At 05:07 PM 8/20/2007, Jim Brown wrote:
>On Mon, 20 Aug 2007 16:50:54 -0700, Jim Lux wrote:
>
> >For folks looking for ways to provide galvanic isolation (which
>can
> >help with pin 1 problems),
>
>You don't need DC isolation to prevent pin 1 problems. All you
>need to do is connect the cable shield to the shielding enclosure.
>What could be simpler (and cheaper)?
IF you actually have a cable shield, and IF there's actually a useful
shielding enclosure.
>This whole myth about the need to separate "RF ground" from "audio
>ground" from "control ground" to prevent "ground loops" has caused
>us lots of un-needed grief.
I would agree.
> So has our reliance on unbalanced
>interconnections.
Even more so..
>There's a section in my RFI tutorial that outlines a very simple
>station layout that virtually eliminates power-related hum and
>buzz on unbalanced interconnections between boxes in our ham
>shacks. http://audiosystemsgroup.com/RFI-Ham.pdf
>
>The executive summary is that in addition to pin 1 problems, 1)
>hum and buzz is due to IR drop from noise current on the shield;
>2) we simply need to minimize the hum/buzz noise voltage between
>that equipment by plugging all of the power supplies into the same
>grounded outlet; and 3) we can further minimize the IR drop by
>using interconnect cables with beefy copper shields. When you need
>multiple power circuits (for an amp, etc.) simply put all of those
>circuits in the same AC quad box.
I was thinking more for those situations where you have long cable
runs, and the common mode voltage difference between the endpoints is
a problem. Also, there's an awful lot of stuff that people want to
use where you're forced to have one of the audio circuit terminals
connected to the chassis (like audio ins and outs for most ham gear)
and, for one reason or another, the two chassis can't be easily
referenced to the same point (i.e. remote controlled box at the antenna).
Jim, W6RMK
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