Talk:Balanced line/Archive 1

Archive 1

Shielding

As far as I know, most balanced lines are shielded, too. — Omegatron 16:12, 1 April 2006 (UTC)

Yes, but not as heavily as unbalanced ones. Common balanced cable (i.e. Belden wire) only uses a thin foil wrapper as shielding around the conductors. Mystic Pixel 10:58, 30 April 2006 (UTC)

Twin feeder is not shielded--SlipperyHippo 01:51, 6 April 2007 (UTC)

Do you mean twin feeder as in loudspeaker cable? I'm not really sure that's actually a balanced line, but I might be wrong. Does it actually use differential signaling? Mystic Pixel 03:25, 7 April 2007 (UTC)

No I mean 300 ohm balnced twin for your FM radio etc.--SlipperyHippo 10:18, 7 April 2007 (UTC)

Oh, right. I was only really thinking of this article in the context of audio, not RF transmission. Oops :) Mystic Pixel 05:34, 9 April 2007 (UTC)

Yeah its at twin-lead and you really wouldnt be able to connect this to an unbalanced coax without some sort of balun and get it working properly at RF.--SlipperyHippo 17:27, 9 April 2007 (UTC)

Accuracy

There are several things going on at once in cables. Although for laymen it's nice to just say "a balanced mic cable cancels out noise and interference", we need to be much more specific here and address what each thing does individually:

• Differential signaling
• Impedance of each conductor to ground (balanced line)
• Shielding
• Twisted wires
• Characteristic impedance (not important for audio but important for everything else)

— Omegatron 14:30, 7 April 2007 (UTC)

Agreed. As the discussion above demonstrates, the article also needs to clearly define the scope of the term "balanced line", and how it applies in various contexts (audio, RF, telecom, etc.) Mystic Pixel 05:34, 9 April 2007 (UTC)

See Talk:Differential_signaling#Accuracy and Talk:Balanced_audio#Incorrect for parallel discussion. — Omegatron 18:13, 22 May 2007 (UTC)

Hit-and-run post, suggestion for somebody else to pursue: the expression "electromagnetic shielding" needs to be looked at. A cable shield provides electrostatic shielding but is not effective against magnetically induced interference. This point should be explicitly made because confusion about the operation and limitation of cable shielding is so widespread. —Preceding unsigned comment added by 209.237.122.81 (talk) 14:06, 9 September 2009 (UTC)

Shielding has naff all to do with balance. Go write it in the electromagnetic shielding article or the shielded cable article. SpinningSpark 18:28, 9 September 2009 (UTC)

Dubius para removed

I removed this as I dont think its accurate. Its also very confusing--SlipperyHippo 11:32, 6 April 2007 (UTC)

Usage

A "balanced" cable can be used in an unbalanced system (the cable itself is not balanced, the complete system is) because the 'hot' conductor is equivalent to an unbalanced line (the cold lead is ignored). The systems cannot be combined in the opposite way. That is to say, an unbalanced line can not normally be used by a balanced receiving system.

It's not really inaccurate, it's just worded in a confusing way. If you have a cable intended for balanced operation, you can still use it to connect unbalanced equipment - you just won't get the benefits that come with using a balanced line with true balanced equipment. Conversely, if you have balanced equipment, you *must* use balanced cable to properly connect it. Mystic Pixel 03:23, 7 April 2007 (UTC)

In using balanced cable in this way you immediately make it unbalanced. You need a balun to interconnect properly. Also you cannot do what the para suggests with a twin feed (300 ohm balanced).--SlipperyHippo 10:17, 7 April 2007 (UTC)

Right, I understand that it makes the line unbalanced - that's what I was trying to say when I wrote "you won't get the benefits that come with using a balanced line with true balanced equipment", I just said it badly. About the twin feed: point noted. Mystic Pixel 05:37, 9 April 2007 (UTC)

With regard to audio etc: If you had say, a twin screened balanced mic cable and you connected one wire to the inside of a normal single screened cable (coax) leaving the other wire not connected to anything, (and connect the screens together) you would immediateley make the whole system unbalanced but it would still work (albeit with a 6dB loss because youre only using half the transmitted signal).

