I did some cleanup, error correcting, and tinkering with the model of the MFJ-1800 2.4GHz Yagi-Uda antenna. Mostly, I tried to make the model as close to the original antenna as possible and recovering the macros to make it easier to tweak:
The NEC2 file is under the "main" mfj-1800.jpg page. Cut-n-paste works.
Data sheet, of sorts:
One remaining issue is that the stamped 2mm sheet aluminum does not have a circular cross section suitable for easy modeling. By trial and lots of errors, I finally settled on a diameter equal to the 2mm thickness of the sheet metal. This is probably not correct, but does result in the best looking gain pattern and VSWR curve.
My thanks to Richard Clark KB7QHC for help with the cross section problem, and answering my questions.
Note that the antenna shows about a 200 ohms impedance at mid band. That settles the debate as to whether the antenna, without the current balun, is 50 or 200 ohms. It's 200 ohms and the 1:1 current balun is quite inappropriate for matching or whatever. The exposed center conductor forms a series inductance or radiator, and certainly doesn't help. With a proper 4:1 matching xformer, the antenna seems quite usable, but as is, it's junk. If I had one to play with (and my HP8620c sweeper elects to cooperate), I could sweep the antenna to be sure.
The coax is RGS-303 PTFE 50 ohms:
Additional photos: