HamCAP Type 13 & 14 Antenna Guide
By Alex Shovkoplyas, VE3NEA
HamCAP is designed to work with antenna model types 13 and 14 that are just tabulated antenna patterns, 2-D and 1-D respectively, vs. frequency. The program may work with other file types as well, but you will not be able to view the antenna patterns. To add a new antenna file, drop it in the HamCap\AntBkup\ folder and restart the program.
It is fairly easy to create your own files of types 13 and 14.
Type 14 is a table of antenna gain vs. the elevation angle and frequency. Use it for omni-directional antennas, like verticals, and for directional rotated antennas. In the latter case, we are not interested in the horizontal pattern because we always point the antenna at the dx, so only the vertical pattern of the main lobe matters.
Type 13 is a huge table of antenna gain vs. azimuth, elevation, and frequency. Use it only for fixed directional antennas.
I used the 4nec2 freeware antenna modeling program to create a 13-type model of my sloper.
The description of another modeling program AutoEZ is very promising, but I have not tried it myself.
Using HFant for generating antenna models
There is another way of creating type 13 and 14 antenna files that does not require 3rd party programs. It is based on the fact that VOACAP generates antenna pattern tables on the fly from other file types when it calculates its predictions. In the following example we will create a model of a 3/2 wl vertical.
1. Start the HFANT program that comes with VOACAP, select File -> New Type -> ITSA-1 IONCAP -> Type 22: Vertical Monopole in the menu, set the antenna parameters, and save the file as 3_2_GP.ANT. The file will look like this:
3/2 wl Ground Plane 7 7 parameters 0.00 [ 1] Max Gain dBi 22 [ 2] Antenna Type 14 [ 3] Ground Dielectric Constant (1-80) 0.00600 [ 4] Ground Conductivity (.00003-5.0 mhos/m) 10.000 [ 5] Operating Freq -1.50 [ 6] Antenna Height (meters, wavelengths if < 0) 0.00 [ 7] Gain above a dipole (dB)
2. Start VOACAP, select 3_2_GP.ANT as transmitter antenna, and run a point-to-point prediction. VOACAP will create a file called GAIN01.DAT in the itshf/run/ directory:
IONCAP #223/2 wl Ground Plane
2. 30. 0.00 57.41 0.00600 14.00000
1 0.00 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
. . . . .
3. Move GAIN01.DAT to the HamCap/AntBkup directory, rename it to 3_2_GP.N14, then open the file in a text editor and replace the first two lines with the header from an existing type 14 file:
3/2 wl Ground Plane
3 3 parameters
0.00 [ 1] Max Gain dBi..:
14 [ 2] Antenna Type..: 30 x (efficiency + 91 gain values) follow
14.0 [ 3] Frequency
1 0.00 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000 0.000
. . . . .
The first line of the header is the antenna name as it appears in the antenna selection combo box of HamCAP.
That's it! Now you can test your model in HamCAP. To view the pattern, select your new model in the antenna combo and click on the frequency button to the left of that combo. I must say that the pattern is not very impressive, the main lobe in the vertical plane is way too high. A shorter antenna would work better, 5/8 wl seems to be the optimum height of a vertical.
The same approach can be used to create models of rotated directional antennas, e.g., yagis. Just be sure to set the receiver location due north of the transmitter so that it is in the direction of the maximum gain of the TX antenna.
Please let me know if you have questions.
73 Alex VE3NEA