On Tue, 26 Sep 2006 22:36:53 -0700, Richard Clark
wrote:
I've been using various flavors of E(L/Z)NEC for more than a decade
and I've never seen such dramatic cogging of the data that was not
attributable to construction (notably fractals). Your data is
stranger yet in having correlated noise on the left, and uncorrelated
noise on the right.

Please look at the ftp://space.mit.edu/pub/davis/misc/nec/swr.png
for a plot of the SWR using a spacing of 0.01 MHz. I suspect that the
noise that is showing up may be due to truncation error. I believe
that spacings of higher values, e.g., 0.2 MHz result in a different
sampling of the noise.

The version I am using (see
http://packages.debian.org/stable/hamradio/nec) contains this warning:

This version contains code which hasn't been extensively tested for
errors, which was input by hand from a report -- use with care. The
numerics are currently only SINGLE PRECISION.

If EZNEC were available for linux, I would look into it. Also, can it
be driven in "batch" mode without a GUI?

Thanks,
--John