DOWNLOADS:
Data Plotter Excel
Spreadsheet/Macro: AA908
Data Plotter rev P and Sample Files
(NOTE: Euro users can now select their mode with ctrl-E command)
PDF Manual
2-30 MHz scan of K7SBK multiband dipole using
AA-908 and his Excel Plot macro
Note all the useful data shown in the
plot: major resonance at 14 MHz, interesting minor resonances at the SWR dips
at 5 and 24 MHz, interesting behavior of resistance and reactance at various
frequencies, and especially on either side of the resonances.
The Excel Data Plotter
program plots a Smith chart when using the Plot function.
The Smith Chart plot is always generated and is available in the rightmost
tab at the bottom of the screen.
The plot shown here is of a 28-foot length of RG-58 coax illustrates the
return loss of the coax.
The trace spirals inward because the cable loss increases with frequency.
OVERVIEW
AA908Plot
is a very useful Excel macro program written by Al Gerbens, K7SBK that
allows you to collect and plot AA908 antenna analyzer scan data on a PC
display. With just a simple keystroke and a click on the uploaded data
file, AA908Plot automatically generates a colorful scaled representation of
antenna measurements for SWR, resistance and reactance – just like the
sample above showing the performance of a multi-band dipole. A Smith Chart is also generated to show additional dimensions of the
scan. Options can be set to show data points of interest on the SWR
curve, as well as indications of the ham band segments along the frequency
axis. Further, you can hover the
mouse cursor over a data point along the curve and a small window will show
the frequency and SWR for that point.
AA908Plot
can also remotely control your instrument over a serial cable to start and
automatically collect/display the results.
Options are available to compare two plots on the same display, and
determine network impedance matching data points for your antenna transmission
line!
AA908Plot
is an Excel workbook containing a macro that imports the data files generated
during the AA908 scan function. It then plots a graph of the data and
leaves you inside Excel to do what you want with the graph and data.
Along
the way, a vastly useful worksheet is created listing the scan settings, all
the data points, and the polar representation of the impedance with reactance
sign!
Multiple
data sets can be handled on separate Excel sheets and then the whole thing can
be saved as a workbook containing the graphs and datasets.
AA908Plot
is a great technical analysis companion to your AA908 antenna analyzer!
INSTALLATION
The
preferred location to install AA908Plot is in a folder called
“AADataFiles” on your hard drive. This
will be the default location for the data files you scan on the instrument or
import to your PC.
Create
a folder at the root of your C: drive with this name and unzip the
AA908Plot.zip file to that folder.
Microsoft
Excel must be loaded on your computer for AA908Plot to work.
OPERATION
The
screen below is displayed upon launching the AA908Plot.xls program.
(You
may need to click “Accept” button if your computer displays a window
asking permission to run an Excel macro.)
CTRL-M
Plot Data File
You
can start the main function of AA908Plot by either pressing ctrl-M
or by clicking on the ctrl-M
button on the menu display.
·
A window will be
displayed showing the contents of the AA908DataFiles and from there you can
select one of the data files to plot. The
data files are text and sometimes have a .dat or .txt extension on the
filename, but it is not necessary. The
distribution zip file has several sample data files you can select and try out
before getting your own files into that folder.
(If the files you are intending to plot are not located in this folder,
you can navigate to the correct location for them.)
·
Once you select the
desired data file, the program will import the data to a worksheet of the same
name (see the tabs at the bottom of the Excel program window) and in just a
moment display new worksheet containing the plot. (It may take up to a minute to import and display a large
data file.)
·
You can print the chart
using the standard Excel menus, or save it as a unique filename like the name
of your antenna or date of the scan.
·
You can also display
additional data plots … just click on the worksheet tab for Sheet3, click on
ctrl-M again and select
the next file to plot.
SWR Data Points may
be enabled by placing a number ‘n’ into the upper box, indicating a n:1
SWR threshold for displaying white circles on the SWR plot.
