Zplots

Impedance Plots using Excel Charts

Contents

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Zplots is an Excel application that allows you to plot impedance and related data obtained from a variety of sources. You can plot on both an XY chart and a Smith chart as well as view the data in tabular format.

The XY chart can be customized with your choice of trace lines. Frequency (in MHz) is always shown on the X axis. On the primary (left side) or secondary (right side) Y axis you can plot:

• SWR - Standing Wave Ratio
• Rs - Resistance, series form
• Xs - Reactance, series form
• Zmag - Impedance magnitude
• Theta (deg) - Impedance angle
• Rho (mag) - Reflection coefficient magnitude
• RL (dB) - Return Loss, plotted as a negative number to show "reverse" scale (see note below)
• Phase (deg) - Reflection coefficient angle
• % Reflected Power
• Q - Quality factor, |Xs| / Rs
• Rp - Resistance, parallel form
• Xp - Reactance, parallel form
• Ls (µH) - Equivalent inductance for series Xs, both positive and negative
• Cs (pF) - Equivalent capacitance for series Xs, both positive and negative
• Lp (µH) - Equivalent inductance for parallel Xp, both positive and negative
• Cp (pF) - Equivalent capacitance for parallel Xp, both positive and negative
Note concerning RL: Return loss is of course a positive number. In Zplots it is plotted as a negative number merely as a convenient way to show a reverse scale, with zero at the top and higher (magnitude) values lower down. This is the typical way of plotting RL.

Negative values for Ls, Cs, Lp, and Cp may be interpreted to mean the amount of inductance or capacitance which must be added, in series or parallel respectively, to "cancel out" the corresponding reactance.

The order of the items in the above list has no special significance other than that the items most likely to be chosen for plotting are near the top. On the secondary (right side) Y axis you can also choose "(none)" to indicate no secondary plot line.

A Mini-Smith chart is shown on the same sheet with the XY chart. To see both the XY chart and the Mini-Smith at the same time you must have your screen resolution set to 1024x768 or higher and you must maximize both the Excel window and the workbook sub-window (using the lower set of size buttons). Alternatively, on the Excel menu you can select View | Zoom and choose a magnification level less than 100%.

Zplots can read impedance data from:

• AIM - Antenna Analyzer AIM430 / AIM4160 / AIM4170 by W5BIG    (more info) / (forum)

On the menu bar select File | Save Graph. The current scan will be saved in two formats. The *.scn file is used by AIM if you want to reload the scan data at a future time. AIM also saves the scan data in *.csv format that can be read by Zplots. Software must be version 547 or later.

• VNA2180 - Vector Network Analyzer by W5BIG    (more info) / (forum)

On the menu bar select File | Save Port A Graph. The *.csv saved file can be read by Zplots. Note that only the Port A file format is supported. Zplots will not recognize the Port B format file.

• VNA4Win - Windows software for the N2PK VNA by GM4PMK and GM3SEK    (more info) / (forum)

After at least one sweep has been completed, the Save Data button will appear when the sweep is stopped. Clicking Save Data opens a dialog box to allow you to save the measurement results as a *.csv file. Zplots can read this file.

• Exeter - VNA Control Software by W8WWV    (more info) / (forum)

An Exeter data set is created whenever a data capture finishes without error. You may then use the Save As button (or File | Save Data Set As on the menu bar) to save the data in *.csv format. Zplots can read this file. Note that Zplots makes use of only the default fields in the file. The file may contain other fields as well; these are ignored by Zplots.

• Refl.exe/Trans.exe/GrpDel.exe - DOS store data programs by N2PK    (more info) / (forum)

These programs can create various .DAT files and Zplots can read these files. If the file contains multiple DUT data sets you will be asked which one you wish to show. Note that it is not necessary to change the file extension to something other than .DAT, although you may do so for other reasons.

• myVNA - GUI program for the N2PK VNA by G8KBB    (more info) / (forum)

Use "Load & Store Data" and then "Save to File". In the "Save as type" drop down list select "CSV Data Set" -or- "VNA4Win CSV files" -or- "Touchstone Format". For Touchstone Format, be sure you have already used "Set Touchstone File Options" and selected 'S' as the "Save Parameter Type". You may choose any option for "Save Format".

• VNA1 / miniVNA / IG miniVNA / miniVNA PRO / vna-J / Blue VNA -
Antenna Analyzer and miniVNA by IW3HEV, et al.    (more info) / (forum)

• VNA1: Save sweep data in *.csv format via File | Save As on the menu bar. Software must be version 1.1.8 or later.

• miniVNA: Save sweep data in *.csv format via File | Save As (.csv) on the menu bar. When prompted to "Select csv Format" be sure to use a comma as the data separator. Software must be version 2.2.8 or later.

• IG miniVNA: Save sweep data in *.csv format via File | Save .CSV for Zplots on the menu bar.

• miniVNA PRO: Use File | Export .csv (Zplots) -or- select the "S-parameters" tab and then follow the procedure for creating either 1-port or 2-port S-parameter files. Software must be version 2.4.0.4 or later.

• vna/J: Use Export on the menu line (or the corresponding toolbar button) to export the scan data in "Zplots" format -or- "S-parameter" format. The DL2SBA vna/J software supports both the original miniVNA and the miniVNA PRO hardware. Software must be version 2.6.4 or later.    (more info)

• Blue VNA: This is an Android only application by YO3GGX to control Bluetooth enabled antenna analyzers or VNAs. Supported devices are miniVNA (equipped with a Bluetooth add-on) and miniVNA Pro (with or without the Extender). See "Exporting data to be used in external applications" in the user guide.    (more info)

• TAPR VNA - TAPR Vector Network Analyzer    (more info) / (forum)

Use File | Export on the menu bar and then choose Rectangular or Polar format (but not csv format).

• DG8SAQ VNWA - DG8SAQ Vector Network Analyzer    (more info) / (forum)

If you have made one-port measurements (such as for an antenna system), on the menu bar use File | Export Data | Trace | S11 and then choose any of the three options to create a file in s1p format. If you have made two-port measurements (such as for a filter), on the menu bar use File | Export Data | S2P and then choose any of the three options to create a file in s2p format.

As an alternative to File | Export Data, you may enable an external tool in the VNWA Tools | Configure Tools dialog panel and check the "Autowrite measurement data" box. If this box is checked (and the tool is enabled), VNWA will automatically write file 'default.s2p' to the folder specified in "Path" for that tool after each scan is completed. Zplots can read this file. (This feature available in VNWA version Beta 33.f and later.)

• RigExpert AA-30 / AA-1400 - with AntScope software    (more info) / (forum)

On the AntScope menu bar choose File | Export to | CSV file or File | Export to | Touchstone file. Zplots can read either of these files.

