In , w_tom wrote:
......Same earthing ground that also connects to AC
electric, telephone, and cable TV wire.....
snip
......... Note an antenna
tower and building each have their own earth ground. Each is
earthed as if it were a separate structure. Every incoming
wire makes a connection to that earth ground. To make the
'system' work better, a ground wire interconnects the antenna
and building earth grounds:
........BAD idea. Tying your ground rods together makes a ground loop, which is
deadly for radio equipment. Use a completely -seperate- ground system for your
radio. Sink a ground rod where the coax enters the shack, tie the coax shield
directly to this rod (don't forget to waterproof the connection), and run your
ground strap and coax as close together as possible. Here's a diagram:
http://www.aimcomm.net/sparky/ground.gif
DON'T rely on your coax shield for a ground strap!!! You can braid a heavy-duty
strap using old power cords and it shouldn't cost you more than a few dollars at
the local thrift shop.
If AC noise becomes a problem, rewire the AC outlets used by the radio so their
ground goes to the new ground rod via the ground strap. Do NOT connect the
neutral (white) wire to this ground!
http://services.erico.com/public/lib...es/tncr002.pdf
Page has moved. Update your link.
Static is irrelevant. A few hundred volts of static will
not damage any properly built radio. You could even static
shock your car radio antenna or a portable radio antenna
without damage. That would be as much as 18,000 volts - and
still no damage.
Many radios aren't built "properly", and most modern radios use JFET or MOSFET
frontends, which are VERY suseptible to damage from static, even from potentials
as low as 50 volts (the breakdown potential of the protection diodes). That's
not the only problem -- static buildup on the antenna causes horrific noise!
Fortunately, the best solution is an easy one: shunt the center conductor of
your coax to ground with an RF choke, something on the order of 1 milliHenry or
larger (even an audio or power supply choke will work). Locate the choke at the
grounding block (see diagram) as any lightning strike will travel through that
choke and you don't want it inside the shack when that happens. On the upside,
it makes a beautiful blob of copper and iron that you could probably sell on
ebay for a decent price (after the smell goes away, of course).
The earthing is required by NEC for human safety AND also
provides transistor safety. If lightning is provided a path
to earth ground via that exterior rod, then it too will not
seek earth ground, destructively, via your radio. Direct
strike lightning damage is that easily avoided.
Wrong. If the coax is plugged into the radio when lightning hits the antenna,
it's safe to assume that your radio will fry. Period. Doesn't matter how much
protection you have. Why? Because lightning packs a few million volts (not an
exaggeration) and will jump just about any gap to ground. But gaps are also
resistors, and since lighting also carries a few million amps (again, not an
exaggeration), you are going to have a SIGNIFICANT voltage potential on your
coax. In fact, the potential and current are so high that the core insulation
breaks down for the full length of the coax and it is literally cooked from end
to end. I've seen it more than once. And that's WITH proper grounding!
Unplug the coax from the radio when not in use. If you want to use a "device",
get one of those big blade switches so there is a big gap, and wire it so the
antenna is shorted to ground when not connected to the radio.
Unfortunately, too many don't have necessary earthing, suffer
damage, and then declare nothing could have helped.
Generations of technical history say otherwise. Its all about
earthing - as even required by code.
Get some field experience. THEN come here and talk about lightning protection.
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