Measuring PCB, Cable and Interconnect Impedance, Dielectric Constant, Velocity Factor, and Lengths

Controlled impedance printed circuit boards (PCBs) often include a measurement “coupon”, which typically includes sample traces, 6 inches long and constructed as part of the printed circuit board panel.  They are measured to assure the PCB stack-up and the accuracy of the PCB transmission lines. These coupons, as well as the actual PCB signal traces, interconnects and cables are typically measured using a Time Domain Reflectometer (TDR).  A TDR is generally a large, expensive instrument that includes a high-speed edge pulse and a sampling oscilloscope.

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