Optimally choosing your measuring cables

elspec Whitepaper

Voice of cables

The optimum measuring cable is not found by accident but is chosen after precise consideration of all relevant criteria.

How to pose the right questions, whether „more expensive“ equals „better“, etc. – we have put this together for you. To our aid came Instrumentation engineer Stefan Burger. Born in Freiburg, Germany, he owns the Delta Gamma RF-Expert consultancy in Hampton, Australia, and travels the world to give support for RF-solutions.

The lab has the most sensitive test-devices ready for use. Staff have been trained extensively on the specifics, and conscientiously prepared for diverse new testing possibilities. Precision and extreme accuracy are a natural for each and everyone of the involved test engineers. The expectations are considerable since a significant budget has already been invested. To ensure the quality chain continues, the very best cables, adapters and connectors should be used.

Which criteria are decisive for reaching the given objective, and how these criteria are ranked in importance. One-sizefits-all- and-every-circumstance does not exist - not with cables, anyway! One cable may withstand extreme temperatures but cannot deal with high pressure while the other cable may not be useable up to 50 GHz or may loose its phase-stability as it is moved and bent. Of course, the budget provided must not be forgotten, either.

The measurement engineer should have thoroughly considered following question:

electrical RF parameter

  • highest operation frequency (Max. Frequency GHz)
  • matching of the confectioned line (Return Loss dB)
  • maximum power to be transmitted at the operational frequency (CW Power Handling W)
  • how small is the overall attenuation given the desired cable length (Loss dB)
  • how strong is the cross-feed attenuation (Isolation dB)?
  • how well is the measurement result reproduced after moving the cable (repeatability)?

In this area, Teledyne has really done great work and offers very good solutions for every use and for various combinations.  For example,the "StormFlex" cable is outstandingly suitable at frequencies above 50 GHz.

service-life and stress

  • are the cables subjected to strong mechanical or thermal stress (to be defined via mil specs?)?
  • how big is the tensile stress (tensile load [N])? * is there (even very small) shock or vibration? 
  • what about the phase fidelity after moving the cable (phase stability)?
  • how strong are phase changes dependent on temperature (Phase Change vs. Temperature ppm)?

Additional characterictics

  • how important is high bending strength and longevity of the plug-to-cable transition (Stability of strain critical connector /cable interface)?
  • which phase changes result in dependance of temperature (phase change vs. temperature ppm)?
  • is resistance against abrasion required (abrasion resistance)?
  • are the cables subjected to high outer pressure (ressure on cable diameter)?
  • are the cables subjected to mechanical pressure (crush resistance [kN/m])
  • how often may the cable be bent (flex life cycles)?