On Thu, 25 Jul 2024 10:43:03 -0700, Jim Brown <jim@audiosystemsgroup.com> wrote:
On 7/25/2024 4:42 AM, john simmons wrote:
> * Where might I find a drawing of the 630m antenna?
On VK4YB's qrz page -- it's the first drawing. It's that middle vertical
section that does the radiating. Everything else is loading.
> * In what issues of QEX were the mobile antenna articles published?
When the ARRL website gets back up, you can look it up there. It was
about ten years ago.
Others can tell you more about that issue with NEC. One way to see it is
to build a model with inductive loading and study the current
distribution table. Without loading, the amplitude and the phase of the
current along an antenna varies as a continuous function, with its zero
amplitude point at the end(s) (mathematically, a "boundary condition).
That also happens in a loading coil, but NEC doesn't show that.
The more expensive versions (now free) of W7EL's EZNEC does include the
capability to break inductors down into many segments, but it doesn't
appear to model mutual coupling between turns, for example, and when
I've used it to model loading coils, the results don't seem to make sense.
-----------------
It should model the inductive coupling between turns (after all, it's a segment
carrying current, and couples to other segments carrying current, which is how
NEC works). I can imagine there are tricky aspects to the segmentation - NEC2,
in particular, is picky about closely spaced wires having matching segment
endpoints.
What it would NOT model is the capacitive effects (or more subtle stuff like
proximity effect causing uneven current distribution in the conductor).
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