Faraday cages and cables

The important thing about twisted pair signals is that the same signal is sent down both wires, but inverted in one wire.

That's got me thinking. I think there are examples where the data line is paired with a 'ground' wire rather than a -ve data (some old versions of IDE and SCSI come to mind,  but I'm just working from memory) - in that case the receiver end can still reject noise in just the same way (by subtracting the signal on the 2nd wire of the pair from the first - it ends up subtracting (0V+noise) from (data+noise) to get just data. Presumably the difference though is the amount of noise the cable creates - with a +ve data line and a -ve data line at a reasonable distance away the two will cancel each other out reasonably well - so reducing the noise seen by other conductors in the system - but with a signal & 0V pair there's no cancelling, so other conductors nearby see increased noise.


  - Andy.

The important thing about twisted pair signals is that the same signal is sent down both wires, but inverted in one wire.

That's got me thinking. I think there are examples where the data line is paired with a 'ground' wire rather than a -ve data (some old versions of IDE and SCSI come to mind,  but I'm just working from memory) - in that case the receiver end can still reject noise in just the same way (by subtracting the signal on the 2nd wire of the pair from the first - it ends up subtracting (0V+noise) from (data+noise) to get just data. Presumably the difference though is the amount of noise the cable creates - with a +ve data line and a -ve data line at a reasonable distance away the two will cancel each other out reasonably well - so reducing the noise seen by other conductors in the system - but with a signal & 0V pair there's no cancelling, so other conductors nearby see increased noise.


  - Andy.