Part of our Building Your First Ham Radio Station guide.
Every antenna, radio, and accessory in this hobby eventually needs a connector, and the four you will run into constantly, SO-239/PL-259, BNC, SMA, and N-type, each have their own strengths, weaknesses, and typical use cases. Picking the right one for the job matters just as much as picking good coax in the first place.
SO-239 and PL-259: the HF standard
The SO-239 (the panel-mount jack) and PL-259 (the cable-mount plug) pairing is the de facto standard on most HF and many VHF radios, tuners, and antenna switches. It is a threaded, non-constant-impedance connector, meaning its actual impedance varies slightly along its length rather than holding a precise 50 ohms throughout, which matters very little at HF frequencies but becomes a real limitation well up into VHF and beyond. It is large, mechanically rugged, and easy to solder or crimp even with basic tools, which is exactly why it has stuck around for decades despite better-performing alternatives existing at higher frequencies.
BNC: quick-connect for test gear and handhelds
BNC uses a quarter-turn bayonet locking mechanism instead of threads, letting you connect or disconnect with a quick twist rather than screwing anything down. This makes it popular on test equipment, some handheld radios, and antenna analyzers, anywhere fast, frequent connect-and-disconnect cycles matter more than the absolute most robust weatherproof seal. It performs well up through VHF and UHF and is a genuine constant-impedance design at 50 ohms, though the connector itself is more delicate than an SO-239 and less tolerant of repeated rough handling in the field.
SMA: small, common on handhelds, easy to damage
SMA is the tiny threaded connector found on the vast majority of modern handheld radios, and it performs well into the microwave range, well beyond what most hams will ever need. Its small size is both its main advantage, letting it fit on compact handhelds, and its main weakness, since the connector’s fine threads and small center pin are genuinely easy to damage through cross-threading or repeated rough antenna swaps. Reverse-SMA, a variant with the male and female center pin arrangement swapped, exists specifically because of old FCC rules aimed at discouraging unauthorized antenna substitution on certain consumer devices, and it trips up more new hams than any other connector confusion in the hobby, since a standard SMA antenna simply will not physically mate with a reverse-SMA radio jack.
N-type: the serious weatherproof choice
N-type connectors are threaded, genuinely constant-impedance at 50 ohms, and built for excellent performance well into the microwave range, with a weatherproof design that holds up far better outdoors than an SO-239 does over the long term. This makes them the preferred choice for permanent outdoor installations, especially anything running VHF, UHF, or higher, where connector loss and weather resistance both matter more than they do at HF. They are bulkier and more expensive than SO-239 hardware, which is largely why HF gear has stuck with the older standard despite N-type’s better technical performance.
Picking the right one, and adapting between them
- HF base and mobile gear: SO-239/PL-259 remains the practical default, matching what nearly every HF radio and tuner already uses.
- Handhelds: SMA or reverse-SMA, matching whatever your specific radio actually uses, check before ordering a new antenna.
- Test equipment and quick-swap setups: BNC, for the fast connect cycle.
- Permanent outdoor VHF/UHF runs: N-type, for the weatherproofing and lower loss at higher frequencies.
Adapters exist between every one of these, and keeping a small assortment on hand, SO-239 to BNC, SMA to N-type, and so on, saves a frustrating trip mid-project when two pieces of gear simply do not speak the same connector language.