The DL1SNG application software for the PC can create a *.csv file containing impedance values in real and imaginary format. Zplots can read this file.

Zplots can read Touchstone s1p/s2p format files that are produced by many different applications, with the following restrictions and limitations:

• Only one-port (s1p) and two-port (s2p) type files are supported. The file name must include the extension .s1p or .s2p.
• Data type S only, not Y, Z, H, or G.
• "Keywords" as described in Version 2.0 of the Touchstone File Format Specification are not allowed.

For s1p files, Zplots will assume that the file contains S11 (reflection) type data. This is the Touchstone standard, although some programs such as the DG8SAQ software mentioned above can create s1p format files containing non-S11 data. Such files can be read by Zplots although the results may be confusing.

For s2p files, Zplots can display various subsets of the s2p data: Reflection (S11 or S22) only, Transmission (S21 or S12) only, or both (S11/S21 or S22/S12), for either the Forward or Reverse direction. If Reflection data is displayed, with or without Transmission data, then a Smith chart is also shown. To change the subset selection use the "Change S2P Subset(s)" button (see below).

Unlike many VNA control programs and other software that can read Touchstone s2p files, Zplots cannot display both forward and reverse data at the same time. However, you can display one type of data, take a Snapshot of the trace(s), and then display another type of data. (See below for more details about Snapshots.)

Every time you run either an SWR sweep using the SWR button or a Frequency Sweep via Setups | Frequency Sweep on the menu bar, EZNEC will automatically create a file named LastZ.txt. With EZNEC v. 5.0 the file is written to the EZNEC home folder, typically C:\Program Files\EZW. With EZNEC v. 6.0 the file is written to the folder specified under Options | Folders | Output Files, typically sub-folder "EZNEC 6.0" under "My Documents". Zplots can read the LastZ.txt file.

Because EZNEC overwrites this file every time a sweep is done you may have decided to make a copy under a different name. You may also have changed the file extension from .txt to .csv to allow more convenient use with a spreadsheet program. Zplots can read the file no matter what name or extension it may have.

Caution for EZNEC v. 5.0 under Vista / Windows 7 / Windows 8 / Windows 10: If you have installed EZNEC v. 5.0 to the default location, under these operating systems the LastZ.txt file will probably be written to folder C:\Users\[UserName]\AppData\Local\VirtualStore\Program Files (x86)\EZW. You must navigate to that folder when attempting to load the file.

• Antenna Model - Software for the Analysis of Wire Antennas by Teri Software    (more info)

After you have done a scan via Calculate | Frequency Scan on the menu bar you will have the option to save the impedance data (and other data) for the model. On the menu bar choose File | Export Impedance Data Points, or press Ctrl-M. A file named [model]Impedances.csv will be written to the Archive folder. (If you want the file to go someplace else press Shift-Ctrl-M instead of Ctrl-M and you will get a Save As dialog box.) Zplots can read this file. Software must be version 635 or later.

Some of the programs mentioned above can create "Transmission" and/or "Group Delay" type data as well as "Reflection" data, either as a separate file or as part of a Touchstone s2p file. Zplots can read this data and show an XY plot for:

• TL (mag) - Transmission loss (also called insertion loss) magnitude
• TL (dB) - Transmission loss in dB, plotted as a negative number to simulate "reverse scale"
• Phase (deg) or Grp Delay (µsec) - Phase shift or Group delay, depending on file contents
When a "Transmission" or "Group Delay" type data is used as input to Zplots the Smith charts and certain other program functions will be disabled.

Zplots shows a large Smith chart on a separate sheet, as pictured in the above screen shot. Note that the marker line / marker dot frequency markers are synchronized on all three charts.

Buttons available on the various sheets are:

Load Data: Read a data file from one of the above-mentioned sources.

Note: You do not use File | Open on the Excel menu bar to read a data file. You would only use File | Open if you wanted Excel to open a different spreadsheet program (also known as a different workbook), such as one you might have created to track the family budget. Although Zplots has the "look and feel" of a normal application program it is important to remember that it is merely a very refined spreadsheet. The operation of Zplots is controlled by the buttons on the various sheets, not by the Excel menu bar.

If you do use File | Open to read a data file, Excel will open that file in a separate workbook window. Excel can have multiple workbooks open at one time, such as one for your family budget and another to track your investments. This can be confusing to new users of Excel because typically one workbook window completely hides any others. Zplots is still there, except it is "underneath" the data file window you just opened. Just switch back to the Zplots window, using the Excel menu bar 'Window' selection (just to the left of 'Help') or by pressing Ctrl-Tab, and Zplots will ask you if you want to load the data from the "other" window.

As an additional reminder, anytime Zplots is active you will see a new first entry in the list of choices under the Excel File menu. The new choice is 'Zplots: Load Data...' and selecting that item is exactly the same as clicking the "Load Data" button.

Refresh: Reloads the current data file (same name, new data) into Zplots. Once you have loaded a data file initially and specified the folder and file name, you can switch back to the window with your hardware control program, do another scan and save the data again (using the same file name and folder), then switch back to the Zplots window and click Refresh.

Enable Polling: If checked, Zplots will automatically run a small macro once per second to check the file date/time of the currently loaded data file. If the file is found to have a newer date/time, it will be automatically loaded. Hence if you do another scan and save the data again (using the same file name and folder), then switch back to the Zplots window, you will find that the new data has already been loaded (or will be within one second).

Some hardware control programs can be configured to automatically save a new data file after each scan. In that case there is no need to manually save the data from the control program and, if the Enable Polling box is checked, there is no need to take any action to load the data into Zplots. If you are doing continuous scans there is no need to return to the hardware control program at all; you can just stay with the Zplots window and watch as the plots are refreshed.

Note that this is not quite the same as "real time display" of your scan data. For example, suppose your hardware control program is set to do continuous scanning and produces a new data file (using the same name) every 0.25 seconds. Only every fourth such file would have a new date/time, since the date/time granularity is 1 second. Even then, Zplots might sometimes "miss" an update because it may take a considerable portion of a second (or even longer) to load the data, especially for files with many data points.

If you enable polling while doing continuous scans you may wish to lock the left and right scales of the Custom XY chart beforehand. That way, each time a new data file is loaded the XY traces will not "jump" because of any possible differences in the way Excel automatically sets the scale min and max limits. If you lock the scales beforehand, any changes in the traces will be due entirely to changes in the data, not a combination of changed data and changed (auto) scaling.

