Published on 10/13/2026
You send over a drawing: 3 meters of RG316, SMA plug on one end, right-angle TNC on the other, boots both ends, swept to 3 GHz. Two weeks later a bag of finished assemblies shows up. What actually happened in between is a chain of small, boring, critical operations, and the quality of each one decides whether your VSWR is 1.15 or 1.6.
This is a generic walkthrough of how a competent cable shop builds a custom coaxial assembly, based on standard industry practice. It is not a photo tour of any specific factory floor, and nothing here describes a particular company's internal paperwork. The point is to show you what a real build process looks like, so you can ask a supplier sharper questions and recognize when a step is being skipped.
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A custom assembly is defined by six things: the cable, the two connectors, the length (and how length is measured, tip-to-tip or over-all), the orientation of any right-angle bodies, any strain relief or sealing hardware, and the electrical acceptance criteria. If any of those six is vague on your purchase order, the build that comes back is a coin flip. A good shop will push back on a vague spec before cutting anything, because rework after termination usually means scrapping the connector and re-stripping the cable.
Length tolerances matter more than buyers expect. On a 150 mm jumper, plus or minus 5 mm changes the electrical length enough to shift phase at 6 GHz. Shops that build phase-matched pairs (see our guide on phase-matched cable assemblies) treat length as an electrical parameter, not a tape-measure reading.
Key idea: A custom assembly is six decisions, not one. Cable, connectors, length definition, orientation, strain relief, and test limits. Get all six in writing.
Before any cable is cut, someone reads the drawing and checks it for traps. Is that connector actually available in a crimp version for that cable? Does the specified cable bend radius survive the routing in the customer's enclosure? Is the frequency range realistic for the connector family, or did someone spec a BNC for an 8 GHz link? Are the test limits stated, with units, at a stated frequency?
This review is where good shops earn their margin. Catching that a 7/16 DIN plug was specified on 0.141-inch semi-rigid cable, or that a customer wants IP67 sealing on a connector pair that cannot be sealed, costs an email. Missing it costs a production lot.
Cable comes off the reel and is cut to length plus a small allowance. Precision shops cut on a measured bench or with a cut-to-length machine, then verify against a steel rule or jig. The cut ends are then stripped to the connector manufacturer's dimensions: outer jacket, braid, dielectric and center conductor each exposed by a specific length, often to a tenth of a millimeter.
Strip quality is inspected before termination: no nicked center conductor, no stray braid wires, no scored dielectric. A single nick in a silver-plated center conductor becomes a crack initiation point after a few thermal cycles.
Termination method follows the connector design: crimp, solder, or clamp. Our comparison of crimp vs solder vs clamp termination methods covers the trade-offs in detail, but the short version is that crimp wins on repeatability, solder wins on certain semi-rigid and high-frequency interfaces, and clamp is mostly field-service territory. A production shop terminates with calibrated crimp tools and the exact die set the connector maker specifies, because a generic die set produces a crimp that looks fine and measures poorly.
Solder work follows workmanship standards: flux control, no solder wicking up the braid beyond the specified line, center contacts filled without voids. After termination, the connector body is threaded or slid home and the assembly is checked for continuity and shorts before it moves on.
Have a drawing or even a napkin sketch? We build to your spec and sweep every assembly before it ships.
The number one killer of cable assemblies is not the connector or the cable; it is flexing right at the cable-entry point. Strain relief boots, heat shrink, or overmolding spread that bend over a longer distance. Our article on strain relief covers why this single feature prevents most field failures. Outdoor builds add sealing: adhesive-lined heat shrink, self-fusing tape, or IP-rated connector boots, as covered in our waterproofing guide.
Before electrical test, each assembly gets a visual pass: connector plating intact, coupling nuts free-running, pin depth correct, labels legible, length within tolerance. Pin and insulator depth on interfaces like SMA are checked against gages, because a proud pin destroys the mating connector's contact. Shops building to IPC/WHMA-A-620 (covered in our quality standards article) document acceptance criteria for each of these checkpoints.
The final gate is electrical test. At minimum: continuity, insulation resistance, and a VNA sweep for VSWR (or return loss) and insertion loss over the specified band. Every assembly SigmaRF ships is VNA-swept for VSWR and insertion loss before it leaves, across our 100 MHz to 40 GHz capability range. A printed or saved sweep trace tied to the serial number is what turns a bag of cables into a verified lot. For what a proper VNA verification looks like, see our companion article on VNA testing for cable assemblies.
Six corners cheap builds cut
How long does it take to build a custom coaxial cable assembly?
For standard cable and connector combinations, build time itself is minutes per assembly; lead time is driven by material stock and queue. SigmaRF ships custom assemblies with lead times as short as 2 days when the parts are on the shelf.
Is crimp or solder better for coax connectors?
For flexible cables, crimp with the correct die set is more repeatable and usually stronger. Solder is preferred on many semi-rigid and high-frequency interfaces. The connector manufacturer's termination instructions decide, not preference.
What should a custom cable assembly drawing include?
Cable type, connector part numbers, length with a stated measurement method, right-angle orientation, strain relief or sealing hardware, and electrical acceptance limits (VSWR and insertion loss at frequency).
Why do two identical-looking assemblies measure differently?
Strip dimensions, crimp geometry, and solder quality vary at the tenth-of-a-millimeter level. At low GHz frequencies those differences are invisible; at 6 GHz and above they show up clearly on a VNA sweep.
Can a damaged end be re-terminated instead of replacing the whole assembly?
Usually yes for flexible cable, if the remaining length still meets your requirement. The old connector is cut off, the cable re-stripped, and a new connector terminated and tested.
What test data should come with a cable assembly?
At minimum a VSWR (or return loss) and insertion loss result over your operating band, ideally with a saved sweep trace tied to a serial number, plus continuity and insulation checks.
A custom coaxial assembly is a chain of small manufacturing steps: spec review, precision cut and strip, correct termination, strain relief, inspection, and electrical verification. None of the steps is exotic. Skipping any one of them is what separates a verified assembly from a bag of trouble. When you brief a supplier, specify all six decisions and ask what their final test actually measures.
Need assemblies built and verified this way?
SigmaRF builds standard and custom coaxial cable assemblies at our Vadodara, India volume facility and our Cleveland-area precision facility in the USA. Every assembly is VNA-swept for VSWR and insertion loss across 100 MHz to 40 GHz before it ships, and lead times run as short as 2 days.