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Re: [TowerTalk] Station Ground

To: <>
Subject: Re: [TowerTalk] Station Ground
From: "Jim Lux" <>
Date: Sat, 15 Jan 2005 06:17:54 -0800
List-post: <>
----- Original Message -----
From: "Keith Dutson" <>
To: <>
Sent: Friday, January 14, 2005 9:22 PM
Subject: RE: [TowerTalk] Station Ground

> Would you care to define "ground loops between pieces of equipment"?
> Here are my thoughts:
> An equipment ground loop is a condition where potential (voltage) can be
> measured between the chassis of two pieces of equipment.  If this voltage
> under .0001 volt, is it still a ground loop?  Perhaps.

The classic ground loop problem is in single ended low level audio signals
(Where microvolts count), and where the dominant interference source is 60
Hz magnetic fields inducing a current in the loop.  Another source of
problems is the parasitic capacitance (winding to core) in the power
transformer coupling some AC into the chassis. Balanced systems (which were
addressed in the white paper) help this kind of thing.

In a multi operator station where you're transmitting at the same time as
receiving, one might have a ground loop sort of problem.  Push a kilowatt
through a piece of coax, and there IS some voltage drop in the braid, so the
Tx end of the coax will be at some (small) RF voltage relative to somewhere
down the line (at the panel passing through the wall?).  If you had a
receiver  that was also connected via coax to the panel, and there was a
separate chassis bonding wire from Tx to Rx, you've got a loop.  Might cause
problems, might not?  [obviously, in this case, a star grounding system,
where the ground wire from the Tx went (by itself) to the panel, and
likewise the bonding wire from the Tx went to the panel, would solve the
problem, if any.

I've also had ground loop problems in low level RF systems where clock noise
from one module would propagate into the RF path.  To a digital designer,
hash of 0.1 volt on the 5V power supply (and ground) is no big deal.  Even
if it's attenuated by 60 dB (down to 100 microvolts), that's a pretty big
signal to a sensitive receiver.

Jim, W6RMK


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