symmetric cables (twistep pair)
Symmetrical cables each consist of two cores, which form a core pair, and a common shield. The two cores are twisted against each other and have symmetry to the ground-related shielding. The transmission characteristics of the two cores with respect to ground are identical.
Since the cores of a symmetrical conductor are fed with push-pull voltages, induced interference signals cancel each other out. The symmetry of the cores is achieved by production engineering processes that are characterized by the lowest tolerances. The cores of a symmetrical conductor are twisted against each other in pairs. The transmission characteristics and the interference of extraneous signals are essentially determined by the stranding of the pairs of cores. For this reason, the stranding is varied by different pitches. Depending on whether the conductor pairs have their own shielding, they are referred to as shielded or unshielded symmetrical conductors: Shielded Twisted Pair( STP) or Unshielded Twisted Pair( UTP). In addition to the shielding of the wire pairs, the balanced conductor can have a common shielding for all wire pairs. This shielding can be foil or braided shielding or a combination of both.
If four cores are twisted against each other, this is called a star quad. It should be noted here that, in terms of transmission, such a cable consists of two pairs of wires.