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Re: [TowerTalk] Station Ground

To: "Towertalk Reflector" <>,"Pete Smith" <>
Subject: Re: [TowerTalk] Station Ground
From: "Tom Rauch" <>
Reply-to: Tom Rauch <>
Date: Sat, 15 Jan 2005 13:48:52 -0500
List-post: <>
> > lead cannot be straight.  Despite my use of copper
tubing for the bus bar
> > and heavy copper ground leads from every piece of
equipment, I found that
> > when I tried to use my sound card for contest "voice
keying" I had fairly
> > severe AC hum on the audio, apparently the result of a
few millivolts
> > potential difference between chassis.  I finally cured
it by
> experimentally
> > connecting the chassis of the computer and radios
directly to one another
> > with heavy copper (not through the bus bar).
> Was the audio transformer coupled, or direct coupled?
> Was there a break in the audio ground side? (so that the
"ground reference"
> for the two single ended audio signals was the busbar)

Jim's answer is a good one that most people miss.

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.

73 Tom


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