Wire Grid Model Generating Software
An Antenna Modelers Dream Tool
By Dan Richardson, K6MHE
Figure 1 NEC-Win Synths display and
spreadsheet windows (screens)
showing the truck model discussed below in the text.
omputerized antenna modeling has become a very widespread activity for radio amateurs. The ability to design the dream antenna, check out manufacturers claims or analyze how an antenna will perform in a particular environment has made this activity very popular indeed. If you use, or are thinking of undertaking, computerized antenna modeling using the NEC calculating engine or one of the popular commercial NEC implementations, using NEC-Win Synth by Nittany Scientific can make your antenna modeling experiences much more enjoyable.
What is It?
NEC-Win Synth (NWS) is not an antenna modeling program in itself; rather it is a software tool used to create wire models of antennas and structures that can be used by other antenna modeling programs. Once the model has been created, its description (wire geometry) may be saved or exported as an ASCII text file that can be read by NEC or imported into other NEC based analysis programs such as NEC-Win Plus1 or EZNEC.2
NWS offers a wide range of predefined models in nine categories. If, for example, you choose the Antennas category the program will display a list of the predefined antennas for your selection. This listing ranges from simple antennas, such as a monopole or dipole, to more complex antennas such as a Yagi or a quadrifilar helix. (See the sidebar for a complete listing of all the categories and predefined models.)
Once a model has been created, you may use the program to add or delete wires, rotate, move or scale the model. You may also add additional models by selecting another structure from one of the categories, or by importing another previously saved model using the Add Model File (discussed below) option. For instance, you could place a Yagi, along with its supporting mast, on top of a tower that you had just modeled. You can get quite creative doing this. As a case in point, you could model a box structure then by adding, rotating and moving additional geometric (rectangular and triangular) structures, you can end up with a model of a building. This would take some time, but it would be quicker than calculating and placing one wire at a time using conventional spreadsheet entry methods. Not to mention the cruel and unusual punishment of using a text editor to enter all those cryptic G commands required by NEC.
The Add Model File option is used to import model files that may have been created by other programs. Using this option you are able to import NEC (*.nec) files3, Autocad® (*.dxf) files or ASCII text (*.txt) files in four different data formats.4
Additionally, NWS has an Add Grid function for making custom grids that has a useful feature. When creating a wire grid structure you may choose to have NWS apply the equal-area rule so that when the grid model is generated it will have the proper wire-diameter-to-spacing ratio that approximates a flat metal sheet.
Easy to Use
When first run, NWS presents a Display Window and a Spreadsheet Window (Figure 1). The Display Window is used for selecting predefined models, adding wire grids or single wires, importing model files, performing geometry checks and, of course, displaying the model itself. A displayed model may be rotated, panned and zoomed for better examination. You may also print a displayed model or save it as a bitmap file (*.bmp).
Figure 2 The wire grid model of
Figure 3 Data input window used
The second window is a spreadsheet that displays geometric data for the individual wires of a model. You use this window for choosing the units of measure (meters, centimeters, millimeters, yards, feet, inches or wavelengths) and frequency to be used when NWS generates the model.
Also editing chores such as deleting, moving, rotating, or scaling of wires are done here. An added powerful feature available is the equation page. After clicking on the Equations tab you are presented with a worksheet where you may enter formulas and variables that can be referenced and used by NWS. Space does not permit an in-depth discussion of this option here, but a good explanation and examples on using this feature are given in the user manual.
Really Saves Time
Where NWS really shines is the time it saves the modeler when creating complex wire structures. Figure 2 is a model I made for my pickup truck using NWS. To make this model I needed only to enter ten data items in a dialog box (Figure 3) telling NWS the overall dimensions of my truck and the number of segments per wavelength to use when generating the model. Total time in making the model was under seven minutes. Of that time five to six minutes was spent measuring and recording my trucks dimensions and less than one-minute of computer time! (This does not count the twenty plus minutes I spent trying to locate my tape measure.)
At this point it is possible to add other structures such as placing an antenna on the truck, or do any additional tweaking. Furthermore, the complete model can be moved, rotated and scaled. When finished, you need only to save the file so your chosen NEC antenna-modeling program may import it.5
One feature that I really like is the wire-identification option. Placing the mouse cursor on any wire of the model in the display area and pressing the right-mouse button changes the wires color and displays the spreadsheet with the selected wires data highlighted. I found this extremely helpful for locating wires that I wished to modify or delete. This feature also works in reverse. You can click on any wire in the spreadsheet and it will be highlighted in the Display window. Believe me, when you have several hundred wires in a model this option is a blessing!
Here is another editing feature that I found quite handy when making spreadsheet entries or edits. If the lower right-hand corner of the display window is used for resizing (dragging with the mouse cursor) and the height of the window is reduced the program automatically crops the window, leaving just the display area itself. This results in the best possible view of the model when using a reduced size window. If you adjust the windows (display and spreadsheet) to the point where they dont overlap, then any editing done on the spreadsheet can be immediately observed in the display window.
|Checking the Model
Segment and geometry checking is yet another feature that makes your modeling chores easier. NWSs Check Model option examines the models geometry and wire segmentation to see that it does not violate NECs rules or guidelines.6 If any violations are found the program will display a list of errors or warnings in the NEC Geometry Warnings and Violations window illustrated in Figure 4. To assist you in making corrections this option also has a wire identification feature. Placing the mouse cursor and clicking on any line in the error list will highlight the implicated wire in both the display and the spreadsheet windows for viewing and editing. If the reported error involves more than one wire you can double-click on the same line and the second wire involved in the error is highlighted in the identical manner. You can toggle back and forth between the two wires by single or double clicking on the error.
