Ground Rod Resistance
Here’s a great video showing how depth and soil type affect the resistance of a ground rod. The video is geared towards linemen however the same rules apply to grounding an Amateur Radio station.
Area Clubs
Jackson County ARES/RACES 
DeKalb County Amateur Radio Club
Huntsville Amateur Radio Club
Huntsville Area Young Ladies Club
Drake Technical College Radio Club
North Alabama DX Club
Gadsden Amateur Radio Club
Chattanooga Amateur Radio Club
Decatur Amateur Radio Club
Cullman Amateur Radio Club
Birmingham Amateur Radio Club
Atlanta Radio Club
DeKalb County Amateur Radio Club
Huntsville Amateur Radio Club
Huntsville Area Young Ladies Club
Drake Technical College Radio Club
North Alabama DX Club
Gadsden Amateur Radio Club
Chattanooga Amateur Radio Club
Decatur Amateur Radio Club
Cullman Amateur Radio Club
Birmingham Amateur Radio Club
Atlanta Radio Club