1. A transmission system for successive data words each comprising a sequence of bits of successive levels of significance, such transmission system comprising a transmitting station and a receiving station interconnected by a transmission medium, said transmitting station comprising an encoder system for redundantly encoding each of such successive data words with redundancy bits; characterized in that said encoder system comprises: a first encoder which by matrix multiplication encodes a set of less significant bits of each such successive data word into a first proto-code word; a second encoder which by further matrix multiplication encodes the remaining more significant bits of each data word into a set of "n" further proto-code words, such second encoder comprising a plurality of delay elements for imparting respective different delays to said further protor-code words, such delays being in multiples of the recurrence times of the successive data words; and modulo-two adding means connected to said first and second encoders for bitwise adding said first proto-code word and said "n" further proto-code words, such "n" further proto-code words corresponding to "n" different data words, so as to derive a final code word having an extended bit length with respect to the bit length of a data word and which comprises a block code of the less significant bits of a data word and a convolutional code of the more significant bits of such data word, said modulo-two adding means having an output connected to said transmission medium.