Johan,
indeed there are some limitations to MMANA. And when getting a
negative radiation resistance one should get cautious.
But for small verticals and small loops MMANA seems to work OK. I am
using version 1.0.0.65 of MMANA-GAL.
73, Rik ON7YD
At 15:27 22/01/2008, you wrote:
Rik Strobbe wrote:
It seems that (at least in theory) even 1200 foot is too short to
be long on 500kHz ...
Or does MMANA not work properly ?
Hello Rik,
MMANA works very well for free space models but since it is based on
MiniNEC, it does not properly model how the "real world" ground
interacts with the near field. As far as I know, it uses the ground
parameters for the far field calculations only. In other words, I
don't think MMANA is able to make meaningful performance predictions
for small antennas close to non-perfect ground.
I just put a 2000m horizontal wire into MMANA and tried different
heights from 1cm to 1m on 500kHz with real ground. Both gain and
impedance figures were ridiculous, >600dB gain difference and
sometimes the real part of the impedance was negative! :-D
Beverages rely on non-perfect ground to work so I saw no reason to
trust the radiation patterns either.
73
Johan SM6LKM
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