When I see this thread, it brings back memories. Doing this accurately
is far more difficult than one would think. If you come away with a
"how hard can it be" - then you are probably not considering the
infinity of error sources.
My solution? Cut the element and measure it in place where it would be
used.
Impossible? then trust the model. If you are building a beam with
insulated elements and no traps, assuming the model matches the build
otherwise, it will probably be "close enough."
Good luck and have fun!
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 4/22/20 1:58 PM, David Gilbert wrote:
I agree. When I bought my Optibeam OB16-3 and OB2-40, Tom (DF2BO)
didn't send me the EZNEC files but he did send me the resulting plots
for gain and SWR. The manual also specified the element lengths and
diameters. I took my own measurements for the 40m coils and the
tribander feed system, and generated my own EZNEC files. My EZNEC
plots are indistinguishable from Tom's.
By the way, with the help of K9RX who lived about 30 miles line of
sight from me at the time (we both lived on high ground with a small
river valley between us) we measured the actual azimuth patterns, and
of course I could measure the SWR plots. They were extremely close to
the models as well.
Modeling unknown traps might be a bit trickier, though, I suppose.
73,
Dave AB7E
On 4/22/2020 9:34 AM, Jim Brown wrote:
On 4/22/2020 7:51 AM, Robert Harmon wrote:
Good luck on getting the files. They won't give you theiir Eznec
files.
Who is the "they" in this post? I looked all through this post and
quoted stuff to find "them." If you're referring to mfrs, what makes
you think they use NEC for design? There are multiple modeling programs.
It's easy enough to produce an EZNEC file for an antenna that doesn't
include inductors or capacitors -- all you need a a measuring tape
and a caliper to determine element diameters. In his very useful
self-published "Array of Light," N6BT includes detailed descriptions
of many Force 12 antennas he designed for the company he owned.
73, Jim K9YC
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
_______________________________________________
_______________________________________________
TowerTalk mailing list
TowerTalk@contesting.com
http://lists.contesting.com/mailman/listinfo/towertalk
|