With polling enabled you are still free to interact with Zplots as normal. That is, you can set markers, take snapshots, and perform other actions. Data refresh will be suspended while you are doing these things but will resume when you are done. If you change the trace selection for the left/right scales of the XY chart, and the scales are presently locked, you may want to relock with new min/max values. Otherwise the new trace may be entirely "off scale" and not visible. For more information see "Set/Lock Scales" below.

The Load Data button, Refresh button, and Enable Polling check box may be thought of as a "hierarchy of convenience" for loading new data into Zplots. With Load Data you specify the file to be loaded using the standard Windows "File Open" dialog. With Refresh, the current file (same name and folder) is reloaded when you click the button. With Enable Polling, the current data file is automatically loaded every time the file date/time changes, at most once per second.

Change S2P Subset(s): Allows you to change which subset(s) of s2p data (S11, S21, S12, S22) are to be displayed. The Change S2P Subset(s) button appears below the information text box which shows the name of the currently loaded file. This information box also shows which subset(s) are currently being displayed. The Change S2P Subset(s) button will be visible only when s2p type files are loaded.

Generate Data: Use this button to create and then automatically load a frequency sweep data file independent of any other program. (More details below.)

Change Zo: Some data sources include the reference Zo value that was used to compute Rho (and hence SWR, Return Loss, % Reflected Power, and Phase). Others do not, in which case Zo will default to 50. You can use this button to change Zo at any time. You may also click directly on the text box in the upper left corner of either Smith chart to change Zo. You may find this convenient when viewing the Mini-Smith.

Main/Axis Titles: (Custom XY chart only) Change the text shown for the main chart title, the X axis title (normally "Frequency"), the primary (left side) Y axis title, and the secondary (right side) Y axis title.

Legend Box: Add or delete the legend box and change the text shown in the box. You can move the position of the legend box by dragging with the mouse. When you are done click anywhere outside the chart.

Copy: Copy the chart (main chart only on the Custom sheet) to the clipboard, with optional resizing. The chart can then be pasted into another application such as Word or Paint.

GIF: Create a GIF file of the chart (main chart only on the Custom sheet), with optional resizing. The GIF file can then be used with email and web pages.

Print Preview: This shows what the chart (main chart only on the Custom sheet) will look like if printed. You can of course then print the chart, but you might also want to use this button just to see a magnified version of the chart which may help in picking out fine details. (Excel 2007 only: The print preview for the Smith chart will show an oval rather than a circle for the outside ring. This is a known bug in Excel 2007. The Copy and GIF functions mentioned above work correctly.)

Dots On/Off: When "On" you can see a round dot for each data point on the chart traces. When "Off" the traces are just lines.

Line Weight: Allows you to cycle through thin, medium, and thick weight trace lines.

Set/Lock Scales: (Custom XY chart only) The min and max settings for the primary and secondary Y axis scales are normally set automatically by Excel. You can use this button to "freeze" the min and max at values of your choice. You can also set the min and max of the X axis in order to "zoom in" on a frequency subset of interest. In addition, for all three chart axes you can set the distance between gridlines.

Warning: The scales will stay locked until you manually reset them. Suppose you are plotting SWR and you set the Y axis min to 1 because you know that the SWR value will never fall below 1. Then you decide to plot Rho. Since Rho values are (almost) always less than 1, the trace line for Rho will be entirely "off scale" and will not be visible. The data is not lost; once you return to automatic scaling the trace will re-appear.

Logarithmic Scaling: This button is also used to select between linear and logarithmic scaling for both the primary and secondary Y axis scales and the X axis (Frequency) scale, all of which may be set independently from the others.

Zoom M1 to M2: (Custom XY chart only) This button offers a more convenient way to zoom in on a frequency range of interest. Set Marker1 with the left mouse button and Marker2 with the right mouse button. Press "Zoom M1 to M2" and the frequency range of the X axis will be changed to match the range between the two markers. When you use this button (or if you do the same thing manually using "Set/Lock Scales"), an additional Full Range button will appear allowing you to return to showing the entire set of frequencies available in the data file.

Snapshots: This button has two uses. On the Custom XY chart you can use snapshots to plot more than two trace lines at the same time. For example, you could plot Xs on the primary (left scale) axis and take a snapshot. Then plot Rs (again on the left axis) and take another snapshot. Then plot Zmag. While you are doing this you can be showing Theta (for example) on the secondary (right) axis. When you are done you will have four trace lines: Zmag, Rs, and Xs using the left scale and Theta using the right scale. On the Custom XY chart, snapshots 1 and 2 are associated with the primary (left scale) axis; snapshots 3 and 4 are associated with the secondary (right scale) axis.

On both the Custom XY chart and the Smith chart you can also use snapshots in order to compare data from one sweep against that from another. Snapshot traces persist when you load new data. Hence you can, for example, load data from one file, take a snapshot, load data from a different file, and see how the two compare. If you are using one of the VNA control software programs you could load a "Transmission" type file, take a snapshot, then load a "Reflection" type file and see the S21 and S11 traces overlaid.

You can also compare data from completely different sources. For example, suppose you modeled an antenna with EZNEC, constructed a "real-world" version of the model, and took some impedance measurements when you were done. You could load the EZNEC SWR sweep data (from LastZ.txt) into Zplots and take one or more snapshots. Then load the data file produced by your AIM or VNA software. Now you can see the difference, hopefully small, between the "as modeled" as "as measured" data. (See below for more on the Zplots 'Add or Subtract Transmission Line' feature which allows you to account for the fact that your modeled impedance [probably] represents the antenna feed point while your measured impedance was [probably] taken at the input end of a feedline.)

Reference Lines: (Custom XY chart only) Use these buttons to add horizontal marker lines to the chart, perhaps to aid in analysis or presentation. You can show up to two reference lines associated with the left scale and up to two reference lines associated with the right scale.

Zplots also has a fifth reference line not under direct user control. Whenever you plot any item on the RIGHT (secondary) axis that is likely to have both positive and negative values, such as Xs or Theta, Zplots will show a dotted line which corresponds to zero on that axis. This may be helpful in situations where there is not a normal gridline at the zero value. Note that when plotting items on the LEFT (primary) scale it is usually possible to set the scale min and max values such that a gridline will show at the zero value, hence there is no need for a "program-controlled" zero line for the LEFT axis.

Zoom In/Out: (Smith chart only) In some but not all cases it is useful to be able to zoom in on the center portion of the Smith chart. The zoom steps correspond to: Full size > SWR 5:1 > SWR 3:1 > SWR 2:1, with some overshoot in the corners at anything other than full size. When you zoom the main Smith the Mini-Smith will follow.

SWR Circle: (Smith chart only) You can choose to show a constant SWR circle at a specified size, hide (not show) the circle, or have the circle auto-size to match the frequency marker. (More on frequency markers below.)

