Both power supplies should be properly grounded thru their AC line cord
third, green wire, connection. The second ground lug is for cases where
the AC ground is RF "long" and there is some RF problems but this only
works, if the alternative ground is RF "short" ie less than a quarter wave
at the bands in use. Otherwise, you have created a ground loop.
Many switchers are isolated and have a Faraday cage shielding system, to
enclose any fields they produce. Their lower frequency emanations should be
grounded by the shield bond to the AC ground cord, but this again, is not
guaranteed by the ham shack layout. Much of the AC grounding with extra
grounds for our RF systems does not make sense.
Most of the time, if you are not having a problem, and are using properly
working 3 wire AC connections, (verified with an AC ground tester), don't
tempt fate by adding extra grounds of probable poor RF quality. It is hard
to get a low impedance RF ground, unless the shack is on the ground floor
and an outside wall or near to known metal water pipes as in a basement.
With balanced antennas, (beams, doublets, dipoles, vertical dipoles) you
should not need extra RF grounds. A safety static discharge ground on the
antenna is useful in case of lightning induced transients; but the balanced
antennas have their own complete reference electrode in the second dipole
element. With some ground mounted and bottom fed quarter wave antennas, if
you cannot get 16 good radials or you have very poor ground conductivity,
you are better off putting in quarter wave elevated radials, or a
counterpoise wire at least, to keep RF out of the shack. In cases where RF
has entered the shack and is on equipment cases, you can add quarter wave
insulated wires around the baseboards to provide the counterpoise and lower
the induced RF levels where you do not want them.
-Stuart
K5KVH
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