[Lowfer] ICOM SoundCrd Interface ...

[John Andrews]

Peter,

> Now a big question. The author suggests breaking a potential
> noise-inducing ground loop by, 1) output the rig's audio into a
> transformer, and 2) coupling the xfrmr to the PC via shielded cable
> that's grounded only at the rig. I suppose this cable is a two-conductor
> type, but wonder if two separately shielded one-conductor cables [more
> common] could also be used?

As long as we're not talking tens of feet of cable, I think the
one-conductor shielded approach is OK.  You are using the transformer to
break the ground path that the cable would normally provide between the
receiver and the sound card. I do this at home, and use single conductor
cable.

Professional audio wiring, where considerable lengths of bundled cables are
involved, is usually done with balanced sources and loads connected by
two-wire twisted cable. The balancing of the source/load is done either with
transformers, or as is now more common, with active balanced circuitry. If a
shield is used, it is grounded at one end only so that there is no direct
audio path through it. The shield offers some protection from electric
fields, and virtually none from magnetic fields. The magnetic field
protection comes from the twisting of the pair of wires. For low level
signals, such as those from dynamic microphones, the shield is important. At
"line" level (50 - 60 dB higher), the shielding may not be necessary at all.
All of this is probably overkill for our ham radio or Lowfer applications.

> Yes, I'm sure it would work, but is it as effective as the pair inside
> one shield.?

As it breaks a potential ground loop, the transformer method is probably
more effective. Just keep the transformer away from strong magnetic fields
(from power transformers, mostly). Mine sits on the floor under the bench.

John A.