Coaxial Cable (RG Type, Impedance)
A signal cable with a concentric construction of inner conductor, dielectric, shielding outer conductor (braid and/or foil) and outer sheath, where the fixed ratio between the diameters of the inner and outer conductor yields a defined characteristic impedance. The historical RG designation (for example RG-6 for CATV/antenna installations at 75 ohms, or RG-58 for 50-ohm applications in test and RF engineering) primarily indicates diameter and dielectric; the impedance must match on both sides of a connection, since a mismatch causes reflections (standing waves) and signal loss. In building installations coax is mainly used for CATV/antenna signals, CCTV video and RF measurements, where separation from power cables benefits EMC immunity.
Bij de aanleg van een CCTV-systeem kiest de installateur RG-59-coaxkabel met een vaste 75 ohm-impedantie en zorgt hij voor minimaal 30 cm scheidingsafstand tot parallel lopende 230 V-groepen om beeldstoring te voorkomen.
Een 50 ohm RG-58-kabel gebruiken op een 75 ohm CAI-aansluiting (of omgekeerd) — de impedantiemismatch veroorzaakt reflecties die tot signaalverlies en beeld- of ontvangststoringen leiden, ook al past de connector fysiek.
See also
- → EN 50117 (coaxiale kabels) Coaxial cable signal loss (dB/100 m) — attenuation is a separate problem from impedance mismatch
- → IEC 60364-5-52 Aluminium cables — cross-section equivalence relative to copper and the 1.6× rule of thumb
- → NEN-EN 1366-3 Fire-resistant cable penetrations — NEN-EN 1366-3
- → IEC 61439-6 Busbar trunking systems (IEC 61439-6) — when to use them instead of cable
- → IEC TS 60034-25 Motor cable for variable frequency drives — symmetrical construction against bearing currents
- → NEN 6069 / IEC 60331 / EN 50200 Fire-resistant circuit-integrity cable — why E30/E60/E90 on a cable means something different from the same class on a penetration seal