Summary: Numerous scientific disciplines and more and more electrotechnical problems call for numeric time domain solutions. The present paper deals with systems with distributed parameters containing - in addition to the common passive elements - also active couplings. These are special MOS- structures, e.g. travelling-wave transistors, as well as fast integrated circuits with active and passive elements along a line. It is for these systems that the possibility of functional transformations is exhausted. The authors demonstrate by a concrete example how it is possible to extend the numerical solution with the help of a few investigations and ways of treatment.