Tom, it's worth adding to this that trying to make current measurements in the
ground using 60hz is pretty useless for another reason: induced currents from
the ac power system (especially in north america). 60hz will be present on just
about anything -- you'll even see it on a scope by just touching an unconnected
probe with your finger.
Commercial ground resistance meters use much higher frequencies (a few hundred
hz up to a few khz if I remember correctly). I've had to design equipment for
measuring fluid conductance before and I used a sine wave of around 450hz (high
enough to avoid 60hz harmonics and "between" the nearest two as well), and a
bandpass filter on the receiving end. Trying to just use 60hz will result in
unpredictable measurement errors and worse yet, those errors will vary
geographically even when moving only relatively small distances.
-Bill
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1.) He used Sevik's method of determining ground conductivity, but that
method is pretty much useless. A measurement of localized current at 60 Hz
doesn't mean a thing at radio frequencies, because skin depths and
dielectric effects are so vastly different.
Anyone using a measurement at 60 Hz to determine characteristics at 2 MHz is
just kidding himself. One can have a skin depth of hundreds of feet, and the
other just a few feet. They are not closely related at all. It was a
terrible method to start with.
[Sent using Blackberry Messaging]
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UR RST IS ... ... ..9 QSB QSB - hw? BK
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