Resistance in parallel with inductors in a series leg of the low-pass filter facilitates changing input and output resistance of the filter with little or no change in the reactance of the inductors. Furthermore, the reactance of the capacitors in the shunt legs of the filter will be substantially unaffected....http://www.google.es/patents/US6895089?utm_source=gb-gplus-sharePatente US6895089 - Pots splitter with line impedance matching
