Coaxial cables measurement Identification method of damaged cables or bad connectors mounting Stéphane Rey – BE/RF – September 20 th, Rev 1.0

Method  What ?  To measure the cables parameters thanks to the Time Domain Reflectometry (TDR)  Benefit ?  Usage of a Vector Network Analyzer (VNA) which is more common than TDR equipment  1 -port measurement when the two hands of a cable are not close to be connected on a VNA.  Gives all the needed parameters in two measurements :  Input return loss  Output return loss  Insertion loss  Cable length Coaxial Cable Measurement – Stéphane Rey – September 2011 – Rev 1.0 2/7

Measurements  Measure only 1 -port S 11 from one hand of the cable with a short circuit and then an open circuit on the other hand  S 11 measurements are saved in two S-parameter result files (Freq, amplitude S 11, phase Phi) Coaxial Cable Measurement – Stéphane Rey – September 2011 – Rev 1.0 3/7

Data post-processing  Convert to complex form :  Produce a virtual pulse & compute its FFT :  Apply this pulse to measured data and compute inverse FFT : Coaxial Cable Measurement – Stéphane Rey – September 2011 – Rev 1.0 4/7

Plotting the processed file Cable shorted :  Input return loss : RLshortIn  Output return loss : RLshortOut  2 x insertion loss Cable loaded :  Input return loss : RLloadedIn  Output return loss : RLloadedOut Plotting the processed file both for shorted and loaded cables provides the cable characteristics. Here is the example of a 30m Andrew Heliax LDF2 Coaxial Cable Measurement – Stéphane Rey – September 2011 – Rev 1.0 5/7

Reading cable parameters The measured cables parameters are then :  Insertion loss [dB] = RLShortOut / 2  Input return loss [dB] = RLShortIn  Output return loss [dB] = RLLoadOut – RLShortOut  Cable length [m] = with : c = celerity = m/s v = cable velocity (cf datasheet) time = propagation time Coaxial Cable Measurement – Stéphane Rey – September 2011 – Rev 1.0 6/7

Example of detected failures Cable overbending giving intermediate return losses Connector bad mounting giving 6dB input return losses Coaxial Cable Measurement – Stéphane Rey – September 2011 – Rev 1.0 7/7