2026-09-21
A familiar factory scene: the CCTV image is clean until the overhead crane's variable-frequency drive starts — then rolling bars appear and the recorder drops frames. Field investigations converge on a simple conclusion: when a coaxial cable picks up EMI, the fault is almost always shield discontinuity, a grounding mistake, or a shield construction too light for the environment — not the camera or recorder.
Coaxial cable is inherently immune to external fields: the signal travels on the center conductor while the shield surrounds it along the full length. An external field induces current only on the outside of the shield; if the shield is continuous and properly grounded, it never reaches the inner conductor. Interference enters through the gaps:
1. Sharp bends or crushed sections open gaps between braid strands;
2. A connector crimped over unevenly distributed braid leaves a circumferential slot;
3. A nicked jacket lets moisture attack the braid, and corrosion degrades both conductivity and coverage.
Countermeasures: control bending radius during installation, use quality crimp tools, and select a shield rating matched to the environment. Handle these three points and the cable will reject external fields effectively.