Add/Subtract Transmission Line (Add/Subt T Line): For modeled antenna data you may wish to "Add" a transmission line to the results to see what the impedance or SWR would be at the transmitter (or tuner) end of the line. Zplots lets you do that without making any changes to the model itself, such as adding a NEC TL card and an extra wire. On the other hand, for measured data you may wish to transpose the measurements to the antenna feedpoint. In that case you can "Subtract" a transmission line. Either way, you can choose from several dozen line types or you can specify your own line characteristics such as nominal Zo and VF. Line loss is included in the calculations. You can 'Apply' the transformation without closing the dialog box, perhaps to see the results as you are viewing one of the charts. It may be helpful, although not required, for you to take a snapshot of the original trace before doing the transformation. This will allow you to visually compare the "before" and "after" impedance values.

Important: The "start point" for the impedance transformation will ALWAYS be the impedance as contained in the source data file that is currently loaded into Zplots. So, for example, if you "Add" a transmission line of length 50 feet and then "Add" 55 feet, the length of the simulated line will be 55 feet, not 105 feet. Similarly, if you "Add" 100 feet and then "Subtract" 100 feet you will not be back to where you started, you will see the results of subtracting 100 feet. To return to the original values use the 'Undo' button.

Measure Transmission Line Parameters (Measure TL Parms): See below for a detailed example of how to use this feature.

Save as S1P: This button may be used to create a Touchstone s1p format file that reflects the current state of the data that has been loaded into Zplots. For example, you may have added or subtracted a transmission line to do an impedance transform on the data. Or you may have generated data from within Zplots and you now wish to use that data in another program that can read Touchstone files. Or you may have loaded data into Zplots from a source whose format is not supported by the other program.

Freq KHz/Hz: Allows you to cycle between displaying frequencies with a 1 Hz granularity or rounded to the closest KHz. Affects hover chart tips (see below for more info) and marker table display of frequency precision as well as what is shown in column A on the Data sheet. On the Custom sheet, this button is visible only when a Marker is being shown.

Min/Max/Avg: (Text, not a button; Custom XY chart only) Shows the minimum, maximum, or average of whatever is plotted for the primary and secondary (if any) axes on the Custom XY chart. Point to the text (cursor shape will change to a left-right arrow) and click to cycle through the three options. If you have zoomed in on a subset of the frequency range only the data points within the zoomed range will be considered.

Example of using the "Add Transmission Line" feature:

 Here are the results of a frequency scan from 13 to 23 MHz on an indoor 20M/15M trap dipole, tacked up to the ceiling about 8 feet off the ground. The measurements were taken at the end of a 23 foot length of RG-58 transmission line using an AIM4160 device. The frequency progression follows a clockwise path on the trace. The blue dot marker and the associated text box show the 13 MHz scan point. (This is the same Smith chart as is shown in the above screen shot, except this image was made using the GIF button with optional resizing. Notice that when you use the Copy or GIF buttons only the chart itself is captured, not including all the various control buttons that are normally shown.)
 Here are the results of an EZNEC SWR sweep for a model of a 20M/15M trap dipole over the same frequency range. The data is from the EZNEC LastZ.txt file and represents the impedance as seen at the feedpoint of the antenna. As you can see, it is not very obvious that these two Smith chart traces have anything to do with each other.
 Finally, here is the original measurement data (red) compared with the modeled data (green), except that a 23 foot length of RG-58 has been "Added" to the modeled results. The traces match fairly well at the higher frequencies of the 15M band. For the lower frequency 20M band it is obvious that the model has some shortcomings, perhaps related to all the interactions with house wiring and roof gutters. (Or perhaps I just didn't do a very good job of creating the model!) But at least now it is apparent that there is some kind of correlation between the measured and modeled data.
 This is the dialog (reduced-size image) that controls transmission lines. Choose Add or Subtract, select a line type, enter a length and select the length units. If you click 'OK' the transformation will be applied and the dialog window will close. If you click 'Apply' the dialog window will stay open after the calculations are complete. 'Undo' is used to remove any previous-applied transformations. The spin button changes the length of the line by +/- 1 or +/- 0.1 (in the current units) and then does an 'Apply' operation. Hence the spinner may be used to make adjustments interactively while you watch the results change on the charts. To use custom values for the transmission line parameters select the last entry in the 'Type' drop down box which is the 'User Specified' line type. Doing so will allow you to set the Nominal Zo, Nominal VF, K0, K1, and K2 boxes. (If you are uncertain about K0/K1/K2 just set the values the same as for a similar line type.)
 Anytime a transformation has been applied a small reminder will appear underneath the "Add or Subtract" button.
 This is a sub-dialog panel that you may find useful to help in determining particular line lengths. It is basically a calculator for the velocity factor equation in different forms. Choose which item you want to solve for and the results will be computed automatically as you change the input fields. For example, suppose you want to know how long a half-wavelength is for a transmission line with a velocity factor of 0.66 at 10 MHz. As the example at left shows, enter values of "10", "0.66", and "0.5" in the appropriate boxes and read 32.458 feet or 9.893 meters as the answer.

Example of using the "Subtract Transmission Line" feature:

 This is a plot of Rs and Xs for a 15M band quad as measured at the transmitter end of 57.5 feet of RG-213. Interesting, but it doesn't really tell you too much about what is going on at the antenna itself. Note that Rs (red trace) uses the left scale and Xs (blue trace) uses the right scale. There is absolutely no significance to the frequency at which the two trace lines cross.
 And here are the results after "Subtracting" 57.5 feet of RG-213. You can see that both the Rs and Xs values are completely different; note the different scales as compared to the plot above. It is also obvious now that the antenna is resonant (Xs = 0) at 21.16 MHz.

