A coaxial cable is a transmission line designed so the centre conductor and outer shield share the same axis. That geometry is the reason coax can move radio, video, and other high-frequency signals far more predictably than ordinary hook-up wire. When engineers talk about RG-58, RG-174, RG-316, LMR-style cable, antenna jumpers, CCTV leads, or test-bench RF pigtails, they are usually talking about coaxial constructions.
The important point is that coax should not be treated as “just a shielded cable.” It is a controlled system. The cable, connector, strip dimensions, crimp ferrule, torque, and bend handling all affect the final electrical result. That is why buyers who only specify length and connector gender often end up with assemblies that pass continuity but fail return-loss or field reliability checks.
Centre conductor carrying the signal
Dielectric spacing layer that sets geometry
Outer shield for return path and EMI control
Most common nominal impedance families
What a coaxial cable actually does
In a coaxial cable, the signal travels on the centre conductor and the return current flows on the inside of the outer conductor. The dielectric keeps those conductors spaced at a controlled distance. That spacing establishes the cable’s characteristic impedance, which is the electrical value that must match the source, connector system, and load if you want low reflection and predictable loss.
Because the electric field is largely contained inside the cable structure, coax resists external noise better than unshielded wiring and also radiates less energy outward. That makes it a standard choice for antennas, telecom radios, GNSS modules, video links, oscilloscopes, network analysers, medical equipment, and dense electronics that need a compact controlled-impedance interconnect.
"Most RF problems blamed on the radio are actually interconnect problems. If the coax geometry or shield termination changes at the connector, a 50 ohm design on paper can behave like a mismatch in production within one build lot."
— Hommer Zhao, Technical Director
For a buyer, the implication is straightforward: if the application depends on frequency response, low noise, or a defined impedance, coax is not optional decoration. It is part of the signal path design itself.
The four layers inside a coaxial cable
1. Centre conductor
This is usually solid or stranded copper, silver-plated copper, or copper-clad steel depending on flexibility and frequency needs. Solid conductors help keep geometry stable. Stranded conductors improve flex life but can change connector compatibility. The centre contact in the connector must match this conductor type exactly.
2. Dielectric insulation
The dielectric is not just insulation. Its diameter and material directly influence impedance, velocity factor, and attenuation. Foamed dielectrics often reduce loss, while PTFE is common in higher-temperature and more stable RF constructions. Crushing or nicking this layer during stripping can ruin performance even when the cable still looks usable.
3. Shield or outer conductor
The shield may be braid, foil, bonded foil, or multiple layers. It provides the return path and blocks electromagnetic interference. Higher braid coverage generally improves mechanical robustness, while foil can improve high-frequency coverage. On real cable assemblies, the shield termination is often the difference between a clean RF build and a noisy one. Our braid-versus-foil shield guide covers that trade-off in more detail.
4. Outer jacket
The jacket protects the cable from abrasion, chemicals, UV, flame, and handling damage. PVC can be economical for indoor use, while PE, FEP, and other compounds fit harsher environments. The jacket does not set impedance, but it does influence flexibility, survivability, and the fit in glands, clamps, and overmolded exits.
Why impedance matters more than buyers expect
The most common coaxial families are 50 ohm and 75 ohm. The reason is application driven. A 50 ohm system is a long-standing compromise between power handling and attenuation, so it dominates radio, antenna, and test applications. A 75 ohm system offers lower attenuation for many video and broadcast uses, so it is common in CCTV, SDI, and other video infrastructure.
Problems start when teams assume connectors that physically mate are electrically interchangeable. A 75 ohm BNC on a 50 ohm test lead might seem harmless, but the mismatch adds reflection. At higher frequencies or tighter margins, that translates into worse return loss, unstable measurement, or reduced radio performance. The same risk appears when a connector was designed for one cable family but is crimped onto another with a “close enough” ferrule.
"For coax assemblies, continuity is the lowest possible quality gate. We care about shield capture, strip dimension, centre-pin retention, and impedance stability, because those are the factors that decide whether the cable still works at 1 GHz, 3 GHz, or higher."
— Hommer Zhao, Technical Director
Useful rule of thumb
If the application spec includes frequency, return loss, insertion loss, VSWR, antenna tuning, SDI quality, or signal integrity, treat the coax assembly as a controlled electrical product rather than a generic cable.
Coaxial cable comparison table
| Cable family | Typical impedance | Main strength | Common risk | Typical use |
|---|---|---|---|---|
| RG-174 | 50 ohm | Small diameter, easy routing | Higher loss on longer runs | Short RF jumpers, compact electronics |
| RG-316 | 50 ohm | PTFE dielectric, good temperature tolerance | Still lossy over distance | Test leads, RF modules, aerospace-style jumpers |
| RG-58 | 50 ohm | General-purpose RF workhorse | Can be oversized for tight products | Instrumentation, radios, industrial RF |
| RG-6 | 75 ohm | Lower attenuation for video/distribution | Not suited to 50 ohm systems | Broadcast, CCTV, video transport |
| RG-214 | 50 ohm | Double shielding, strong durability | Large bend radius and weight | Harsh-duty antenna and infrastructure runs |
If you already know the connector family but not the mating interface detail, our RF connector guide and BNC connector guide help translate the cable decision into a production-ready interconnect.
