I wrote this program for myself, but some others have found it useful.


EZNEC will do a frequency sweep, but its results go into a large, cumbersome file.  SimData will extract the most useful data from that file and place it into a new compact file that can be loaded easily into Excel, Mathcad, or other analysis program.


Optionally, SimData will draw graphs of gain versus frequency for one or more antennas, graphs suitable for publication.  SimData created this graph:




SimData is a Windows program that will run on Windows 2000 and newer, including Vista.  SimData is compatible with EZNEC 4, and probably other versions of EZNEC, but I am not sure which.


Running SimData the first time is not trivial.  It will take you some time to set things up properly.  But if you run SimData many times it can dramatically reduce your workload.  SimData is optimized for mistake-free repetitive usage.



There is no formal installation procedure.  You just download it and run it.  It is not a “registered” program and does not show up in the list of installed programs.


The second file below is a “graph control” file.  Such a file tells SimData how to draw a graph.  You can create this file from scratch, but it is easier to make a copy of the file below, and then modify it to do what you want.


Create a folder where you want SimData to reside.  We shall call this the “execution folder”.  It can be anywhere and have any name, but it should not be read-only.  Download both of these files into that folder.  You may want to create a desktop icon for starting the program.


Download SimData.exe now.     (468 KB)

Download graph DB8 gain.txt now.     (3 KB)


If you try this program, send me a note at kq6qv@aol.com and tell me how it worked out.


Running SimData

SimData assumes the execution folder has a sub-folder for each antenna type.  I keep the .ez file there.  SimData will create two identical copies of its output file.  One is placed in the sub-folder and is named “xxxDATA.TXT”, where xxx is one of these: VLF, LF, MF, HF, VHF, UHF, SHF, or EHF.  We shall call that file the “band data” file.  The second copy is called SIMDATA.TXT and is placed in the execution folder.  (I found this second file more useful for Excel, but you might have no use for it.)


SimData extracts the raw gain for the straight ahead direction only (The EZNEC X-axis direction).  Each line of the band data file is for one frequency, and contains the vertical gain, horizontal gain, SWR, terminal impedance, and frequency.


SimData assumes the execution folder has a file called SweepData.txt which was put there by EZNEC. 


The EZNEC main window has a space at the top for the name of the antenna.  This name is copied into the sweep file.  SimData takes the first word of this title and uses it as the antenna folder name.  So you must make the first word of the title match the antenna folder name.



SimData checks the validity of data, but it is not completely thorough in this.  If SimData blows up, you fed it bad data.  SimData is a little dumb. 


To create the Band Data file:

  1. Start EZNEC.  Make sure the first word of the title is the antenna folder name.  If the title is “CM4228: Channel Master 8-Bay” then CM4228 will be the antenna folder name.  (If the name ends in a colon, the colon will be deleted.  Otherwise an invalid file name would be attempted.)
  2. Click Setups > Frequency Sweep.
  3. Turn on Frequency Sweep.  (I usually read the frequencies from a file, but this is not necessary.)
  4. Check the box “Data file”.  Beside it, enter the file name “xxx\SweepData.txt”, where xxx is the execution folder.
  5. There is a group of 5 check boxes labeled Data File Contents.  Check the top 2 box only (Field Strength Table and Source Data).
  6. Click OK and run a simulation.  The SweepData.txt file will be created.
  7. Execute the SimData program. 
  8. Click the “Get sweep data” button.  The window will show the antenna name it found, the band name, a frequency count, and a termination message.  If the termination message is anything other than “Done” then something went wrong.



To draw a graph:

Create the graph control file.  Do this by copying an existing graph control file.  Putting the new file in the execution folder is recommended.  The new file must have the name “graph YYY.txt” where YYY is anything (something uniquely describing the graph).  YYY can have upper and lower case and can have spaces, but “graph “ should be lower case.


You can use Notepad to customize this file.  The file contains an explanation of what it does.  You will want to change the “Main graph parameters” in the top part of the file.


The Color Table is in the center of the file.  You may add additional colors.


The bottom of the file specifies which antennas are to be plotted and how they are to appear.


When the graph control file is ready, execute SimData and click “Draw graph”.  It will prompt you for the file name.


The “Regraph” button does the same but reuses the previously specified control file.  Neither SimData nor Notepad holds the file open, so both can be running at the same time.


The “Write to file” button saves the graph in SimData.bmp, in the execution folder.  You can use Paint to convert it into a GIF file.


(The graph data is taken from the band data files.  The program ignores data for frequencies outside the limits of the graph.  The files do not have to match each other in terms of what frequencies are present.  All plots are drawn as continuous, breaking only at the graph edges.  The program is not properly though out for when a file or graph crosses a band boundary.  So what the program will do when the data spans 3MHz or 30MHz or 300MHz is not known.  The first frequency the program sees determines which band it thinks it is in.)


Getting all this working will be a challenge.  But after the first time it becomes easy.










This page is part of “An HDTV Primer”, which starts at    www.hdtvprimer.com