[Antennaware] Why I use modeling software
Guy Olinger K2AV
olinger at bellsouth.net
Sat Mar 6 20:34:21 PST 2010
When I first started using modeling software, the temptation was to
accept those results as real and I quickly succumbed. I came up with
some models that showed excellent gain and put one up.
I quickly discovered that there were some gotcha's in modeling where
free/inexpensive programs got lost in computer floating point issues.
I discovered that my particular backyard dirt was not the same as the
assumptions in the programs and measurements could vary wildly from
the model, especially with low-band vertical antennas, that wire in
and on dirt was still a considerably unsolved problem.
I discovered that the simple act of winding wire around an end
insulator changed the apparent electrical length of the wire and could
not be handled by some programs, requiring freehand SWAG "adjustments"
to wire lengths for end insulators.
"Modeling kingdom" was a kind of magic space where wire elements came
to a straight ends with nothing to support them. Where feedlines did
not make the middle sag. Where one did not need a space shuttle to
put up an antenna in "free space". Where dirt could be a perfect
conductor. Where you could buy super-conductor wire that had no
resistance for free. Where common mode current on feedlines never
occurred. Where there were no miscellaneous conductors to warp and
destroy patterns. Where one could put up an inverted L without
including the tower system that supported it. And on and on.
I started out ham life doing haul up, prune, haul up, prune.
Accumulate anecdotal results, recycle.
I have returned to that mode, BUT with some powerful new tools.
I no longer trust modeling for 'pute, cut, hang and play. HOWEVER....
Modeling lets me throw away the ridiculous without all the trouble to
cut, hang and operate only to discover AFTER all the work that it's
Armed with a list of gotchas to avoid, modeling allows me to find
solutions that have no mountain of anecdotal success stories like
dipoles and yagis, lets me discover the counter-intuitive. When I go
to the backyard, I know the solution IS going to require haul up,
prune, measure, and accumulation of anecdotal evidence. But I also
know it has a far better chance of working than the proverbial
snowball in h*ll.
Modeling allows me to rediscover old solutions that have become
neglected, and in some cases discover the essential modification that
overcomes the issue that caused it to fall into disfavor, such as the
single wire windom. It allows me to discover a whole other world
beyond RG8 coax and 1:1 SWR.
I cringe when I see elaborate dissertations based on no more than
models, but the models allow me to watch the effect of adding some new
consideration to an antenna's performance and gives me a line on what
to expect when it gets real and measured.
There are places where modeling does not explain the surprising degree
of success, as in end-fed half-wave inverted L's. There are places
where modeling quite precisely identifies certain modes of failure and
mostly explains wild variations in anecdotal results as in ground
mounted current feed HF verticals, or BOG listening antennas.
Since ham radio is half antennas and half equipment, one can say we
have two eyes, understanding antenna theory and understanding
electronic theory. Many hams start out limited to being appliance
operators, using both equipment and antennas designed by others, and
clearly understanding neither.
Building equipment and immersion in the fellowship of ham operators
are but two of the ways of gaining sight in the equipment eye. But
looking back over more than a half century of hamming, "sight" in the
area of antennas did not really occur until we had PC's and modeling
programs with the monstrous capacity to compute the millions of
interactions between locations on wires and add them all up for
display and analysis.
Without learning modeling one is at least partially blind to some of
the great pleasures of the hobby. To be quite honest, for me, getting
started in modeling was a royal pain in the *ss. NOTHING explained
anything. I got totally lost in the really very excellent help files
To fairly critique myself at the starting point, it is really hard to
explain cars when one doesn't understand how a wheel rolls and has no
knowledge of certain exploding liquids. Only immersion and a growing
p*ssed-off determination that I was not going to allow "it" to beat me
got me past the original confusions. It was just like 8th grade
English class when all of a sudden one day diagramming sentences came
clear. I neither understand the earlier confusion nor what flipped
I completely identify with some of the complaints about getting
started. But don't look to me for any answers about getting started
quick. No such experience for me. One either wants to be able to
"see" there, or wants to spend their precious spare time elsewhere. I
get it either way. But if antenna behavior p*sses you off, I would
offer that without understanding modeling you will stay p*ssed off,
give up on it.
On the other hand, if you tough it out getting into modeling, you will
only be p*ssed off for six months or a year, with all that
enlightenment on the other side.
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