How does connector torque affect the VSWR of a coaxial connection?

Connector torque directly affects the quality of the electrical contact between mating coaxial connectors, which in turn affects the VSWR (impedance match) of the connection: (1) Undertorque: insufficient tightening force causes incomplete contact between the center conductors and/or the outer conductor shells. The result: air gaps and misalignment at the interface plane. The air gaps create a small impedance discontinuity (the impedance of the air gap differs from 50 ohms). VSWR impact: VSWR can degrade from 1.05 (properly torqued) to 1.3-1.5 or worse (undertorqued). This effect is worse at higher frequencies (shorter wavelengths make the interface discontinuity more electrically significant). (2) Proper torque values: SMA connectors: 5-8 in-lb (0.56-0.90 N-m). Typical recommended: 5 in-lb (0.56 N-m) for stainless steel. N-type connectors: 12-15 in-lb (1.36-1.70 N-m). 7/16 DIN connectors: 20-25 in-lb (2.26-2.82 N-m). 3.5 mm and 2.92 mm (K connector): 8 in-lb (0.90 N-m), use a torque wrench (these precision connectors are easily damaged by overtorque). 2.4 mm and 1.85 mm connectors: 8 in-lb (0.90 N-m), always use a torque wrench. (3) Overtorque: excessive tightening can damage the connector: strip the coupling nut threads, crush the center contact (especially on subminiature connectors), distort the outer conductor shell (changing the impedance geometry), and crack the dielectric support bead (creating a permanent impedance discontinuity). Overtorque damage is often invisible from the outside but creates a permanent VSWR degradation. (4) Best practices: always use a calibrated torque wrench (never pliers or standard wrenches for precision RF connectors). Make connections finger-tight first, then torque to specification. For 2.4 mm and smaller connectors: use the manufacturer-specified torque wrench adapter. Clean the connector interfaces before mating (debris causes poor contact and VSWR degradation). Inspect connectors before mating (bent center pins, damaged threads, contamination).