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How to Tune a Tank Coil With MFJ

Tank circuits consist of a capacitor and a coil in parallel. The interesting attribute of a tank circuit is that it reacts differently to different frequencies. Depending on the size of the capacitors and coils, a ̶0;resonate frequency̶1; goes through the tank circuit with little opposition. The farther a frequency is away from the resonate frequency, the more opposition the tank circuit offers to the signal. Changing the value of one of the components -- usually the capacitor -- allows you to change the resonate frequency of a tank circuit.

Things You'll Need

MFJ tool

Instructions

- 1
  Use the MFJ tool to calibrate a tank circuit. This tool will let you match an antenna to a tank circuit, so that the range the capacitor can determine the resonate frequency of the tank circuit matches the desired limits. Typically, these limits are the boundaries of the broadcast bands such as the AM radio band.
- 2
  Connect the MFJ to the tank circuit by induction. Place the coil of the MFJ near the coil of the tank circuit. The MFJ is not part of the tank circuit; it just reacts to the behavior of the magnetic field of the tank inductor.
- 3
  Set the capacitor to its lowest setting. Set the MFJ to the lowest setting for the band you are calibrating. Adjust the tap on the tank inductor until the reading on the meter on the MFJ is zero.
- 4
  Tune the capacitor to its highest setting. Set the MFJ to its highest setting for the band you are calibrating. Add or remove coils to the tank inductor, until the reading on the meter on the MFJ is zero. If you do change the coil to make it fit the upper limit, you should recalibrate the lower limit.

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