How does Twinax, a form of shielded twisted pair, address some of the shortcomings of coax?
First of all, any sort of twisted pair implies the use of balanced signals, which means that the drivers and receivers are already designed to minimize the effects of common-mode signals. Also, all of the signal current flows in the twisted pair, and the shield does not carry signal current at all.
Secondly, twisted pair is inherently resistant to the effects of external fields (both electric and magnetic), because any effects (mostly) cancel out on adjacent half-twists. However, this effect backfires when the wavelength of the signal or interference approaches the pitch of the twist.
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