A T-Network Tuner Simulator, Kevin Schmidt, W9CF

This is a simulator for the popular, series capacitor, parallel inductor T-network tuners. The three knobs across the bottom adjust the three components. They can be turned by moving your mouse to a knob, click and hold down the mouse button and drag the mouse around the outside of the knob. The knob should turn. The capacitor knobs have 10 turns between stops, and the coil knob has 30 turns between stops.

No java

The SWR is shown both digitally in the upper left and on the SWR meter. The loss in the tuner is shown as a percentage of input power and the equivalent loss in decibels. Clicking the autotune button will attempt to have your computer calculate values of the components that should perfectly match the load and minimize the loss in the network assuming that the capacitors have much higher Q than the coil. For some values of the load the autotuner will fail and a message will be written in the panel to the right. The Set Up button allows you to change the maximum values of the three components and their Q values. Initially the capacitors are 250 pF, Q=2000 and the coil is 30 microH, with Q=100.

The three fields on the right allow you to change the load and the frequency in MHz.

One way to use this applet is to pick a load resistance and reactance, and then adjust the knobs of the tuner for a match as you would do on a real tuner. Note the percent loss in the tuner for your adjustment and then click the autotune button to see if the computer adjusts the tuner for less loss.

To run this locally, you can download the file tuner.jar and the file you are looking at tuner.html into any convenient directory and point your browser at the tuner.html file. Old browsers may require you to unzip the tuner.jar file in that directory (Jar files are just zip files with an extra file that describes the contents). Alternatively, you can run this as a Java application. For example under Microsoft Windows with Internet explorer installed you already have a near Java run time. To run this locally without the browser pop up a DOS box, and type

jview -cp tuner.jar Tuner
in the directory containing tuner.jar.

Java Source code for the applet is distributed under the GNU general public license. The source is available in tunersrc.zip.

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