MiniVNA Program
I have developed a PC program to analyze antennas with a miniVNA box, and am using this program a lot to check my multi band Diamond W-8010 dipole. This antenna is one of the few dipoles to cover the 80-40-20-15 and 10 meter amateur bands.
It's drawback, as with all shortened antennas, is the narrow bandwidth on 80 and 40 meter. On higher frequencies it's a "full-blown" full length antenna.
I also have an all-band vertical of an unknown origin which I seldom use, in particular not for DX-ing.
Here what my W-8010 looks like from 3 to 30 MHz (click on images to see a larger view) while I explain the MiniVNA program.
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This graph shows that the antenna is resonant on 80, 40, 20, 15 and 10 meter bands. SWR (VSWR) is less that 1.5:1 on all these bands. |
The narrow bandwidth on 80m requires some more investigation:
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First I change the lower and upper frequencies to fit this band, and click in the diagram on the desired frequency to investigate it further, and a crosshair marks the frequency, and the SWR which now is available for this frequency in the little table above the graph. This table shows the electrical attributes at this specific frequency: VSWR=1.5:1 @ 3.7 MHz and the reactances, percent reflected power etc. To plot these extra values you have to check the check boxes on the right hand side. Remember: Plotting of other parameters other than SWR cannot be done while the miniVNA is reading data from the antenna system. Theses values are computed as a result of other fundamentas values from the miniVNA.
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The SWR is always on the left axis, while the other parameters will be shown on the right axis. The bottom axis is the frequency.
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Next I check out the 20 meter band, and click to see the electrical data with the minimum SWR. Again the cross hair marker appear and I can read that the VSWR is 1.4:1 @ 14.16 MHz. R= 43.4 Ω The bandwidth on this band is much wider than on lower bands and covers the whole band within reasonable SWR limits. |
As you can see, it's easy to change the start and end frequency, together with frequency step and nominal antenna system impedance. You also have the choice to make a single sweep or multiple sweeps. Multiple sweeps are in particular useful if the antenna has a bad connection; if this is the case the values and the graph will change during multiple sweeps.
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In this example I am plotting the antenna's resistance. Where the antenna shows the lowest SWR, resistance is very close to 50 Ω, and reactances should be close to 0, giving an impedance also close to 50 Ω. Rs is the series resistance equivalent of the antenna system. |
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The same graph, this one is showing the reactance as |Xs|. The reactance is the combined reactance of Ls and Cs. Note that the right axis shows the reactance values. |
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In this graph the antenna impedance is plotted. It should be close to 50 Ω for a low SWR. |
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Reflected power as percentage. There is also a calculator in the upper right corner where you can fill in the transceiver power output i Watts, and see how much is reflected back to the transceiver. In this case, 15 W out with an SWR of 1.4:1 reflecting 0.4 W back to the transceiver as a result of SWR. |
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The Table tab shows numerical data for the antenna system being analyzed. You can scroll up / down to examine all values / frequencies of interest. |
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The phase of frequencies in degrees is an indicator of the sign of the reactances. |
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Multiple plots: Rs, |Xs| and Z. |
Settings
On the settings menu, you can configure which comport to use depending on your system.
On the File menu you can Save a measurement for later use.
To save a plot: Click on the right hand side Save Plot button.
System requirements
Windows XP, Vista or Win-7. 32 or 64 bits version.
A USB cable connected to a miniVNA box.
Price: € 10 (or equivalent (USD 15)) via Pay Pal.
Available during October-November 2011