[TenTec] PS grounding

Edward Crawford w4wvw at msn.com
Tue Dec 9 23:16:02 EST 2003


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 at 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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