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Re: [TenTec] RF Ground

To: Rick Denney <rick@rickdenney.com>, Discussion of Ten-Tec Equipment <tentec@contesting.com>
Subject: Re: [TenTec] RF Ground
From: Stuart Rohre <rohre@arlut.utexas.edu>
Reply-to: Discussion of Ten-Tec Equipment <tentec@contesting.com>
Date: Wed, 08 Apr 2009 15:23:58 -0500
List-post: <tentec@contesting.com">mailto:tentec@contesting.com>
The general rule is to minimize the distance from your station ground to 
the electrical service ground, to minimize rise of potential difference 
in surges or strikes.  But, in general, you don't want the surge/ strike 
to prefer to go from the electrical panel ground back to your equipment 
ground.  A way to disconnect your antennas, control cables and power at 
the rig is a good way to minimize any chance of spreading the current 
paths in a fault to electrical ground.  Many radio stations use a 
central grounding panel where power, telcom and RF all come into the 
building from outside, together, to group these cables to minimize 
potential differences between them in case of a fault.  For lightning 
effects, remember that you are dealing with thousands of amps for a very 
brief time, and even very low resistance conductors have a big voltage 
drop along a length due to Ohms Law and the extreme amount of current.

For a mast, put a ground rod at the mast base to provide an easy path to 
ground, of lower impedance then your feedlines and controls.  Even put 
multiple rods out close to the antenna mast or tower, to spread any 
possible hit to earth as quick as possible.  If the mast is some 
distance from the house, don't run a large conductor between them to 
bond, the coax shelds would be a lower impedance conductor than wire, if 
you bond them to an earth system just outside the building.  This is the 
reason many radio stations use a copper or aluminum panel to pass thru 
feedlines.  That panel gives you a single point ground to attach to 
earth.  While having a VHF beam may not be adversely affected by all 
metal guy wires; usually for HF, you break up guys with egg insulators, 
or use synthetic guys to avoid stray resonances.

A review of the white papers on the Polyphaser site should guide you to 
good solutions.

-Stuart Rohre

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