EMC Question of the Week: March 1, 2021

Spectrum Analyzer with BNC and N-type connectors. There is an SMA adapter on the N-Type connection.

Which 50-Ω coaxial connector type would never be secured using a torque wrench?

  1. BNC
  2. TNC
  3. N-Type
  4. SMA


The best answer is “a.” BNC connectors are secured with a quarter-turn of the coupling nut on the outer conductor. The other options are all secured by threaded outer conductors. 

BNC is an acronym for Bayonet Neill–Concelman. Bayonet refers to the bayonet-style locking mechanism and Neill-Concelman refers to the inventors, Paul Neill and Carl Concelman. TNC is a similar connector with a threaded outer conductor. N-Type connectors have a larger diameter and are often secured without using a torque wrench, but (like all threaded connections) have a recommended torque for optimum performance. SMA connectors have a smaller diameter than BNC connectors. A loose connection can perform poorly, while over-tightening can damage the connector. Torque wrenches are generally recommended when making SMA connections.

BNC connectors are very convenient in situations where cables are routinely connected and disconnected. They are widely used in test laboratories. On the other hand, threaded connectors are typically used when high-precision or mechanical stability are the primary concerns.

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