[600MRG] NEC4 cost

[Rudy Severns]

W0RPK looked up the present costs for a NEC4 license, thanks Ralph:

 

"From https://ipo.llnl.gov/technologies/nec I learn that an academic and
non-commercial NEC license is currently $300."



If you want to model wires close to ground or buried you must use NEC4 for
which there is a license fee.  I paid for my license some 20 years ago when
it was much more expensive.  I had to forgo an upgrade to the station to pay
for it but I've never regretted it.  NEC2 does quite well for elevated wires
but cannot be used for buried wires and the accuracy degrades as you
approach ground.  The freebee versions of NEC2 will do most of what we need
for LF-MF.  It's more than adequate to evaluate and optimize irregular wire
top-loading configurations and determine the lossless value for Rr, the
radiation resistance, which you can multiply by the square of your antenna
current to get your radiated power.

 

4NEC2 comes with a NEC2 calculation engine.  However, it can also work with
NEC4 if you have the license and the software you'll be given.  In the
latest issue of the IEEE transactions on Antennas and Propagation there is a
wonderful article on NVIS propagation.  That work used 4NEC2 with the NEC4.2
engine and WSPR.  It's a fascinating bit of work by some Dutch engineers.
It appears at least some of them were hams to boot.   The article suggests
to me the use of a similar technique for LF-MF propagation investigations.

 

Over the years I've repeatedly compared modeling predictions to experimental
results from antennas I've built.  I've been lucky to have good
instrumentation which really helps.   When I was careful the results agreed
very well, when I was sloppy, not so good.  There are several reasons why
modeling and experiment may not agree: not observing all the modeling
conventions, the model does not correlate closely with the actual antenna,
poor instrumentation for the measurements and/or poor experimental
technique.  Field measurements on antennas can be tricky.  I plead guilty to
spending uncounted hours making absolutely worthless measurements with very
expensive equipment.  I've had numerous opportunities to write articles for
JOIR (the Journal Of Irreproducible Results)!  Few amateurs will have
professional equipment and in the past the low end test gear available to
hams has been pretty marginal.  But that's changing, we're beginning to see
really good instruments (the AIM4170 for example) well under $1k and some
now even below $500.  These days, I rarely use my fancy old HP boat anchors.
The new instruments are so good and very convenient to use.  There are also
many old instruments for sale on-line and at flea markets at reasonable
cost.  One example I've been fooling with is a very elderly GR650 impedance
bridge: black Bakelite panel, varnished wooden case.  These are usually
given or thrown away!  The bridge originally operated at 1 kHz but it seems
to work just fine when excited at 475 kHz.  Just the thing to measure your
feedpoint impedance on 630m and 2200m.  Further testing and a write-up is a
winter project!

 

The article on my web page I referred to earlier has a cutesy title stemming
from a problem with a receiving antenna (a BOG) but the bulk of the article
represents a serious attempt to check the validity of NEC4.2 modeling for
wires close to ground or buried.  I needed to do this so I could
convincingly explain the source of my problem.  In the Sept/Oct issue of NCJ
Carl Luetzelschwab, K9LA, has an article on a BOG, he mentions replicating
some of my modeling using NEC4.1 and got very similar results.  You don't
have to have the very latest version although that's what you'll get if you
buy a new license directly or the latest version of EZNEC Pro/4.

 

My suggestion is to start with the freebee 4NEC2.  I'll bet that once you
get into modeling and having a lot of fun (it's addicting!), the license
cost will not look so bad.  Christmas is coming!

 

73, Rudy N6LF