In this work, the concept of linear relay network code [1] for an arbitrary number of relay nodes is extended to scalar frequency selective channels. Furthermore, we present performance criteria derived from the pairwise error probability (PEP) of a maximum likelihood sequence estimator (MLSE). By neglecting the transient processes of finite frames, deeper insights into the performance of FIR linear relay networks can be gained. Finally, the performance of a linear relay network using an MLSE sphere decoder at the destination is illustrated by some Monte Carlo simulations.