Everything About Coax for CB Radios (Part 1): Types, Terminology, and How to Choose
Coax cable carries the RF signal from the CB radio to the antenna. The right coax type matters more than most people think: RG-8X is the standard for mobile CB installs (flexible, low-loss, durable), RG-58 is a thinner cheaper alternative with more signal loss, and LMR-400 is the low-loss choice for long base-station runs over 25 feet. All coax should be 50-ohm impedance for CB use. Coax has four layers — center conductor, insulator, shield, and jacket — and each one matters.
That's the fast answer. Part 1 covers what coax is made of, the terminology every installer should know, and how to compare the common types. Part 2 covers PL-259 connectors, cable length, and how to build your own coax runs.
What's in this guide
- The four layers of coax
- Coax terminology you need to know
- Impedance and why 50 ohms
- RG-58 vs RG-8X vs LMR-400
- Coax type comparison table
- Stranded vs solid center conductor
- Foam vs solid insulation
- How to choose coax for your install
- FAQ
The four layers of coax
Every coax cable is built from four concentric layers, from the middle out:
- Center conductor — the metal wire at the core. Copper is the standard. Carries the RF signal.
- Insulator (dielectric) — a plastic or foam sleeve around the center conductor. Keeps the center from touching the shield and determines how fast the signal travels through the cable.
- Shield — a woven braid, foil wrap, or both, around the insulator. Blocks external interference and contains the RF signal inside the cable. Higher-quality coax has double or quad shielding.
- Jacket — the outer plastic sleeve. Protects everything inside from water, UV, and physical damage.
Coax terminology you need to know
- Impedance — the coax's opposition to AC signal flow. All CB coax is 50 ohms. Mismatching impedance raises SWR.
- Velocity factor — how fast the signal travels through the cable relative to free-space light. Typically 0.66–0.83 depending on the insulator.
- Attenuation / loss — how much signal the coax eats up per foot. Measured in dB per 100 feet at a given frequency.
- Shielding percentage — how much of the shield actually covers the insulator (95% is good, 98% is excellent).
- Return loss — a measurement related to SWR that describes how well the coax matches at 50 ohms.
Impedance and why 50 ohms
CB radios and CB antennas are all designed for a 50-ohm system. That's the industry standard for two-way radio. If you use TV-style 75-ohm coax on a CB, you introduce an impedance mismatch that raises SWR and wastes power — no matter how good the cable itself is.
Rule: always use 50-ohm coax for CB. Every cable we sell in the CB Radio Coax Cable collection is 50 ohms.
RG-58 vs RG-8X vs LMR-400
The three coax types you'll actually encounter for CB:
RG-58
Thinner cable (about 0.195" outer diameter). Flexible, lightweight, and inexpensive. Signal loss is higher than RG-8X — about 4.5 dB per 100 feet at 27 MHz. Fine for short mobile runs (under 15 feet).
RG-8X (sometimes called "mini-8")
The sweet spot for CB. About 0.242" outer diameter — flexible enough to route inside a vehicle but thick enough to keep loss low (about 3.5 dB per 100 feet at 27 MHz). Better shielding than RG-58. Standard on most quality mobile installs.
LMR-400
Low-loss cable (about 0.405" OD) designed for long base-station runs. Roughly 1.5 dB per 100 feet at 27 MHz. Too stiff for mobile use, but essential for base station installs where the antenna is on a pole 30–50 feet from the radio.
Coax type comparison table
| Coax Type | OD | Loss @ 27 MHz | Flexibility | Best For |
|---|---|---|---|---|
| RG-58 | 0.195" | ~4.5 dB / 100 ft | Very flexible | Short mobile runs |
| RG-8X | 0.242" | ~3.5 dB / 100 ft | Flexible | Standard mobile CB (best all-around) |
| LMR-400 | 0.405" | ~1.5 dB / 100 ft | Stiff | Base stations, long runs |
Browse specific brands: RG-58 · RG-8X · Times Microwave LMR-400 · RG-213 · Dual/Cophase coax.
Stranded vs solid center conductor
The center conductor can be a single solid copper wire or several thinner wires twisted together (stranded).
- Stranded — more flexible, better for mobile installs where the cable will move or bend often. Slightly higher loss than solid.
- Solid — lower loss, more durable long-term, but stiffer. Better for permanent runs, base station installs, or anywhere the coax won't be flexed.
For most mobile CB installs, buy stranded RG-8X.
Foam vs solid insulation
The dielectric (insulator) around the center conductor comes in two forms:
- Foam polyethylene — lower loss, higher velocity factor (~0.78–0.83), but more susceptible to crushing. If a car door pinches it, the shape distorts and impedance changes.
- Solid polyethylene — higher loss but tougher against physical damage. Better choice if the coax will be routed through door jambs or under carpet.
Premium coax (like Belden or Times Microwave) uses foam dielectric with a supporting structure that resists crushing. That's the best of both worlds if you can afford it. See the Belden and ABR Industries collections.
How to choose coax for your install
- Mobile install, short run under 15 ft: RG-8X stranded with a foam dielectric is the standard. Every quality mobile CB install uses this.
- Mobile install, long run 15–25 ft: RG-8X stranded, but pay attention to loss. Anything longer than 20 feet in a vehicle is unusual.
- Base station, 25 ft or more: LMR-400 or RG-213 solid. Loss adds up fast at long lengths.
- Dual antenna (semi truck cophase): Purpose-built cophase harness — see Dual/Cophase coax. Do not build your own from RG-58.
- Rough environment (off-road, marine): Solid polyethylene with a double or quad shield. UV-resistant jacket if it's outdoors.
Also: buy the correct length. Some antennas are designed around specific coax lengths (18 feet is common for CB). Cutting coax to length can change how the antenna tunes.
FAQ
What kind of coax is best for a CB radio?
RG-8X is the standard for mobile CB installs — flexible enough to route inside a vehicle, low-loss at CB frequencies, and durable. For base stations with long cable runs, use LMR-400.
Can I use TV coax for a CB antenna?
No. TV coax is 75 ohms; CB coax is 50 ohms. Using the wrong impedance raises SWR and wastes transmit power.
Is RG-8X better than RG-58?
Yes, for CB. RG-8X has lower signal loss, better shielding, and stays more consistent over time. RG-58 is thinner and cheaper but wastes more power over the same length.
Does coax length affect SWR?
Cutting an odd length can change how the antenna appears to the radio at 27 MHz. Some antennas (like Firestik) specify an 18-foot cable for a reason — sticking to the recommended length prevents surprises during tuning.
What's the difference between the center conductor being stranded or solid?
Stranded is more flexible and better for mobile installs where the cable will bend often. Solid has slightly lower signal loss and is more durable long-term. For most mobile installs, buy stranded.
Do I need special connectors for CB coax?
Yes, PL-259 (also called UHF connectors). They're the standard for CB and ham radio. Part 2 of this guide walks through installing them properly.
Bottom line
Coax is not "just a wire." The four layers, the impedance, the shielding, and the type of insulation all affect how much of your radio's transmit power reaches the air. For 99% of mobile CB installs, buy 50-ohm stranded RG-8X. For base stations with long runs, buy LMR-400. Route it without pinches or coils — see our installation guide for the physical rules.
Not sure which coax fits your install? Email me at lance@cbradiosupply.com — I answer every message personally from the shop in South Bend, Indiana.
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