I want to clarify my point in saying to AVOID leaving ungrounded feeders
around a shack. If they are disconnected and laid out on the operating
desk, they might move over and touch a grounded metal chassis or case
during a surge event.
The cases should, and are grounded by a proper grounding protocol.
(Three wire AC cords for units containing AC supplies). But the 3 wire
cord should not be carrying the currents that might come in on a coax.
And ultimately the grounds should be joined at the Service entrance by
external ground rods, and adequately large earthing conductors, and even
joined to a halo ground around the building in the ideal case.
You don't want the grounding to be casual, during a surge, to a chassis;
you want a place to plug feeders into a dedicated ground bus that then
is directly connected out side to earth with a large down lead.
High currents through coax can cause the coax to jump or move, and the
free end might flop around and carry a surge to ground through a smaller
conductor, (the radio) than a properly grounded coax. You DON'T want the
end of a coax connector arcing to your other equipment.
Surprised at the statement coax can move? We had a high voltage, high
current plasma generating experiment in the University laboratory. When
we dumped a room full of racks of capacitors into the plasma tube,
the coaxes acting as high voltage cables jumped a couple of feet up and
down although tied off, before crossing the ceiling between rows of racks.
That was a life lesson not lost on me when later I constructed lightning
simulators for testing Army field electronics.
-Stuart Rohre
K5KVH
_______________________________________________
TenTec mailing list
TenTec@contesting.com
http://lists.contesting.com/mailman/listinfo/tentec
|