At 09:04 PM 10/8/2005, you wrote:
>Rob,
>
>Each installation has different circumstances that can be solved in
>different ways. One of the biggest obstacles I see with a great number
>of hams is they do not really understand what single point grounding
>means. If you put some time into really understanding what is going on
>with that concept you are way ahead of the game no matter what the
>budget is. Just the way things are plugged in at the shack can make a
>big difference.
>
>For example, it is not necessary to have the mains power coming in the
>same place as the coax lines. Just run a power line from a convenient
>place over the where you have your antenna entrance panel. Put your
>power line protectors there. Now run ALL your shack equipment from that
>one power point.
If I interpret what you are saying correctly, you're going to need a seriously
large neutral conductor between the shack and the mains panel... if a strike
occurs to the antenna, and it's looking for "Earth".... if that conductor
can't
momentarily handle about a bazillion amps, it's going to fail in a very spec-
tacular fashion. And then, lightning, being the fickle beast that it is, is
going
off in search of something else betwixt it, and "Earth". Methinks that "some"
of the protection that "single point entry" offers is that, worst-case, the
whole
damned thing might flash-over to, ideally, the ground rod right underneath it.
I have no knowledge or qualifications that lead me to that thought, but, in my
"mind's eye", that's what would occur.
>The protectors for the power can be as little as some large mov's that
>will give some protection. Add some gas tubes of the appropriate type.
>If you want to go a little farther add some series inductors in the
>power line ahead of the mov's and gas tubes.
It sounds like an "old wive's tale", but, it doesn't cost anything to tie knots
between the equipment and the outlet...spikes *hate* inductance...
BTW, it's worth noting that MOV's failure mode is "open".. yer never
gonna know if it craps out, and they DO only take X number of whacks
before they go...much like a guard dog you never knew that you had, and
therefore never knew when it died.
>Look at what is in some of these protection devices. It isn't magic it
>is just proper selection of components.
>
>As far as Polyphaser protection devices go, you really don't need them
>if you disconnect the lines from the equipment and ground the shield and
>center conductor of the coax when not in use.
Assuming that you aren't using them when that first "bolt from the blue"
occurs. That first strike from the cumulo-nimbus is going to hit "somewhere"
and... it's often very far ahead of the visible bottom of the cloud that shows
rainfall. Here in FL the tops of the thunderhead are often *miles* ahead of
the rain. Hereabouts, that's what IS known as the "bolt from the blue"; the
rule of thumb with me is: if you can hear thunder, you are currently in danger,
and have BEEN IN danger...
>A polyphaser device is a convenient way to ground the shield of the coax
>line at your entrance point. You can do the same thing with a clamp
>around the cable or connector, or plugging the connector into a mating
>connector that is fastened to your ground.
If that was true, then you'd just need to ground the tower...assuming a DC
ground type antenna. Otherwise, you'd just have the polyphaser at the base
of the tower, right by that teensy, single, galvanized steel rod.
>The only other thing that the protection device does for you is shunt
>any lightning energy on the center conductor of the coax to ground when
>you don't have it removed from the rig and connected to ground.
Lightning doesn't really care what path it takes, and I suspect it's far
happier
going down both the shield AND/OR center conductor than for me to tell it which
way to go..
>It is more important to connect grounds in the right place than it is to
>have elaborate ground systems.
Ideally... I'd do both. Failing that, undoing all the wires from the tower
to the rig and flinging them out the window is pretty good. But if you
think that that will make lightning find Earth somewhere else, you're just
kidding yourself. Do the best you can, and say your prayers.
73 de
KZ4RV
Randy
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