Talk:Twisted pair

message: Haven't we had this discussion on another article?  A balanced line does not imply differential signalling (although diff. sig. can be used on a balanced line).  Typically, balanced lines are transformer floating so saying the signals are equal and opposite has no meaning as it is not possible to state the voltage to earth, or any other reference.  It is even possible to tie one leg of the pair to ground (through an impedance) and still maintain the balance. SpinningSpark 23:29, 2 August 2019 (UTC)
replies: text: This article is about twisted pair and not about balanced line.  There is no requirement to use differential signaling or equal source impedances for the two wires making up the twisted pair.  I reverted Omegatron’s edit not because it was wrong, but because, in my opinion, what came before was marginally more useful to an uninformed reader.  A mention of a common type of signaling means more than a discussion of source impedances.  But, there is room for both a discussion of impedances and signaling.  There is plenty more that can be said.  The old TTL differential drivers had one impedance when driven high and a different impedance when driven low and the high and low levels were both positive with respect to ground.  The telephone folks use a clever arrangement of transformers to use both the differential mode and the common mode to create a “phantom” channel.  Constant314 (talk) 00:25, 3 August 2019 (UTC)
replies: text: My point is that saying  is definitely wrong.  This could be reworded to something like  which is both true and avoids introducing other concepts.  I am fully aware of phantom circuits, I wrote most of that page, but I fail to see the relevance of that, or differential TTL to this discussion, other than to emphasise the wrongness of your preferred version of the article. SpinningSpark 00:51, 3 August 2019 (UTC)
replies: text: No-one is going to make a twisted-pair with different wire sizes for the two wires of the pair.  It obviously works best to be both current and voltage balanced, but that might not always be needed. How well you maintain balance depends on how much EMI (both directions) you can stand. Near field the voltage (capacitive coupling) is more important, far field current (inductive coupling).  As well as I know, if you drive a twisted (or untwisted) pair with an unbalanced voltage, the current (at the important frequencies) will be close to balanced. (Probably depends on appropriate bypass capacitors on the drivers.)  Also, ferrite rings are commonly put on cables to reduce common-mode currents (they won't see voltage) and so reduce EMI.  Otherwise, you don't need to say the voltage to earth down to DC, if it is balanced at the important (high) AC frequencies.  But I think the important part about twisted-pair is that it can be balanced and have minimal RFI. Gigabit ethernet through UTP cable is pretty amazing. Gah4 (talk) 01:05, 3 August 2019 (UTC)
replies: text: Who said anything about the two wires having different gauges?  Balance of the circuit depends on the impedance inserted into the circuit by the source and load as well as the impedance of the line.  It does not depend on the symmetry of the applied signal one bit. SpinningSpark 01:21, 3 August 2019 (UTC)

text: My preferred version is to say something about the signals and not just about the impedances.  Lines without signals are not very useful.  I have no objection with saying that a twisted pair can be used as a balanced line.  I have no objection to making it less wrong.  The TTL driver is a counter example to the line having the same source impedance on each wire of the pair. Constant314 (talk) 02:07, 3 August 2019 (UTC)
replies: text: A fairly common case is flat ribbon cable with odd wires grounded. (There are twisted pair ribbon cables, but they are more expensive, and so relatively rare.)  If you drive one wire with the rest ground, the signal will go down that wire, with an appropriate impedance, and most of the return current going through the two adjacent ground wires. The far end is the terminated in the appropriate impedance to ground, and so minimizes the reflection. If there is no reflection, then source impedance mismatch doesn't cause much problems. If you drive a coax cable from TTL with the shield grounded, current will go down the outside of the center conductor, and return current on the inside of the shield.  If you drive a UTP cable the same way, current will go out on one conductor, and mostly return on the grounded conductor. If the common mode impedance is relatively high, the common mode current will be relatively low. Close enough for common usage. So, the current is close to balanced, even when the voltage is not. Gah4 (talk) 07:35, 3 August 2019 (UTC)
replies: text:  All those examples are not true balanced.  Ribbon cable obviously isn't.  It is not relevant that most of the return current goes down the grounded wire (and that's ignoring the elephant in the room that the return current is split between multiple wires).  The issue is that the induced common mode current will be radically different between a hard grounded wire and one with kΩ of impedance.  Likewise, differential TTL is not balanced so is not a counterexample.  Differential signal != balanced line.  I don't know why we are even discussing these cases. Constant314, you say you want to write something about signals, but remember, you are writing it in an article about a line.  The properties of the line should be the focus, not the signals it might carry. SpinningSpark 09:57, 3 August 2019 (UTC)
replies: text:  I don't have any other comments.  Do what you want. Constant314 (talk) 17:49, 3 August 2019 (UTC)

text: But "what came before" was wrong, and you reverted to it.  — Omegatron (talk) 13:45, 3 August 2019 (UTC)

text: As well as I know, twisted pair was first used for telephone wiring, not so long after RFI sources were created near phone lines, and with balanced signalling. Balanced differential signalling is a common, but not the only, use for twisted-pair cable.  Gah4 (talk) 04:56, 5 August 2019 (UTC)
replies: text: Balanced lines were used in the telegraph era in some places to overcome interference from power cables, particularly from trams.  However, these were not twisted pairs which, as you say, was invented specifically for telephone lines. SpinningSpark 15:23, 26 November 2019 (UTC)
thread_title:  Balanced line and differential signalling 

message: I've changed this article back to British English.  The very first version of the article was clearly BritEng by the use of "cancelling" rather than "canceling".  The article was changed to American English with this edit with the rationale "spellchecker".  Per WP:ENGVAR there is no standard variety of English on Wikipedia and per MOS:RETAIN the original established variety should be retained unless there is consensus to do otherwise. SpinningSpark 17:53, 4 August 2019 (UTC)
thread_title:  ENGVAR