Where coaxial cables are used in real assemblies
Coaxial cables are common anywhere engineers need stable high-frequency transmission or a protected low-level signal path. In Australia that includes telecom infrastructure, radio systems on mining equipment, GNSS and telematics hardware in transport fleets, instrumentation in defence and industrial plants, and medical devices where noisy surroundings can corrupt sensitive signals.
Coax also appears inside products, not just on external antennas. Compact modules may use micro-coax for board-to-board or module-to-antenna links where normal RF cable is too large. If your application is space-constrained, our micro-coaxial cable assembly service is a closer fit than a generic RG-style build.
Buyers should separate field-routed coax from internal coax. External cables usually prioritise jacket toughness, bend support, and environmental sealing. Internal assemblies prioritise diameter, routing density, and controlled stripping. Treating those as the same sourcing problem is one of the fastest ways to select the wrong cable family.
How to specify a coaxial cable assembly correctly
A useful coax enquiry needs more than “BNC cable, 2 metres.” At minimum, the supplier should know the system impedance, the connector series on each end, the exact cable family, the finished length and tolerance, the operating frequency range, the install environment, and the test requirement. If any one of those is missing, the quote may still come back, but the engineering risk just moved into production.
Seven details that prevent rework
- Nominal impedance: 50 ohm or 75 ohm
- Exact cable family, not just “coax”
- Connector series, gender, and any bulkhead or right-angle requirement
- Finished length with tolerance, for example 500 mm ±10 mm
- Operating frequency or protocol target
- Mechanical environment such as vibration, outdoor UV, or repeated flex
- Validation requirement such as continuity, VSWR, insertion loss, or pull test
"If you want repeatable coax supply, buy the assembly as a cable-plus-connector system. When teams source the cable separately from the connector and let the assembler improvise strip data, the process variation shows up later as return-loss drift and intermittent field faults."
— Hommer Zhao, Technical Director
For higher-speed or tighter-margin applications, it is also worth defining how the result will be verified. A continuity-only release is rarely enough for a coax that supports a radio, measurement channel, or controlled video link. That is especially true when the assembly feeds into broader signal-integrity-sensitive systems.
Common coax buying mistakes
Assuming connectors are interchangeable because they mate
Mechanical fit does not prove impedance match, conductor compatibility, or frequency suitability.
Choosing by diameter only
Small cable may route better, but attenuation and power handling may become unacceptable over the required length.
Ignoring bend radius at installation
Coax can be damaged by tight routing long after it leaves the factory. Dielectric deformation changes electrical performance before the jacket shows obvious failure.
Accepting continuity as the only release test
Continuity proves copper path, not RF quality. Critical programs should define insertion loss, VSWR, or other application-relevant checks.
Leaving the cable family undefined in the BOM
“50 ohm coax” is not a purchasing specification. RG-174, RG-316, RG-58, RG-214, and low-loss constructions behave very differently in size, loss, and connector fit.
Frequently asked questions
What is a coaxial cable in simple terms?
A coaxial cable is a shielded cable built around one centre conductor, one insulating dielectric layer, one conductive shield, and an outer jacket. Because the conductors share the same axis, the cable can carry high-frequency signals with controlled impedance such as 50 ohm or 75 ohm.
What is the difference between 50 ohm and 75 ohm coaxial cable?
A 50 ohm coax is typically chosen for RF power transfer, radio equipment, antennas, and test systems. A 75 ohm coax is commonly used for video, broadcast, and some data links because it offers lower attenuation for those applications. Mixing them can create a mismatch around 1.5:1 VSWR, which is often unacceptable in controlled RF systems.
Why is coaxial cable better than ordinary two-wire cable for RF signals?
The shield and dielectric geometry hold the electrical field inside the cable and maintain predictable characteristic impedance. That reduces radiated noise, ingress, and reflections. Ordinary parallel wire does not control geometry as tightly, so performance becomes unstable once frequency rises into the MHz or GHz range.
How far can a coaxial cable run before signal loss becomes a problem?
That depends on cable family, frequency, and connector count. A short RG-316 jumper may be acceptable at 2.4 GHz for less than 1 metre, while a larger low-loss coax can run tens of metres at the same frequency. Buyers should request insertion-loss limits in dB at the operating frequency, not just overall length.
Can coaxial cables be repaired in the field?
Sometimes, but field repair is risky when impedance and shielding matter. Even a 1 mm strip-length error or poor braid capture can change return loss and long-term reliability. For production equipment, replacing the full assembly is usually safer than making an unverified field splice.
What information should I send a supplier for a coaxial cable assembly quote?
Send the system impedance, connector types, cable family, finished length, frequency range, bend constraints, shielding requirement, and test expectation. A usable RF enquiry normally includes at least 7 data points: connector A, connector B, cable type, length tolerance, impedance, environment, and validation method.
Need help choosing or building a coax assembly?
If your team is comparing connector families, replacing an imported RF lead, or trying to convert a loose sample into a controlled production part, we can review the cable type, connector compatibility, strip data, and test plan before release.