Here is a good overview technical article that discussing earth grounding
and how to measure it. This info is for 60Hz AC system and equipment
grounding saftey and protection grounding, not antenna ground systems.
Be sure to look at the pictures and figures.

http://www.duncaninstr.com/Gr_article.htm

Here is another useful paper. Item number 14, Ground System Testing.

http://www.kilowattclassroom.com/ArchiveCatalog.htm

Ronnie, N5CSE

"AG4QC" wrote in message
...
I was wondering if anyone built some sort of ground resistance tester? I
read that the NEC requires 25 Ohms or less.. But I don't understand how to
measure that. I certainly could use a ohm meter between a ground rod and
the test subject, but then the ground rod I use as a reference could be
faulty.. It seems to me it must be measured in some other manner. Maybe low
frequency signal and then measure how much it's absorbed in the earth?.. I
know they sell a clamp on ground resistance tester for big bucks.
Considering it's a clamp on, it certainly don't have any external
reference.. Anyway, I was wondering if anyone had any experience with these
testers and maybe building one?

Joe AG4QC