N connector
Type N connector (male)
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| Type | RF coaxial connector | ||
|---|---|---|---|
| Designer | Paul Neill | ||
| Designed | 1940s | ||
| Diameter |
Male: 0.800 in (2.03 cm) Female: 0.620 in (1.57 cm) (outer, typical) |
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| Cable | Coaxial | ||
| Passband | 0-11 GHz, often up to 18 GHz | ||
The N connector (in full, Type N connector) is a threaded, weatherproof, medium-size RF connector used to join coaxial cables. It was one of the first connectors capable of carrying microwave-frequency signals, and was invented in the 1940s by Paul Neill of Bell Labs, after whom the connector is named.
Originally, the connector was designed to carry signals at frequencies up to 1 GHz in military applications, but today's common Type N easily handles frequencies up to 11 GHz. More recent precision enhancements to the design by Julius Botka at Hewlett Packard have pushed this to 18 GHz. The male connector is hand-tightened (though versions with a hex nut are also available) and has an air gap between the center and outer conductors. The coupling has a 5/8-24 thread. The center coaxial contacts are identical to TNC and BNC connectors. Amphenol suggests tightening to a torque of 15 inch-pounds (1.7 N·m), while Andrew Corporation suggest 20 inch-pounds (2.3 N·m) for their hex nut variant. As torque limit depends only on thread quality and cleanliness, whereas the main operational requirement is good RF contact without significant steps or gaps, these values should be seen as indicative rather than critical.
The peak power rating of an N connector is determined by voltage breakdown/ionisation of the air near the center pin. The average power rating is determined by overheating of the centre contact due to resistive insertion loss, and thus is a function of frequency. Typical makers' curves for a new clean connector with a perfect load (VSWR=1.0) give limits of ≈5000 W at 20 MHz and ≈500 W at 2 GHz. This square root frequency derating law is expected from the skin depth decreasing with frequency. At lower frequencies the same maker recommends an upper bound of ≈1000 V RMS. To achieve reliable operation in practice over an extended period, a safety factor of 5 or more is not uncommon, particularly when generic parts may be substituted, or the operating environment is likely to lead to eventual tarnishing of the contacts.
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