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Re: [TowerTalk] Station Ground

To: Jim Brown <>,"Tower Talk List" <>
Subject: Re: [TowerTalk] Station Ground
From: Jim Lux <>
Date: Fri, 14 Jan 2005 16:14:37 -0800
List-post: <>
At 02:55 PM 1/14/2005, Jim Brown wrote:
On Fri, 14 Jan 2005 14:37:52 -0800 (PST), N6KJ wrote:

>Why do you need "beefy" connections from bus-bar
>to ground when you use much smaller wire
>connecting the equipment to the bus-bar?

It's all part of fooling ourselves about the basic physics. The
impedance of a conductor at RF is FAR more dependent on its
INDUCTANCE than upon its resistance.  So the only value of that
"beefy" wire is that it might take a microsecond longer to melt in
the case of a direct lightning hit. The smart money is on wide
copper strap, not braid, for lower inductance and longer life.

There's a discussion of some of this in a power and grounding white
paper on my business's website.

Jim Brown K9YC

One hopes that you're not depending on the chassis ground connection of your radio to carry the lightning surge. Presumably, you've got some sort of transient suppression/lightning arrestor/other path for the lightning transient to take to ground, which DOES need a short low inductance path.

However, I think that the "ground lug" on amateur equipment is more in the nature of a "equipment ground" which is not expected to carry any significant RF power. It's sort of an open question whether it could be considered a "technical ground" (as described in your white paper). Since grounded, exposed metal connectors are the norm in the RF world, and I suspect that not much ham gear uses balanced audio with galvanic isolation from chassis, separate chassis grounds might cause more problems than they solve.

(e.g. the "starter motor current through the radio" problem in mobile installations)

However, I'm open to discussion. If someone has a credible scenario where the chassis ground, in ham equipment, is going to be asked to carry significant RF power (where inductance would make a difference), let's roll it out and take a look.

I'll be the first to admit that effective grounding system design is a challenge.

Jim, W6RMK


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