Charles: You might want to do a Google for "three point method" and "fall of potential". These are the two standard methods for measuring grounding resistance. You should easily find tutorials from manufacturers of testing equipment.
EWE's are at or near the top of the list of antennas that are picky about having a good ground. Were it my EWE, I'd follow standard RF grounding practice and put it at least 3 8' ground rods separated by at least 5 feet. With average soil or better, that should suffice. With poor ground, buy a silver mine and install it under the antenna. Chuck -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Charles A Taylor Sent: Friday, July 13, 2007 12:13 PM To: irca@hard-core-dx.com; [EMAIL PROTECTED] Subject: [IRCA] Measuring D-C resistance of ground rods to earth DX Crew, Mr and Mrs. America, all the ships at sea and pesky CEs who are snooping on this reflector: I wanted to get a good handle on the D-C or A-C resistance to ground of a 8-foot driven ground rod here on the coastal plains of North Carolina. I first took the gutless route and measured the D-C resistance from an 8-foot rod driven 7½ feet into the ground, using the house ground and neutral back to Progress Energy lines as the reference. I measured (with a multimeter) 1.4 kilo-ohms with the probes connected one way, and a down-scale reading the other way. That wasn't getting me anywhere, and besides it doesn't account for earth currents that flow from one ground to the other. These would render invalid what ever reading I do get. When I measured A-C voltage between house ground and the rod, I measured about 15 millivolts (0.015 volts). Not helpful, but it goes to show how RFI can get into a system that has two or more grounds. Using a D-C power supply sourcing 15.5 volts, I sank current into the rod via the same multimeter on D-C current scale. With the power supply bringing the ground system with one polarity. I measured 51 mA of current; polarity reversed, 52 mA. Dividing the supply voltage of 15.5 volts by the average of the two D-C currents got me 300.9 ohms. Note that 300.9 will be on the high side of just such a ground because this one rod is driven 1 foot from the side of our house and so blocks access to earth on one side of the rod. Since the R-F resistance of a rod in earth is likely to be lower because the rod is also capacitively coupled to earth and that capacitance is in parallel with the D-C resistance. Which brings up the point that a EWE antenna could, in principle, be terminated just on a rod, barefoot. The problem is to get a handle on the R-F resistance of an 8-foot ground to earth. I'm thinking about firing up my Heathkit DX-35 CW transmitter and repeating this process at 1,600 kHz with about 10 watts. (it's crystalled for 1,600 kHz, and I have some low-range R-F ammeters. Anyone else have any experience at this? Perfesser Chuck Charles A Taylor, WD4INP Greenville, North Carolina _______________________________________________ IRCA mailing list IRCA@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: irca@hard-core-dx.com _______________________________________________ IRCA mailing list IRCA@hard-core-dx.com http://montreal.kotalampi.com/mailman/listinfo/irca Opinions expressed in messages on this mailing list are those of the original contributors and do not necessarily reflect the opinion of the IRCA, its editors, publishing staff, or officers For more information: http://www.ircaonline.org To Post a message: irca@hard-core-dx.com
