Topband: Modeling "Ground" and losses

[James Wolf]

Jim,

This brings up something I have been wondering about.   You make several
good points that I agree with.  However, on one hand we have a very lossy
earth (for instance sand) which would mean less coupling to the ground from
the radials - acting more *like* a raised radial field.  But if indeed a
less lossy ground means that fewer radials are needed to be placed in the
field, then the coupling to the less lossy ground is greater which I would
expect to mean more loss in the radial field which would then require more
radials to reduce the effect.  I agree that radials shield the field from
the earth; however it seems that it is not quite as simple as it first
seems.  

Jim - KR9U

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I agree with Tom's analysis -- a good radial system SHIELDS the field from
the earth, returning the field and the IN PLACE OF the lossy earth.

Studying N6LF's excellent work lit up the light bulb for me in several ways.
First, by noting that current in a radial inductively couples to the lossy
earth underneath it, which dissipates power. He also emphasized the
importance of current in elevated radials dividing as equally as possible
between them to minimize loss. The logic is simple
-- since power is I squared R, uneven division causes a greater increase in
the loss of a radial with more current than the decrease in the loss in the
radial with less current.

That led me to this very simple, but very fundamental concept. Each time we
double the number of radials, the current in each is divided by 2, but the
power in each divides by four. This beautifully and simply corresponds to
what we know about the power lost in radials.

Now, that simple analysis assumes a homogeneous earth, which we know is not
real, so current division, and power lost in the earth, will vary as a
result of that irregularity. But the fundamental concept remains the same.
it also explains why we don't need as many radials to hit "diminishing
returns" when the earth is less lossy.

73, Jim K9YC
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