[Elecraft] AX-1 -- with and without counterpoise

[David Gilbert]

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