Also known as: N connector, Type N, N-type
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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.
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.
Where to buy
For a fixed listening post, run N-terminated low-loss coax all the way from the rooftop antenna and step down to the dongle’s SMA port only at the very end. The cheap enabler is an SMA-to-N adapter kit covering all four gender combinations (around $12), so you have the right part whether the feedline ends in an N plug or an N jack. If you also juggle BNC or UHF gear, the all-in-one SMA adapter kit bundles those too.
For the outdoor feedline itself and a mast-mounted LNA, see the SDR cables and connectors guide.
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Sources
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N connector — Wikipedia, on the weatherproof gasketed design, 5/8-24 thread, air dielectric, power handling, and ~11 GHz range. ↩
Frequently asked questions
Which N-to-SMA adapter should I buy for an SDR?
An SMA-to-N adapter kit that covers all four gender combinations (around $12) is the pick, because an outdoor antenna feedline almost always ends in N while the dongle’s port is SMA. Buying the small kit means you have the right gender on hand whether the feedline presents an N plug or an N jack, rather than discovering the mismatch on the roof.
Why do outdoor antennas use N instead of SMA?
N is weatherproof and low-loss. Its gasketed, threaded shell keeps water out of the joint for years on a mast, its part-air dielectric adds only a fraction of a dB across VHF/UHF, and it handles far more power than the miniature SMA. SMA is chosen for size on a crowded dongle edge, not for a rooftop — so a good install runs N up the mast and adapts down to SMA only in the last few centimetres.
Where should the N-to-SMA transition go in the chain?
As close to the receiver as practical. Keep the low-loss N-terminated coax running all the way from the antenna, then step down to the dongle’s SMA (or to a mast-mounted LNA) with a single adapter or short pigtail. Adapting to a lossy miniature connector at the top of the mast, before the long cable, throws away signal you cannot get back.
Is 50 Ω or 75 Ω N right for scanning?
Use 50 Ω N — it matches your SDR, antennas, and coax. A 75 Ω N (from broadcast/cable plant) has a different centre-pin diameter, and forcing a 75 Ω plug into a 50 Ω jack can spread and damage the contact, so the two are genuinely not interchangeable.