Talk:Balanced line

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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)

[edit] 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)

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)

[edit] Dubius para removed

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

[edit] 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)