Originally Posted by ChrisWiggles
Um, no, thats the reason wires are twisted together, it is so that any noise induced on the conductors are as close to equal as possible, and in a balanced connection that noise cancels out. Without the twist, the induced noise is not equal and won't fully cancel.
On a read back through my original post I now see that I mistakenly did say "common" mode noise rejection and it clearly should have been differential mode noise rejection that I said. For that reason I agree you do have a half a point here. However both duvetyne and jarrod1937 were were both arguing that twisted pairs offers no immunity to any noise at all which clearly isn't true. I made a simple and honest mistake in my original wording which is obviously wrong. Is this what you are taking issue with?
The half point removed is due to your own sloppy wording since wire twisting does nothing in itself to reduce common mode noise only differential noise.
That has nothing to do with it.
It is unclear what you disagree with. That differential noise can be recieved on a conductor via antenna effect or that twisting reduces it. Please explain what your disagreement is and attempt to explain why you disagree. As it stands now I disagree with your disagreement.
Try googling twisted pair instead.
That's probably a good one too but the search I recomended gets the job done when correctly taken in the context of the originl topic and the point I was disagreeing with jarrod1937 on where he was agreeing with duvetynes statement "Twisted conductors don't reject noise". It really helps to keep things in the context they were clearly intended to be taken in.
A balanaced line (which isn't necessarily differential and doesn't need to be),
This turned out to be the interesting search for me. I looked at balanced vs differential and now understand. My wording in response to jarrod1937 was bad, wrong, whatever. However to the original topic and my original post this is irrelevant. I do, however, concede this point.
No, again you're missing the entire point. A balanaced line (which isn't necessarily differential and doesn't need to be), ensures that any noise induced on both conductors travels back to ground and cancels out because the impedance to ground in a balanced line is the same.
Actually this time it is you who is missing the point. The original question was regarding twisted pairs. Twisted pairs does increas differential noise immunity which I now see balanced circuits absolutely would be susceptible to just as unbalanced circuits will be. The point made about differential not equal balanced, while correct, is irrelevant to the point being made in my first post to OP and the point I thought I was making in my reply to jarrod1937 which I now understand where that replys weakness lies. Thanks for the one thing, but in this case you may want to rethink the other.
Your differential signal twice the SNR explanation is bologna, that has nothing to do with it at all.
While it may have nothing to do with the topic as I've now learned thanks to your motivating post it absolutely is not balogna. The explanation given about why differential signaling is used and useful is correct.
but you really NEED to have shielding to protect an unbalanced line, whereas a balanced line protects itself, and is aided by the twist geometry.
On the one hand I partly agree in that balanced lines with or without twisted conductors are would appear to be more immune to differential noise than unbalanced by circuit design. There is still something wrong about what you said.
The more correct statement is: Both balanced and unbalanced circuitry carrying either single ended or differential signaling are susceptible to differential noise which is reduced by using twisted conductors. Also all purmutations of balanced and unbalanced circuitry combined with single ended and differential signal types could potentially see reduced noise from shielding. Balanced circuitry can be more immune to differential noise than unbalanced and differential signaling is more immune to differential noise than single ended signals.
None of this says anything about common mode noise which may or may not be dealt with by design as well.
Of course capacitance is real. What does that have to do with noise rejection? Nothing.
Who said it did? Perhaps you ought to put the statement in the context it was given. Shielding causes its own signal integrity issues just as it can eliminate other types of signal integrity issues and part of it is due to the capacitance between the shielding and signal conductor pairs. It is the signal integrity issues it causes I was pointing out.
In summary: yep you've helped me see some real booboos I made. Thanks for that and I apologise to all who may be reading for any confusion it caused. At the same time I am even surer now than ever that both duvetyne and jarrod1937were completely incorrect and you made a doozy or two yourself.