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Role of characteristic impedance

Short answer

Characteristic impedance is the voltage-to-current ratio of a travelling wave on an infinite line. If source, line and load are matched, all power is delivered and no reflection occurs; mismatch creates reflections, standing waves, power loss, echo and possible transmitter damage. Cables and equipment are designed to a common Z0.

Explain the role of characteristic impedance in the flow of radio signal from one equipment to another equipment.

Characteristic impedance Z0Z_0 is the ratio of voltage to current of a wave travelling along an infinitely long line:

Z0=R+jωLG+jωCZ_0 = \sqrt{\frac{R + j\omega L}{G + j\omega C}}

(≈ 50 Ω or 75 Ω for coax, ≈ 100 Ω for twisted pair, ≈ 600 Ω for telephone lines).

Its role in carrying a signal from one equipment to another:

  • If the source, line and load are all matched (ZS=Z0=ZLZ_S = Z_0 = Z_L), all the power is delivered to the load and nothing is reflected.
  • A mismatch causes reflection (reflection coefficient Γ=ZL−Z0ZL+Z0\Gamma = \frac{Z_L - Z_0}{Z_L + Z_0}), standing waves (high VSWR), power loss, echo and ghost images, and in transmitters even damage.
  • So cables, connectors and equipment ports are all designed for the same Z0Z_0.

✓ Answer checked by Claude Opus 5.5 (high effort)

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