[Fwd: [TenTec] DSP & COMPUTER NOISE]

[Carter Grabarczyk]

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Message-ID: <35B3D14E.6712EBC2@ameritech.net>
Date: Mon, 20 Jul 1998 19:22:54 -0400
From: Carter Grabarczyk <k8vt@ameritech.net>
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To: geraldj@ames.net
Subject: Re: [TenTec] DSP & COMPUTER NOISE
References: <00d701bdb387$43cff160$7aefffcc@n4lq.iglou.com> <35B32A09.E47DBA59@ameritech.net> <35B33B3B.249A@ames.net>
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Dr. Gerald N. Johnson, P.E. wrote:
> 
> While the green and black wires are shorted together at the main panel,

Don't you mean green and WHITE? I believe black is "hot" and white is
"neutral". Major league fireworks or at least instantly blown protective
device if black and green are tied together.

> that's only a DC short and there could easily be RF noise between them
> so a capacitor between them in the offending box CAN be of benefit.
> There can be up to 100 feet or more of loop to be an antenna or to have
> impedance to ground.

True, but not necessarily relevant (see below)


> If they are tied together at the receptacle that's a violation of the
> National Electrical Code and a distinct safety hazard.
> 
Absolutely correct- but I don't think the original poster meant to put
the capacitors in the utility/outlet box/receptacle box on the wall, but
rather was talking about within the computer case. To re-iterate, a
capacitor from the green wire to ground (within the computer case) would
just be shorted, as the green wire is (should be) already grounded  in
the case.

The point of a capacitor from each conductor to ground and ACROSS each
conductor (the black and white) is the old
transverse/longitudinal/common mode noise (or as we say in the phone
company, longitudinal noise and noise metallic). Please note that this
is the way the over-voltage devices in all good AC surge protectors are
wired.

Your mileage may vary...   :-)

Regards,
73/Carter/K8VT

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