1. Grounding wire handling: directly short-circuit PDH and SDH and the fault stands still.
2. Clock and interface measuring: the 2M waveform, inherent frequency and output/input jitter of PDH and SDH are measured to be up to standard.
3. To self loop segment by segment repeatedly for two days to find that, at the interconnection point, the fault remains where PDH self loops to SDH side, but disappears where SDH self loops to CC08 switch. So we are now certain the fault is from the connection point where PDH and SDH interconnect.
4. Both 2M cable and 2M jumper at the interconnection point are measured to be normal. Finally, replace 2M line for a try, the fault disappears and 2M interconnects stably.
5. After some analysis, the impedance of the replaced 2M line turns out to be of 14?, while that of the 2M line before replacement is 6?, thus we can conclude that the signal interference is caused by the too-short 2M line.