Coax Connectors and Termination for Ham Radio
A poorly installed coax connector is one of the most common causes of high SWR, intermittent connections, and signal loss in ham radio stations. A connector installed with a poor solder joint, a cut braid, or incorrect assembly can introduce significant insertion loss and allow moisture ingress that destroys the cable over time. Learning to install connectors correctly is a fundamental skill that every ham should master — it pays dividends in every antenna installation.
| Connector | Impedance | Frequency | Primary Use |
|---|---|---|---|
| PL-259 (UHF series) | 50 ohm | DC–300 MHz usable | HF and 6m — industry standard despite its name |
| N-type | 50 or 75 ohm | DC–11 GHz | VHF/UHF/microwave — best connector for 2m and above |
| BNC | 50 or 75 ohm | DC–4 GHz | Quick-connect for portable and test equipment |
| SMA | 50 ohm | DC–18 GHz | HTs, SDR dongles, small portable equipment |
| TNC | 50 ohm | DC–11 GHz | Threaded BNC — more secure than BNC |
| SO-239 | 50 ohm | DC–300 MHz | Panel-mount mate for PL-259 |
Prepare the cable end
Cut the coax cleanly with a sharp knife or coax cutter. Strip 22mm of the outer jacket. Fan out the braid and fold it back over the jacket. Strip the dielectric (foam or solid polyethylene) to expose 10mm of centre conductor. Tin the centre conductor with a small amount of solder — this prevents fraying and makes the final solder joint cleaner.
Slide on the coupling ring
Before assembling the connector body onto the cable, slide the coupling ring (the outer threaded part of the PL-259) onto the cable with the threads facing away from the cable end. This is the most commonly forgotten step — having to disassemble a completed connector because you forgot the coupling ring is a classic mistake.
Insert the connector body
Push the connector body onto the prepared cable end. The centre conductor should protrude slightly through the pin hole in the tip of the connector. The folded-back braid should be visible through the side holes in the connector body. Twist the connector onto the cable if using the screw-on type.
Solder the centre pin
Apply solder to the hole in the tip of the connector where the centre conductor protrudes. Use enough heat to flow solder cleanly into the joint — PL-259 connectors require a higher wattage iron than typical electronics work (60–80W minimum). A cold or incomplete solder joint on the centre pin is a very common cause of intermittent connections.
Solder the braid
Apply solder through the side holes in the connector body to bond the braid to the connector shell. Again, use adequate heat — the mass of the connector body requires a hot iron. Fill each hole with solder until it is fully bonded. Allow to cool before handling. Thread the coupling ring onto the connector body.
PL-259 limitations
Despite being called the UHF connector, the PL-259 is not a constant-impedance connector above about 300 MHz. At 2m (144 MHz) and 70cm (432 MHz), PL-259 connectors introduce measurable insertion loss and impedance discontinuities. This is acceptable for many applications but represents a genuine performance degradation compared to N-type. At 1.2 GHz and above, PL-259 is essentially unusable. For any installation where VHF/UHF performance matters — a good antenna system for 2m EME, for example — N-type connectors are the correct choice.
N-type advantages
N-type connectors maintain constant 50-ohm impedance through the connector body, have a weatherproof design suitable for outdoor use without additional sealing, and are rated to 11 GHz. They are mechanically more robust than PL-259 and the threaded coupling is more secure than PL-259's slip-on coupling ring. The downside is slightly higher cost and the need for specific crimp tooling for quality installation. For outdoor coax runs to VHF/UHF antennas, N-type at both ends (on the antenna and on a bulkhead at the building entry) is the professional-grade choice.
Should I solder or crimp PL-259 connectors?
Both methods work. Soldered PL-259 connectors have been the standard for decades and a well-soldered connector is fully reliable. Crimp connectors (which use crimping tools rather than soldering) are faster to install and consistent in quality, but require dedicated crimping tools that are worth buying only if you install connectors regularly. For occasional use, a well-soldered connector is the better choice. The key is using adequate heat — a 25W pencil iron is not sufficient for soldering PL-259 connectors to RG-8X or RG-213.
How do I weatherproof outdoor coax connectors?
Self-amalgamating (self-fusing) tape is the standard method — wrap the connector joint with two or three layers of self-amalgamating tape, stretching it as you wrap so it fuses into a watertight seal. Start below the connector and extend well above it. For additional protection, overwrap with standard vinyl electrical tape. PL-259 connectors should not be left exposed outdoors without weatherproofing — moisture ingress causes rapid degradation of the connector and cable end. N-type connectors with their threaded weatherproof design are more tolerant of outdoor exposure but benefit from sealing as well.
What causes intermittent coax connections?
The most common causes are: an incomplete solder joint on the centre pin (the connection opens and closes with temperature or movement), a fractured or poorly bonded braid-to-connector shell connection, physical damage to the connector from being stepped on or bent, or corrosion from moisture ingress. To diagnose, flex the coax near the connector while monitoring SWR — an intermittent connection will show as erratic SWR changes. The fix is usually replacing the connector entirely rather than attempting repair.