[TowerTalk] Ground Probe Calculator

[Brian Beezley]

A ground probe lets you measure your local ground permittivity and 
conductivity for antenna analysis. Accurate models of verticals and low 
horizontal wires need realistic values. The probe uses two metal rods 
about a foot long spaced a few inches apart. You insert it in the ground 
and connect it to a VNA. My Windows program converts measured S11 values 
to ground permittivity and conductivity.

Ground probes are susceptible to common-mode current caused by any stray 
RF path from the probe shield to ground. The path may include the cable 
to the VNA, the VNA itself, or anything it connects to or couples to, 
including your body. It is possible to suppress common-mode current at 
the probe by adding a switch (requires two measurements) or a wideband 
balun transformer (one measurement).

The latest program version provides a new method to suppress common-mode 
current. You simply connect the rods between the VNA ports with two 
cables. The program then uses S11 as well as S21 to extract the series 
impedance when a shunt impedance is present at each port due to a stray 
RF path to ground.

http://ham-radio.com/k6sti/gnd.htm

Brian