Example of using the "Measure Transmission Line Parameters" feature:

 The Zplots "Measure Transmission Line Parameters" feature allows you to measure and plot several different items having to do with transmission lines, namely: The line's characteristic impedance (Zo) in terms of magnitude |Zo|, real part Ro, and imaginary part Xo; The true velocity factor and time delay at any frequency; The matched line loss in terms of dB loss over total line length, dB/100ft, dB/100m, and the equivalent S21 insertion loss magnitude in dB; The distributed R/L/G/C (resistance, inductance, conductance, capacitance) line characteristics in both "per foot" and "per meter" terms. Before you do anything with Zplots you must create the appropriate data file(s) and for that you can choose between two different methods. For the first method create a pair of files, one using an open circuit termination and the other using a short circuit termination. That is, terminate the transmission line in question with an open circuit and use your VNA or analyzer hardware to run a sweep over a frequency range of interest. Then change the termination to a short circuit and run another sweep, using exactly the same frequency range and step size. Save the data from these two sweeps in a format that can be loaded into Zplots. Important: As much as possible, try to keep the electrical length of the line exactly the same between the open and short termination conditions. Ideally you would terminate the line with the same standards that were used to do the hardware open/short calibration. The second method is to attach both ends of the line to a VNA and create a Touchstone s2p format file that contains both S11 and S21 data. Of course this assumes that you have a two-port device (like a VNA, not an antenna analyzer), that you have performed the necessary "transmission" as well as "reflection" calibration steps, and that you are using control software that can produce Touchstone s2p format files. Note: This method may be used for lines of any characteristic impedance; it is not restricted to just "50 ohm" type lines. After you have created the necessary file(s) click the Zplots "Measure TL Parms" button. On the first panel shown (at left, top) use the check box to indicate whether you have created a pair of files (check box unchecked) or a single file (check box checked). Then you will be asked to enter the physical length of the line. After that you will be prompted to either a) load the open circuit termination file and then the short circuit termination file, or b) load the single Touchstone s2p file. When loading the files you will be presented with the standard Windows "Open File" dialog. If you lose your train of thought and can't remember which file you are to load, just check the title bar of the standard dialog. You'll see a prompt informing you of which file is expected.

After a few seconds of processing Zplots will automatically switch to "Transmission Line (TL) Parameters" mode. Since you will no longer be viewing normal impedance data the drop-down selections for the left and right axes of the Custom XY chart are completely different. In addition, the Smith chart and certain buttons will not be available since their use is not compatible with "TL Parameters" type data. To return Zplots to the normal "Reflection" plot mode, either load a standard data file or click the text box reminder that appears in the upper right portion of the Zplots window.

When the Zplots display is in "TL Parameters" mode you can plot:

• |Zo| - Characteristic impedance magnitude
• Ro - Real component of characteristic impedance
• Xo - Imaginary component of characteristic impedance
• VF - Velocity Factor
• Loss (dB) - Matched line loss in dB for the length of the line
• Loss/100ft - Matched line loss per 100 feet
• Loss/100m - Matched line loss per 100 meters
• |S21| (dB) - Equivalent S21 loss in dB for the length of the line (mathematically derived from the open/short termination data files if necessary)
• Dist R (mohms/ft[m]) - Distributed resistance, mohms per foot (or meter)
• Dist L (nH/ft[m]) - Distributed inductance, nH per foot (or meter)
• Dist G (µS/ft[m]) - Distributed conductance, µS per foot (or meter)
• Dist C (pF/ft[m]) - Distributed capacitance, pF per foot (or meter)
• Delay (ns) - One way time delay for the length of the line

 For example, this is a plot of the measured loss corresponding to scans from 1 to 160 MHz on 37.9 feet of Radio Shack (Tandy) RG-58. Scans were done with an AIM4160 device. Notice the slight "wiggles" in the trace, representing noise or other anomalies of the data.

 And here is the velocity factor plot for the same sample of RG-58, plotted with a logarithmic frequency scale and clipped at 100 MHz. Note the significant amount by which the velocity factor changes at lower frequencies. VF approaches the "nominal" value of 0.66 only at very high frequencies.

 The nature of the underlying calculations is such that the loss and velocity factor curves will in general be smooth. However, curves for the characteristic impedance (|Zo|, Ro, Xo) will have "bumps" corresponding to the quarter-wave point frequencies. With a nominal velocity factor of 0.66 the 37.9 foot sample of RG-58 is a multiple of one-quarter wavelength at approximately 4.2, 8.4, 12.6, etc. MHz. As shown, the |Zo| curve has moderate perturbations at the odd quarter-wave points and severe swings at the even quarter-wave (half-wave) points.

The same will be true when displaying the distributed R/L/G/C curves. In order to avoid these "bumps" you can either use a shorter section of transmission line or reduce the maximum frequency of the scan.

 In addition to showing plots for various parameters Zplots will also calculate and display the five electrical characteristics that are needed to define a mathematical model of the transmission line. These are the "nominal" values for Zo and VF along with the K0/K1/K2 loss coefficients. (K0 is associated with the DC resistance of the conductors which is a constant for any given line type. K1 is associated with the "skin effect" or "high frequency" resistance of the conductors which varies in proportion to the square root of frequency. K2 is associated with the dielectric loss which varies directly with frequency.) These five items, along with the length, completely define a transmission line. The calculated values will automatically be assigned to the 'User Specified' line type. You may then make use of the 'User Specified' line in two ways: You can use this line when you "Add" or "Subtract" a transmission line in order to see the effects of the impedance transform. For example, suppose the 37.9 foot length of Radio Shack RG-58 from above is now pressed into service to feed a 20M dipole. You could use your AIM or VNA device to scan the 20M band at the transmitter end of the line, and then use the "Subtract" feature to see what the R and X values would be at the antenna terminals. Or you could use EZNEC to model a 20M dipole and then "Add" a transmission line to see what the R and X values would be at the transmitter. Note that the frequency range used when you "Add" or "Subtract" a transmission line need not be the same as that used when you "Measure" the line. You can use this line in conjunction with the "TL Parms" tab of the "Generate Data" feature of Zplots. A detailed example appears farther down the page.

Example of using the "Generate Data" feature for normal impedance data:

 This is the dialog (reduced-size image) that controls the generation of frequency sweep data internal to Zplots. Specify the desired start, stop, and step values for frequency. The Number of Points box will be recalculated automatically as you are making changes to the frequency range or step size. The Number of Points box is read-only, but if you don't care about the frequency step size in MHz you can specify the number of points to be generated by putting a 'p' after the number in the "Step" box. That is, if you want 100 data points enter "100p" (no quotes) in the box. Note that using the 'p' option may result in some very odd frequency steps between the Start and Stop frequencies. You can also specify that the points are to have exponential spacing instead of linear spacing by appending 'e' instead of 'p' after the number of points. The frequency steps will then be closer together at the low end of the frequency range and farther apart at the high end. Then if you use the "Set/Lock Scales" button to specify a logarithmic X axis (Frequency) scale, the data points will be evenly spaced. (Hint: Use the "Dots On/Off" button to see the difference.)

For the type of data to generate you can choose a simple R and X combination (which will not vary as the frequency changes), a series combination of R and L, a parallel combination of R and C, R-L-C components arranged in a trap configuration, or a model of a quartz crystal with Rs, Ls, Cs, and Co.

Note: If you don't see the tab for the type of data you want to generate you may have to click the left or right scroll button as indicated in the red circle on the image above.

