## Modified duo-binary signalling |
In-depth |

#### A useful extension of the duo-binary signalling method is modified duo-binary which has an overall frequency response which contains a spectral null at dc. This approach is thus well suited to channels which have poor low-frequency response (see Section 4.4), where an alternative, Manchester coding, is discussed. The encoder involves a two-bit delay, causing the intersymbol interference to spread over two symbols. As for the basic duo-binary method, error propagation necessitates the use of a pre-coder which can again be implemented using an exclusive-or gate. |

| #### Detection of the modified duo-binary signal with pre-coding also involves rectification and a threshold set at +V volts as before.