Below this SWR level each SWR data point will be marked with a small
white circle on the red SWR line in the plot. This indicates where the
SWR curve falls below a reference level and shows the position of each data
point in this area. Hovering the mouse cursor over each white circle
produces a display of the frequency and SWR for that data point. The default
setting is 1:1 which is the same as turning this feature off.
Ham
Band Indicators may be
specified in the lower box. This step results in a reference SWR
level being plotted as a thick black line indicating where the Ham frequencies
are located. Note that this line is continuous at frequencies
where data points exist with Ham bands. That’s not exactly the same as
absolute ham band edge indicators but the differences are generally very small
in this system. This feature provides dual information – ham frequency
location on this plot and the SWR reference level of my choice. The default
SWR level is 2:1. Both SWR level features can be used at the same time.
Getting
Data Files from the AA908
– Most AA908 owners are familiar with the procedure for setting up their
instruments to generate the data and importing it to the PC. This is specified in the AA908 manual as well as in a AA908
Application Note. For a refresher
on the technique, see the Appendix in this document.
Formatted
Data File – After
the data file is plotted, the worksheet containing the data is named with the
filename you originally specified. The
imported data points are displayed with column headings, and the polar
representation of Z is displayed in the worksheet.
The scan settings are displayed at the top of the worksheet, forming a
great numerical/text record of the antenna being analyzed.
(See the example shown below.)
CTRL-T
Remote-Control Scan & Data Import
The
ctrl-T command uses the
TeraTerm terminal program to remotely command the AA908 to perform a scan. The
data collected from the scan is placed into a data file in the A908DataFiles
folder on the PC, and control is returned to the AA908Plot main menu. From
there, you can select the ctrl-M
Plot command to display the plot of your newly-collected data file.
The
AA908 must be connected to the PC with the serial cable. The AA908 must also
be turned on and have the setting of “Send during scan” set in the Data
item of the Setup menu on the instrument.
You
must also have the TeraTerm dumb terminal program installed on your PC. All
AA908 owners have this program and have it installed for software upgrade
purposes as well as in using other Data features of the instrument. (When you installed TeraTerm, the application was very
probably placed in a folder with path name “C:\Program Files\TTERMPRO”. This
is where AA908Plot looks for the application and if not there will ask you
where its located. If TeraTerm is not at this location it is probably a
good idea to install it there, or change the macro to look in a different
location.)
CTRL-C
Generate Comparative Plot
The
ctrl-C command generates
a comparative plot of two
separate data files. Operation is simple, just enter the location of the two
data files when prompted, and both plots get displayed on a single graph.
These
graphs are basically XY scatter plots and so it is possible to arrange them
such that all six parameters are plotted against frequency (X axis). The
program uses the minimum frequency of the two data sets as the minimum and the
maximum frequency of the two data sets as the maximum in determining the
frequency range of the graph. So if you plot two 40 meter data sets they’ll
look pretty good in comparison. If you plot a 160 meter data set and a 10
meter data set, you will not going to be too happy with the result, although
it is not too likely that you would want to do that anyway).
Because
there is so much going on with 6 parameters being plotted on the same graph,
the hamband indicator and SWR data point marker options were
eliminated.
The
SWR and SWR2 curves are wide lines for emphasis and the Res, Res2, Rx and Rx2
lines are very thin to help the observer maintain sanity.
As
you’re looking at any of the graphs, remember that all of Excel’s
functions are available to you to tinker with. For example if you would like
to remove a plotted line, use your mouse to select that line, right click on
the mouse and edit that series to eliminate the line, change its color, change
its width, add data point markers, etc. When
you’ve got it looking right, just save the workbook with your own unique
filename.
Above
is a comparative plot using a test antenna circuit consisting of RLC mounted
on a BNC connector. The circuit
is held firmly between thumb and forefinger when generating the second
dataset. You can clearly see the
downward shift in resonant frequency and the reduction in circuit Q.
Evaluating the effect of antenna modifications using before and after AA908
data scans and overlaying them using the ctrl-C macro should be very
interesting.
CTRL-L
Determine Network Impedance Matching Data Points
The
ctrl-L command
determines network impedance matching data points for your antenna
transmission line. This
function designs an impedance-matching L network for each data point in the
data file you select. The input
to the L network is 50 ohms resistive and the other end of the network is the
complex impedance of individual
data points.
