  This paper provides a construction of non-binary LDPC convolutional codes,
which generalizes the work of Robinson and Bernstein. The sets of integers
forming an $(n-1,w)$-difference triangle set are used as supports of the
columns of rate $(n-1)/n$ convolutional codes. If the field size is large
enough, the Tanner graph associated to the sliding parity-check matrix of the
code is free from $4$ and $6$-cycles not satisfying the full rank condition.
This is important for improving the performance of a code and avoiding the
presence of low-weight codewords and absorbing sets. The parameters of the
convolutional code are shown to be determined by the parameters of the
underlying difference triangle set. In particular, the free distance of the
code is related to $w$ and the degree of the code is linked to the "scope" of
the difference triangle set. Hence, the problem of finding families of
difference triangle set with minimum scope is equivalent to find convolutional
codes with small degree.
