Reply to W8JI post of Sat, 28 Feb 2015 19:14:07 -0500:
The source of the r-f current flowing on buried radials is the r-f current
flowing in the earth as a result of radiation from the vertical monopole.
(etc)
It seems to me that answer ignores other effects.
1.) If we remove the earth, the radials still have current.
Yes, but then the origin of that current is via a direct, metallic path back
to the 2nd terminal of the source (transmitter), using either balanced or
coaxial transmission line.
That operating configuration is different than when the radials are buried.
2.) If we place a conductor almost anywhere near any antenna, connected or
not, it has current. If the wire is long and at 45 degrees or less, it can
have very high current.
But if those conductors are not buried, then the source of that current did
not incur losses by traveling from the monopole to, and through the lossy
earth around the base of the monopole -- to reach those radials.
3.) With the same applied power, a single radial in earth, despite being in
the same dirt, has more current than the same radial with just one opposing
radial. It's collecting from the "same dirt".
A single buried radial may have more current as you suggest (I'd have to
model this), but that might be expected because a relatively small amount of
the earth current flowing near the location where an opposing radial might
have been can then collected by the remaining radial.
No doubt the total current collected using both radials in this scenario is
greater than when using either one of them, alone.
4.) Groundplanes still have current in radials
See comment to 1.) above.
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Reply to KR9U post of Sat, 28 Feb 2015 21:23:50 -0500:
... If I add an imperfect ground with the radial buried just below the
ground, I would expect that the efficiency of the antenna would drop. NEC4
shows it loses about 10 dB vs. free space, with about 6 dB of directivity
in the direction of the radial wire using average ground. If I use dry
sandy ground, then we gain back about 3 dB with a very similar pattern. ...
Wouldn't that tend to show that a monopole system using a very high-loss
ground plane should have greater gain than when driven against a very
low-loss ground plane?
Given that your NEC4 model is a 160-meter monopole system and other things
equal, what does it show when only one 0.5-meter radial wire is used, and it
is buried several centimeters below the surface of 0.1 mS/m d.c. 5 earth?
If you are correct, then we should all be using uninsulated wires for
radials. ??
EM radiation/current passes through the insulation of buried radial wires as
easily as it does through the insulation of aerial wires.
R. Fry
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