More "Food for Thought" re ConvergenceTest & AGT Adjust
My thanks to 300Ohm and mclapp for their comments:
300Ohm (post 68) --> http://www.digitalhome.ca/forum/showpost.php?p=1111831&postcount=68
mclapp (post 70) --> http://www.digitalhome.ca/forum/showpost.php?p=1112072&postcount=70
Like 300Ohm, I have used the AGT adjust "procedure" in all my past posted 4nec2 nec files. I never really questioned the effect of different wire diameter, on this AGT adjustment, because the results never indicated any significant wrong results.
After recently reading j3d's post on the subject, and with a re-read Cebik's modeling guide, part 4 ( the last 2 pages under the heading "Testing Models"
), I thought it would provide a better understanding of 4nec2 limitations, if jed's question could be answered with some detail and if possible some reference links.
Reference link to j3d's post
For me, the questions that need answers is simply this: ... in the case of the AGT adjust procedure, do two wrongs actually may a right
" and along with that, do other modelers, besides DigitalHome.ca forum members, use this AGT adjust procedure?
The recent posting (post 61) by Nikiml re Convergence Tests on his model, provides some "food -for-thought" and I invite comments. If the majority of readers on this subject feel, that this is somewhat of a waste of time, I will stop posting on this subject, as I have plenty of other activities to keep me busy. The only way I can "measure" the interest in this subject is from the posts that are made.
Food - for - Thought Comments
Nikiml's post 61, Convergence-Tests showed, that up until segment-check errors occurred, the raw gain varied from 13.13 dBi (total_segs=328
) to 12.99 (total segs=1004
). Reference link (post 61):
By extrapolation of Nikiml's data, 21 segments per 1/2 wave raw gain would be 13.03 dBi. For this specific model, the Convergence Test reveals the "most accurate" raw gain convergence is 12.99dBi. So does the recommended model at 21 segments per 1/2 wave using the AGT adjust procedure, give a more accurate result, not only for this model, but for any model, regardless of the complexity? The beauty of the Non-adjusted AGT Test and the Convergence Test is: you can depend on the results
, regardless of antenna model differences (GH vs Yagi or BowTie etc)and the antenna's complexity.
In an effort to continue this discussion, here are some more "food-for-thought
1. Arie's 4nec2 Forum
The AGT is off - Why? A bug?
2. Practical Antenna Modeling - WX7S
3. Antenna Modeling for Radio Amateurs
Here is an excellent overview about some of the history of antenna modeling with references to mathematical models. There is a brief discussion about limitations of the various modeling approaches and a summary of EZNEC and 4nec2 is included. This pdf doc was written by Steve Stearns, K6OIK.