Field Guide · hardware

Also known as: N connector, Type N, N-type

N-type (Type N) is a medium-size, threaded coaxial connector built for weatherproof, low-loss outdoor use, usable to roughly 11 GHz in its standard form.1 Its gasketed, threaded shell and air-spaced interface make it the default choice for base-station feedlines, roof-mounted antennas, and the thick low-loss coax (LMR-400 and similar) that runs between them. The connector was designed by Paul Neill at Bell Labs in the 1940s — the “N” is for Neill — and predates the smaller BNC and SMA that borrowed its ideas.

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An N-type plug threads onto a jack and its gasket seals the joint against weather; it carries higher power and lower loss than BNC or SMA.

Overview

Where SMA is chosen for size and BNC for quick handling, N-type is chosen for ruggedness and sealing. The 5/8-24 threaded coupling clamps a captive rubber gasket that keeps water out of the joint — essential for a connector that lives on a mast for years. The internal geometry is partly air-dielectric, giving low insertion loss and letting the connector handle far more transmit power than the miniature types.

What it is

An N joint on good coax adds only a fraction of a dB of loss across the VHF/UHF land-mobile range, which is why serious antenna installs terminate in N rather than adapting down to a lossy miniature connector at the top of the mast. Its size is the price: N is too big for a crowded SDR board edge, so the last few centimetres before the receiver usually transition to SMA or BNC. Standard N is rated to about 11 GHz; precision variants push higher.

Variants

  • 50 Ω N is the RF and land-mobile standard.
  • 75 Ω N is used in some broadcast and cable-TV plant; the centre-pin diameter differs, and forcing a 75 Ω plug into a 50 Ω jack can spread and damage the contact, so the two are genuinely not interchangeable.
  • Reverse-polarity N (RP-N) appears on some Wi-Fi and licence-exempt gear to discourage antenna swaps, mirroring the RP-SMA idea.
  • Weatherproofing is still finished in the field with self-amalgamating tape over the gasketed shell for a fully sealed outdoor joint.

Relevance to SDR

For a fixed listening post, the antenna and its feedline almost always use N-type at the mast and the radio end, because minimising feedline loss and keeping water out of the joint directly protect the weak signals a scanner cares about. A short adapter or pigtail then steps N down to the SMA port on the dongle or the low-noise amplifier mounted near the antenna. GopherTrunk is decode software and never touches hardware, but its results ride on that feedline: a well-made, sealed N joint on low-loss coax preserves the signal-to-noise ratio that the decoder ultimately depends on, while a corroded or water-ingressed N connector degrades every capture no matter how the DSP is tuned.

Sources

  1. N connector — Wikipedia, on the weatherproof gasketed design, 5/8-24 thread, air dielectric, power handling, and ~11 GHz range. ↩

See also