PC was the video board.
So...this is all quite frustrating - having the control lines
disconnected outdoors did nothing to protect the equipment. It looks
like I will need to disconnect at each box in the shack, also. The
MOV's on the terminals of the TIC ring control boxes were blown apart.
I'm guessing that the nearby hit caused a hefty ground surge, which
induced a high voltage on the 40 feet of disconnected control lines (20
feet runs underground inside conduit, 20 feet is laying on the ground).
I don't think the tall tower took the direct hit - only the CATS rotator
on the top was damaged - the two TIC ring rotors down lower on the tower
were fine - not even the Bourne's potentiometers were damaged. Only one
of the connectors on the bulkhead showed any damage.
This has been quite a learning experience. I was able to repair all of
the damage myself, and decided it was not worth filing a claim with my
insurance company - save that for a real event ! I'm quite thankful
that there was no damage to the house, or most of its contents. This
was probably just a wake-up call to prepare me for a real strike on the
tower.
73,
Steve London, N2IC/5
_______________________________________________
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|