Sound Devices' word clock connections on 7-Series recorders do not have a 75 ohm terminating impedance. We do this because several units can be connected without over-loading the unit driving it. In most situations, using no termination works just fine.
However, on longer cable runs, cable reflections can cause higher jitter in the driven units with no termination. A simple solution for this is to use a BNC "T" connector and a 75-ohm termination plug. However, only one 75-ohm termination plug should be used per word clock feed no matter how many driven devices are connected.