Coax Cable and Connectors

The coax cable between your radio and antenna carries your signal in both directions. A poor cable or bad connector can lose more signal than you'd gain by doubling your transmit power. Understanding your options helps you choose the right cable for your setup.

Coax cable types

At GMRS frequencies (462-467 MHz), signal loss in coax cable is significant - much more than at lower frequencies. Shorter runs with better cable make a real difference.

• RG-58: thin (~5mm), flexible, inexpensive. Loses about 6.5 dB per 100 feet at 462 MHz. That's a 75% signal loss. Only acceptable for very short runs under 10 feet, such as a short jumper between a radio and a nearby antenna switch
• RG-8X (mini-8): mid-size (~6mm), moderate loss - about 4.5 dB per 100 feet. A good compromise for mobile installs where flexibility matters and runs are 10-25 feet
• RG-213 / RG-8U: thicker (~10mm), about 3.5 dB per 100 feet. Decent for moderate base station runs. Less flexible than RG-8X
• LMR-400: thick (~10mm), low loss - about 1.5 dB per 100 feet. The standard choice for base station installations. Worth the extra cost for any run over 25 feet. Stiff and harder to route, but the performance is dramatically better

Recommended cable by installation type

• Mobile (vehicle): RG-8X is the practical choice. It's flexible enough to route through doors and under trim, handles the tight bends in a vehicle, and keeps loss acceptable for the typical 10-20 foot run from radio to roof antenna
• Base station: LMR-400 for any run over 25 feet. For shorter indoor runs to a nearby antenna, RG-213 is acceptable. Don't use RG-58 or RG-8X if you can avoid it - base stations often have 50-100 foot runs where the difference is dramatic
• Portable / handheld: the antenna screws directly onto the radio, so coax isn't involved for typical use. If you add a remote antenna via a short jumper, RG-8X or LMR-240 (a slimmer low-loss cable) works well

Connector types

• PL-259 / SO-239: the most common connector for mobile and base station GMRS radios. PL-259 is the male plug; SO-239 is the female jack (on the radio). Sometimes called "UHF connectors," despite being designed decades ago for what was then considered UHF
• SMA: a small threaded connector used on handheld radios. SMA-Male has a center pin and external threads; SMA-Female has a center socket and internal threads. Note that different radio brands reverse which gender is on the radio versus the antenna - always check before ordering
• BNC: a quick-connect bayonet-style connector found on some test equipment and older radios. Easy to connect and disconnect. Less common on GMRS gear
• N-type: a precision connector used on higher-end antennas and commercial equipment. Better weatherproofing and lower loss than PL-259 at UHF frequencies. Some base station antennas use N connectors

Crimp vs. solder connectors

Both types work well when installed correctly. The choice comes down to tools and preference.

• Crimp connectors require a proper crimp tool for your connector and cable size. A good crimp makes a consistent, mechanically strong, gas-tight connection that resists corrosion. Faster to install once you have the tool. Less forgiving of wrong technique - a bad crimp is worse than a bad solder joint
• Solder connectors require only a soldering iron and solder. Good for occasional installs or field repairs. Risk of cold solder joints or melting the cable dielectric if the iron is too hot. Tinning both the connector and braid before joining gives the best result
• For PL-259 connectors on LMR-400 or RG-213, many operators solder the center pin and crimp or clamp the braid - a hybrid approach that's reliable and straightforward

Testing your coax

A bad cable or connector is one of the most common causes of poor radio performance, and one of the easiest to overlook. Two practical ways to check:

• SWR meter: connect an SWR meter (or antenna analyzer) between your radio and antenna. Transmit briefly on a GMRS frequency and read the reflected power. SWR of 1.5:1 or better is good; 2:1 is acceptable; above 3:1 suggests a problem with the antenna, cable, or connectors. See antenna basics for more on SWR
• Continuity check: disconnect both ends and use a multimeter. Check that the center conductor has continuity end-to-end, the braid has continuity end-to-end, and there's no continuity between center conductor and braid. Any failure points to a damaged cable or bad connector

Signs of bad coax

• Intermittent signal: signal that fades when you move the cable or flex it near a connector usually means a broken center conductor or a connector that's come partially loose inside the crimp or solder joint
• High SWR that changes with position: a cable with an internal short or open will show SWR that varies as you move the cable. A consistently high SWR that doesn't change is more likely an antenna issue
• Water damage: a connector that's been exposed to rain without weatherproofing will show green or white corrosion. Even a small amount of moisture inside the dielectric causes severe signal loss. If you can see corrosion, replace the connector or the cable - cleaning rarely restores performance fully
• Physical damage: crushed, kinked, or tightly coiled cable can permanently deform the dielectric spacing, raising impedance and loss at the damage point

Cable routing best practices

• Keep away from power lines and electrical wiring: AC wiring induces noise into the coax shield. Route coax at least a few inches from household wiring where possible, and cross at right angles if paths must intersect
• Avoid sharp bends: follow the cable's minimum bend radius - typically 5-10 times the cable diameter. LMR-400 is stiff and will kink if forced into tight corners. Use a gentle sweeping curve instead
• Protect from UV exposure: most coax jacket compounds degrade in direct sunlight over time. For outdoor runs, use cable rated for direct burial or UV exposure, or enclose the cable in UV-resistant conduit. Black polyethylene jackets hold up better than gray PVC
• Drip loops at entry points: where coax enters a building or a radio, form a downward loop before the entry point so water runs off the cable rather than following it inside. See grounding and lightning protection for entry point best practices
• Secure but don't over-tighten cable ties: zip ties cinched too tight deform the cable. Snug is enough - the cable should not move, but the jacket should not be compressed

How long does outdoor coax last?

Installed well, quality coax lasts 10-20 years outdoors. LMR-400 with a UV-rated jacket in a sheltered or conduit-protected run may last considerably longer. The connectors typically fail before the cable itself - inspect weatherproofing tape every few years and replace it when it hardens or peels. Direct burial cable rated for outdoor use is the most durable option for runs along a roofline or down a tower. Any cable showing jacket cracking, stiffness, or discoloration should be replaced regardless of age.