Table of Contents
Quick Answer: What Is a Coaxial Cable?
A coaxial cable is a controlled-geometry cable built around one center conductor and one surrounding shield that share the same axis. That arrangement is why the cable is called coaxial. The center conductor carries the signal, the dielectric holds spacing, the shield contains the field and blocks outside noise, and the jacket protects the whole structure from mechanical abuse.
In practical cable assembly work, coax is used when signal integrity matters more than a simple conductor count. That includes antennas, wireless modules, RF instruments, cameras, video distribution, telecom links, and some medical or defense systems. If you are sourcing a finished coaxial cable assembly, the real decision is not only cable family. It is the full path: impedance target, connector series, strip dimensions, bend control, sealing, and test plan.
For background terminology, the public references on coaxial cable, characteristic impedance, and standing wave ratio cover the theory well. The production challenge is turning that theory into a repeatable build that still performs after crimping, routing, and installation.
"When an RF cable fails in the field, the root cause is often not the cable name. It is a 50 ohm path that was quietly broken by the wrong connector geometry or by a bend tighter than about 10 times the cable diameter."
Impedance Control
State 50 ohm or 75 ohm explicitly. A missing impedance callout creates avoidable assembly and sourcing errors.
Shield Path
Foil, braid, or dual-shield construction affects EMI resistance and how the connector ferrule must be terminated.
Frequency and Length
The same cable that works at 10 MHz over 1 meter may fail badly at 3 GHz over 15 meters.
Connector Match
Coax connectors are not generic end fittings. Strip length and center-contact geometry must match the exact cable.
How a Coaxial Cable Works
Coax works because each layer has a controlled job. The center conductor carries the signal. Around it sits the dielectric, usually foam or solid polymer, which keeps the conductor centered and sets the electrical spacing to the shield. Around that sits the outer conductor or shield, usually foil, braid, or a combination of both. The outer jacket protects the structure from abrasion, UV, fluids, and routing damage.
That geometry is what keeps the electromagnetic field mostly inside the cable instead of leaking into the surrounding machine. It also makes coax fundamentally different from ordinary multi-conductor cable. When the shield coverage, dielectric thickness, or connector transition changes, the impedance changes too. That is why coax builds need tighter process discipline than a simple low-frequency power cable.
In manufacturing, the weak points are usually at the ends. A cable may be perfectly specified, then lose performance because the ferrule was over-crimped, the braid was cut too short, or the center contact was sized for a different dielectric. If you are comparing connector families, our coaxial connector types guide breaks down where BNC, SMA, N-Type, TNC, and FAKRA fit.
"A continuity tester can tell you the conductor is connected. It cannot tell you whether the assembly still behaves like 75 ohms end to end, or whether the return loss is already outside target above 1 GHz."
Four parts every buyer should understand
- Center conductor: solid or stranded, sized for the signal and flex demands.
- Dielectric: controls spacing, velocity, and part of the loss profile.
- Shield: foil, braid, or both, affecting leakage and EMI resistance.
- Jacket: determines abrasion resistance, flexibility, and environmental fit.
Common Coaxial Cable Types Chart
People often ask for the "best" coax cable, but the better question is which family matches the frequency, length, routing envelope, and connector style. The table below is a practical starting point for production discussions.
| Cable Type | Impedance | Best Use | Strengths | Main Limits |
|---|---|---|---|---|
| RG58 | 50 ohm | General RF, lab leads, radio, antennas | Balanced flexibility, cost, and durability | Loss rises on longer runs and higher frequencies |
| RG174 | 50 ohm | Tight packaging, small devices, embedded routing | Small diameter and easy routing | Higher attenuation and lower durability than RG58 |
| RG316 | 50 ohm | Higher temperature zones, compact RF jumpers | PTFE dielectric and good heat resistance | More expensive and still relatively lossy |
| RG59 | 75 ohm | Video, CCTV, legacy broadcast paths | Good fit for 75 ohm signal distribution | Not appropriate as a default for 50 ohm RF systems |
| RG6 | 75 ohm | CATV, broadband, satellite drops | Lower loss than RG59 in many longer runs | Larger and stiffer than compact coax families |
| Low-loss 50 ohm cable | 50 ohm | Longer antenna runs, outdoor RF, infrastructure | Reduced attenuation and stronger shielding options | Larger bend radius and heavier connector hardware |
The practical lesson is that cable families are not interchangeable just because they are all coax. A smaller cable may solve routing but add unacceptable attenuation. A larger low-loss cable may improve RF margin but create connector bulk and bend-radius problems inside the enclosure.
50 Ohm vs 75 Ohm Coaxial Cable
The most common coax question after "what is it?" is whether to use 50 ohm or 75 ohm cable. In simple terms, 50 ohm coax is dominant in RF power, wireless, radio, antennas, and test assemblies. Seventy-five-ohm coax is more common in video, broadcast, CATV, and other signal-distribution systems. Neither is inherently better. They solve different system targets.
The mistake is treating the mismatch as minor. If a drawing calls for 75 ohm video hardware and the supplier substitutes a 50 ohm BNC or cable because the parts appear similar, the assembly may still pass a basic electrical check while creating reflection and margin problems in the real signal path. The same rule applies in reverse for 50 ohm RF systems. Impedance must stay consistent through the cable, connectors, adapters, and instrument ports.
