Topband: Ground parameter measurements

[Tom Rauch]

> For those who would like to have some estimate of their
local ground
> parameters at HF there are ways to make reasonable
measurements with
> simple test gear .

Rudy,

I respectfully disagree that a probe or series of probes 18"
deep (or whatever) can measure conductivity at radio
frequencies, especially on the case of a Beverage.

Soil moisture content and conductivity near the surface
greatly affects the conductivity measured by shallow probes,
yet the skin depth of 160 meters can be around 12 meters
deep or deeper! Soil 30-40 feet down can affect radio
signals, so what does a measurement one or two feet
guarantee?

The antenna is 500 feet long. If we measure near the house
what good does it do for determining characteristics 100
feet away, let alone 500 feet?

When dealing with attenuation of a large wavefront traveling
dozens of miles along the ground, like BC signal, localized
conductivity changes average out. We really only want to
know the typical (within a few dB) signal attenuation based
on a averaged slope of attenuation with distance.

When dealing with small localized things like conductivity
under a radiating wire or a ground rod, the amount of effort
to measure the soil is a waste of time.

If I wanted to know the loss under a Beverage antenna, I'd
measure current along the length of the antenna. If I wanted
to know the effectiveness of a few ground rods, I'd measure
the end impedance change when I added a known good ground
with no other change in the system.

73 Tom