The figure shows the house plan at AA6E and how I am looking at the grounding problem. (Click for full scale view.)
The proposed stages of the grounding project, in order of increasing difficulty:
- Cross-connect ham radio "Single Point Ground" bulkhead to AC Service Ground at water pipe entrance using 1.5" or 3.0" copper strap.
- Develop a new buried ground system outside radio room. This would involve ground rods or cable buried in a trench in our shallow soil over rock ledge.
- Run a perimeter ground cable connecting the two lightning grounds, the AC service ground, and the ham SPG.
One fairly strong argument for option 3 is that the tower is bonded to the lightning ground system (the bottom one), which could lead to problems if the ham SPG is not cross-connected.
6/16/2006 Note: Finally installed the 1.5-inch strap -- about 30 feet -- from the SPG panel to the waterpipe entrance ground (1-inch copper pipe). Before connecting the strap to the SPG, I measured a 3 mV AC differential. That's somewhat reassuring. "Soundings" in my lawn show that there is only 4 to 10 inches of soil above our rock ledge. That limits my ability to make a good new exterior grounding system.