PL-259, SMA, BNC, and N-Type: Which RF Connector Do You Need?

Walk into any RF workspace and you'll see a zoo of connector types — large silver barrels, tiny threaded fittings, bayonet-lock ports, and weatherproof hex-nut couplings. Each was designed for specific frequency ranges, power levels, and use cases. Ordering the wrong cable is the most common mistake in RF setups, and it's almost always a connector confusion issue. This guide cuts through it.

PL-259 (UHF Series): The Ham Radio Classic

The PL-259 male connector mates with the SO-239 female socket. Despite the "UHF" series name — a legacy from WWII-era nomenclature — PL-259 was never actually designed for UHF frequencies. Its geometry is uncontrolled above about 300 MHz, making it unsuitable for serious VHF/UHF work at the antenna end. However, it remains on virtually every HF transceiver ever manufactured: Icom, Kenwood, Yaesu, and the classics. It's large (about 0.87 inches diameter), easy to solder, and handles high power well at HF frequencies.

If your transceiver has a large silver barrel-type connector labeled "ANT," it's almost certainly an SO-239, and you need a PL-259 on the cable end. For HF-to-HF connections:

RG-58 PL-259 to PL-259  |  LMR-400 PL-259 to PL-259

SMA vs RP-SMA: The Most Common Ordering Mistake in RF

SMA (SubMiniature version A) is a precision threaded connector rated from DC to 18 GHz. It's found on SDR receivers, GPS modules, laboratory instruments, cellular modems, and professional RF equipment. The male has a center pin; the female has a center socket. The threads are 1/4-36 UNS.

RP-SMA (Reverse Polarity SMA) looks externally identical to SMA. Same body diameter, same thread pitch, same wrench size — but the center pin is reversed. An RP-SMA male has a center socket; an RP-SMA female has a center pin. They will not mate with standard SMA. RP-SMA was created to prevent consumers from accidentally connecting non-approved antennas to FCC-regulated WiFi equipment. Consumer WiFi routers from Asus, Netgear, TP-Link, and most Ubiquiti UniFi gear use RP-SMA. SDR dongles, GPS modules, and professional equipment use standard SMA.

Before ordering, look inside the port: if you see a pin protruding, it's a female (of either type). If you see a socket, it's a male. Then check the center conductor of the mating device: pin-to-socket must match. When in doubt, look for "RP" markings on the equipment or check the manufacturer's spec sheet.

RFC195 RP-SMA to RP-SMA Cable  |  RFC195 N-Male to RP-SMA Cable

BNC: The Quick-Connect Standard

BNC (Bayonet Neill-Concelman) uses a quarter-turn bayonet locking mechanism that lets you connect and disconnect one-handed. It's rated from DC to about 4 GHz and is found on oscilloscopes, spectrum analyzers, signal generators, portable radios, and CCTV equipment. The body is about 14mm in diameter.

The critical gotcha: BNC comes in both 50-ohm and 75-ohm versions that are physically identical. 50-ohm BNC is used on RF and test equipment. 75-ohm BNC is used on CCTV cameras and video distribution gear. Mixing them creates a small impedance mismatch (4%), which is measurable but minor in most applications. The real issue is that people sometimes buy cheap 75-ohm BNC jumpers at camera stores and use them in 50-ohm test setups. Check the markings on the device if you're uncertain.

TNC: The Threaded BNC

TNC (Threaded Neill-Concelman) is electrically very similar to BNC but uses a threaded coupling instead of the bayonet. This makes it significantly more resistant to vibration loosening and provides better weatherproofing than BNC. TNC is rated from DC to 11 GHz. It's commonly found on military equipment, aviation radios, and outdoor installations where vibration or weather would cause bayonet-lock connectors to loosen. The threading makes it slower to connect but much more secure.

RFC195 RP-TNC to RP-TNC Cable

N-Type: The Professional Outdoor Standard

N-type was designed by Paul Neill at Bell Labs in the 1940s. It's a precision threaded connector with a 7/16-inch hex nut, rated from DC to 11 GHz, and IP67 weatherproof when properly mated. It handles 500+ watts at 1 GHz. N-type is on outdoor antennas, cellular signal boosters, commercial access points, repeater installations, and lightning arrestors. For anything outdoors at VHF frequencies and above, N-type is the correct connector.

When you need to connect an N-type outdoor antenna to a PL-259-ported transceiver, or to RP-SMA WiFi equipment, you need a cross-connector cable:

LMR-400 N-Male to PL-259  |  LMR-400 N-Male to RP-SMA

Connector Identification Guide

SMA Torque Warning

The maximum specified torque for SMA is 12 in-lbs. This is much less than most people apply when hand-tightening. Over-tightening distorts the PTFE dielectric, deforms the center pin geometry, and permanently degrades the connector's return loss. Never use pliers on an SMA connector. For bench work, finger-tight is adequate for non-critical connections. For calibrated measurements, use a proper torque wrench set to 8–12 in-lbs. Never use any tool on MMCX connectors — they're designed for finger-tight only and will be destroyed by wrench force.

Common Mixed-Connector Cables

Real-world installations constantly require mixing connector types. Here are the most common combinations:

• PL-259 to SMA: HF transceiver to SDR or compact measurement gear — RG-58 PL-259 to SMA-Female
• BNC to N: Test bench oscilloscope/analyzer to N-type antenna — RG-58 BNC to N-Male
• BNC to SMA: Test equipment to SDR or SMA-port device — RG-58 BNC to SMA-Female
• N to SMA: N-type outdoor antenna to SDR receiver — RFC195 N-Male to SMA
• N to RP-SMA: Outdoor antenna to WiFi equipment — RFC195 N-Male to RP-SMA

How to Identify an Unknown Connector in 3 Steps

Step 1 — Measure the body diameter. Under 10mm is likely SMA or MMCX. Around 14mm is BNC or TNC. Around 21–22mm is N-type or PL-259.

Step 2 — Check the coupling mechanism. Bayonet (quarter-turn with pins) = BNC. Threaded with fine pitch = SMA, TNC, or N. Threaded with solder sleeve = PL-259.

Step 3 — Check the center pin. A protruding pin = male (in standard SMA) or female (in RP-SMA). A recessed socket = female (standard) or male (RP). For BNC and N-type, the standard orientation applies: male has a pin, female has a socket.

Still not sure? The cable configurator lets you select connectors by description, and our team is happy to help identify an unknown connector from a photo.