Hi Cigarsmoker. I'm certainly not as experienced as others may be with respect to EzNEC. However, I do know that 4nec2 can produce output radiation patterns that are largely in a text format compatible with Proplab3. Just a little editing of the text file may be required.
Using 4nec2, load your antenna project. Then under the Settings menu option, make certain that the ITSHf sub-option "Calculate output plot file" is checked. I also have the "Create 'point' input file" checked. Then use the "Calculate -> NEC-output-data" function to create a radiation pattern plot display. You can select the Far Field option. When that display appears, the "Plot -> 3D Plot" function will create a file that contains the radiation pattern you need.
The format will be something like this...
0 -90 -31.82
10 -90 -31.82
20 -90 -31.82
30 -90 -31.82
40 -90 -31.82
320 -90 -31.82
330 -90 -31.82
340 -90 -31.82
350 -90 -31.82
360 -90 -31.82
0 -80 -19.61
10 -80 -21.88
20 -80 -22.88
30 -80 -19.53
40 -80 -15.72
The first column represents the azimuth. The second column represents the elevation angle (you only want positive elevation angles) and the third column represents the radiation intensity (this example is in dBi - Proplab requires
the radiation intensity in dBi.
Also, note that the radiation angle increments above are every 10 degrees. Proplab needs them to be every 1 degree, so change the settings when you Calculate.
Proplab3 is only interested in the maximum radiation intensities. That is, find the elevation angle that corresponds to the maximum azimuthal radiation intensity and use that. You will have to hand-edit the file so that it matches the format used by Proplab3. To see the format that is used, go into the Antennas folder and look at the format of the files there using a text editor like Notepad. There is a blank template file called BLANK.DAT that is empty. You can change it to fit your needs, then when you save it, use Save As... to change the filename to something like Windom.dat.
There is also a way that you can write ITSHF format files (the HFAnt format in VOACAP) using 4nec2, but I'm not entirely familiar with that process. If it will write true ITSHF format files, the utility included in Proplab3 should be able to convert it to an equivalent Proplab3 antenna file.
I hope this helps.