[TZ] Elevated radials vs buried ones

[Harold Hallikainen]

Interesting subject! The elevated "ground radials" seem like we're driving
the center of a dipole turned vertical with one side "flared out." The
relationship to "ground" is interesting. I always think of a horizontal
dipole or inverted V or similar as having a drivepoint that is balanced
with respect to ground. With the vertical with elevated radials, one side
of the antenna is definitely closer to ground, but not necessarily at
ground potential. As I recall from reading the Beverage article this
morning (and I first met Charles when he worked for CCA and came to check
a new FM installation), one of the elevated ground systems ran the coax
through some ferrites. The ferrites provide common mode attenuation and
not differential mode attenuation. That would let us ground the coax
shield on one side of the ferrite and have it float on the other. I
suspect the voltage on the radials at the base are perhaps 1/4 the voltage
at the base of the tower with respect to ground. The radials probably
reach ground potential part way down the radial, then start going up
again. Just guessing here.

On losses, it seems that having fewer radials would not necessarily
increase loss but would perhaps just change the driving point impedance.
We might think of a tower with one radial as an inverted V turned on its
side. If one side is particularly close to ground, we may get losses due
to that (current through a resistive material).

Anyway, interesting stuff to think about.

Harold

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