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IEC 60096-2: Radio-Frequency Cables — Specifications for High-Frequency Signal Transmission
50 Ω or 75 Ω? The Physics and Economics Behind Coaxial Cable Impedance Choice
IEC 60096-2 specifies RF coaxial cable electrical characteristics. Why does RF test equipment use 50 Ω while broadcast TV uses 75 Ω? The choice represents an engineering trade-off between power handling and attenuation.
Why 50 Ω: For air-dielectric coax, maximum power handling occurs at Z0 ≈ 30 Ω, while minimum attenuation occurs at Z0 ≈ 77 Ω. 50 Ω is the compromise — near the geometric mean of 30 and 77. This is why radar, RF testing, and wireless communications universally use 50 Ω.
Why 75 Ω: Broadcast TV reception prioritizes low signal loss — attenuation is the dominant constraint — so the choice approaches the minimum-attenuation value of 77 Ω (standardized to 75 Ω). Mixing 50 Ω and 75 Ω creates VSWR = 1.5:1 and ~4% power reflection — which in high-power transmitters can destroy the final output stage.
TN Lab — 50 or 75 ohms: a dual optimization of physics and economics behind one number.
