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:
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