Cecil Moore wrote:
Buck wrote:
Cecil Moore wrote:
EZNEC agrees. With four radials one foot above ground the gain
is -0.53 dBi. With one radial one foot above ground the gain
is -1.62 dBi in the direction of the one radial and - 6 dBi
in the opposite direction.
How does it rate it with that one radial buried in the ground as in
the OP rather than above the ground?
I don't have NEC-4 so I can't bury radials. Perhaps Roy will
do the honors. Incidentally, the above simulation was done
for a 33 ft vertical with 33 ft radials on 40m.
I've been extremely busy lately, but found a few minutes to run this.
This is for a 33 foot vertical with 33' ground wires buried 6 inches
deep. The model was run with EZNEC/4 using the NEC-4 calculating engine.
All are for average ground, and the gains are at the elevation angle
where gain is the maximum -- 26 degrees in all cases.
With one radial, the gain in the direction of the radial is -5.94 dBi,
-6.7 dBi in the opposite direction. It's interesting to see how much
difference it makes to have the radial just a foot above the ground, as
Cecil modeled, rather than six inches below. When the radial is above
the ground, the current distribution looks pretty much the same as the
vertical wire's. So it contributes significantly to the pattern. But
when buried, the current decays rapidly in an exponential-looking
fashion, so it doesn't contribute much to the radiation.
With one radial, the gain at right angles to the radial wire is -6.49 dBi.
With two radials, the gain in line with the radials is -4.33 dBi, and at
right angles essentially the same, -4.58 dBi.
With four radials, the gain is -2.95 dBi essentially in all directions.
With 8 radials, the gain is -1.79 dBi. This is just about what you get
in the favored direction with a single radial elevated one foot.
According to NEC-4, anyway. These would be some interesting experiments
to do with a real antenna.
And, running EZNEC using MININEC-type ground gives the gain you'd get
with a perfect radial system -- -0.02 dBi.
Roy Lewallen, W7EL
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