This could be as inflammatory as the lightning topic,
and I sense we're getting wrapped around the axle.
Having written several white papers on grounding and shielding
in instrumentation, and having been a ham since 1958, I think I
have something to contribute here:
First, let us separate out the functions of ground, and
examine each.
1) power line safety. Provided by your line cords. Meets NEC,
but insufficient for station operation. See #3.
2) Lightning protection...already well covered...this happens
outside the house, not in, at earth level, not en route to the second floor.
We've already treated this in extremis in the past week.
3) Chassis Equi-potential at RF in the shack
4) "ground" for the antenna system.
Only 3 and 4 merit further comment.
3) All chassis in the station should be connected together with
the shortest possible strap or braid, such that there is one common
point defined as 'ground' in the shack. This is station equi-potential,
not 'ground'. In my case, it's 3" strap which runs along the back of the
table,
and to which short chassis braids are bolted. I do this to minimize the
possibility
of common mode currents on coax runs raising a chassis above the rest of the
equipment.
It's also a safety against a failed electrical safety ground. I've had
three line
cords fail in my career.
If you're feeling frisky, you could run 2 or 3" strap down the outside
of the house, and tie it to a more extensive ground system. BUT IT WON'T BE
AT GROUND POTENTIAL FOR ANY FREQUENCY WHERE THE LENGTH OF THE STRAP IS .25
WAVELENGTH, OR AN APPRECIABLE FRACTION OF SAME. i.e. 10, 12, 15, 17, 20
meters.
I don't do this...I don't think it will help much. stay tuned...
4) "Antenna Ground" As a concept, this is much more complex, because
antennas
are more complex.
* I run all antenna feeds in coax. I GROUND that coax as close to
beneath
the antenna as I can, and I use ferrite rf chokes to get rid of common mode
currents on the outside. I run all coax on-ground. I also ground the coax
AGAIN at the
house perimeter ground (if available), and use another rf choke at the point
where the coax
leaves earth to go upstairs. If no perimeter ground exists, I make a ground
point
with several rods linked by strap, the center of which is just beneath the
2nd floor shack.
I want the path from ground UP to the shack to be high impedance for
anything
riding on the outside of the cables. All rotor and control cables go to
that point,
and are choked before going upstairs.
All cables go aloft as a strapped bundle...no dangling, drifting wires.
If
you've
elected to run a vertical ground strap, tie-wrap the cables to it.
* If an open wire feed is used, it must be balanced, and not voltage
fed.
That is...an 80m dipole on 80 is fine fed with 67' of OWL. But that same
antenna on
40 is going to be hot as hell at the feed end, presenting something like
2000 ohms load.
This means that multi-band use of an 80m dipole is at best problematic in an
elevated
shack.
* Stay away from end-fed or single-ended antennas, like LW's or
Windoms.
In that
case, your "ground" is the other end of the antenna...the tuner is in the
middle...and
things will be most interesting, indeed. Particularly if you haven't forced
chassis
equi-potential, as in #3. Not only will you not be at 'ground' potential,
you'll be
driving power into the 'ground' path.
* Off Center Fed Dipoles and "Carolina Windoms" are workable, but
require
common mode
chokes on the feedlines. I've used both successfully, and will continue to
do so.
In my case, I use the earth end of my cable run, at the house, as a "single
point ground".
All cables which go into the shack are located on a common panel, such that
I can disconnect them,
in the event of severe weather. That common panel is usually located at the
point
of entrance, and is closely connected to the station equi-potential 'ground
plane'.
There is a similar panel at the single point ground, at earth level. If
'ground' strap is
run, it bolts to each of these panels.
I hope that adds useful insight, rather than heat and smoke.
Also, I commend to your attention the treatise on Second Floor Shacks
written by Jim, at
Radio Works. <radioworks.com>. He knows whereof he speaks. I have no
commercial interest
in his business, other than to buy stuff from him occasionally.
N2EA, Jim
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