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BT

The carpet is probably not much younger than the cable !, we used to call the wire six and a half pound wire, because a mile of the copper weighed 6.5 pounds, I guess they don't call it that any more
 
Here's a sample of some 4-core telephone cable I stripped back (carefully, to avoid untwisting any twists). Note the phone-type colour scheme:

phone_wire.jpg


Doesn't look very twisted to me!

So, where is the discrepancy? The 6-core I have to the master socket does look twisted (at first sight). Is it a difference between 6-core primary and 4-core extension cable?

(I do wish people wouldn't assume, because they believe contrary to me, that I am just arguing black is white for the sake of it. It is invariably a quest for truth and to extract truth from opinion dressed up as truth. I have no objection to finding I must update my opinion - but I will only do so when the facts are certain.)
 
In your eyes, your opinion always has more weight than someone else's and it always needs half a dozen contrary opinions to sway you. All cable of this sort used by the GPO - PO - BT from 4 core to 200 core is twisted and always has been. If the cable in your photo was supplied by a telecoms company it will be twisted, you may need strip it back over a longer length to see it
 
Fair enough, but as I had evidence in my hands to the contrary you can see my point. What half a dozen?
 
Ezra Pound said:
If the cable in your photo was supplied by a telecoms company it will be twisted, you may need strip it back over a longer length to see it
Click to expand...
I don't know where it came from, but it definitely isn't twisted (unless the twist pitch is more than 100mm).

I am struggling to find any reference on the web to domestic telephone cable being twisted. It is not mentioned in any product specification, and the pictures relating to "BT specification CW1308A" simply don't look like twisted pairs. I'm not saying you're wrong, but at the moment it's only you saying they're twisted. Can you find a reference - you might know where to look?

http://www.maplin.co.uk/p/telephone-cable-cw1308-four-core-white-priced-per-metre-xr66w
 
At last! I think I have bottomed this out, I found this reference (how authoritative it is I don't know): http://www.adslnation.com/support/cables.php
Non-Twisted Telephone Cable
Most telephone cables that you can buy in a DIY store are not twisted pair. They are cheaper, general purpose low voltage cable as used for house alarms. You often see it labeled as telephone/alarm cable. This cable has straight through connections that have no rejection to interference. This cable is fine for voice but can only be used in short runs in a typical home/office environment where there are lots of sources of electrical interference. It is not a good idea to use this sort of cable for ADSL installation especially if more than 20m of cable is required, it would be best is this type of cable is avoided altogether.

CW1308 Twisted Pair
tphone-cable.gif
Proper telephone cable is twisted pair (the official standard is BT reference number CW1308). It is typically manufactured from 0.50mm solid tinned copper and each of the pairs of wires is colour coded and loosely twisted together. This is the same type of cable that a BT engineer will use if you have them install an extension.

This cable is used for and works well for voice and ADSL as its twisted pair construction provides some resistance to interference. As the CW1308 cable is essentially the same spec cable is used throughout the whole telephone network, it known to work well. A good long run of CW1308 cable can be used for ADSL, 50m can typically be easily achieved without any noticeable degradation. CW1308 is a economical way to ensure a reliable connection and its reliably small diameter means it is not unsightly and easy to pin to skirting boards etc.

CAT5/CAT5e/CAT6
Quite often CAT5 cable is recommended as the ideal cable to use for ADSL wiring. CAT 5 cable is a twisted pair cable so it is perfectly suitable for the purpose of ADSL. CAT5 cable is designed for Ethernet networking applications that run at much higher frequencies and higher data rates than those of any variant of ADSL. As a result the wire used is thicker and the cable has a higher number of twists per meter than CW1308 cable as it is required for the higher frequency signal. Similarly CAT6 cable has even more turns per meter and even thicker wire is used to account for gigabit Ethernet speeds. There is very little benefit in choosing CAT5 or CAT6 cable over the standard CW1308 cable as the extra twists will not benefit the ADSL signal. CAT5/6 cable is much bulkier than CW1308 as it typically has 4 pairs (8 wires) and is usually supplied in a grey finish making more difficult to hide. Our recommendation is that if you are already installing CAT5 cable for networking and are able to hide it away then it there is no harm in using it for ADSL extension wiring at the same time as you probably have bought a drum of it and have some spare.

ADSL Nation Pro+
Our Pro+ cable has been specially designed for ADSL Installation where there are problems with interferenc or very long runs of cable. By using a twisted pair wire with the optimum number of twists per meter for use with ADSL, ADSL2, ADSL2+ installations it achieves the best possible interference rejection properties. In order to further reduce interference a foil screen is included. For really difficult situations such as electrically noisy machine rooms our Pro+ Installation cable includes a shielding braid that can be used as a drain wire to safely carry interference to an earth connection.
Click to expand...

The key is that it says "loosely twisted". I stripped back a 6" section of the cable in question, and the blue pair have about four twists in the section (not very even though - is it random?) while the orange pair have hardly any.

I'm happy - knowledge extended - thanks for the input.
 
