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Re: [TowerTalk] Ground Windows

To: "Tower Talk List" <>
Subject: Re: [TowerTalk] Ground Windows
From: "Jim Brown" <>
Date: Fri, 28 Jul 2006 08:29:19 -0700
List-post: <>
On Fri, 28 Jul 2006 14:19:19 +0000, Phil Camera wrote:

>Also to this SPG, you will run your shack equipment ground out to 
>it and also connect the SPG to your tower ground and your 
>electrical service entrance ground.

Yes. But:

There is considerable misunderstanding (and junk science) 
regarding so-called "single point grounds." There is a tutorial on 
power and grounding on my website. While it is specifically 
written for pro audio and video, it is directly applicable to ham 
installations as well. 

In general, single point (often called "star") grounding provides 
the greatest noise immunity low frequencies (below about 100 kHZ), 
and multipoint grounding (often called "mesh") grounding provides 
the greatest at radio frequencies. 

A connection to "earth" is important ONLY for lightning protection 
(and it is VITAL for lightning protection). In general, for 
lightning safety:

1) Multiple paths to "earth" are better (that is, safer) IF they 
are all bonded together by a low inductance connection. 

2) SHORT paths (that is, low inductance) are better. That's 
because the energy in lightning (and other power system faults) is 
broadly centered around 1 MHz, with lots of energy several octaves 
above and below 1 MHz. 

3) ALL earth connections must be bonded together BY LOW INDUCTANCE 
paths. This includes the power system earth bonding, telephone 
bonding, cable TV bonding, ham antenna bonding, TV/FM receive 
antenna bonding, satellite TV antenna bonding!  

4) Ideally, these bonds should be outside the house, but often 
this isn't practical. For example, a power service entrance may be 
on the opposite side of the house from one or more of the other 
wiring that needs to be bonded. 

5) Low resistance (that is, big copper) is better ONLY because it 
can carry more current in a strike before it vaporizes. Inductance 
is what limits current (and safety), not resistance. 

6) AVOID shunt-mode surge protectors (MOV's) on branch circuits. 
These nasty devices that are, unfortunately built into almost any 
multi-outlet strip nowadays, "work" by shoving the lightning 
strike into the protective ground (green wire). This raises the 
voltage of the green wire AT THAT OUTLET, which can destroy 
equipment powered at other outlets and connected via low voltage 
wiring to the "protected" equipment. 

For SAFE surge suppression on branch circuits, use only SERIES-
MODE suppressors. SurgeX and Brick Wall are the only ones I know 
about, and license the same patented circuit. SurgeX is built for 
the pro audio market, where big dollars are invested in equipment. 
I use them on all my office equipment, computers, audio gear, and 
ham equipment. They aren't cheap. 

The ONLY safe place for SHUNT-MODE surge suppressors is at the 
service entrance, where they raise the entire "ground" bus above 
earth by the same voltage. (this is the so-called "whole-house" 
surge suppression). 

The purpose of all of this is to minimize the voltage between 
different parts of your house wiring and systems in the event of a 
strike. INDUCTANCE is the major factor that increases the voltage.

RE: RF grounding and noise:  It is important to remember that any 
wire, including your earth connection, will act as antenna. That 
is, it will RADIATE noise if it carries RF noise current (from the 
power system, for example), and it will RECEIVE noise if it 
carries RF noise current (for example, noise radiated by equipment 
near you). In general, many short connections to earth are better, 
all bonded together. In other words, the same as for lightning 
protection. Earth is NOT a sink for noise, but it CAN be a return 
path for noise current, and that current will cause the noise to 
be either received or radiated or both. 

The bottom line: We MUST bond our equipment together and connect 
it to "earth" for safety. We do NOT need those connections to make 
our ham stations or antennas work (or work better), nor to reduce 
noise. A "SPG" does NOT mean only one ground rod. Rather, it means 
ALL grounds are bonded together by beefy low inductance paths. 


Jim Brown K9YC


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