A new postdetection method of dispersion is proposed, based on a scheme previously implemented, and that additionally uses a Bit Error Rate (BER) analyser, which allows the extending of the monitoring window. The monitoring method was tested with transmission rates of up to 40 Gbit/s. It showed monitoring windows of at least ± 300 ps / nm, as well as the ability to adapt to different modulation formats, with symmetrical spectrum. The method also allowed high sensitivity (1 dB/( ps/nm).