> Hi;
>
> Has anyone tried to model a single K9AY receiving loop using EZNERC ?.
> What are your experiences ?. Somehow I cannot obtain the rejection
> below 15 dB and certainly not with resistors of 400-500 ohm. The best I
> was able to achieve was abt 15dB (front-to-back) with resistors around
> 750 ohms. I will try to optimize it a bit more but I'm just wondering
> if there is anyone out there who has tried this already.
>
> 73 Art VE3PND
Art and all...
It is not possible to accurately model the K9AY loop -- it is connected
to ground, and such connections result in significant uncertainty (and
possible major errors). NEC can't reliably model ground currents with
antennas connected to real ground, although it will usually give results
that are "in the ballpark" such as the 15 dB F/B you are seeing. We are
lucky that NEC does a reasonably good job with Beverages and some
other types of antennas.
The "MININEC" ground will give consistent results, but they do not
represent the antenna's observed performance. It is, however, useful
for comparative adjustments.
I rarely share the model I use because it uses fewer segments than
recommended for NEC modeling. I have, in essence, adjusted the
model to correspond to the measured performance. It has been useful
in my own investigations, but I unable to say whether it can be applied
more widely.
The ultimate test of this antenna is measured performance, verified
by repeatability. With hundreds of K9AY loops in use around the world,
I am relieved that it has consistently worked "as advertised," with a
deep null (up to 40 dB) off the back when properly installed and
terminated with an optimum resistance. Modeling can get you started,
but it takes some experimentation to get to the final design.
73, Gary
K9AY
|