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## Re: [TowerTalk] Ground resistance

 To: Re: [TowerTalk] Ground resistance "Keith Dutson" Wed, 9 Aug 2006 08:50:16 -0500
 ```It seems to be well known that planting an antenna over salty water will greatly enhance radiation. Is this advantage in the near or far field, or both. Would installing radials under a tower with horizontal antennas be worth the time and effort? 73, Keith NM5G -----Original Message----- From: towertalk-bounces@contesting.com [mailto:towertalk-bounces@contesting.com] On Behalf Of Jim Jarvis Sent: Wednesday, August 09, 2006 6:30 AM To: towertalk@contesting.com Subject: Re: [TowerTalk] Ground resistance John asked: "Is there any simple way to measure the impedance of the ground radial system as you install them to know when you have enough of them in the ground?" Others suggested using a Megger or Hipot tester to measure ground resistance. While it is true that one can measure resistance between two rods in the earth, and from that determine earth conductivity....that wasn't the question. The answer to the question is NO. The answer depends, of course, on whether you intend the ground system to dissipate charge, and in the event of a lightning strike, peak current, OR, if you're looking for a radial field which will be effective as part of an RF antenna. But in both cases, the DC measurement is either misleading or irrelevant. If you have radials and rods in the ground, you could measure the resistance of the ground system, through earth, to a reference ground rod, a known distance away. When you run a radial and rod system closer to your reference, the earth path resistance will go down. But that's because you introduced a shorter measurement path. Suppose you put in a very effective ground in the other direction? The measurement MIGHT see a lower resistance due to the larger system, but would that data MEAN anything? I doubt it. If you're talking about the RF efficiency of a radial system, then the only way to do it is to use a field strength meter, or a calibrated receiver using a known antenna at a known distance, and take field strength readings as you increase the ground system. When you start getting diminishing returns, you can stop adding radials. As Dave Robbins said, "WAY, yes. Simple, no." My answer is, "why bother?" As a practical matter, you will be limited by resources in constructing the ground system. If the price of copper doesn't get you, then the pain in your back will, as you install radials. You KNOW you won't pull in 120 of them. You KNOW that 4 isn't enough, unless elevated. Empirical work done by AT&T in the 1930's, and reported in public literature, showed that 16 to 20 radials resulted in field strengths within 10% of the results with 120 radials. So plan for 16, and increase from there if you have the wire, inclination, and Advil to support the effort. Measuring the signal will entail use of instrumentation which will either be relative in its reading, or will cost you more than the ground system you're testing. Even to rent. n2ea jimjarvis@ieee.org _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk _______________________________________________ _______________________________________________ TowerTalk mailing list TowerTalk@contesting.com http://lists.contesting.com/mailman/listinfo/towertalk ```
 Current Thread Re: [TowerTalk] Ground Resistance, (continued) Re: [TowerTalk] Ground Resistance, David Robbins K1TTT Re: [TowerTalk] Ground Resistance, Travis W. Pederson Re: [TowerTalk] Ground Resistance, Jim Brown Re: [TowerTalk] Ground Resistance, Jim Lux Re: [TowerTalk] Ground Resistance, Pete Smith Re: [TowerTalk] Ground Resistance, Gary Schafer Re: [TowerTalk] Ground Resistance, Jim Lux Re: [TowerTalk] Ground Resistance, hasan schiers Re: [TowerTalk] Ground Resistance, Bill Turner Re: [TowerTalk] Ground resistance, Jim Jarvis Re: [TowerTalk] Ground resistance, Keith Dutson <= Re: [TowerTalk] Ground resistance, Dan Zimmerman N3OX [TowerTalk] Ground Resistance, Phil Camera