Cabling Schemes

• Unbalanced Line
  • Pair of conductors to carry signals which have unequal impedances along their lengths and to ground and other circuits
  • Examples: Coaxial cable, Earth Return Telegraph
• Balanced Line
  • Pair of conductors to carry signals which have equal impedances along their lengths and to ground and other circuits
  • It reduces common-mode noise and interference when fed to a differential device such as a transformer or differential amplifier
  • It eliminates common-mode noise because it has equal impedances, even if the signalling scheme is single-ended
    • That is, just like differential signals, the voltage differential eliminates the common-mode noise, with the original signal retrieved.
    • However, the difference is that due to the polarity being the same, the retrieved signal will have a voltage which is the difference of the wires, while differential signals will have double the voltage due to opposing polarities.
  • Examples: Twin-lead, Twisted Pair cable (reduces EM radiation from crosstalk)

Notes

• Twisted Pair cable may be shielded for additional noise immunity - Unshielded Twisted Pair (UTP) and Shielded Twisted Pair (STP) cables
• Coaxial cables were described by the Telegrapher's equations, used in Transatlantic submarine telecommunication cables.
• Balanced lines are not to be confused with differential signalling, which is a signalling scheme.