What do you want to measure? These testers, as well as the "fall of
potential" method, measure the impedance to earth at dc and low audio
frequencies.
It's important to remember that a connection to earth is for lightning
protection, and does not make a TX antenna work better.
If you want to measure your soil conditions, N6LF shows a method on his
website. It uses a driven rod that passes through an opening in a wire
screen. Z between the rod and the screen is measured using a vector
impedance analyzer, first before the rod is driven, and again after
being driven to its full length, and soil parameters are computed from
the two measurements. I've thought about doing this, but never got
around to it. This measurement yields the data on the soil conditions
that affect the performance of vertical antennas.
73, Jim K9YC
On Wed,4/22/2015 6:00 AM, Paul Christensen wrote:
"Do you use a earth tester? Which brand do you know is very good and
accurate to consider?"
Jorge,
If you can, try and find a "clamp-on" earth tester rather than the
type that relies on the fall-of-potential method with electrodes.
There are several good clamp-on units by Megger, Fluke and AEMC. I
recently acquired an AEMC model 3711. It wasn't supplied with a
calibration loop, but I found one from Fluke that quickly checks
calibration at 100, 50, 12.5, and 0.5 ohms. You'll want that
calibration loop to validate the accuracy of the clamp tester,
especially if you use an off-brand model from Asia.
N4CC and I recently installed a large grounding field, with some
ground rods driven down to a depth of 24 ft. The clamp-on device was
useful for quick validation. Had we used a unit with electrodes, it
would have taken us much longer to perform our tests. By the way, in
sandy/clay type soil here in north FL, we found that connecting 8 ft.
rods end-to-end to form a 24 ft rod substantially lowered earth
resistance by a factor of 10x.
Paul, W9AC
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