Everything About Coax for CB Radios (Part 2): PL-259 Connectors, Cable Length, and Building Your Own Runs
Part 2 covers the hands-on side of CB coax: connectors, cable length, and how to build your own runs. PL-259 (UHF) is the standard CB connector — solder or crimp, both work when done right. Coax length matters more than most installers think: many antennas are designed around specific electrical lengths (18 feet is the classic Firestik spec), and cutting or coiling the cable can change how the antenna appears at the radio. Excess coax should never be tightly coiled — figure-8 it or leave gentle bends instead.
Part 1 covered the anatomy of coax and how to pick a cable type — read it here if you haven't. Part 2 is the practical guide to actually installing it.
What's in this guide
- PL-259 connectors and the CB standard
- Solder vs crimp PL-259
- How to terminate a PL-259 (step-by-step)
- Coax length and why 18 feet matters
- The right way to store excess coax
- How to route coax in a vehicle
- How to test a coax run before you trust it
- Common coax mistakes that ruin SWR
- How to build a custom coax run from scratch
- FAQ
PL-259 connectors and the CB standard
The PL-259 (also called the UHF male connector) has been the CB and amateur radio standard since the 1940s. Every quality CB radio, SWR meter, and antenna stud uses matching SO-239 (UHF female) ports. If your coax has anything else on the end — BNC, N-type, F-type, RCA — it wasn't built for CB.
PL-259 comes in several body sizes to match different coax diameters:
- PL-259 for RG-58 — smallest body, needs a UG-175 adapter to properly grip the thinner cable
- PL-259 for RG-8X — mid-size, sometimes uses a UG-176 adapter
- PL-259 for RG-8 / RG-213 / LMR-400 — full-size body, no adapter needed
Buying the wrong size PL-259 is one of the top reasons a home-built coax run fails. If you're not sure which one you need, buy pre-terminated cable in the Coax Cable collection.
Solder vs crimp PL-259
Two ways to attach a PL-259 to coax:
Soldered PL-259
The classic method. The center conductor is soldered into the pin at the tip, and the shield is soldered through four solder holes on the connector body. Done right, a soldered connector will outlast the coax itself.
Crimp PL-259
Uses a hex crimp die to compress a metal ferrule around the shield. Faster to install and doesn't require a soldering iron. Quality is excellent when the correct crimp die is used.
Both perform electrically the same at CB frequencies. Pick based on what tools you have. If you plan to build multiple runs, a good crimp tool ($40–80) pays for itself.
How to terminate a PL-259 (soldered) — step-by-step
- Cut the coax square with a sharp cable cutter. A ragged cut makes strip lengths inconsistent.
- Slide the PL-259 coupling ring (the outer nut) onto the coax first. Don't skip this — the ring cannot go on after the connector body is attached.
- Strip the outer jacket back about 3/4" (19 mm). Do not nick the shield braid.
- Fold the shield braid back over the jacket temporarily, exposing the dielectric.
- Strip the dielectric back about 5/8" (16 mm), exposing the center conductor. Do not nick the center wire.
- Un-fold the shield braid and trim it flush with the end of the outer jacket, or leave a small tail depending on the specific PL-259 style.
- Slide the connector body over the coax. The center conductor should protrude just past the tip of the pin.
- Solder the center pin — heat the pin from the outside until solder wicks into the hole and fills it flush. Don't overfill.
- Solder the four side holes — heat the connector body around each hole and let solder flow onto the shield underneath. The braid should be tinned but not sloppy.
- Screw the coupling ring back down over the connector body.
- Ohm-test with a multimeter: center pin to shield should read open (infinite resistance). If it reads short, you have a solder bridge.
The whole process takes about 5 minutes once you've done a few. Practice on a scrap piece of coax before you cut into your real cable.
Coax length and why 18 feet matters
Coax has an electrical length that's related to but not the same as its physical length. The velocity factor of the cable (from Part 1) determines how many degrees of the CB waveform fit inside a given physical length.
Some antennas — most famously Firestik — are designed to see a specific electrical length of coax at the feed point. Firestik's spec is 18 feet of RG-58 or RG-8X. That length was chosen because it's roughly a half-wavelength at 27 MHz (accounting for velocity factor), which makes the antenna feed impedance repeat exactly at the radio end.
Practical consequence: if you cut a Firestik's 18-foot coax down to 12 feet to make the install cleaner, the SWR you tune at the tip may not match what the radio actually sees. That's why the tuning guide (see step-by-step SWR tuning) is done with the coax the antenna manufacturer expects.
Rule: if the antenna specifies a coax length, use that length. Deal with excess by routing it, not by cutting it.
The right way to store excess coax
Coax stores RF energy in its own electromagnetic field. If you coil the cable tightly (like winding it around your hand), you turn the coax into a small inductor. That inductance changes how the antenna appears at the radio and can raise SWR — sometimes dramatically.
Two right ways to handle excess:
- Figure-8 the excess — lay the cable in an alternating figure-8 pattern. This cancels the inductance because each loop is wound in the opposite direction.
- Loose S-curves — route the excess in gentle, wide bends. Never tighter than a 4-inch radius for RG-8X.