If your program is centered on a specific cable family, our RG58 coaxial cable guide shows how one common 50 ohm option fits into real assembly decisions, while our BNC connector types guide covers one of the easiest places to make an impedance mistake.
"If the RF drawing does not explicitly call out 50 ohm or 75 ohm, the purchasing team is being asked to guess. That guess can easily cost more than 3 dB of performance margin once adapters, connectors, and cable substitutions stack up."
Where Coaxial Cable Is Used
Coaxial cable shows up anywhere a designer needs controlled impedance and shielding in the same package. Common examples include antenna jumpers, Wi-Fi or cellular leads, CCTV video, broadcast racks, CATV drops, test bench cables, radar links, and some medical imaging or detector systems. Many automotive RF applications also depend on coax constructions, especially when the assembly uses keyed interfaces such as FAKRA cable assemblies.
Not every signal cable should be coax. Differential data systems, for example, may use twisted pair, twinax, or shielded multi-conductor cable instead. That is why the first design decision is always the electrical interface, not the connector name. When the system really needs coax, though, the cable should be treated as a controlled RF component rather than a generic wire with a shield around it.
Cable Assembly and Testing Considerations
Coaxial cable assembly work is mostly about preserving geometry. The strip dimensions must expose enough braid for a reliable ferrule crimp without collapsing the dielectric. The center contact must fit the conductor exactly. The rear support must prevent cable movement from pushing stress into the launch area. In outdoor or washdown service, sealing features such as boots, adhesive heat shrink, or overmolding may be required as well.
Testing also has to match the risk. For low-frequency internal jumpers, continuity and shorts may be enough. For antenna leads, test cables, or long 75 ohm video paths, engineers often add return loss, VSWR, insertion loss, shielding checks, or pull-force verification. Programs above 1 GHz deserve special care because small process changes become visible quickly.
Release checklist for a production coax assembly
- Call out cable family, impedance, and nominal length tolerance.
- Specify connector series and cable-specific contact or ferrule kit.
- Define routing limits such as minimum bend radius and strain-relief strategy.
- Set the required electrical test method, not only a generic "100% test" note.
- Verify the environment for UV, temperature, fluids, or sealing requirements.
Common Sourcing Mistakes
The first mistake is assuming all coax is the same. The second is assuming all connectors with the same family name are also the same. BNC, SMA, N-Type, and FAKRA parts all have cable-specific variants. The third mistake is underestimating mechanical stress. A cable that tests perfectly on the bench can fail after installation if the assembly is forced into a tight turn behind a panel or if the cable weight hangs directly on the connector body.
The last mistake is vague documentation. Notes such as "coax cable, equivalent accepted" invite uncontrolled substitutions. A stronger release lists the cable family, impedance, approved connector set, strip dimensions or process reference, and the required validation. That is what turns a broad material category into a repeatable product.
Frequently Asked Questions
What is a coaxial cable in simple terms?
A coaxial cable is a cable with one center conductor surrounded by a dielectric, a shield, and an outer jacket that all share the same axis. That geometry lets the cable hold a controlled impedance such as 50 ohms or 75 ohms and carry RF, video, or data signals with better shielding than ordinary two-wire constructions.
What is the difference between 50 ohm and 75 ohm coaxial cable?
Fifty-ohm coax is common in RF, radio, wireless, and test assemblies because it balances power handling and attenuation. Seventy-five-ohm coax is common in video, CCTV, CATV, and broadcast paths because it offers lower attenuation for many signal-distribution uses. In production, the cable, connector, and equipment port must all match the same impedance target.
What are the main parts of a coaxial cable?
The four main parts are the center conductor, dielectric, outer shield, and jacket. Many production cables add extra foil layers, dual braids, drain wires, or armored jackets, but the controlled relationship between the conductor, dielectric, and shield is what creates the cable's nominal impedance and signal performance.
Which coaxial cable type is most common for cable assemblies?
There is no single best type, but RG58, RG174, RG316, RG59, RG6, and various low-loss 50 ohm cables are among the most common families. The right choice depends on frequency, length, flexibility, temperature, shielding needs, and whether the assembly uses BNC, SMA, FAKRA, N-Type, or another connector family.
Can I use any connector on any coaxial cable?
No. Coax connectors are cable-specific. The ferrule size, center contact diameter, dielectric support, and strip dimensions must fit the exact cable construction. A connector that physically fits over a jacket can still create poor VSWR, weak pull force, or shield discontinuity if it was released for a different cable family.
How do you test a coaxial cable assembly?
Basic tests include continuity and short checks, but critical coax assemblies often need impedance-aware verification such as return loss, VSWR, insertion loss, shielding integrity, and mechanical pull checks. Above roughly 1 GHz, a cable can pass continuity and still fail the actual application because the connector launch or routing changed the signal path.
Need a production-ready coaxial cable assembly?
If your program includes RF connectors, sealed antenna leads, video cabling, or cable-specific test requirements, we can help review the right coax family before release and build the assembly around the real electrical and mechanical constraints.