Questions & Answers

Quantum - EMI from computer in monitors

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asked Nov 27, 2017 in Thunderbolt - Quantum by jamesbarber2 (190 points)
Tested my new Quantum-based rack this weekend and found a significant issue that may or may not be specifically related to the Quantum itself.

It appears that substantial computer noise (RF) is being conducted over the Thunderbolt cable. The only way I can get the noise out of my live monitor system is to run the Quantum mains through my active DI box with the grounds lifted. That isn't workable in production for several reasons that would distract from the issue at hand.

I have a spectrum analyzer and EMI probe and will verify that the noise is indeed coming over the Thunderbolt cable, but assuming I'm correct what's the best-practice fix? I can wind several turns of the Tbolt cable through a Mix 31 or Mix 75 ferrite cable suppressor, and/or ground-bond the computer and each unit in the rack. Anything else? The computer and rack are roughly 30" apart, with the only common connections being the Tbolt cable and the power safety ground. The rack and computer are currently powered from the same power strip, and that strip *supposedly* offers 40 dB broadband RF noise suppression, but I don't know if that includes all possible conduction paths.



1 Answer

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answered Nov 29, 2017 by AlexTinsley (825,470 points)
Best answer
Make sure you're using shielded balanced cables to your monitors. Most often unbalanced, non-shielded cables will pick up RF and as most folks have their levels cranked on the monitors, any RF will be amplified as you're describing.