A coaxial assembly passes electrical testing on the bench, then fails after installation introduces mechanical stress. Installation can damage a coaxial assembly without creating an open circuit. The jacket looks fine while the dielectric underneath has been crushed, stretched, or pinched out of shape.
People Also Ask
1. What happens when coaxial cable is bent too tightly?
The dielectric deforms and the braid distorts. That can change impedance at the bend, increasing reflections and reducing return loss.
2. How is minimum bend radius specified?
Manufacturers specify minimum bend radius in the cable datasheet, either as a dimension or a multiple of the outer diameter.
3. Will continuity testing catch routing damage?
Often not. Continuity confirms a connection, not RF performance. Return loss or voltage standing wave ratio (VSWR) testing can reveal impedance changes that continuity testing misses.
The cost lands late in the build. Intermittent faults surface during system level integration or after shipment, when diagnosis is slow and rework touches finished product. In medical monitoring equipment and aerospace assemblies, a marginal coax run can pass initial test and fail under vibration months later.
Coaxial cable bend radius is one routing requirement that affects assembly performance. Below are six mistakes that show up repeatedly on the production floor, along with the practical fix for each.
1. Bend Radius Tighter Than Specified
Check the specified minimum bend radius for the selected cable and assembly. Distinguish installation limits from repeated flexing limits where provided. Permitted bend radius depends on cable construction. Follow the selected cable’s datasheet rather than judging flexibility by feel. Installers often ignore the number because the cable bends without visible damage.
The damage is internal. A tight curve compresses the dielectric on the inside of the bend and stretches it on the outside. Spacing between the center conductor and the shield changes, and so does the impedance of coaxial cable assemblies at that point. The impedance change can increase reflections even when electrical continuity remains intact.
When panel spacing restricts routing, evaluate a right angle connector that meets the mechanical and RF requirements.
2. Missing Strain Relief at Connector Ends
The cable termination can be vulnerable to mechanical stress. Cable weight, vibration, and handling all transfer force into the termination. Without suitable coaxial cable strain relief, these loads can stress the conductor connections, shield termination, and jacket retention.
Typical failures include:
- Braid strands pulling back from the crimp
- Center conductor fatigue at the solder joint
- Jacket separation behind the connector body
- Intermittent contact under vibration
Use strain relief designed for the assembly. Specify clamp placement according to connector guidance, bend clearance, and expected mechanical loads. Termination method matters as well, since crimped and soldered coaxial cable terminations behave differently under repeated flexing.
3. Routing Alongside High Current Wiring
Coax is shielded, but shielding is not absolute. Long parallel runs near motor leads or switching circuits can increase interference coupling, depending on separation, shielding, and circuit characteristics. Braid coverage and shield termination quality decide how much gets through.
Nearby power wiring can expose the cable to heat. Check local temperatures against the cable’s rated limits.
Separate parallel runs and clamp them independently. Low level signals in automotive sensor systems can be sensitive to interference. Specify separation from battery and motor wiring according to system requirements.
4. Excess Length Coiled Behind Panels
Service loops make sense for maintenance access. Trouble starts when slack gets coiled tight to fit a gap behind a panel. A coil violates the bend requirement when its radius falls below the specified minimum.
Excess cable also adds insertion loss and changes electrical length. In phase matched circuits, that difference alone can fail test.
Order assemblies cut to installed length wherever the layout is fixed. Where slack is required, form a wide loop and secure it flat instead of winding it.
5. Overtightened Clamps Compressing the Jacket
Clamps and ties hold routing in place. Overtightening turns them into a point load. Excessive tie tension can compress the jacket and deform the dielectric beneath it.
The mark is easy to miss during visual inspection. Excessive compression can create local impedance changes. Multiple damaged points can further affect RF performance.
Use cushioned clamps sized to the cable. Use approved ties and specified tension settings that secure the cable without compressing its jacket. Consistency here comes from written work instructions, not operator judgment.
6. Routing Not Documented in Build Drawings
The first five items are installation errors. This one is a documentation gap that causes them repeatedly. Without specified routing paths, clamp positions, and bend allowances, installation can vary between operators.
When OEMs specify coaxial cable assemblies, drawings should define:
- Routing path and separation from power wiring
- Clamp and tie locations
- Minimum bend radius for each cable type
- Service loop size and orientation
- Connector orientation at both ends
These details support consistent installation as custom coaxial cable assemblies move from prototype to volume production. Documented requirements help operators repeat the approved routing.
Conclusion
Testing before installation cannot detect damage introduced during routing. Faults that emerge during vibration testing or field operation can require additional diagnosis and rework. Bend radius, strain relief, separation, slack management, clamping force, and documentation belong in design review rather than the debug cycle. Defining these requirements early supports consistent installation and repeatable performance across production builds.
Contact Star Engineering Inc. to discuss custom coaxial cable assemblies, wire harness assemblies, and production requirements.
Frequently Asked Questions
Does bend radius matter more at higher frequencies?
Yes. As wavelength shortens, small impedance discontinuities at a bend have a larger effect on return loss.
How close to the connector should the first clamp sit?
Close enough to carry cable weight and vibration load before it reaches the termination. The build drawing should specify the location.
Can a crushed coaxial assembly be repaired in place?
Usually not. Replace an assembly with permanent dielectric damage. Retermination may be suitable only if the damaged section can be removed and specifications remain satisfied.
Which test finds routing damage after installation?
Return loss or VSWR testing, supported by insertion loss measurement. Continuity checks can miss routing damage that affects RF performance.
