Reverse is not zero coding with high level according to binary "1", low-level said binary "0",
This should not be type transmission, dc, for the following reasons: (a) have generally near the zero frequency channel is difficult to transmission frequency component; (b) and receiving the decision threshold is associated with signal power, is not convenient to use; (c) cannot be directly used to extract a sync signal, because do not contain in the NRZ bit synchronization signal frequency components; (d) for transmission line have a grounded,
