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House ground layouts
Be sure to read the RFI
grounding page
Stations on the second story or higher have a unique grounding problem. Lead lengths
to the grounding system are much too long to provide a “low-impedance”
RF ground.
Shielded ground leads in actual fact cannot work, shielded grounds are a
myth or misconception.
With a second story (or worse) station, ground rod or
rods (or even buried radials) have
very limited
effectiveness except
on very low frequencies.
Still, we should
probably have or attempt to have an RF
ground when using an antenna feed system with high common mode current, or when
using any
antenna located close to the operating area.
Electrical safety is a separate issue from radio frequency problems.
Electrical safety requires a properly working safety ground path back to the
breaker panel, and is more a matter of wire resistance at near dc frequencies.
Lightning safety primarily deals with how entrance cables are routed and
bonded to dwelling power mains grounds, and usually or often will require a
ground level cable entrance panel.
Curing RFI Upstairs
I’m sure I’m not alone in situations where obtaining a short ground lead is
impossible, but first an important fact! Remember this, because it is important!
A ground to “earth ground” is never required for RFI mitigation. RFI is NOT
caused by the lack of a ground, but rather by a lack of proper bypassing or
shielding. RFI is aggravated by poorly installed or designed antenna systems,
and sometimes we have no choice in this matter. For example even with all my
land and spread out antennas, I still have a tower close to my contest barn. An
80-meter antenna and ten-meter antenna on this tower are only about 80 feet or
so from the upstairs contesting room. With 1500 watts, and especially with the
high gain 40-foot boom ten-meter antenna pointed right into the radio room,
considerable common mode currents can be induced on shack wiring and equipment
cabinets.
Installing a ground plane at room level is the most practical way to minimize
RF in the above-ground shack.
This ground system
or more correctly counterpoise can be strips of
foil laid under the
carpet, a screen, or something under the floor. The conductive wide strips or
screen should connect
back to a wide
station equipment
ground buss. Stained-glass hobby suppliers sell adhesive backed copper foil that
works very well, and is solderable. As an alternative to copper foil strips, a
metallic screen or
grid of wires at
room level can be used. Whatever is used, be sure the electrical connections
between wires are good.
This type of counterpoise system makes
the entire room, including the operator, “rise”
in voltage to match
the equipment
chassis voltages. It also
disperses or spreads
the current and
voltage around, reducing intensity of localized electric and magnetic fields.
The feed line, if it has common mode problems, should
be kept away from
the operator and
other equipment. The feed line should exit the room with as short a path as
possible.
A grid of foil does not need to be too dense. Below 30 MHz, spacing foils one
to two feet apart is nearly as good as a solid sheet.
If you can’t do that, then sometimes a 1/4 wave counterpoise along the
baseboard will work.
The outside ground is only for AC mains safety.
also see desk grounding
My actual Application
My application is a little bit atypical, because I have quite a few antenna
feed lines and radios to deal with. I have a “contest barn” with an upstairs
radio room. There is one tower within 75-100 feet of the barn, and the lowest
ten meter antenna is not too far above the room level. Even with 1500 watts and
a six-element antenna pointed right back at the operating position, there are no
RF problems. Here is how I handled RFI (and lightning) problems in my contesting
barn:
Entrance panel is bonded to the electrical entrance. This is at ground level.
Bonding at this point is primarily for lightning protection.
Strapping from the copper wall panel to the entrance panel is short, and I
cleaned the paint off the box under the screws and tinned the cover. In addition
the copper wall panel extends under the panel edge and is bolted to the breaker
panel wall.
The various antenna switches can be quickly
patched in for
special radio and antenna setups
in the operating room. Three contesting transmitting antenna cables and one “boat anchor”
transmitting antenna
cable come down
from the four individual desks in the operating room above.
Sixteen or more trunk cables
exit to various
towers or antenna
locations.
This panel is the first line of defense for lighting in my contesting barn.
All cables eventually going upstairs are bundled or parallel after they leave
the ground floor entrance common point:
All cables are parallel. This “closes the loop” made by long leads and
ensures cables do not have much voltage differential from lightning.
The wide very heavy heavy braiding going upwards is not for lightning. It
ties the counterpoise system in the ceiling (contesting room floor) into other
grounds.
While flashing would be better, I had thousands of feet of braiding and it
was much easier to make bends.
Because I have old boatanchors with two-wire cords, and because I use ground
leads as power returns for things like antenna switches and controls, I want
good low resistance low frequency paths. Lightning is mitigated at the entrance,
not by these leads to the contesting room “counterpoise”.
Some cables enter plastic rain gutters that I use as a cable tray. The
gutters allow quickly pulling of new cables and keep cables bundled or parallel
for lightning and RFI safety. Metal trays or large conduit would have been better yet,
but was cost and time prohibitive for me.
Left silver outside tray= shielded control cables (48 pairs)
Left tray= receiving and receive switching
Center bundle= computer and telco
Right tray= transmitting and TX antenna controls
Ground strap. This strap is part of the “grid” of wires that establish a
ground below the floor.
The orange and yellow wires are the power line feeds to the radio room
If you look at the lower right corner, you can see the wide ground straps
that are being installed to form a closed screen or grid below the radio room’s floor.
The entire ceiling, which is the floor of the radio room, has braiding that
forms a large counterpoise.
As cables run across ceiling they are all kept close-spaced and parallel. I
group them by function, such as receive cables and control cables, high power RF
cables, AC power lines, and computer or telephone cables.
Even the metal flashing that is part of a drip edge for the siding, seen just
above the horizontal 2X4, is bonded into the grounding grid at multiple points,
as is the frame for the garage door.
Immediately below the desks, I have another common point. This is for
amplifier power distribution and receiving antennas. Wiring here is just being
installed. Note the very large ground straps that also form a “grid”.
These two wall panels are for receiving antennas and control cables. The
breaker panel to the left is 240 volts for seven 15-ampere amplifier outlet
feeds.
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