Measuring Coaxial Cable Assembly Mechanical Length

Reference Plane to Reference Plane

We have seen several methods of dimensioning the mechanical length of coaxial cable assemblies.  Due to the fact that connector dimensions can differ from manufacturer to manufacturer, the only reliable method is to adopt a best practice for specifying mechanical length is Reference Plane to Reference Plane.
Assemblies specified and manufactured using the Reference Plane for each connector ensures that the effective mechanical length, accounting for connector engagement, always results in the expected length within an assembled system or test fixture.
Below are several examples for several common connector configurations.  Similar configurations in different connector series typically have similar Reference Plane locations.  The exact location of each Reference Plane differs from connector to connector and can be found within each connector specification.
SMA Straight Plug (m)

SMA Straight Jack (f)

SMA Panel-mount Jack (f)

SMA Right-angle Plug (m)
SMA Bulkhead Jack (f)
SMP Blind-mate Straight Plug (f)
Of course, this is only a small sample of the many, many connector series and configurations available.  If you need assistance calculating the Reference Plane to Reference Plane mechanical length for your assembly, please feel free to give us a call.

Mechanical Length Tolerances

  2"-18" >18"-30" >30"-48" >48"-60"
Soldered Flexible Assemblies ± 0.030" ± 0.060"   ± 0.125"  ± 0.250"
Soldered Hand-formable Assemblies  ± 0.030" ± 0.060"  ± 0.125"  ± 0.250"
Soldered Semi-rigid Assemblies  ± 0.030"  ± 0.045"  ± 0.060"  ± 0.125"
Crimped Assemblies  ± 1/8"  ± 1/4"  ± 3/8"  ± 1/2"

If you your application truly requires tighter tolerances or longer lengths, or if you have any questions; please feel free to give us a call.