> The ONLY place an audio cable should be grounded is at a
> single point in the system. This is true for audio outputs
> or inputs.
> At times we get away with running unbalanced or balanced
> audio lines with shields grounded at both ends, but it
> actually is a very bad idea on line level or less lines. It
> even can be a problem with speaker or high level lines.
> I've handled numerous "RF in audio" complaints that weren't
> RF at all. They were DC ground loops from power supplies of
> SSB rigs caused by microphone inputs having external
> grounds. Good low resistance station ground busses reduce
> such problems, but the real problem is having ground paths
> at each end of a shielded (or unshielded) audio cable.
Life isn't made much easier by having virtually all consumer oriented
equipment (which includes most ham gear) use single ended audio, and the
lack of ready availability of shielded cables with the shield connected only
at one end.
I note that a couple weeks ago, I was down at the local musical instrument
store, and there was a whole wall full of assorted transformers/isolators,
balanced/unbalanced adapters etc.. This kind of thing is essential in the
performing musician's world.. long cords, low levels, lots of sources of
interference (phase controlled light dimmers are audio evil!), etc. They
weren't cheap, but neither were they hideously expensive.
On a related audio note, there's a lot of very interesting and inexpensive
equipment available for muscians to interconnect with computers that might
be quite useful in a ham shack. One of those nifty "digital music control
surfaces" might make a dandy rig controller... nice big knob (normally used
for shuttle/jog, but also would work for frequency control or antenna
rotation), switches, sliders, etc, all that generate USB or Midi events.
LCD displays, etc. as well. And, of course, (balanced) audio inputs and
See: http://www.mscomputer.com for "Self Supporting Towers", "Wireless Weather
Stations", and lot's more. Call Toll Free, 1-800-333-9041 with any questions
and ask for Sherman, W2FLA.
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