Hi All
I thought I would follow up on my post a couple of
months ago on lightning damage. I think I will back on
the air in a limited fashion within the next few
weeks, but the strike damaged much of my shack
equipment, and it will be a long time before
everything is repaired. The insurance company has been
very good, but my homebrew equipment generally can't
be replaced with commercial and time is the greatest
enemy.
I apologise for the length of this post but hope
others will find this useful.
The major damage was caused by a surge travelling down
the OUTER of the coax hardline feeding my remote
beverages. I have not been able to find any place
where a direct strike occured, so am assuming that the
event is linked to ground potential being dramatically
different at different points along the cable. There
are two main remote beverage feed points with boxes
containing switching electronics, about 1500' and
2000' from the shack. Of course all the electronics
was fried, but what was interesting was that the
ground connections to the coaxes were evaporated. As I
went towards the shack things got worse, and at one
point the control cable (4 wire armoured telephone
cable) was melted. Although I believe that it was the
outer that gathered the strike, a big voltage was
presumably induced onto the inner. Unfortunately,
there was significant interconnection of power
supplies in the shack and this fact allowed lots of
equipment to also be fried.
I have changed the following and would appreciate
comments:
1. The system was physically grounded at each remote
point - just a 2m copper pipe buried horizontally
under the few cms of soil in this very rocky area. Now
that is only used for the beverage grounds and
supplemented by several radials. The feed coax is now
only grounded at the shack.
2. The control wire armouring was previously
disconnected, but is now joined at each switch box to
the coax outer/0V DC.
3. I already had relays at each box which disconnected
the control wires and grounded the electronic inputs.
I now also have relays which disconnect the power
(sent along the coax inner) and ground the electronics
V+ inputs. In both cases when there is no power
applied the relays drop out. Some of these relays had
contacts welded after the strike.
4. I now have relays where the control wires and the
coax enter the shack which totally disconnect both
sides of the coax and the control wires when the shack
is not powered up.
5. I already had electronic surge suppressors just
about everywhere - they were all fried by the strike -
now they really are everywhere! I am however very
unconvinced of their value in this sort of case. The
telephone line was also hit and that destroyed the
Bell fusebox, the commercial lightning protector, a
fax machine, a telephone and the computer dialup
modem. I can't see how an electronic surge suppressor
can protect better than a relay which totally
disconnects a line - or am I wrong?
I'm not expected any more major lightning storms until
next summer, so I guess I have some time to change
things, but should I let the remote electronics float,
as now, or was I better with the previous arrangement?
Looking forward to meeting you on the air again soon.
73 Roger
VE3ZI
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