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Re: [TowerTalk] Station Ground

To: "Jim Lux" <>,"Tower Talk List" <>
Subject: Re: [TowerTalk] Station Ground
From: "Tom Rauch" <>
Reply-to: Tom Rauch <>
Date: Sat, 15 Jan 2005 10:35:31 -0500
List-post: <>
> > Headlights aren't that high in current.
> 130 W plus isn't unusual these days. That's 10A, a
substantial current,
> especially if it's being carried by a "sneak path".

It almost seems like we make extreme circumstances that are
largely if not totally non-issues into answers for general
or worse yet entirely different applications.

The mobile rig has coaxial cables connected to ground (as
does a properly wired home station).

Adivce to maintain a high resistance ground buss to
connection prevent power supply currents from flowing in
that buss becuase something somewhere else might be
drastically screwed up in some extreme circumstance is not a
good answer.

The ground buss connection should be low resistance and
reasonably low impedance if possible. If the manufacturer
fuses the ground lead, then leave a fuse in the ground lead.
Anything else is makes no sense.

> > Starters and alternators ALWAYS ground to the engine
> > as does the battery.
> In theory... Interestingly, my old Datsun 280Z has a
ground cable from
> starter attachment bolt to battery (and that's the only
way the block is
> grounded, because the motor mounts are rubber). And,
another separate ground
> wire to the chassis.

All vehicles have the main ground to the engine block or
other major engine components that are securely attached
(cylinder heads). A smaller ground always runs from the
negative lead to the chassis, to prevent current from
flowing through bearings and other unreliable grounds to the
vehicle chassis.

If that lead through some error (almost certainly by a
goofball at the local repair garage) somehow becomes
unbol;ted from the very large bolt securing it,  the
electrical system in your vehicle will generally be toast
long before the radio has a problem. That's why you use a
negative lead fuse in a mobile when grounding a radio
(stupidly) directly to a battery post connection.

The solution isn't to make the radio have a poor ground.
It's not the smartest solution to make a poor power ground
from the radio just in case some other ground might be

> Certainly I agree, and I'd never advocate a deliberately
bad ground. My
> contention is that there can be unintended side effects
from "install a
> really good chassis ground on that box", and you shouldn't
just wire it up
> any old way.

Nonsense Jim. First this is in the house. A good chassis
ground buss system REDUCES equipment current loops through
low current cables, it does not increase them. Second, if in
a vehicle, a good chassis ground is no issue at all. Good
grief, next thing  we will be telling people to insulate the
mounting brackets and float the coax shield from the
chassis. What a needless worry.

73 Tom


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