Measurement of Soil Conductivity

So do you want to know the conductivity of the soil in your backyard? Well here’s a method I obtained form the ARRL Antenna Handbook. It does work but the results are almost sure to depress you.

Acquire 4 rods.......9/16" diameter (1/2” is fine too) that are 14 inches long. They must me made of a conductive material such as copper, galvanized steel or aluminum etc.

Now nail the 4 rods into the ground 18 inches apart in a straight line. Drive each of them down 12 inches.

See drawing: Attach one side of the 120 AC line to a 100 watt light bulb. Attach the other side of the 120VAC to stake #4. Attach the other side of the 100W light bulb to the resistor and the other side of the resistor to stake #1. The 14.6 ohm resistor (15 ohms is fine too) can be made by paralleling 5 resistors; 3 of which are 68 ohm 1 watt and the other 2 are 82 ohm 1 watt.

You now have two AC voltage test points......V1 is across the resistor. V2 is voltage measured between rods #2 and #3.....

In general these two voltages should be around 2 to 10 volts but with the conductivity of Sussex County, expect a lot worse.

The Formula for calculating Millisiemens (mS) per meter is:

mS = 21 x V1/V2 

The measurements can vary considerably depending on moisture content of the soil at the time of the test but even when wet, my results weren’t good. I came up with 0.2 mS which is below poor. See table below.

Millisiemens (mS)

Bad 1

Poor 4

Average 8

Good 15

Excellent 30

I also included a map of the US for reference purpose. As you can see, North Dakota is great.

Note: That the light bulb will not light unless the conductivity is good to excellent.

Note: If you run an A/C extension cord to a outdoor ground fault outlet, it will trip the outlet.