The event deadzone is specified as 1 meter. The user expects the OTDR to locate and identify the 1 meter patch cord and possibly make loss and reflectance measurements. As shown in Figure 1, the attenuation deadzone (ADZ) is defined as the distance, usually for a single “good” connector reflective event, between the rising edge of the pulse to the 0. The backscatter level is the sloping line on the. Optical Time Domain Reflectometer (OTDR) is a widely used testing instrument in the field of fiber optic communications for evaluating transmission performance and locating faults.