Coax connector chart: UHF, N, BNC, SMA and more
The right connector for the frequency, the cable and the weather it will live in.
The short answer
Use UHF connectors, the PL-259 and SO-239 pair, for HF and 2 metres. Use N connectors above 300 MHz and for anything outdoors, because they are constant impedance and weather resistant. Use BNC for test equipment and low power, and SMA for handhelds and small portable gear.
- UHF useful to
- About 300 MHz
- N useful to
- 11 GHz
- BNC useful to
- 4 GHz
- SMA useful to
- 18 GHz
- Best outdoors
- N
- Amateur standard
- UHF
Coaxial connectors look interchangeable and are not. They differ in frequency range, whether they maintain a constant 50 ohm impedance through the joint, how much power they handle, how well they survive weather, and which cable diameters they accept.
For amateur work the choices are narrower than the full catalogue suggests. This chart covers what you will actually meet, what each one is for, and which combinations to avoid.
The connector families
Connector reference
Every connector you will meet in amateur radio
| Connector | Useful to | Impedance | Power | Best for |
|---|---|---|---|---|
| UHF, PL-259 and SO-239 | 300 MHz | Not constant | High | HF and 2 m, the amateur standard |
| N | 11 GHz | 50 ohm constant | High | UHF and above, all outdoor use |
| BNC | 4 GHz | 50 or 75 ohm | Low to medium | Test gear, portable, low power |
| SMA | 18 GHz | 50 ohm constant | Low | Handhelds, small modules |
| RP-SMA | 18 GHz | 50 ohm constant | Low | Wifi gear, reversed pin, not interchangeable |
| TNC | 11 GHz | 50 ohm constant | Medium | Threaded BNC, better in vibration |
| 7/16 DIN | 7.5 GHz | 50 ohm constant | Very high | Repeater and commercial sites |
| F | 1 GHz | 75 ohm | Low | Television, not for amateur use |
| Mini-UHF | 2.5 GHz | Not constant | Medium | Mobile installations, compact |
| Motorola | Low | 75 ohm | Low | Broadcast receivers only |
The UHF connector is not constant impedance, which is why it is technically poor above about 300 MHz. In practice the mismatch it introduces is small enough that the amateur world has used it on 2 metres for decades without complaint.
Reducers and cable fit
A PL-259 is sized for RG-8 and RG-213 class cable, around 0.405 in outer diameter. Thinner cable needs a reducer that screws into the connector body.
Reducers
Which reducer for which cable
| Cable | Outer diameter | Reducer | Notes |
|---|---|---|---|
| RG-213, RG-8, LMR-400 | 0.405 in | None | Enters the connector body directly |
| RG-8X, LMR-240 | 0.242 in | UG-176 | The most common amateur combination |
| RG-58, LMR-195 | 0.195 in | UG-175 | Thin cable, easy to overheat when soldering |
| RG-59 | 0.242 in | UG-176 | Seventy five ohm, receive use only |
| RG-142 and similar | 0.195 in | UG-175 | PTFE dielectric, tolerates heat well |
Buying connectors as a kit with the correct reducer avoids the classic problem of a connector that will not close on the cable. Assembly detail is in how to install PL-259 connectors.
Choosing by application
- HF station, indoors and out: UHF connectors throughout. Universal on amateur equipment, high power handling, and the frequency limitation is irrelevant below 30 MHz.
- 2 metres and 70 cm: UHF is acceptable and N is better, particularly on 70 cm and particularly outdoors.
- Anything above 440 MHz: N connectors, without exception. The mismatch a UHF connector introduces becomes measurable.
- Outdoor and mast top: N connectors, because they are designed to be weather resistant and their construction seals better. Weatherproof them anyway.
- Handheld antennas: SMA, in either polarity depending on the radio. Check which way round your model is before ordering an adapter.
- Test equipment: BNC for speed, N for accuracy above about 1 GHz.
- Repeater and duplexer work: N or 7/16 DIN, because intermodulation performance matters and UHF connectors are a known source of it.
