Inductive output networks.

A family of matching networks in which the load is placed inside a coil and energy is coupled in magnetically.

Inductive output L

The inductive output L network is able to deliver power into a relatively large output coil, limited only by practical voltage ratings of the tune capacitor and by the self resonant frequency of the coil. It is possible to mitigate the effects of a large coil by inserting series capacitors at points along it's length, but if the voltage becomes excessive a lower operating frequency should be sought.

Modified 'L' network

This network looks like the PI configuration at first glance but as the load coil and the tune capacitor are in series I would classify it as a 'L' network.

Locating the coil between the two capacitors makes little or no difference electrically but may be mechanically convenient as it means the bodies of both capacitors are grounded, so high RF potentials do not appear on the control shafts.

Inductive output 'T'

The inductive output 'T' network has few uses as the allowable coil size is limited. The reactance of the coil has to remain below 50ohm.

 It is well suited to some induction heating applications where the coupling to the load is very poor. The advantage is that although the current in the load and the load capacitor is huge, the tune capacitor only has to pass the output current of the RF Generator which is much smaller. This network is best used in applications where the coil is small, otherwise the tune capacitor may need to tune to an excessively low value and will be subject to high RF voltage.

This configuration is very capable of tuning into its own losses in the absence of a load, meaning that the full RFG output may be dissipated in the coil. A water cooled coil is almost essential even at powers of only 600w.