Round-Trip Echo Takes Two Trips - Magnetism, Induction, and Transmission Lines Step by Step

A round-trip-echo-takes-two-trips scan holds the one-way delay fixed and checks that the source echo arrives after two trips, t_echo = 2 * t_one-way, on top of the launch time row by row. The arithmetic is exact only for the stated lengths, signal speeds, one-way and round-trip delays, and rows in the ideal uniform-line, constant-speed model. Real lines add dispersion, loss, connector mismatch, finite rise time, cable tolerance, probe/calibration limits, finite precision, and measurement uncertainty.

An echo returns after two checked one-way delays. Exact arithmetic here means exact results for the stated model inputs; measured inputs still carry uncertainty and significant-figure limits.

highlighted = computed this step

A reflection must first reach the load

The one-way trip is 4 seconds before any load echo can start back.

t_{\text{one way}}=4\ \text{s}

The source sees the echo after two trips

Launch at 0 seconds plus a round trip of 8 seconds gives echo time 8 seconds.

0\ \text{s}+8\ \text{s}=8\ \text{s}