Re: [SI-LIST] : Single-ended SCSI vs. di

Fred Townsend (
Fri, 19 Sep 1997 23:45:45 -0700

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> This sounds good for ribbon cables. How about for external SCSI cables,
> which are round and therefore have the various wires "scrambled?"
> Different signal wires would seem to have significantly different
> impedances due to the variegated physical arrangement of ground wires
> (especially that signal's "own" ground wire). Still a lot better than a
> single ground system, I suppose.

The round cables use twisted pair that is spirally wound similar to
cables used for T1 transmissions (1.544 MHz). Impedance runs 100-110
ohms. The surge impedance does not depend on a ground. Rather it is
like TV twin lead except it is twisted and much closer together. The
biggest impedance bump comes at the connectors where the round cable
must be converted back to ribbon for termination.

Fred Townsend
DC to Light Consulting Services
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