Initial condition

摘要

The PCB (printed-circuit-board) transmission line in Figure la lacks an end termination. If you leave switch S_1 closed for a long time, the line comes to rest in a state with precisely OV at all points. The transmission line in Figure lb behaves similarly. With S_2 closed, it also comes to rest in a state with OV at all points. The voltages in the two situations are the same, but the currents differ. In the first case, the line at rest carries no current. In the second case, the end termination supplies a substantial current as long as you hold the line in a low state.