Test invented in Fumay goes viral

Let’s undo the twist

With twisted copper wires carrying data at ever-higher speeds, next-generation 40 Gbps cables have to be tested up to and above 1600 MHz, which is difficult. High-frequency tests are often inaccurate since the pair has to be untwisted first. A new procedure, which is becoming an international standard, improves return-loss and impedance results 10 times.

Accentuate the positive…

There are three ways to correct errors: fix the theoretical model, compensate for deviations, or use “gating,” i.e. a Fast Fourier Transform (FFT) algorithm to measure time instead of frequency. This reveals two peaks at the beginning and end (the cable extremities). We mathematically reset these to zero, and retest frequency. However, gating loses other data.

Eliminate the negative…

First, we tried to improve sample preparation and the test fixtures, but without success. Then, we needed correction procedures to remove the unwanted effects from test results.  But they were insufficient to deal with the intended frequency range (2000 MHz). Finally, we abandoned the usual procedure, based on two-port theory, and invented a graphical or “fitted impedance” approach. We extracted the unwanted and unusual behavior, and subtracted it from the results.

Latch onto the affirmative…

Normally, we would have just measured the cable, calculated the effect of stray inductance and subtracted the effect. However this works only up to 1000 MHz. At high frequencies, the cable ends act like two tiny impedance transformers.  Our “fitted impedance” approach corrected this, and was shared with other cable manufacturers in a round-robin test. This new international IEC standard will vastly improve the speed and accuracy of inter-computer communications.