However, if you had an unscreened pair and connected on wire to earth and the other to the input, you would have rather large aerial wire that would pick up anything from mains hum upto GHz! In this case, it is not recommended to unbalance such a cable! Hope that makes my staements clearer,--SlipperyHippo 17:39, 9 April 2007 (UTC)

I understand -- I'm not trying to disagree. I never intended to imply that connecting things up that way was a good idea... :) Mystic Pixel 01:21, 10 April 2007 (UTC)

Balanced line ?= differential signal

I was wondering if differential signalling is nothing but balanced line.

Balanced lines make use of differential signaling, but differential signaling has more general applications. Mystic Pixel 10:58, 30 April 2006 (UTC)

Could someone please give an example of where a balanced line is used without differential signalling? My understanding was that balanced lines are specifically intended to be used with differential signals. The sentence "Balanced lines are often operated with differential signals" seems to imply that this is not always the case. --RadioTheodric (talk) 16:22, 21 April 2009 (UTC)

An example of a line that is of balanced construction, but which does not carry a balanced signal, is the Zeppelin antenna, illustrated at http://www.cqham.ru/lw-ant.html --Jc3s5h (talk) 16:52, 21 April 2009 (UTC)

FTFA "Lines carrying symmetrical signals (those with equal but opposite voltages to ground on each leg) are often referred to as balanced, but this is an entirely different meaning. The two conditions are not related."

I'm not convinced.

Balun links here from 'signals that are balanced about ground (differential)'.

The distinction seems pedantic or purely theoretical/hypothetical.

The Zeppelin aerial - isn't that just a Balun implemented in transmission-line ? The metalwork is asymmetric at the aerial end, but the input signal is balanced/symmetric ?

I suppose the difference is that one is the hardware, the other is the signal, but they certainly do belong together, rather than 'entirely different' or 'not related' !

You could put whatever signal you wanted into a 'balanced cable' but why would you use it for anything other than Differential signaling ? See Talk:Balanced_line#Dubius_para_removed

There are other kinds of Differential signaling - but the kind in balamced lines is certainly one of them !

--195.137.93.171 (talk) 20:36, 30 December 2010 (UTC)

Applications

Wtshymanski's recent edit has done a lot of good for the organisation of this article but we seem to have lost a few things from the applications section;

1. Telephone lines - hugely important and should be mentioned. Admittedly the lost text was only a short, not very informative sentence, but this should be expanded, not deleted.
2. Ethernet - this has contrived to get itself under the audio heading - I don't think so!
3. The second para under Audio Systems starts "Another example..." but then continues discussing the same example.

Can I suggest that a sub-heading after "Audio systems" for "Other applications" to park telephone and ethernet until they can be expanded?

I am also planning to create some graphics of various balanced line types for this article. If you have any suggestions please let me know. SpinningSpark 19:22, 8 September 2009 (UTC)

wire labeling in quad line pictures

The description in the main text sounds right, but the wire labels in both quad line pictures look wrong, as if to maximise cross talk and minimise common mode rejection. --SpecMade (talk) 01:09, 2 December 2013 (UTC)

You are correct, the image is wrong. I have deleted it for now; hopefully it can be corrected in the future. Binksternet (talk) 01:20, 2 December 2013 (UTC)

Thanks for confirming; I have for now removed the other quad line picture as well for consistency. But I notice, only now, that our removals have created a gap in the numbering of the pictures, and figure 5 refers back to the now removed figure 2. At least the way the quad line is used in figure 5 agrees with the main text rather than the labeling in the removed picture, confirming that the picture needs fixing.

Anyway, before we start changing more, let's give User:Spinningspark a chance to say what he thinks. It looks he originally created both the text passage and the pictures in 2009 and is still looking after the article. --SpecMade (talk) 02:28, 2 December 2013 (UTC)

Haven't we had this discussion before? The diagrams are not incorrect, you are probably misreading the meanings of GO and RETURN. See here for an explanation of the telecomms understanding of GO and RETURN. Once we are on the same page on what the definition of the terms is, please either restore the diagrams or explain why you still think it is wrong. SpinningSpark 03:06, 2 December 2013 (UTC)

Sorry, I'm all turned around. The images are indeed correct. Star quad uses opposite conductors soldered together at each end of the cable to make one effective conductor. D-M cable (found mainly in Germany) solders the ends together of two neighboring conductors which are twisted around each other throughout the length of the cable. Restoring. Binksternet (talk) 03:33, 2 December 2013 (UTC)

You are right Spinningspark, I misread the meanings of GO and RETURN as hot and cold (probably because I was thinking of a music stage or a recording studio rather than bidirectional telephony). So I agree the diagrams are not incorrect.

