After recent discussions on the Topband and Antennaware lists, I took =
some time to review modeling of the K9AY Loop. At the suggestion of =
WX0B, I took another look at an accepted ground model for NEC-2 -- a =
system of radials a small height above ground...
I started with (8) 30-foot radials 0.5 ft. above ground. The results =
were consistent with NEC-2 guidelines, including smooth convergence as =
the number of segments was increased. While this small ground system =
worked, it was sensitive to symmetry, which is improved by using a =
larger number of radials. When evaluating the K9AY Loop with this model, =
please note the following:
1) The termination resistance for the deepest null is substantially =
different from what was empirically determined for the published design =
(600+ ohms vs. 390 ohms).=20
2) The vertical angle of the rearward null in this model is much higher =
than I have observed.=20
These factors may be accurate results -- this is a better quality ground =
than the single ground rod of the original design. Adding more radials =
to the model and/or making them longer increases the amount of =
deviation. Hopefuly, hams who have installed a K9AY Loop with an =
enhanced ground system can add their observations.=20
This model does show noticable, but fairly benign, interaction with a =
grounded metal support. First, a slight null fill-in can be fixed with a =
small change in terminating resistance. Also, the presence of the =
support pole appears to change the vertical angle of the null, which may =
be an improvement or degradation, depending on the predominant arrival =
angle of QRM at your location.
While I do not have measurements to verify that this modeling method is =
real-world accurate, and although it does not quite represent the =
original design -- it is useful for exploring the general behavior of =
this antenna in a manner consistent with NEC-2 guidelines.=20
73, Gary
K9AY
--- StripMime Report -- processed MIME parts ---
multipart/alternative
text/plain (text body -- kept)
text/html
---
|