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Radio signal in twisted pair and coaxial cable

Short answer

Twisted pair carries the signal as a voltage difference between two balanced wires; twisting makes induced noise equal in both and cancels it, limiting use to about 100 MHz over short distances. Coaxial cable confines the field between centre conductor and shield, giving little radiation or pick-up, fixed 50/75 ohm impedance, and RF operation up to several GHz.

Explain the transmission of radio signal in twisted pair and coaxial cable in case of telecommunications.

Radio/electrical signals travel along guided copper media as an electromagnetic wave between two conductors.

  • Twisted pair: two insulated wires are twisted together. The signal travels as a voltage difference between the wires (balanced line). Twisting makes noise picked up by both wires nearly equal, so it cancels at the receiver, and it reduces crosstalk. Loss and radiation rise quickly with frequency, so it suits voice, DSL and LAN signals up to about 100 MHz over short distances.
  • Coaxial cable: a centre conductor surrounded by a dielectric and an outer braided shield. The field is confined between the conductors (unbalanced line), so there is very little radiation or pick-up. It has a fixed characteristic impedance (50 Ω or 75 Ω) and carries RF up to several GHz, used for antenna feeders, cable TV and old carrier trunks.

✓ Answer checked by Claude Opus 5.5 (high effort)

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