BergeronDemo

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A travelling-wave (Bergeron) transmission line showing how a step propagates and reflects.

A 100 V step is applied at the sending end $V_s$ of a distributed (Bergeron) line; after the line's propagation delay it arrives at the receiving end $V_r$, where a selectable termination (50 / 100 / 200 Ω) sets how much reflects back.

An ideal 100 V DC source is applied directly to one end of a distributed-parameter line. Because the line has a finite propagation delay, the disturbance travels from one end to the other and reflects off the terminations instead of appearing everywhere at once. The deliberately short time window captures those reflections, while the text readouts and plot track the terminal voltages.

This is the one sample where distance matters: a lumped R-L-C changes everywhere at once, but a distributed line carries the 100 V step as a wave that needs real time to cross. With Zc = 100 Ω and τ = 250 µs at a 50 µs step, the delay is exactly five time steps. When the wave reaches V_r, the fraction that reflects is set by how far the termination is from Zc — the matched 100 Ω load swallows it cleanly, while 50 Ω or 200 Ω bounce part of it back to re-reflect at the source. The selector is a three-way chooser among those loads, not a series breaker; step it between the three resistors and watch the staircase of reflections change character. Because the transit time is short, the run uses a brief window so the bounces do not blur together — the travelling-wave story behind the EMT course's line models, used in Chapters 8 and 9.