There are contradictions in AC vs. RF grounding. One has to try to tie the
two together without creating long paths for RF. Long, in the sense of
fractions of a wave approaching quarter waves.
There are issues to what makes a ground loop. Any dual wire path where the
ends come together but the dual ground wires are somewhat separated forms a
magnetic loop coupling to and from any source of stray AC. This might be
using a braid between chassis but then a different path for the DC negative
lead. If the braid is very long at some RF band in use, you could have an
RF ground loop as well. Wide flat copper strap is even better than braid
in RF low impedance.
You could, if your DC conductors are single wires, form a magnetic loop at
power frequencies. Twisting the heavy conductors that are your DC path is
always a good idea. Running the braid with them or using shielded heavy
power cable is another good idea.
The DC connector on any rig should be adequately sized. Over time, we have
seen some marginal Molex connector applications, mainly thru the oxidation
of the solder coated type of contacts used. The ground braid should not be
making up for such a fault. Another line of radios for years used banana
plugs for power connection. They were on the hairy edge of adequate current
capacity, but they did split the load among two plugs. A standard banana
plug is rated at 15 amps, and they were probably pulling 16 amps on SSB
peaks. Duty cycle saved them from overloading problems.
Have adequate wire gauges to supply the radio with full voltage, to assure
dependable power operation. I usually use no less than 12 gauge for the 20
amp, common 100 watt radios. The distance you have to run to supply in a
mobile application may dictate larger conductors.
Sadly, few amateur publications adequately separate the various purposes of
grounds, and many hams waste time trying to drive 8 foot rods in rocky soil,
or despair of having safe installation and do nothing until they are zapped
by Nature. They may drive a rod thinking that will take care of the quarter
wave "all band" trapped vertical when it would improve their RF efficiency
greatly to use some counterpoise or radial wires, especially elevated ones.
Many studies have shown that big returns are gained from going to 16
radials, if no better antenna is in use than conventional monopoles.
The safest thing is to unplug all power leads and antenna leads from radios
when your shack is not in use. It is just a routine you need to learn, to
disconnect at end of operations and to reconnect before going on air. Can
save costly installations, if you are unplugging outside the shack at the
entrance of your feeders, and hopefully you also have other paths protected
by disconnects there in the ideal case. Don't overlook telephone, computer
and modem lines if those end up on the operating desk or next to it. The
lightning bolt that just traveled 10 miles across the sky will not respect
the four feet between your computer case and the radio antenna feeder, if
the computer case is grounded well as it should be, to the AC power ground.
RF in the shack often comes from use of unbalanced or random antennas. The
Marconi, shorty mobile loaded schemes, and other single element radiators
can lead to problems as can other end fed antennas. The lowly dipole,
even if you cannot feed it with perfect symmetry of angle (feeder to
radiating pair of wires), will lessen your stray RF issues, if at an
adequate height to function as a dipole. Throwing out a piece of wire may
work in locales with good moist ground, but in two QTHS with poor
RF ground character, I have failed in getting good radiation from Marconi
antennas that ranged from 30 to 400 feet in length. In both cases, it was
lack of adequate RF grounds that kept performance down. My QSO rate went
way up upon switching to a dipole. The antenna is part of a system that
includes the ground conditions, location of the radiator, height, direction,
etc. Overlooking what nature provided (or not provided), may limit your
success.
-Stuart K5KVH
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