BNC Connector Installation
BNC is a true impedance-controlled connector with a fast quarter-turn bayonet lock — the standard fitting on most test equipment (including the NanoVNA), handhelds, and shorter thin-coax runs. This guide covers the crimp-type BNC, the version most hams actually use, including the part-assembly order that trips up nearly everyone on a first attempt, matching connector to cable size, and correct crimping technique.
Why BNC shows up on test equipment and handhelds
Unlike the PL-259/SO-239 pair (see the PL-259/SO-239 guide), BNC is built with a controlled dielectric that holds its characteristic impedance through the connector body, so it doesn't introduce the same growing mismatch as frequency rises. Combined with its fast quarter-turn bayonet lock — connect or disconnect in under a second, no threading required — this makes it the natural choice for equipment that gets connected and disconnected often, like a NanoVNA, signal generator, or handheld radio antenna port.
Crimp vs. solder-type construction
A crimp BNC uses a dedicated crimp tool to compress a metal ferrule over the braid and a separate crimp pin over the center conductor, giving highly consistent results once you have the right tool and technique. Solder/screw-on types exist and don't require a crimp tool, but are fussier to assemble well and less commonly stocked today. This guide covers the crimp type, since it's both the more common option and the one that benefits most from clear step-by-step guidance — the assembly order is the single detail most likely to trip up a first attempt.
Cable size matters more than it looks like it should
- RG-58: the most common cable paired with BNC in ham use — patch cables, radio-to-tuner jumpers, and general HF/VHF work.
- RG-59: a similar-looking but electrically different cable (75Ω video-grade coax, not 50Ω) with a different center conductor and dielectric diameter — BNC connectors are sold sized for one or the other, and the ferrule/pin from an RG-58-sized connector generally won't crimp correctly onto RG-59, or vice versa.
Always confirm the connector's specified cable compatibility against your actual coax before starting — mismatched connector/cable pairing is one of the most common causes of a BNC crimp that looks fine but performs poorly.
Bayonet lock: fast but less secure under strain
BNC's quarter-turn bayonet coupling is fast and reliable for equipment that stays on a bench or in a pack, but it isn't as mechanically secure under sustained vibration or cable weight/strain as a threaded connector like N-type. For a permanent outdoor antenna feedline run, N-type is usually the better structural choice; for test gear, handhelds, and shorter indoor/portable runs, BNC's speed advantage wins.
| Cable Type | Impedance | Connector Size Needed | Typical Use |
|---|---|---|---|
| RG-58 | 50Ω | RG-58-specified BNC crimp connector | HF/VHF patch cables, radio-to-tuner jumpers, general ham use |
| RG-59 | 75Ω | RG-59-specified BNC crimp connector | Video/CCTV-style runs, not typically used for 50Ω RF work |
| RG-174 / thin patch cable | 50Ω | Miniature/RG-174-specified BNC crimp connector | NanoVNA test leads, short bench jumpers |
Materials for a crimp-type BNC connector
Crimping a BNC connector's ferrule onto RG-58 coax after the center pin has already been crimped and seated.
Installing a Crimp BNC Connector
The part-assembly order matters here just as much as it does for a PL-259 — dry-fit everything before crimping anything.
Slide the ferrule onto the cable first
Before stripping or crimping anything else, slide the crimp ferrule onto the coax, well back from the end. Like a PL-259's coupling ring, this has to go on before final assembly — there's no way to add it after the connector body is in place.
Strip the cable in three steps
A crimp BNC needs three distinct strip depths: the outer jacket stripped back to expose the braid, the braid trimmed to the length that will sit under the ferrule, and the dielectric stripped to expose the center conductor for the pin. Follow the connector's package instructions for exact lengths, since these vary slightly between manufacturers.
Crimp the center pin
Slide the pin over the exposed center conductor so it's fully seated with no gap, then crimp with the tool's correctly sized die. Check that the conductor is visible at the pin's tip and that the crimp looks uniform and centered, not lopsided.
Insert into the connector body and crimp the ferrule
Insert the pin/cable assembly into the connector body until it seats fully (you should feel or hear it click into place on most designs), fold the braid back over the body's barrel if the design calls for it, slide the ferrule forward over the braid, and crimp with the ferrule die.
Test the finished connector
Check continuity center-pin-to-center-pin and confirm no short between the center pin and the body's outer shell with a multimeter. For a cable that will see real RF use, a quick NanoVNA check confirms the connector isn't introducing an unexpected mismatch before you rely on it.
| Symptom | Most likely cause | Diagnosis | Fix |
|---|---|---|---|
| Ferrule is missing after the connector body is already crimped | Forgot to slide the ferrule onto the cable before assembly | Check the cable behind the connector body for the ferrule | Cut the connector off and start over with the ferrule on the cable first |
| Crimp looks complete but the connector pulls off the cable with light tension | Wrong die size used, or the crimp tool wasn't fully closed/ratcheted | Compare the crimp's shape against the tool and connector manufacturer's reference photos | Re-crimp with the correct die and a full tool stroke, or replace the connector if the ferrule is already deformed from a bad first attempt |
| Multimeter shows no continuity through the center pin | Center conductor wasn't fully seated in the pin before crimping, or the conductor broke during stripping | Inspect the pin tip for a visible, intact center conductor | Re-strip and re-crimp with a fresh connector, ensuring the conductor is fully seated before crimping this time |
| Multimeter shows a short between the center pin and the shell | Stray braid strands bridging to the center pin during assembly | Inspect the strip job for loose or splayed braid strands near the center pin | Re-strip more carefully, trimming any stray strands before reassembly |
| Connector fits but doesn't lock securely onto the mating jack | Connector isn't fully seated in the crimp body, or the bayonet mechanism is damaged/worn | Check that the pin/cable assembly was inserted all the way into the connector body during step 4 | Disassemble and reinsert fully if not seated; replace the connector if the bayonet slots themselves are damaged |
Crimp or solder BNC — which should I use?
Crimp is the more common choice today and gives highly consistent results once you have the correct crimp tool and dies. Solder/screw-on types work too and don't need a crimp tool, but are fussier to assemble well and less commonly stocked — this guide covers crimp as the more broadly useful default.
Can I use an RG-59 BNC connector on RG-58 cable?
Not reliably — RG-58 and RG-59 have different center conductor and dielectric diameters, and BNC connectors are sized for one or the other. A mismatched pairing typically crimps loosely or won't seat correctly, even if it looks superficially fine. Always match the connector to your actual cable per the compatibility table above.
Why does my NanoVNA use BNC connectors?
BNC's controlled impedance and fast bayonet connect/disconnect make it well suited to test equipment that gets connected to many different things during a single session — exactly the use pattern a NanoVNA sees during antenna and connector testing.
Is BNC good enough for a permanent outdoor antenna feedline?
Electrically, yes — but its bayonet lock is less mechanically secure under sustained vibration, wind loading, or cable weight than a threaded connector. For a permanent outdoor run, N-type is usually the better structural choice; BNC is best reserved for equipment connections, test leads, and shorter or less exposed runs.