Ha! I did the same thing last night only with slightly parameters:
0.2 inch diameter 4 ft. rod (average diameter of AX1?) with the base 5
ft above average ground. Counterpoise (#18 wire) drops 4 ft from the
feed point then trails out 9 ft to about 2 inches above ground. The base
loading coil was 11.3 uH with a 6.7 ohm series resistor for a Q of 150.
Not surprisingly, the gain plot showed best gain in the direction of the
counterpoise: -0.37 dBi at 30 degrees elevation. Gain in the opposite
direction was -4 dBi. So if you are in a QSO with someone, you should
be walking away from them. :-) SWR at 14.050 MHz resonance was
calculated at 3:1.
Interesting exercise!
72,
Brian, K0DTJ
On 9/26/2022 12:15, David Gilbert wrote:
I modeled something similar to an AX1 with EZNEC last night. I used a
base loaded 4' length of 1/2 inch diameter tubing for the whip, a
roughly 10 uH coil with a Q of 200 (25 turns, 1.5" diameter, 3"
length), and a 13 foot #14 counterpoise wire. It was oriented
vertically with the bottom end of the counterpoise wire being 2 feet
above "typical" ground. The frequency was about 14.1 MHz.
It looked surprisingly decent for both SWR and field pattern ... only
about -2 dBi ... although of course we should be suspect of the
accuracy for a model that severe.
The calculated field strength without the counterpoise wire was about
-10 dBi, but that's clearly unrealistic because the SWR was 700 (no
exaggeration). In practice I'm sure that other things (human body,
coax shield if used, proximity of the rigs case to ground, etc) have a
moderating effect, and they all likely introduce additional loss. I
don't think there is any way that EZNEC can accurately model something
like that, and we also have the issue of how much loss there might be
in the tuner trying to match such a difficult load.
Thus the urge to do a real world test, although I'm coming to believe
that no matter how hard I try, it probably isn't possible to control
proximity effects well enough for the case without the counterpoise
wire to get a truly definitive comparison. That SWR of 700 in the
model was because the feedpoint had a capacitive reactance of 35,000
ohms (!!). It is certainly debatable whether that figure is accurate,
but there can be no doubt that it is very high. A ballpark
comparison is therefore about the best I expect whenever I find myself
able to do the test.
73,
Dave AB7E
On 9/26/2022 4:05 AM, Gerry leary wrote:
I have used my AX2 both ways, and I have never found it to be
advantageous to use that antenna without a counterpoise.
Gerry Leary Wb6ivf
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