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General discussion

Twisted Cable - different tighnest

Sep 11, 2004 6:47PM PDT

I read that twisted wired for network cable is twisted differently between the pair.

http://www.networkclue.com/hardware/network/termination.php

I quote:
"One thing that I have noticed though is that in CAT5e, the orange and green pairs are twisted tighter than the blue and brown pairs. So do not expect to get the CAT5e quality on the network drop using the split pairs (brown and blue)."

Is this True - If so, Why they do that for?

Secondly I read about Punchdown cable color code, Which use Blue/Blue White as the main color to be used, What is this related to?

Thank You

Discussion is locked

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Re: Twisted Cable - different tightest
Sep 11, 2004 11:18PM PDT

Twisting the wires has been around since the first telephones were installed. As an AC signal (voice frequencies) travels in the DC carrier, an effect called mutual induction occurs. This has the effect of creating cross-talk in adjacent pairs. Since voice frequencies are in the 200-3400 Hz bandwidth, only a few twists per foot are needed. Self induction is also present which has the effect of canceling or dropping the signal level.

Enter High speed.

Because of the higher frequencies of ADSL (unknown to most, these are analog like voice, but in the 80 KHz to 1.1 MHz range), tighter twisting was needed. The same effect is in digital signals like ISDN, T-1, etc. There is an effect called Apparent Frequency which mimics an analog signal, and will have the same canceling effect as an analog signal. Therefore, tighter twisting is needed.

Hope this helps,

Telephony facts, analog/digital explained.
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Ok, thanks... but
Sep 12, 2004 6:20AM PDT

it didn't answer my questions, regarding the LAN cable and 'punchdown' thing.

Is it true (and if so), why the green/white green and Orange/white orange pair are twisted tighter then the blue/white blue and brown/white brown pair.

And what is 'punchdown' terminal? and why they use blue/white as the main cable to be used? -- what this punchdown thing related to, or use for?

Thank you

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Oh. . .
Sep 12, 2004 11:07AM PDT

All the conductors in the sheath should be twisted the same amount per foot. There is a minimum for high speed signals, and those you are describing may be twisted a little more.

The standard color code for telephony is as follows, for pair one through five:

bl-w/w-bl
o-w/w-o
g-w/w-g
br-w/w-br
sl-w/w-sl

Ring conductors are blue, orange, green, brown, slate. Tip conductor is white. For the next 5 pairs, the tip is red. Next five tip is black. Next five tip is yellow. Next five tip is violet. This method will produce a 25 pair cable.

Here is a punch down terminal, called a 66-block.

http://www.smarthome.com/8610.html

This is a newer model, I learned how to punch down on a 6 clip/pin block back in the 60s. The designation "66" came from the Western Electric design.

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Re: Oh. . .
Sep 12, 2004 7:37PM PDT

that's where I start my confusion... the different color code between the telephony and LAN wired.

Thank You very much for clearing my confusion.