On 29 Oct 2002 at 14:24, Roger Parsons wrote:
> 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.
> (snip)
> The major damage was caused by a surge travelling down
> the OUTER of the coax hardline
> (snip)
> 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?
>
> 73 Roger
> VE3ZI
>
Hi, Roger-
It sounds to me like you might get a lot out of
PolyPhaser's book on the subject- it is called
something like "The Grounds for EMC (EMP?) and
Lightning Protection". They make some of the best
lightning arrestors on the market, so I gather.
http://www.polyphaser.com/
(I have no financial stake in this company)
One concept that particularly stands out for me
is the absolute necessity of a 'bulkhead'
approach to grounding, i.e. single-point grounding
at the station entry location.
Good setups route *everything* through a common
metallic (Cu) panel and all lines, coax and control,
run through arrestors. Also a *perimeter ground*
is supposed to be very important for conducting
a big pulse around rather than through your station.
Somehow those relays sound *awfully* shaky to
me. I bet a big lightning pulse just laughs at them
and jumps the gaps- despite lines being grounded
through relay contacts at the time. No substitute
for a voltage-limiting element with a hefty current
spike capability, as I understand it. That would be
gas tubes or similar, the sort of thing that they sell.
MOVs are problematic for radio installations, and
are probably best deployed only to protect the
primary sides of our power sources. We do see
them used some for front end protection in modems
as well (sometimes). But we also see gas tubes
and semiconductors in this role.
The more I read about this subject, the more I am
impressed as to the difficulty of really doing this
design and installation job right. My setup is
probably not right. And lightning can be *so* sneaky
and destructive- it can enter your station via
power or telephone lines even though you have
disconnected all coaxes and control lines and
thrown them out the window (or use a patch panel
like me). :o) The importance of a *single* ground
for *all* conductors cannot be overstated- and few
of us actually have that! Read that book and see...
73, David K3KY
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