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I am using a SCSI-2 Half-Pitch DB50 connector as an I/O expansion connector, due to size constraints. However, it seems as if pretty much all cables manufactured in recent years are differential twisted-pair cables. This creates a lot of problems for me, because the twisted pairs will crosstalk with each other in a pretty nasty way.

I have searched the typical vendors (digikey, l-com, mouser, newark) but I cannot find a single-ended SCSI cable. They can sometimes be found on ebay, etc, but I am not comfortable using those for production units.

My question is, assuming I can't find a reliable source of single-ended SCSI cables, is there some method that I can use to prevent crosstalk between the twisted pairs of a SCSI cable?

EDIT:

Digital and analog signals are run in the cable. The digital signals are 5V inputs and outputs. Data rate is max of maybe 10 MHz, typically less than 1 MHz.

There are no differential signals. The decision to use the SCSI connector was made before it was known that single-ended SCSI cables are a legacy product that are difficult to find. I know that twisted-pair is designed to couple the wires; it's unfortunate that I discovered late in development that modern SCSI cables are twisted-pair. I am considering potential solutions, but I wanted to see if there wouldn't be some "easy" way to decouple the wires before investigating other solutions (e.g. SCSI connectors that attach to ribbon cables)

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  • \$\begingroup\$ are you running analog or digital signals through the cable? What kind of signal voltages or data rates? \$\endgroup\$
    – Michael
    Commented Jun 1, 2012 at 2:08
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    \$\begingroup\$ Are you sending differential signals through each twisted pair, like you should be? Because there's not much you can do to prevent the pair wires from coupling to each other. They're kind of designed with that in mind. \$\endgroup\$
    – Connor Wolf
    Commented Jun 1, 2012 at 4:44

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Yes, there is method to minimize crosstalk. Use very low speed and 1 turn pass-through transformer for every pair. Small ferrite bead with 2 wires = 4 ends. This will decouple each individual pair. On the picture below the ring is horizontal, wires enter ring from top and bottom.

copper wire A ---\ /--------\ /----------\  /----- A'
                  X  twists  X         [======] ferrite bead does "untwist"
copper wire A'---/ \--------/ \----------/  \----- A
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