Weatherproofing
- Assemble and tighten the joint completely before wrapping anything.
- Wrap a layer of ordinary electrical tape as a release layer, so the seal can be removed later.
- Wrap Self-amalgamating rubber splicing tape over that, stretched to roughly double its length so it fuses into a solid block, extending well onto the cable jacket at both ends.
- Finish with a layer of electrical tape as UV protection, because self-fusing tape degrades in sunlight.
- Alternatively use Hand-moldable sealant tape, which is faster to apply and easier to remove.
- Form a drip loop below the connector so water runs away rather than sitting on the joint.
What to keep on hand
Connector supplies
Spares are cheap and the fix is very often a fresh connector.
Fanbalunke
PL-259 solder connectors with reducers, 6-pack
PL-259 connectors with reducers, the amateur standard and the most common replacement part.
Check price$9.99
exgoofit
SO-239 barrel couplers, 6-pack
Barrel connectors for joining runs and for splitting a cable during fault finding.
Check price$9.99
Max-Gain Systems
Max-Gain Systems bulkhead SO-239 feedthrough
A bulkhead feedthrough for a wall or entry panel, so outdoor and indoor runs are separate cables.
Check price$35.00
Maxwel
Self-amalgamating rubber splicing tape
Self-fusing tape, the correct way to seal an outdoor joint.
Check price$9.99
NAC
Hand-moldable sealant tape
A faster sealing option that peels away cleanly when the joint needs opening.
Check price$9.69
AURSINC
NanoVNA H4 vector network analyzer
Sweeps a finished cable so a bad connector shows up as a measurement rather than a mystery.
Check price$89.90
Common questions
Questions people ask about this
Can I use UHF connectors on 70 cm?
You can, and amateurs do constantly. The UHF connector is not a constant impedance design, so it introduces a small mismatch that becomes measurable above about 300 MHz. On 70 cm the effect is real but modest, typically a fraction of a decibel. For a new installation on 70 cm or above, N connectors are the better choice and cost very little more.
What is the difference between SMA and RP-SMA?
The pin and socket are reversed. A standard SMA plug has a centre pin and the socket has a receptacle; RP-SMA swaps them, so an RP-SMA plug has a receptacle. They screw together mechanically and make no electrical connection at all, which is exactly the trap. Check which polarity your handheld uses before buying an antenna or adapter.
Which connector is best for outdoor use?
N, because it is designed with a weather resistant interface and its construction seals far better than a UHF connector. That said, no connector is genuinely weatherproof on its own outdoors. Every outdoor joint needs self-fusing tape and a UV over-wrap regardless of type, because water inside coax wicks along the braid and destroys the whole run.
Do adapters cause problems?
Each one adds a small discontinuity, a possible water ingress path and a potential source of intermodulation, particularly at a repeater site. One adapter in a test setup is harmless. Three stacked at the top of a mast is a fault waiting to happen. In a permanent installation, fit the correct connector to the cable rather than adapting.
Why does my SWR change when I wiggle a connector?
The connection is intermittent, which almost always means a poorly soldered braid, a centre pin that has pushed back, or corrosion from water ingress. Replace the connector rather than trying to improve it. An intermittent connector will work at low power and fail under transmit conditions, which makes it one of the most frustrating faults to chase.
Keep going
Related on this site
Keeping your own cut lengths, SWR sweeps and exposure record? The Station Build & Antenna Planner is the paid version of these pages: 8 printable worksheets you fill in with your own numbers, plus the full PDF, $29.
Disclaimer Researched guidance for planning purposes, not professional engineering, electrical or legal advice. Antenna work, RF exposure, mast and tower work, grounding and battery handling all carry real risk that depends on your specific site and installation. Verify anything safety-critical against current FCC rules, the National Electrical Code and the manufacturer's own documentation, and hire a professional where the job calls for one. We research equipment from published specifications, regulatory documents and verified owner reviews rather than claiming hands-on testing we have not done.