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Author Topic: Twisted pair  (Read 3267 times)

Weaver

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Twisted pair
« on: October 18, 2016, 12:06:42 PM »

How much of BTís copper access network is twisted pair? (As opposed to not twisted.) Dumb question, I know.
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Black Sheep

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Re: Twisted pair
« Reply #1 on: October 18, 2016, 12:07:47 PM »

All of it is twisted pair ......  :)
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Weaver

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Re: Twisted pair
« Reply #2 on: October 18, 2016, 12:13:31 PM »

Said it was a dumb question.  ;D
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licquorice

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Re: Twisted pair
« Reply #3 on: October 18, 2016, 03:46:00 PM »

Except for old drop wire, and 40lb copper open wires for that matter, but not much of the latter still about.  ;)
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Black Sheep

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Re: Twisted pair
« Reply #4 on: October 18, 2016, 05:16:30 PM »

Yeah, good point.
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PhilipD

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Re: Twisted pair
« Reply #5 on: October 19, 2016, 04:02:48 PM »

Hi

Of course there is twisted pair and there is better twisted pair, as I understand it the BT normal stuff isn't twisted enough for the sort of frequencies pushed through it for ADSL/VDSL :'(  It's all a hack for data over POTs.  If you strip back telephone cable it isn't always obvious that it is twisted as the twists are far apart (okay for voice but not good enough for higher frequencies), whereas data cables like Cat 5, Cat 6 etc have many more twists per metre to better prevent crosstalk and interference.



Regards

Phil

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Ronski

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Re: Twisted pair
« Reply #6 on: October 19, 2016, 06:45:16 PM »

Perhaps BT stands for barely twisted  ;D
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NewtronStar

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Re: Twisted pair
« Reply #7 on: October 19, 2016, 08:37:56 PM »

The dropwire looks twisted CW1417 2 Pair BT ref Dropwire 10B Cable and link is
http://www.netshop.co.uk/product/820/cw1417-2pr
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Black Sheep

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Re: Twisted pair
« Reply #8 on: October 19, 2016, 09:01:38 PM »

It has been for the last circa 30yrs, NS. Prior to that, DW3, DW6 were parallel wires.  :)
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NewtronStar

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Re: Twisted pair
« Reply #9 on: October 19, 2016, 09:17:25 PM »

It is know wonder the drop wire 10B is very steady during 70 Mph wind gusts with those three steel strainer wires and the tension bar at the premises
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burakkucat

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Re: Twisted pair
« Reply #10 on: October 19, 2016, 09:26:51 PM »

b*cat remembers when the aerial drop to his home was two separate, uninsulated, cadmium-copper wires each with its own porcelain insulator.  ;)

And there is a vague memory of aerial junction (or would they have been trunk?) circuits, where a "twist" was created for each pair by swapping insulators used at either end of each pole-pole section.
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NewtronStar

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Re: Twisted pair
« Reply #11 on: October 19, 2016, 09:50:57 PM »

Was looking on the net as one does this link comes from a so called BT engineer says most drop wires become corroded at the top of DP (Pole)

http://www.andywatts.co.uk/work-bt.html

is this a true engineer experience
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licquorice

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Re: Twisted pair
« Reply #12 on: October 19, 2016, 10:18:22 PM »

b*cat remembers when the aerial drop to his home was two separate, uninsulated, cadmium-copper wires each with its own porcelain insulator.  ;)

And there is a vague memory of aerial junction (or would they have been trunk?) circuits, where a "twist" was created for each pair by swapping insulators used at either end of each pole-pole section.

Hence my reference to 40lb copper wires above. ;) It wasn't at every pole, they were called transposition poles where the pairs were not only reversed but also moved around within the nest of wires. There were complicated transposition rules governing what went where. I couldn't find any UK stufff on the web but found this http://the-electric-orphanage.com/wp-open-wire-transpositioning-systems/
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c6em

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Re: Twisted pair
« Reply #13 on: October 19, 2016, 10:43:11 PM »


I have an old but full and detailed pdf spec from B3 cable solutions for external 2 pair drop wire compliant with BT spec CW1411.

The 'lay' ie distance between twists of the cable pairs is as follows
pair 1 Orange/white 89mm
Pair 2 Green/black 95mm

The breaking load is quoted as being between a minimum of 1350 Newtons and an max of 1550 Newtons

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burakkucat

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Re: Twisted pair
« Reply #14 on: October 19, 2016, 11:01:10 PM »

I couldn't find any UK stufff on the web but found this http://the-electric-orphanage.com/wp-open-wire-transpositioning-systems/

Thank you. That was an interesting read.  :)
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