Zplots will create a file named '\$Zplots\$Generated.csv' in the same folder that contains the Zplots.xls workbook. This file is then automatically loaded. The file is not erased when the operation is complete. You are free to modify the contents of this file if you wish, perhaps cutting and pasting from another application. (Don't change the first two lines. And note that the file contains columns for only Frequency in MHz, series form R, and series form X no matter what type of data was specified in the dialog window.) You can then load the modified data into Zplots just like any other data file. The file name will be reused the next time you use the "Generate Data" feature, so if you modify the contents you may wish to also rename the file.

 This shows what the above R-L combination looks like after being transformed via 39 feet of RG-58 transmission line. In this particular case I had soldered two 47 ohm resistors in parallel between the braid and center conductor at the far end of a length of coax. The small value for L is used to account for the inductance of the short length of wire on either side of the resistor bodies. I then simulated what the impedance would be at the input end of the line so that I could compare it with measurement readings over a frequency range from 1 to 50 MHz.

The above is an example of how you can simulate a transmission line with an arbitrary load over a frequency range of interest. That is, generate the load first and then add a transmission line.

Below is another example of using the "Generate Data" feature, this time for a quartz crystal. The parameter values are shown in the dialog box on the left. Note that when you model a crystal Zplots will automatically calculate the series and parallel resonant frequencies as you change the values for Ls, Cs, and Co.

The results of the simulation are shown on the right. The resonant frequencies are the points where Theta (impedance angle) crosses the zero line.

Example of using the "Generate Data" feature for transmission line parameters:

 The "TL Parms" tab of the Generate Data dialog lets you create "Transmission Line Parameter" type data based on mathematical models as opposed to actual measurements. In the example at left the choice for Transmission Line Type has been set to 'User Specified'. Notice that all of the fields have been pre-loaded with the values that were calculated in the example above concerning transmission line parameter measurements. In this particular example the frequency range and the line length are also the same as when the line was measured, but that is not a requirement. The "definition" of a transmission line is not frequency dependent and the length is used only if a) an impedance transform is being done, which is never the case when displaying "TL Parameter" type data, or b) you wish to plot the loss for a particular line length, say 75 feet, in which case you can specify any length desired.

 This is the plot that will be shown when you click "OK" and choose "Loss (dB)" as the parameter to be displayed on the primary (left) vertical scale. The values plotted are those calculated using the K0/K1/K2 coefficients that were determined when the line was measured. Notice how the "wiggles" have been removed. That's because the data shown here has been "curve fit" to the values that were calculated for the multiple discrete frequencies in the measurement example.

 Remember all the "bumps" that were present in the plot for |Zo| when the line was measured? The chart at left compares the original measurement data (green trace) with |Zo| as generated based on the derived parameters (red trace). In general this is a technique you can use to remove the "bumps" from measured data. That is, measure the line to determine the electrical characteristics (nominal Zo, nominal VF, loss coefficients K0/K1/K2), then generate data from a mathematical model that is based on those characteristics. Then select the desired parameter to plot from the drop-down list.

 Of course you are not restricted to showing plots for just lines that you have measured. To create the plot at left I first changed the frequency range from 1-160 MHz to 1-1000 MHz, keeping the Transmission Line Type as 'User Specified'. Then I changed the plotted parameter to "Loss/100ft" and took a snapshot. Next I chose 'Tandy Cable RG-58' as the line type, resulting in a loss plot according to the manufacturer's specifications. Then the "Set/Lock Scales" button was used to select logarithmic scaling for both the left vertical axis and the horizontal (Frequency) axis.

When dealing with "TL Parms" type data there may be times that you wish to switch back and forth between displaying measured data versus generated data. There is no need to repeat the entire measurement process as described in the earlier example. Just click the "Reload Measured Data" button. This button will be visible only when you are working with transmission line parameters, after you have done a measurement, and after you have switched to "Generate" mode as opposed to "Measure" mode.

Example of using the "Generate Data" feature for a transmission line at fixed frequency:

 The "TL FF" (Transmission Line at Fixed Frequency) tab of the Generate Data dialog lets you examine the response of a transmission line from a different perspective. Rather than seeing the results at the input or load end for a transmission line of fixed length over a frequency range of interest, you can see the response along a transmission line at a fixed frequency. As the panel at left shows, the input fields for this particular "Generate" mode are not the same as for the other "frequency varies" modes. Instead of setting the start, stop, and step frequencies you set the start, stop, and step line lengths for a single, fixed frequency. You also specify the impedance (Z), current (I), or voltage (E) at the input and/or load end of the line. In the example at left the line is set to 100 feet of Belden 8240 RG-58 at a frequency of 14 MHz. The impedance R±jX is set to 150+j0 ohms at the load end of the line. The current magnitude and phase at the input end of the line are set. However, in this example a value for the "Input Power" field has also been entered; hence the current magnitude at the input will not be 1 amp, although the phase will be 0 degrees. (This is just an arbitrary example used to illustrate that the Z, I, E settings can be mixed between input and load ends, with some restrictions.)

 Given the above conditions, this is what you would see if you plotted the "normal" SWR on the primary axis and the true SWR on the secondary axis. Note that both values decrease as you move from the load end of the line (on the right) to the input end (on the left) due to the attenuation of the line. However, although the true SWR (which is based on the line's characteristic impedance of approximately 52.03-j0.49 ohms at this particular frequency) decreases in a linear manner, the normal SWR (which is based on a fixed value of 50 ohms in this case) oscillates.

Important: Whether you specify the Z, I, E conditions at the input end or the load end, or a mixture of both, the charts will always be shown with the input end of the line on the left and the load end of the line on the right. The X axis of the chart always shows the "Distance from Input" in whatever line length units you have chosen, as circled in red for the exampe above.

 This chart shows the magnitude of the voltage between the line conductors on the primary axis and the magnitude of the current through the line conductors on the secondary axis. As noted above, because a value of 100 watts was entered for the input power level the current at the input end is 1.88 amps and not 1 amp. You can also see the actual voltage standing waves (as in Voltage Standing Wave Ratio) along the line. Near the line center the voltage peak is 102 V. About 10 feet closer to the input end the voltage low is 43 V. The ratio 102 / 43 equals 2.37 which is (roughly) the true SWR on the line at the midpoint.