Black Hole said:
I don't know where it came from, but it definitely isn't twisted (unless the twist pitch is more than 100mm).
Click to expand...
If the pairs are twisted, you need to strip back the sheathing by pulling the nylon thread backwards in order cut the sheathing along its length, if the the sheathing is pulled off the conductors, the 'twisting' can be remove in the process
 
No it's not only EP that says they are twisted. It's me as well. Now stop bloody bickering.
 
Black Hole said:
I will report what happens when the micro-filters are removed (I'll have a wager that the phones will work fine but the broadband won't).
Click to expand...
The phones might sort-of work without filters and the broadband might sort-of work without filters, but they most definitely will NOT 'work fine'.
Black Hole said:
My point is that with the (possibly unusual, but within spec) circumstance of four loads in parallel shorting out the ADSL frequencies if there were no micro-filters, the presence of the micro-filters may be essential to my broadband connection when maybe others can get away without them.
Click to expand...
No they are essential to all users with telephones, to isolate the telephone handsets from the line at ADSL frequencies, otherwise said HF carriers might get 'buggered up' (that's a technical term!).
I am curious about EP's and AF123's assertion that micro-filters are not essential to ADSL
Click to expand...
They are not necessary if you only have an ADSL modem on the line, but they provide a useful physical interface adapter, as the plugs are not the same.
It probably boils down to a disagreement on the semantics.
Click to expand...
You have just clouded the issue.
I will have a play when I get my service back!
Click to expand...
You don't want to p**s about too much, as lots of that will make the other end think your line is unstable and raise your target SNR margin. This is especially important after you have had a fault fixed as it will probably have been reset.
Telephone wire isn't twisted pair. Fitting Cat5 cable in place of telephone wire will improve the situation upstream of a micro-filter.
Click to expand...
Proper phone cable definitely is. Fitting Cat5 won't improve it unless you have dodgy cable.
Those flat plug-in extension cables you can get are not twisted and therefore not balanced. They pick up interference and are bad news. Do not use them upstream of filters, and minimise the length used elsewhere.
Certainly the ring wire can impose an additional impedance, and most modern phone installations do not rely on it, but it is part of the POTS specification and best left in circuit - downstream of the micro-filter.
Click to expand...
The problem with the ring wire is that it is a single wire and thus forms an unbalanced circuit. This makes it susceptible to interference pick up, which reduces your SNR and therefore speed. Wire 3 should NOT be connected in the linebox to your extension wiring (it is regenerated in filters anyway, as someone said up-thread).
Black Hole said:
Here's a sample of some 4-core telephone cable I stripped back
Click to expand...
That isn't telephone cable. End of.

FWIW, my line is not particularly well balanced and picks up MW interference. There is a reasonably high power TX not far from here which puts quite a hole in my ADSL spectrum. I can also see more distant/lower powered ones. Even Droitwich makes its presence felt on the graph (from RouterStats in case you were wondering) in some small manner.
 
I'm guessing this to provide an alternative ring circuit on the spare pin 4 conductor to telephones, so that it doesn't interfere with the 'normal' ring circuit housed in the master jack that has a 1.8uf capacitor from pin 2 to pin 3, otherwise the two lots of capacitance would be 'doubled up'. Although the diagram doesn't show an existing connection from pin3 of the BT line plug to pin 3 of the phone socket anyway
 
That is strange as, IIRC, pin 4 was for earth recall. Ha, remember that? It has been along time since I 'played' with telephones and sockets though.
 
It's either a mistake on that schematic or a dodgy ADSL filter. There are lots of bad ones around unfortunately - wiring faults, tiny capacitors or just generally shoddy components.
 
Ezra Pound said:
I'm guessing this to provide an alternative ring circuit on the spare pin 4 conductor to telephones, so that it doesn't interfere with the 'normal' ring circuit housed in the master jack that has a 1.8uf capacitor from pin 2 to pin 3, otherwise the two lots of capacitance would be 'doubled up'. Although the diagram doesn't show an existing connection from pin3 of the BT line plug to pin 3 of the phone socket anyway
Click to expand...
This is just gibberish. What would a phone do with a signal on pin 4 that it expects to be on pin 3??? "Spare... my arse" as Jim Royle might say.
af123 said:
It's either a mistake on that schematic or a dodgy ADSL filter. There are lots of bad ones around unfortunately - wiring faults, tiny capacitors or just generally shoddy components.
Click to expand...
My money's on 'cheap crap from China'.
Classically, the capacitor should be between (B) 2 and 3 as well, not from (A) 5 to 3.
 
prpr said:
This is just gibberish. What would a phone do with a signal on pin 4 that it expects to be on pin 3??? "Spare... my arse" as Jim Royle might say.

My money's on 'cheap crap from China'.
Classically, the capacitor should be between (B) 2 and 3 as well, not from (A) 5 to 3.
Click to expand...
Obviously not complete gibberish then, as I pointed this out in #56, i.e. "a 1.8uf capacitor from pin 2 to pin 3", or are you just repeating the gibberish?
 
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