MatchMaker - RF Impedance Matching Tools

Make your radio fall in love with your antenna all over again

For this example, we will start with the following impedance data for the antenna:

Frequency   Resistance    Reactance
7.0 MHz     10.0          -60.0
7.2 MHz     16.5          -55.0
7.4 MHz     20.0          -50.0

We want to match all the points with an SWR of 2.0 or better.

First, let's start with a new window (ignore the impedance/SWR values from the cursor position):
Next, we need to enter in our impedance Data. Double click on Load Impedances:
We're presented with an empty list of frequency and impedance pairs. Click on Add Entry, and a new line will be added, with a frequency of 0:
Double click on the 0 to edit it. Change it to 7 for 7 MHz. Do the same for the resistance and reactance values to change them.

Repeat to add the impedances for 7.2 and 7.4 MHz:
Click OK.

Now we can see a plot of the impedance values. The SWR for each point is also calculated:
We want the impedance of the center frequency, 7.2 MHz, to be fairly close to 50 ohms, for a good match. A shunt inductor will move the point to 50 ohms (while a shunt capacitor would move it the opposite way).

Click Add, select a Shunt Inductor from the popup menu: We'll try an initial value of 2 uH, so enter in 2, click Apply. Click the new entry for Shunt Inductor 2 uH on the main window, to see the updated impedance in red:
The impedance is too high, closer to 100 ohms, so we need more inductance. Trying 3 uH, we get 44 ohms, closer, so now try 2.8, we get about 49 ohms, close enough:
next we need to move the cluster of points into the green SWR=2 circle in the center of the graph, using a series inductor. Click Add, and select Series Inductor We'll try 1 uH first, and find ou that it is not enough. trying 2 uH, we find that it is much closer, and 2.1 uH centers the impedances nicely:
Note that when we started, our SWR values ranged between about 5 and 12, now they are all under 2!

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Last modified January 28, 2010