When Zplots is in "Transmission Line at Fixed Frequency" mode you can plot:

• SWR - Standing Wave Ratio based on a fixed reference resistance
• Rs - Resistance, series form
• Xs - Reactance, series form
• Zmag - Impedance magnitude
• Theta (deg) - Impedance angle
• Rho (mag) - Reflection coefficient magnitude
• RL (dB) - Return Loss
• Phase (deg) - Reflection coefficient angle
• % Reflected Power
• E-mag (V) - Voltage magnitude
• E-phase (deg) - Voltage phase
• I-mag (A) - Current magnitude
• I-phase (deg) - Current phase
• Power (W) - Power
• Pwr Loss (dB) - Power loss in dB
• True SWR - Standing Wave Ratio based on the line's characteristic impedance
 Finally, when dealing with any type of generated data there may be times when you wish to change the scales for the primary or secondary axes, change what item is plotted on the axes, or take a snapshot. Normally you would have to close the "Generate Data" dialog panel in order to perform those actions. The three buttons shown at left are available for each of the generate tabs so you can click "Apply" to generate data while keeping the panel open, see the results and possible modify the chart as desired, then click "Apply" again (or just press Enter, since "Apply" is the default action) to see a new set of results.

When you hover the mouse pointer over any data point on the Custom XY chart a small "Chart Tips" box will appear. The first line in the box will show the name of the item being plotted, such as Zmag or Theta. (Different versions of Excel may show additional information.) The second line will be in the form (xx,yy) where xx is the frequency at that point and yy is the data value.

Excel 2007 only: Under Excel 2007 the "Chart Tips" box will not appear unless you "activate" the chart first. You can do that by clicking on (or just inside) the chart border. To return to normal operation click anywhere outside the chart boundary or press the Esc key.

On the (large) Smith chart, a similar box will appear showing the R±jX value for the point under the cursor, but you must click on the chart border first under all versions of Excel. Also note that this feature is not available on the mini-Smith chart, only on the large chart on the Smith sheet tab.

To see more information for a given data point, click the point with your mouse. On the Custom XY chart a vertical line frequency marker will appear. On the Smith charts the frequency marker will be a large dot. In both cases a large text box (optional) will show other data values for that particular frequency. The same information is also shown in the marker table below the chart. To see a second marker use the right mouse button.

To move to a different frequency click on a new data point, use the spinner button, or use the keyboard arrow keys. (Up and Right increase the frequency, Down and Left decrease the frequency. The keyboard arrow keys control Marker1 only.) All three charts are synchronized, so when you click on a new point (or use the spinner or arrow keys) to change the frequency marker on one chart it will be changed on the other two charts as well. To remove the frequency marker(s) and associated text box(es) click anywhere outside the chart boundary or press the Esc key.

For users familiar with the AIM software, please note that the vertical line is not a cursor. You don't drag it to a new position on the chart. Instead, use the arrow keys or click a new point. Also note that Zplots does not do any interpolation between the data points. The vertical line will move from one scanned frequency to the next, not from one chart pixel to the next as with AIM.

Changing trace line colors and other visual aspects of the charts:

Zplots has built-in "Color Dot" buttons that allow you to easily change the colors for the chart trace lines, the frequency marker line/dot, the SWR circle on the Smith charts, and the horizontal reference lines on the Custom XY chart. These buttons are visible only when the associated item is being displayed. For example, if you are not currently plotting anything on the XY secondary (right) axis then the color button for that trace line is not shown.

 When you change the color for either the left or right axis trace line on the Custom XY chart you will also be given a choice to change the color of the scale numbers and axis title. Choose "Yes" and the text color will match the trace color. Choose "No" and the text will be standard black.

 To change things like the background fill color of the charts you can use the standard Excel user interface. In most cases the easiest way to do that is to hover your mouse pointer over the item to be changed and verify that the "Chart Tips" box shows what you intend to change, such as "Chart Area" for the outer area of the chart or "Plot Area" for the inner area. (Excel 2007 only: Click just inside the chart border first in order to activate the "Chart Tips" box.) Then hold down the Shift key, RIGHT click the mouse, and choose "Format ..." from the context menu that will appear. Usually 'Patterns' is the tab you will want to select in the dialog box that will follow. Make changes as desired. When you are done just click outside the chart boundary to return to a normal state. (Holding down the Shift key when you click on a chart signals Zplots that you do not want to show or change the frequency marker.)

Important: You may wish to keep a backup copy of Zplots if you intend to experiment with various format changes. If you are not very familiar with Excel it is possible that you may make changes from which you don't know how to recover, or which cause Zplots to fail. If that happens just close the Zplots workbook (File | Close, without saving) and you will be back to where you started. If you have already saved your changes and get into trouble, you can always start fresh with the backup copy that you made.

Download Zplots.zip.  Free.  Requires Excel 97 or later. Low-cost back-level versions of Excel (Office) can frequently be found on eBay (link).

VNWA users, see "What is ZplotsLink?" below. If you are not using the VNWA software you may disregard the ZplotsLink.xls file included in the download package.

Important: You must allow Excel macros to be enabled or none of the Zplots buttons will work. Please see Understanding Excel Macro Virus Warnings for more details.

Excel 2007 users: You must have Service Pack 2 installed. Click the Office Button > Excel Options > Resources. If you do not see "SP2" in the "About" section, click the Check for Updates button to download the required updates. Zplots will not operate correctly under earlier releases of Excel 2007.

Zplots does not work with other spreadsheet software such as Open Office Calc, Quattro Pro, Microsoft Works, or versions of Excel earlier than Excel 97. None of these other spreadsheet programs fully support the macros used by Zplots.

Sorry, the specialized programs Zplots+ and Zplots-AIM are no longer available.

Note to international users: You need not make any changes to your Control Panel Regional Settings for language or number format in order to use Zplots with the comma-separated-values (*.csv) files from the programs mentioned above. Zplots will read these files correctly even though they are formatted with a period as the decimal point and commas as field separators.

What is ZplotsLink? (applies to VNWA users only):

ZplotsLink serves as the (optional) interface between Zplots and the DG8SAQ VNWA program Tools menu (VNWA version Beta 33.f or later). Be sure to put ZplotsLink in the same folder as Zplots, not in the folder with the VNWA software (unless that is also where you have put Zplots). In the VNWA Configure Tools dialog, specify the Path to ZplotsLink, not Zplots. Leave the Argument field blank and use anything for the Name field. (Of course, "Zplots" or "AC6LA plotting tool" would be a good choice for the name, but the choice is up to you.)

Caution: If you have installed the VNWA software in a location under \Program Files\ such as C:\Program Files [(x86)]\VNWA\, do not put ZplotsLink or Zplots in that location. Instead, create a separate folder which is not under \Program Files\. Something such as C:\Zplots would be suitable. In the VNWA Configure Tools dialog, specify the Path to ZplotsLink in that folder.

