I'm with Grant on that. The real value of modeling is not that it will
ensure you build a good antenna, but rather it will help you avoid
building ones that have no chance of working the way you wanted. All
from the relative comfort of your chair.
There are a lot of reasons why an antenna that modeled well did not work
when you put it up, but most of those involve things in the environment
that were not part of your model. The model thinks that the antenna and
maybe the ground exist, but nothing else does. In the real world, there
is a LOT of stuff around, even if you live in the country.
73/jeff/ac0c
alpha-charlie-zero-charlie
www.ac0c.com
On 9/12/19 10:41 AM, Glenn Pritchard wrote:
Well said Grant.
Glenn, VA7UO
On Thu, Sep 12, 2019 at 8:18 AM Grant Saviers <grants2@pacbell.net> wrote:
On 9/11/2019 9:45 PM, David Gilbert wrote:
I think most of that is fairly misguided advice when it comes to
antennas.
I would agree and the rest well said.
The NEC programs continually amaze me how well they predict behavior and
performance. There is very little magic left beyond Maxwell. Creative
ideas? Great - give them a spin in the NEC washing machine. I must have
200 bad ones thankfully never built. Plus, EZNEC has some nifty
generation routines. Want a tapered wound spiral vertical? - easy. A
few hours of modeling and then we built one - resonance F and R very
close, measured A/B gain in the predicted minus few db ballpark. Was
that model perfect? - of course not, some significant variables were not
possible to model, but the prediction was very close to reality. As
W8JI pointed out, without controlled A/B performance testing, there are
just too many variables to declare any sort of victory. That pretty
much wipes out experimental optimization unless you have a real antenna
range.
I find it depressing to see hams put up at great effort even simple wire
antennas that just don't work very well. No need to debate which yagi is
better. Now when asked to help build a DOG of an antenna, I pass.
Especially if I was asked and counseled against it. The folklore that
causes folks to build (and buy) them has amazing staying power.
Junk antennas are likely one reason folks get frustrated and quit the
hobby. So, I think we have a self interest to encourage building (or
buying) good ones.
Grant KZ1W
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