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In Reply to: Re: In a grounded metal chassis, no shielding is needed for TWISTED pair. posted by kurt s on April 30, 2007 at 22:58:09:
The difference between a differential signal and balanced lines.See normally a differential signal would travel on balanced lines. In a balanced line the two wires have the same impedance to ground. This increase the line's ability to reject common mode interference as interfering fields/current will introduce the same potential in both lines.
All differential means is that the two signals, on the two separate wires, are complementary. Differential doesn't have to be on balanced lines though. The center tap you mention forces balanced. Without it you only have differential. Which mean the receiving end sees the difference between the two signals. Its advantage over single ended is that effective signal voltage is doubled so it takes twice the noise voltage to cause the same problem as on a single ended line.
Follow Ups:
HiWe were talking about unbalanced twisted pair needs a shield or not in the original post.
Someone came in with balanced signal transfer concept which is a good idea but, IMO, wrongly applied to the short short run signal paths in an audio amp. Who needs those hig guns in an audio amp?
Someone even confused the issue further with differential signals via a transformer without CT while we were on balanced signal transfer which must have a CT.
Kirt may have confused somewhat in the terminology. But he is correct
in the basic prinicple of balanced signal transfer & his idea of LOW impedance situation which aproximates balanced line transfer.This explains why an unbalanced pair wiithout shield can handle low signal transfer like MC phono cartridge.
c-J
Jack, you can drive a saint to drink! Countless people have spent a lot of time and effort trying to insure that everyone understands.But it always seems to be you that never gets it. Kurt sees where he made his mistake and if I had read that post I would not of made my post.
Another individual gave you info on telcom standards and you insult him and act as though you doubt his expertise when it is clear you know nothing of the man. Do yourself a favor and look up SITA and see if you still think he knows nothing about telcom. Then you can wonder about how I associate him with that company.
Dave Cigna has considerable knowledge in physics and has spent countless hours with you and all you can do is act rudely towards him.
You act as though everyone is out to get you and that proving someone wrong wins points. Stop that silly game because you are the only one playing. We are all here to learn and help. That only works when people are free to debate until there is common understanding. But you are clearly not interested in obtaining a common understanding.
Go back to prop head. It is a better place for you. We aren't interested in insults and obscurring the truth.
Hi.Talk technical, & stop getting personal, please.
If you think I am citing some wrong stuff from a wrong perspective (who never screws up?), go ahead to correct me with technical substantiation, instead of behaving like a social godfather. This a a technical forum not a social gossip place where lip service works out. Sorry, I look at you this way.
I repeat what I quoted: Kurt is correct in the basic principle of balanced signal transfer which needs a CT. He was led to confusion 'cause someone brought in something else - differential signals - to ocnfuse the balanced system issue.
Someone you may consider a god of telecom or a professor of "physics". So what if that someone chooses to put his expertise in the wrong place? How helpful could it be to the readers at large.
I never dispute about the validity of whatever telecom standards being cited here (which got nothing to do with tube DIY anyway). IMO, this is a complete waste of bandwidth here other than a show-off of one's self-regarded expertise in the WRONG place. Is this a telecom forum?
But to quote "ALL twisted pair for delivery of LOW speed STUFF" is very debatable. Hence I challenge it.
Instead of counter challenging my post with your technical substantiation, you started talking social on how much you know about the poster. Sorry, I don't buy lip service.
You speak for him because he is your acquaintance or because his quote is correct? Your habitual behaviour as such leads me ask this question.
c-J
PS: Again, who needs lip service in a technical forum. I can post anywhere in AA. Only the Bored can tell me stop posting somewhere or nowhere. But not YOU.
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