There
are 8 possible L configurations. Most
matching problems can be solved with 2 of the 8 and the two most desirable are
the so called ‘low pass’ configuration.
These are the two primary solutions given by LNET
a third alternative (TYPE B) is also calculated and presented whenever
it’ll work. A single L network
configuration cannot solve all matching problems.
Determining
the sign of the reactance turned out to be a source of error.
Some of the limitations result from not being able to sample the
reactance outside of the data set range,
an occasional ‘weird’ data point (s)
and the method itself. This
program attempts to smooth the data and remove ‘outliers’ but could never
get all of them.
There
are a lot of reactance vs. frequency inflection points in many observed data
sets.
A
screen capture of the LNET worksheet is shown above.
The three network configurations are diagrammed at the top of the page
with the 50-ohm input (coax) indicated leftmost.
The TYPE column indicates the configuration, and the C and L columns
contain the capacitance (in pF) and inductance (in uH)
required to build a network matching 50 ohm coax to the complex
impedance in your data set Res +/- Rx. (If
R is less than zero, no design is reported.)
Depending
on your dataset you’ll find an occasional point or small region of points
that don’t make a lot of sense and in most cases looking at the data set it
will be obvious why, generally they’ll be connected to a bump in the data
that produces a reactance sign transition that possibly is not real or may not
be significant to your application.
If
you want, for example, to operate
your 20m dipole on 17m you should be able to derive a workable impedance
matching network using the designs from this program. Just scan your dipole
(including 18 MHz ) with feedline, generate the data file, execute LNET and
select a matching configuration in the 17 meter region of the spreadsheet.
There
are several good L network
impedance matching tools on the Internet and in HamCalc (by VE3ERP), but I
thought it would be interesting to see the designs vary by frequency in a
spreadsheet format – something none of them can provide.
Looking at the design C and design L variation with frequency can be
helpful in selecting components you may already have, etc. It turned out that
the spreadsheet format provides a
good overall view of the context for the design of each data point and can
allow for construction of a workable L matching network for your application.
CTRL-E
Select European Data Format
The ctrl-E
command instructs Excel to use the “,” (comma) as the “decimal
point” in the data file instead of the “.” (period) as is customary for
computers in the US and UK. Otherwise,
in computers with non-US language pack settings, the data file is not
interpreted correctly.
APPENDIX:
Manually Importing AA908 Scan Data to the PC
The
Micro908 Antenna Analyst may be configured to send raw scan data during a Scan
operation over its RS-232 serial port to an external computer.
Link908 and AA908Plot are programs typically used on the external
computer to plot the data on the computer screen, thus displaying convenient
SWR, Resistance and Reactance graphs for the antenna system under analysis.
The
raw scan data may also be collected and manually organized for additional
views or for preparation into other software analysis programs.
PROCEDURE
1)
Configure the AA908 to send data during a Scan – This selection
can be made in the Config item called Data Options.
Select the “Send During Scan” option, then Exit.
2)
Specify the Scan Settings – Select the desired Band on the
AA908 instrument. (Remember, if
the Custom Band is selected, you will also need to set the Start, End and Step
values in the Setup menu.)
2)
Select “Log to File” in TeraTerm – Open TeraTerm and in the
File menu, select the Log function, which prompts you for a filename to use
for the data being collected/displayed in the TeraTerm window.
If you specify the data file to be located in the AA908DataFiles folder
on your C: drive, you will be all set to import the data to the AA908Plot
program.
3)
Perform a Scan – Using the scan button on the AA908, initiate a
scan. You will see line after line of data being displayed to the TeraTerm
window on the PC, representing all of the measurement points being sent by the
AA908. The scan operation will
take longer because of data being sent to the PC, but it will eventually
complete and the minimum SWR point will be displayed on the AA908 LCD, as
normally done.
WHATTA TOOL!
Thanks a ton for your effort
Al. This is a great accessory program for the Antenna Analyst
and a great way to archive graphic results of one's antenna work.
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