In addition, again assuming you have checked the "Autowrite measurement data" box, VNWA will re-write the 'default.s2p' file after each scan. So you can either select Tools > Zplots again or just switch to the Zplots window and click "Refresh" to see the new data. If you are doing continuous scans with VNWA you can "Enable Polling" in Zplots and the new data file will be loaded automatically, at most once per second.

If you have not checked the "Autowrite measurement data" box in the VNWA Configure Tools dialog, selecting VNWA Tools > Zplots is the same as just switching to the Zplots window, or starting Zplots if it not already running.

Manual entry of data for display with Zplots:

You may have collected data points from a device that does not produce any type of computer file or whose file format is not recognized by Zplots. In that case you can enter the data into a "Zplots Generic" csv file and then load that file into Zplots. The ManualEntrySampleUS-UK.csv and ManualEntrySampleIntl.csv files included in the download package show examples of the format to use. ManualEntrySampleUS-UK.csv uses a period as the decimal point and a comma as the field separator; ManualEntrySampleIntl uses a comma as the decimal point and a semi-colon as the field separator. Using whichever one is appropriate for your regional settings, open the sample csv file with Excel and replace the sample data with your own. Use as many rows as necessary but do not alter the first two header rows. Save the csv file under any name, such as MyDipole.csv, then start Zplots and use the Load Data button to read the file.

Remote control of the AIM and/or VNWA devices:

Workbooks RemoteAIM.xls and RemoteVNWA.xls provide a remote control link between Zplots and the W5BIG AIM device or the DG8SAQ VNWA device, respectively. You enter the desired scan/sweep settings on the Remote workbook and that workbook invokes the appropriate device control program to do the actual scan/sweep. Then Zplots is automatically opened (if it is not open already) and the data is loaded.

Use of either workbook is completely optional. They are provided merely as a more convenient way to collect and display scan/sweep data. A complete description may be found here and abbreviated instructions are included in each workbook. If you do not have either of the mentioned devices you may disregard these workbooks.

Change history:

• Version 2.4, uploaded 30 Apr 2016.
• When loading data files, saving in *.s1p format, creating GIF files, and saving or recalling snapshot traces, in some cases with newer operating systems the selected folder was not retained for use as the default path for subsequent actions.
• Delete invalid first frequency point in certain ill-formed data files.

• Version 2.3, uploaded 1 July 2015.
• When using the "Measure Transmission Line Parameters" feature, an option is now available to terminate the line with high and low resistance values in place of open and short circuits. This may lead to more accurate results since calculations with almost-infinite and almost-zero impedances will be avoided.
• Accommodate AIM csv files with either negative or positive Return Loss values.
• Cosmetic change when a legend is added to a chart.

• Version 2.2, uploaded 25 April 2011.
• Recognize either commas or semi-colons as field separators in "Zplots Generic" csv files.

• Version 2.1, uploaded 6 April 2011.
• Do not allow "smoothed" AIM data to be used with the "Measure Transmission Line Parameters" function.
• Refinement of VF calculations over a wide frequency range as part of the "Measure Transmission Line Parameters" function.
• Support for DL1SNG FA-VA format csv files.

• Version 2.0, uploaded 10 March 2011.
• New feature "Measure Transmission Line Parameters" added to measure and plot various items related to transmission lines.
• New "TL Parms" tab under "Generate Data" added to generate transmission line (TL) parameter data based on mathematical models. May be used stand-alone or as a way to compare with measured data.
• New "TL FF" tab under "Generate Data" added to show various items associated with transmission lines along the length of the line at a fixed frequency.
• Extensive examples added to the web page to cover the above items.
• When adding or subtracting a transmission line, the time delay and loss (at the mid-point of the frequency range) are automatically computed and shown. This may be of interest to users of other software when dealing with transmission lines.
• "Save as S1P" button added.
• Show Min, Max, or Average of plotted values on the Custom XY chart. (Click to cycle through the three options.)
• Show R±jX values on the large Smith chart by hovering over any plot point. (Note: Chart must be activated first.)
• Avoid file conflicts when polling rapidly-changing data files.
• Avoid Excel 2007 bug (and subsequent crash) when attempting to set markers under certain conditions.
• Support for myVNA standard (not extended) format csv files.
• Add ability to set 'Gridline Spacing' in the "Set/Lock Scales" dialog.

• Version 1.6, uploaded 11 August 2010.
• "Refresh" button and "Enable Polling" check box added.
• "Change S2P Subset(s)" button added, replacing the previous method of being asked on each file load which subset(s) of s2p data are to be displayed.
• "Modified" date/time is shown in the information text box which shows the name of the currently loaded file.
• "Set Scale(s)" button text changed to "Set/Lock Scales".
• Fixed bug introduced in v1.5 related to transmission line calculations.

• Version 1.5, uploaded 26 July 2010.
• Support for general purpose Touchstone s1p/s2p format files.
• Support for the miniVNA PRO device, where the phase data already has the correct sign. (Phase data from the original miniVNA device remains unsigned.)
• On the Custom XY chart, snapshots 1 and 2 (only) are associated with the primary (left scale) axis; snapshots 3 and 4 are now associated with the secondary (right scale) axis.
• Changed the default trace color for the Custom XY chart secondary (right scale) axis from gray to blue. (All trace colors continue to be under user control.)

• Version 1.4, uploaded 18 Feb 2010.
• Support for the Port A (not Port B) format files produced by the W5BIG VNA2180 software.

• Version 1.3, uploaded 6 Dec 2009.
• Support for Excel 2007. No functional changes. Many thanks to Jochen, DG1PSI for his help in diagnosing several obscure bugs in Excel 2007. Thanks also to Harry, W5PNY for doing some Excel 2007 testing.

• Version 1.2, uploaded 3 Sep 2007.
• Support for the s2p format files produced by the TAPR VNA software.
• Fixed bug related to saving Snapshot data in an external file.

• Version 1.1, uploaded 11 Jan 2007.
• Version number shown on the Data sheet along with web page and email links.
• Phase (reflection coefficient angle) and Q (quality factor) added to list of available XY plot items.
• For the "Add or Subtract Transmission Line" feature: The dialog window is initially positioned to the right of the chart, if possible. The spinner can now change the line length by +/- 1 or +/- 0.1 in the current units. Less screen flashing when using the spinner. The amount of line added or subtracted (if any) is shown below the "Add or Subtract" button.
• File name shown on print preview and on printed charts.
• "Color Dot" buttons added for convenient color changes.
• Two frequency markers. Marker1 is controlled by the left mouse button, Marker2 is controlled by the right mouse button.
• "Zoom M1 to M2" and "Full Freq Range" buttons added as a convenient way to zoom in on a frequency range of interest.
• Units (MHz, dB, deg, etc.) automatically removed from the default title on the XY chart.