On Tue, 17 Nov 2009 20:29:08 -0800, Jeff Liebermann
wrote:

On Tue, 17 Nov 2009 18:35:15 -0800, Jeff Liebermann
wrote:
http://802.11junk.com/jeffl/antennas/mfj1800/
The annotated NEC2 file is attached to the "Main" JPG. Cut-n-paste
should get you something to play with.

A few changes. I changed the simulated folded dipole into something
more closely resembling the original MFJ folded dipole. I also
changed the characteristic impedance to 200 ohms so that more closely
resembles a 4:1 match to 50 ohms. Of course, the VSWR went from
tolerable to horrible (10:1). I suspect I did something wrong in
locating the feed point, but I'll fix that later. When using a
geometry editor/generator, I turned my nice neat NEC macros into
unreadable gibberish. Sigh... I'll also fix that later.

Gain is still 14.1dBi.

More changes(tm). I fixed the feed point on the flattened folded
dipole and the VSWR magically came down to normal (1.47:1 into 200
ohms). Vertical gain dropped to 13.1dBi, but horizontal gain dropped
to 6.35dBi. Something (else) is wrong.

I'll fix the macros so that the NEC2 file is readable, later.


--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558