1. A digital data encoder for encoding a total of M characters, each with a length of m information bits, comprising: (n,k) convolutional encoder means selected such that m.gtoreq.k; means for feeding each character, followed by k-1 flush bits, to said (n,k) convolutional encoder; M output storage registers, each register of length (mn/k)+(k-1).times.((n/k)-1); storing means for storing each convolutionally encoded character M in a predetermined one of said M output storage registers; and output means for outputing the contents of said M output storage registers in a predetermined interleaved sequence.