Never zip-tie coax into a tight bundle. Never coil it on a metal surface (like the fender well or under a truck bed). Never let it lie next to a power cable running the same direction — you'll pick up alternator whine.
How to route coax in a vehicle
- Start at the antenna mount and work toward the radio. Leave a small service loop at the mount so future removal is easy.
- Avoid door jambs where the cable can be pinched. If you must go through a door jamb, use the OEM grommet or drill a proper feed-through and seal it.
- Cross power wiring at 90 degrees, not parallel to it, to minimize RFI pickup.
- Keep coax away from ignition wires, computers, and Bluetooth modules when possible.
- Secure with cushioned clamps or foam-lined zip ties. Bare-plastic zip ties over time will cut into the jacket.
- Leave the excess accessible under the seat or behind the radio, not buried under the carpet. You may need to shorten later.
How to test a coax run before you trust it
Once terminated and routed, don't just plug it in and hope. Test:
-
Continuity check with a multimeter:
- Center pin (end A) to center pin (end B) = 0 ohms (solid connection)
- Shield (end A) to shield (end B) = 0 ohms
- Center pin to shield (either end) = open / infinite (no short)
- SWR sweep with your meter and radio: With the antenna connected, sweep channels 1, 20, and 40. A bad coax run often shows up as SWR that changes wildly across the band rather than a smooth curve.
- Wiggle test: While transmitting a carrier, gently wiggle each connector. SWR should not jump. If it does, you have a loose connection.
Common coax mistakes that ruin SWR
- Nicked center conductor during stripping — creates a weak point and can short over time.
- Solder cold-joint on the shield — looks fine visually but has high resistance. Reheat until it flows.
- Bent PL-259 pin — from over-tightening a coupling ring. Discard and re-terminate.
- Water in the connector — CB coax at the antenna end must be weatherproofed with self-vulcanizing tape or coax-seal putty. Even a drop of water at the connector will spike SWR and eventually corrode the shield.
- Tight coils under the seat — see the figure-8 rule above.
- Coax running parallel to power wiring — causes alternator whine on transmit.
- Wrong-size PL-259 on RG-58 — the coupling ring won't grip and the cable pulls out under vibration.
How to build a custom coax run from scratch
Full parts list for a mobile install:
- 1 spool of RG-8X coax (buy a few feet longer than the antenna spec)
- 2 PL-259 connectors sized for RG-8X
- Coax stripper or sharp utility knife
- Soldering iron (40W minimum) and 60/40 rosin-core solder — OR a crimp tool and matching PL-259 crimp connectors
- Multimeter for testing
- Self-vulcanizing tape for the antenna-end weatherproofing
- Cushioned clamps or foam-lined zip ties for routing
Steps:
- Measure the run from antenna mount to radio location. Add 12" of service loop at each end.
- Cut the coax to length.
- Terminate each end using the step-by-step above.
- Ohm-test both connectors before installing.
- Route the cable per the routing rules above.
- Weatherproof the antenna connection with self-vulcanizing tape.
- SWR sweep and adjust the antenna per our tuning guide.
Prefer to skip the build? All coax in our Coax Cable collection is pre-terminated with quality PL-259s and tested before it ships.
FAQ
Is PL-259 the same as UHF connector?
Yes. PL-259 is the male UHF connector. Its mating female is called SO-239. Both terms refer to the same physical connector standard used across CB and amateur radio.
Is soldering PL-259 better than crimping?
Electrically they perform the same at 27 MHz. Soldered connectors are more forgiving of tool quality; crimp connectors are faster and require a specific hex die. Both are professional-grade when done correctly.
Can I cut CB coax to any length?
Not if the antenna specifies a length. Firestik and several other antennas are designed around 18-foot electrical runs. Cutting shorter can change what the antenna looks like at the radio and affect SWR. Store excess coax with a figure-8 pattern instead of cutting it.
Why does coiled coax raise my SWR?
A tight coil turns the coax into a small inductor that alters the impedance the radio sees. Use a figure-8 layout or loose S-curves to store excess without adding inductance.
How do I weatherproof a CB coax connector?
Wrap the connector at the antenna end with self-vulcanizing tape (also called coax seal or self-amalgamating tape). Stretch it slightly as you wrap so it bonds to itself. Cover 1–2 inches on either side of the joint.
How do I test a coax cable for damage?
Use a multimeter: center pin to center pin should read 0 ohms, shield to shield should read 0 ohms, and center to shield should read open (infinite). Then sweep SWR on channels 1, 20, and 40 with the antenna connected — a bad cable often shows erratic SWR readings that change when you wiggle the connectors.
Bottom line
Good coax is only half the job — proper termination and routing is the rest. Use the correct PL-259 size for your cable, solder or crimp cleanly, respect the antenna's specified coax length, figure-8 any excess, and weatherproof the outdoor connector. If you build the run right the first time, it'll last as long as the radio.
Questions on a specific install — semi truck, boat, RV, base station? Email me at lance@cbradiosupply.com with photos and I'll walk you through it. I answer every message personally from the shop in South Bend, Indiana.
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