Topband: Apparent ground

[Brad Rehm]

"I have a question about the "quality" of the ground around my
station.  I
have also been pondering an interesting experiment but am only
interested in
attempting it if the results would provide meaningful results."

Ford,

I wonder about the value of knowing the "Apparent Depth of Ground?"
Comments on this reflector suggest that if an antenna ground plane is
more than a few inches below the surface it would be irrelevant so far
as antenna performance is concerned.  Losses in the top layer of soil
would make it inaccessible to the currents flowing in the
antenna-counterpoise system.

Here's a guess about would happen if you were to lower a radio into
the 1-ft. diameter hole.  The signal from the broadcast station would
fall off rapidly a few feet from the surface because the cutoff
frequency of the waveguide (the hole) is a lot higher than the
frequency of the station.

I'm sure there would be some ground penetration, and I know the
behavior of the hole as a waveguide would depend largely on the
conductivity of the soil.  But I suspect the effect would be a lot
like what you see when you drive a car into a tunnel.  The signals
fall off rapidly when you enter.  They don't entirely disappear
because a small portion of the wavefront does enter the tunnel and
propagate through it.  But for practical purposes, the signal is gone
when you leave the zone in which the antenna can "see" the outside
world.

Brad, KV5V
Jarrell, Texas