Good info from K4TAX.
Personally, over the last half century plus of playing with RF I have always
figured the RF should be inside the TX/tuner/coax, etc., and any and all
attempts at an RF ground should be done between the TX and the antenna. And the
closer to the antenna the better. If the RF isn't confined - thinking about
one 20 KW RF heater/sealer I dealt with many years ago - the operator is
likely to have problems. But the solution to that problem is to stop the leak,
not shunt RF to ground.
Of course, twinlead of any and all sorts is a different matter but unbalance in
an open wire fed system should not occur, and any that does occur should be
taken care of automatically in the line to antenna matching network.
Now, the NEC requres a power ground under the "meter base," "meter loop," or
whatever sort of box the electric service connects to. In my experience that
ground connection is a hangover from the times when most houses had cotton
covered wiring and a few bare bulbs hanging from the ceiling. It's usually
adequate for about three amps and pitiful when the load becomes more unbalanced
than that. Or when those big sparks are trying to go to ground and that high
resistance ground leaves them looking for a better path through everything in
the house.
Since I have looked into the corpses of a few thousand lightning hit and
unrepairable devices I prefer something with a little more current carrying
capacity.
Here - there's three double extended ground rods going down over 20 feet,
connected together with 32 feet of half inch soft copper refrigeration tubing
brazed to the rods. Along with the mandatory run of #10 from the power line
neutral to the center rod. Of course, that chunk of #10 is paralled by a piece
of 2/0 copper so there is a pretty low resistance electric service ground;
along with a "whole house surge protector" in the box. The system seems to be
working since I have had no damage even when most of the houses in the
neighborhood had severe lightning damage.
The tower is also fairly well grounded. Taking some advice from the local two
way guys I sank an 8 inch hole to below the mininum water table through the
bottom of the base excavation. Two sections of "drill stem," essentially 6"
schedule 80 steel pipe, with ground lugs welded to the top provide a
substantial ground rod for the tower; and substantially stiffen the tower
structure as well. "Starter cables" from the NAPA store provide a low
resistance path from the tower proper to the ground in the center of the tower
base.
The coax runs through tower mounted ground blocks, and both the coax and rotor
cables go through lightning arrestors mounted on the drill stem. From there
they run to a grounded bulkhead at the shack. There are reduntant arrestors on
all incoming lines at the bulkhead, and a "line isolator" inboard of the
bulkhead to discourage any remaining energy from coming visiting. And yes,
there is a piece of #10 from the bulkhead to the power line ground and another
to a tower base bolt.
With more than 90 "lightning days" a year I'm not surprised the tower takes a
hit a couple of times a year. My neighbors are good about telling me about it,
too. I think the nonogenarian lady down the hill sits in her window and stares
at my tower every time it thunders! However, I have had NO damage in the shack
of any sort whatever. Now the first remote antenna switch was another matter.
Anyhoo, that's my war story on the subject. And from observation, if you can
put one in a "Ufer" ground is far superior to any ground rod - and backing a
Ufer ground in the slab up with a halo ground around the protected building is
even better.
73 Pete Allen AC5E
--
Never squat with your spurs on
> This is excellent. I've believed for many years that most amateur ground
> system present more of a hazard to equipment than a help. Manufacture's
> manuals all recommend a "good ground" however but this could be just a CYA
> thing. Connecting the tower and coax shield grounds to your power line
> ground isn't often easy and is seldom done. My Electrical entrance is
> grounded to one old, beatup looking piece of conduit driven outside many
> years ago and it's effectiveness is questionable. Running a large wire
> between the coax of my dipole and that ground rod would be very difficult
> and very long.
> One thing I've done over the years is to use a large knife switch to
> disconnect and ground my antennas when I've not on the air. The station
> ground is not connected to the rig at all and the antenna ground rods are
> used only to ground the antenna when I'm away. Somehow I got the idea that
> having that big wire over the house, connected to ground acts as a constant
> path for static buildup and may even help protect the house.
> Having 2 ground systems, one for the electrical and one for the rig is
> really asking for trouble and I suppose the interconnecting wire is the
> cure. I'm going to revisit this in my shack and see if it can be done.
>
> Steve N4LQ
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