I believe the person who originated this thread said one of their supplies was
an Alinco DM-330.
My Alinco DM-340MV supply (35 amp max; linear) has no ground on the AC line
cord.
One of the chassis screws on the rear panel is designated as a ground.
What is the rule of thumb to follow in that situation? Is it a safety or
performance issue?
I have never used an RF grounding system in the shack and have never had
reports of RF on the audio.
I know Ten-Tec specifies all their equipment should be tied together to the
ground lug on the supply,
and the supply tied to the station ground. All the T-T supplies I have are
grounded thru the AC cord.
Seems like this dual ground would, as you say, create a ground loop and a
probability for problems.
I have tried bonding the equipment to the ground lug on the T-T supply just to
see; could not tell
any difference in performance one way or the other.
I guess my question is, am I confused or what? <g>
73. Ed/w4wvw
----- Original Message -----
From: Stuart Rohre
To: tentec@contesting.com
Sent: Tuesday, December 09, 2003 2:44 PM
Subject: Re: [TenTec] PS grounding
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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