To: <topband@contesting.com>
> Date: Wed, 18 Mar 1998 02:57:46 -0500 (EST)
> From: k6se@juno.com (Earl W Cunningham)
Virtual antennas over virtual ground. The use of models requires
real world verification. To this very day, the only verification
offered are scattered BC field proofs that could easily have several
dB error.
On the other hand, every direct A-B measurement (which eliminate
many of the errors inherent in the "FCC proof" method) I've been
able to find disagree with NEC models.
> One of Christman's conclusions is, "When modeling elevated vertical
> antennas, EZNEC (and presumably, other NEC2-based software packages)
> appears to give results which are nearly identical to those derived from
> the more recently developed NEC-4.1".
That's not very comforting to me.
In 1970 Hagn and Barker made gain measurements of a low dipole
antenna over known soil. Jack Belrose (director of Radio
Sciences for Canada) compared the Hagn-Barker low dipole data to
NEC-2 predictions. At .01 wl above ground, NEC-2 showed the FS in the
virtual reality antenna was about 5 dB in error. NEC-2 indicated the
FS was HIGHER than it was in the real world antenna.
When Roy Lewallen and myself compared current measurements in
Beverages with NEC models, there was a fairly large error in current
loss in the antenna. NEC showed less loss than measured in the real
world.
If a program can't handle a low horizontal wire accurately, it
almost certainly can't handle a radial system at the same low
height.
73, Tom W8JI
w8ji.tom@MCIONE.com
--
FAQ on WWW: http://www.contesting.com/topband.html
Submissions: topband@contesting.com
Administrative requests: topband-REQUEST@contesting.com
Problems: owner-topband@contesting.com
|