GREETINGS !! WE'RE OPEN AND SHIPPING EX STOCK FROM CHRISTCHURCH AND ACCEPTING: Visa, Mastercard, ShopPay, Afterpay, ZIP, ApplePay, Google Pay, PayPal, JCB, Amex, PoliPay and Bank Transfers

TECHOMAN GUIDE: PL259 Connectors and Connections

The following information covers many of the misconceptions about the classic PL-259 plug and matching SO-239 socket and there practical considerations in RF systems. It contains valuable advice, especially for amateur radio operators, CB radio operators, makers of RF cables, RF engineers, and hobbyists working with VHF/UHF gear.

Understanding PL-259 Connectors (UHF Connectors)

The PL-259 connector - also known as the UHF connector - has been a reliable component in RF systems since its invention nearly a century ago. Despite their longevity, the PL-259's and SO-239's have limitations, especially at higher frequencies.

Frequency Performance and Design Limitations

  • Originally designed in an era when frequencies above 30 MHz were considered “UHF.”
  • Today, UHF is defined as 300 MHz to 3 GHz.
  • PL-259 connectors begin to show performance degradation above 30 MHz.
  • Poor impedance matching occurs at VHF and especially UHF, leading to signal reflection and power loss.
  • Performance is highly dependent on:
    • Quality of manufacturing
    • Correct installation
    • Proper maintenance and protection

Installation and Handling Best Practices

  • Soldering:
    • Avoid excess solder on the centre pin. If too thick, it can damage the SO-239 socket.
    • The pin should insert snugly with slight resistance—not be loose or overly tight.
  • Connector Fit:
    • Ensure a clean fit between the plug and socket.
    • Carefully align when inserting—never force at an angle.
    • Cross-threading the outer shell can damage the connector.
    • Always hand-tighten. Never use pliers or tools.
  • Cable Considerations:
    • Heavy cables (RG-8, RG-213, LMR-400, etc.) require extra care to avoid damaging bending the SO239 socket barrel during insertion.
  • Cleanliness:
    • Remove all flux, solder residue, grease, or dust from the centre pin.
    • Use isopropyl alcohol and a soft cloth to clean the centre pin.
    • Avoid touching the centre pin with bare fingers to prevent contamination.

Maintenance and Wear

  • PL-259 connectors wear over time, especially with frequent connect/disconnect cycles.
  • Repeated use can:
    • Wear down plating on the centre pin and socket
    • Reduce conductivity
    • Lead to increased SWR and RF loss
  • Damaged, bent, or corroded connectors should be replaced immediately.
  • A damaged connector can impact your transmitter and overall system performance.

Weatherproofing (Outdoor Use)

  • PL-259 connectors are not weatherproof by design.
  • For outdoor installations:
    • Use high-quality self-amalgamating rubber tape
    • Seal both the connector and the adjacent cable area thoroughly
    • Inspect seals regularly

Key Takeaways

  • Use high-quality PL-259 connectors with matching SO-239 sockets.
  • Ensure clean, precise soldering and connector alignment.
  • Protect all connectors from corrosion, moisture, and mechanical stress.
  • Replace worn or damaged connectors promptly to avoid performance issues.
  • Always verify a clean and secure connection before transmitting RF signals.