If segment length violations are found you are given the option of having the program correct them for you. By clicking the Fix button the program will automatically correct the wire that is highlighted in the error listing or you may choose to correct all the segmentation errors at once by clicking the Fix All button.
I found it beneficial, when combining several wire grid structures in a complex model, to check for errors after each structure addition. It was much easier for me to make corrections as I went along rather than waiting until the whole model was finished.
Saving Model Files
You may save data files from either the display or spreadsheet windows. There are four file saving options available in NWS. You may choose to save the model as a native NWS file (*.nws). It is a good idea to save your model data using this option regardless of what other file saving options you may choose. By doing so you can create a library of models that can be opened by NWS for use at a later time.
The second option is a NEC input file (*.nec). If you select this option the program saves the wire data in a properly formatted ASCII text file which can be read by the NEC calculating engine or can be imported into other NEC type antenna analysis programs such as NEC-Win Plus.
The third saving option is an ASCII text file (*.txt). When using this option you are given the choice of saving the file in one of four different data arrangement formats that best suits your application.4
The fourth and final file saving option is an EZNEC ASCII text file (*.ezt). This option is provided for users of both the professional and standard versions of EZNEC. Importation into EZNEC of this specifically formatted file is done through EZNECs Wires page.7,8
For NEC-Win Plus Users
NWS has also been designed to run seamlessly from within Nittany Scientifics own NEC2 implementation NEC-Win Plus. If NWS is run from NEC-Win Plus an additional button is displayed on the toolbar which, when selected, will transfer all the wire geometry data to the NEC-Win Plus program and close NWS, sparing the additional steps of saving and then importing the data file.
There really isnt anything about this program that I was unhappy about or disliked. All in all, I found it to be quite robust and user-friendly. Anyone with even a small amount of antenna modeling experience should be comfortable using NWS. The user manual includes a fine tutorial section that will get you up and running in short order.
When you consider the short amount of time it took me to generate my truck model (Figure 2) that contained 182 wires with 499 junctions and 996 segments it is easy see how advantageous this program is. Just imagine how much time that it would take to construct that same model using conventional methods. Calculating and entering each wires end coordinates with proper segmentation without errors would require hours of work using conventional antenna modeling programs that only took a few minutes using NWS!
NWS can help you in many modeling endeavors such as trying different VHF/UHF ground plane systems, grids, circles, and even domes. Other structures can easily be put in an antenna field to check for interactions or test the consequences of the radiated field by modeling mobile antennas on a variety of vehicles and positions. These are just a few of the possibilities that you can easily do utilizing NWS with your NEC antenna modeling software.
I truly feel that for anyone who does serious antenna modeling this is a must have tool. The speed one can achieve to quickly and accurately generate wire grid models makes this program a godsend. If you havent surmised by now, I really like this program!
I have no association with Nittany-Scientific, except as a satisfied and enthusiastic user. This review is meant solely to pass along some useful information to other antenna modelers. -30-
Publisher/Distributor: Nittany Scientific, Inc., 1733 West 12600 South, Suite 420, Riverton, UT 84065; 801-446-1426; www.nittany-scientific.com . List Price $99.
1 NEC-Win Plus, Nittany Scientific, Inc, 1733 West 12600 South, Suite 420, Riverton, UT 84065; 801-446-1426; www.nittany-scientific.com .
2 EZNEC, Roy Lewallen, P.E., W7EL, P.O. Box 6658, Beaverton, OR, 97007, 503-646-2885; www.eznec.com
3 NEC input file commands supported are: CE, CM, GW, GS, and FR. If the input parser finds any other commands you will be warned but the supported commands will still be read in.
4 ASCII file format data arrangement options are #Segments X1 Y1 Z1 X2 Y2 Z2 Radius, #Segments X1 Y1 Z1 X2 Y2 Z2 Diameter, X1 Y1 Z1 X2 Y2 Z2 Radius, and X1 Y1 Z1 X2 Y2 Z2 Diameter.
5 NWS saves files that include the wire geometry (coordinates, diameters, and segments) data plus the frequency only. The additional required modeling data such as sources, conductivity; ground type and etc. are entered after you import the file into your modeling program. NEC users must add the additional NEC commands.
6 The Check Model feature tests for following errors; segments within volume of each other, wires parallel and too close, segments that cross at midpoint, wires which are parallel and overlapping, segments intersecting at midpoint, zero length wires, non valid junctions, segments too long and segment length less than radius.
7 From EZNECs Wires page menu choose [Other/Import Wires From ASCII File].
8 EZNEC standard version users: Care must be taken that the model does not exceed the standard versions limit of five hundred segments.
June 2001 antenneX Online Issue #50.
BRIEF BIOGRAPHY OF THE AUTHOR
Dan Richardson, K6MHE was first licensed in 1955 and has been enjoying amateur radio ever since. Dan was an electronic technician in the late 50s' and early 60s' and served in the US Coast Guard. He returned to the family Foundry business upon completion of military service. Dan later sold the Foundry business and retired a few years ago. He moved up to the North Coast of California, USA and has been playing with antennas and computers ever since. There, in a rural area, among the tall trees and without any CC&R limits he pursues his favorite pastime of stringing up and experimenting with antennas. He has also authored several articles on this favorite subject of antennas. Dan enjoys working with computers and spends a great deal of time testing and evaluating antenna design software.
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