[TowerTalk] the value (or not) of modeling

[corneliuspaul at gmx.net]

1.)
>Modeling is wonderful!  It lets you experiment in nice cozy warm comfort
>while it's raining outside, or while the sunspots are few, or while you're
>just too darn lazy to go out and build it to try it.  Especially now, with
>2+GHz computers available for $350 from Dell, running half a dozen
>speculative cases is so quick that there's no excuse not to.

2.)
>On the other hand, there's no substitute for going down to Home Depot and
>buying 500 ft of AWG 12 THHN wire and stringing up some antenna, and just
>giving it a shot!


3.)
>Use that model for insight:
>
>- maybe I want to know how critical the dimensions are
>- even though losses are tough to model accurately, you can get
>   a feel for the impact of the loss.
>- etc



Very well said.

Still I would like to point out, that for developing complex antennas
such as e.g. multiband designs, modeling (if applied properly and carefully)
lets us develop things that are very very difficult, if not impossible to 
achieve
by method #2 (cut & try).

It really took me a huge amount of time and playing with various configurations
until I came up with the spiderbeam design for a highly efficient wire yagi
covering 20-15-10m (and lately even 20-17-15-12-10m) because of the
interaction between all the various individual elements for all those bands.

The 3-band version has 11 elements (20m/3, 15m/3, & 10m/4) and the
5-band version has 15 elements (20m/3, 17m/2, 15m/3, 12m/2 & 10m/4).

Try to tame such a monster by cutting/measuring/trying !!
For me it would have been simply impossible.
Modeling reduced the time to something more reasonable, albeit still
a huge effort.

The secret is then to understand how to transform the numbers gained
from modeling into reality. You will need some experience, knowledge
about the shortcomings of your modeling software, about other influences
like e.g. velocity factor, etc.
This experience comes from combining method #1 and #2 often enough,
and measuring the results as close as possible.

And in the end it is very rewarding to see how close a well built antenna
can resemble the predictions of your modeling efforts...

Have fun experimenting!

73s,
Con DF4SA

www.qsl.net/df4sa/spiderbeam.htm