Which OTDR configuration setting must always exceed the length of the span under test?

The correct answer is that the range setting on an Optical Time Domain Reflectometer (OTDR) must always exceed the length of the span being tested. The range setting determines the maximum distance the OTDR can analyze, enabling it to capture reflections and backscattering signals from the optical fibers. By ensuring that the range is set beyond the length of the span, the OTDR can effectively measure and analyze the entirety of the fiber, including any potential faults that may occur along its length.

If the range is configured to be too short, it can lead to incomplete testing, as the OTDR may not reach the end of the fiber, preventing a full assessment of the fiber’s performance. This is critical for accurately identifying splice losses, connector losses, and faults in the fiber.

In contrast, although other settings like pulse width and duration are important for the resolution and sensitivity of the measurements, their configuration does not directly link to exceeding the span length in the same way that the range setting does. Gain can also affect the signal strength but does not play a role in the required distance the OTDR must cover for a complete analysis. Therefore, setting the range exceeds the length of the span ensures comprehensive testing and accurate results.