Return Loss – the often neglected
Astonishingly, one value is often neglected in practice: the return loss or RL.
Wherever the signal path changes, so-called impact points are created for electromagnetic waves. Such a change may be the transition from the cable to a connector or a socket or the transition between socket and connector. But it can also be a geometrical change of the cable, for example a kink or a deformation due to a cable tie being fixed too tightly.
Part of the electromagnetic wave is reflected at such impact points. In Gigabit and 10 Gigabit Ethernet in which signals are transmitted in both directions on every wire pair, the reflected signals are interpreted as incoming useful signals – i.e. as "real" data – which leads to high bit error rates.
Impact points and the resulting bit errors can be avoided, apart from by proper installation, above all by cabling systems with components that are exactly adapted to each other.