But you did say that people have misunderstood it before, so perhaps it could be improved. I think using the word channel would have avoided the misunderstanding in me. --SpecMade (talk) 05:12, 2 December 2013 (UTC)

I am not against amending the annotation in the diagrams in priciple but I wouldn't like channel. That is not how this is usually described in sources and I don't think we should be making up our own terminology. But honestly, the best approach is to make the meaning clear in-article, any alternative term is open to misinterpretation by somebody. The terms are already explained in the article. If you feel it is necessary, why don't you improve the explanation, or make it more prominent? SpinningSpark 09:01, 2 December 2013 (UTC)

This tripped me up, too. I think the issue is that the order in which the information within a legend item is given violates the hierarchy of the wire pairs: “A leg insulator GO” etc suggests that “go” and “return” are components of “A leg”, whereas it’s actually “A leg” and “B leg” being components of “Go”. (It’s how, in a parts list, if you saw “wire, 14ga, red”, you’d understand that “wire” is the object, and “14ga” and “red” being modifiers, but arguably with 14ga being “dominant” over the color, insofar as one would typically consider wire gauge to be a more critical specification than the color, and as such, wire would typically be sorted (in a list, or on a shelf) by gauge first.)

As such, I propose that the legend be amended to:

1. GO pair, wire A insulator
2. GO pair, wire B insulator
3. RETURN pair, wire A insulator
4. RETURN pair, wire B insulator

Such a wording (which I would then also suggest updating in the other images for consistency) leaves no ambiguity as to which of go/return and A/B refer to the pairing.

— tooki (talk) 12:37, 13 April 2020 (UTC)

P.S. Such a wording also eliminates the need for prior knowledge in order to correctly parse the legend, which I think is the issue here. — tooki (talk) 12:45, 13 April 2020 (UTC)

I'm fine with that suggestion. You can go ahead and make the change as far as I'm concerned. SpinningSpark 13:55, 13 April 2020 (UTC)

Clarified symmetrical signals

I’ve changed the term «antiphase» to «equal and opposite polarity». Antiphase means phase shifting by 180° and while I would agree that phase shifting all the component frequencies of a complex signal by 180° would indeed result in (and be mathematically equivalent to) a polarity reversal, the electronic circuits involved inverts the amplitude (reverses the polarity) of the negative differential line; no time based shifts are involved. Gutten på Hemsen (talk) 22:28, 11 June 2021 (UTC)

Antiphase does not mean 180° phase shift. The latter implies a delay while the former does not. As used in this article, it means signal inversion. Here is an audio book using it in this sense "By cross-feeding antiphase signals, the width of a stereo image can be increased." And from Principles of Transistor Circuits, "In the circuit illustrated the antiphase signal is obtained from the secondary winding which feeds the following transistor." I reverted you because your replacement text is actually wrong. The current polarity cannot be equal and opposite. A polarity is a binary value so two polarities are either equal or they are opposite but not both. SpinningSpark 20:00, 12 August 2021 (UTC)

@Spinningspark: You are absolutely right. I have now corrected the mistake. Please take a look :-) Gutten på Hemsen (talk) 20:19, 12 August 2021 (UTC)

@Gutten på Hemsen: Re the link you made [[Differential signalling|symmetric signals]], these are not synonyms exactly. Differential signals can have both legs offset by a DC value (as is the case in the output of a long-tailed pair) or they can be completely floating like a transformer output. I can't think of an example offhand, but in principle the voltages could be offset by any random waveform. SpinningSpark 11:53, 8 September 2021 (UTC)

@Spinningspark: Thanks for the heads up! I hadn’t considered that. Gutten på Hemsen (talk) 12:22, 8 September 2021 (UTC)