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The Importance of Connecting ADSL and FTTC Broadband via Twisted Pair Cable

Posted Monday, February 3rd, 2014 (1:44 am) by Mark Jackson (Score 7,852)
rj11_and_rj45_twisted_pair_telephone_cable

It’s often painfully easy to find yourself buying or receiving the wrong sort of RJ11 telephone cable to connect between a BT faceplate / master socket and your ISPs broadband ADSL / VDSL (FTTC) modem or router. Sadly this can have an impact on your lines performance so it’s important to understand why and if you should care.

Some people might be surprised to learn that ISPs sometimes ship non-twisted (straight) DSL cable with their pre-packaged broadband routers. BT’s HomeHub 5 kit (here), which ships alongside the operators top-end superfast up to 38Mbps or 76Mbps “fibre broadband” (BTInfinity) FTTC package, is a prime example.

A BT Spokesperson told ISPreview.co.uk:

The BT Home Hub 5 Router comes with a cable which has been tested as being suitable for application. This cable passes the TR100 tests.”

Indeed it’s true, the cable BT bundles with its HH5 kit has been tested and does pass the TR100 tests but that doesn’t mean to say you aren’t losing performance because of it. Similarly Sky Broadband has also told us that they “use non-twisted cables“. Meanwhile other ISPs, such as TalkTalk, claim to include twisted pair cables with their kit. Some do, some don’t.

But does it really make any difference (twisted vs non-twisted)? Some ISPs have been doing this for years and very few consumers ever seem to notice any directly related problems, although there are usually bigger issues to worry about than the local cable and if the connection itself appears to work then consumers might not always be aware of what they’re missing.

Explaining the Twist

The first thing to understand is that Radio / Electromagnetic Interference (EMI) is everywhere, it leaks to varying different degrees and over various different spectrum frequencies from your power adapters, TV, microwave ovens, DECT phones, home computer, radio, Christmas tree lights, passing high speed trains, space.. and the list goes on.

Sadly some of this EMI, which is mostly at a level that is harmless to humans, can find its way into your telephone cables and cause a performance loss or sometimes even connection problems. But today we’re taking a look at interference in the home and not the national telecoms infrastructure as a whole.

Thankfully most reputable companies ensure that their devices are properly manufactured to include good shielding and components, which reduces the local levels of EMI. But tackling interference is a constant battle and over the years various methods have been invented to mitigate the problem, which leads to a cleaner transmission and thus better performance.

twisted cable

One of the simplest and most elegant inventions came from Alexander Graham Bell in 1881. Bell realised that twisting cables around each other could reduce interference on the line (i.e. crosstalk, RFI and EMI) and thus clean up his signal, which works because the direction of the noise ‘current’ is the opposite from the ‘current’ in other parts of the cable and this acts to reduce the interference. It also helps to stop the cables from separating, which can create additional problems.

alexander_graham_bell_twisted_pair

Admittedly we’ve over-simplified things but the rule is clear enough, twisted + shielded cable (i.e. shielding conductor sheath / electrostatic shield) = good.

The Difference

In a straight cable, which is cheaper to make, the noise current just flows in the same direction and this makes it much more of a problem, especially if you happen to be running your connection over several metres of extension cable. In this situation the likelihood that EMI will leak into your line and hamper the connection increases as the length of line grows.

The solution is to A) keep the cable between your socket and router/modem very short (i.e. less than 1 metre is always a good idea.. we use about 0.25m on ours) and B) spend a small amount on a proper shielded twisted-pair RJ11 lead (example 1 and example 2) that will usually set you back no more than £5 or so (it’s better to ask for these in shops like Maplin as online the delivery often costs more than the cable).

On top of that it’s also wise to keep your router and cable as far away from other electronic devices as possible, just to limit the potential harm from any EMI that might find its way into your cable.

But does any of this actually help? The answer is yes, although whether or not you’ll notice the difference is another matter and experiences will vary (you’re more likely to see a benefit if you currently use several metres of non-twisted extension cable). For example, on some FTTC and ADSL2+ lines you might potentially notice a tiny speed boost that could at most be equivalent to perhaps +1-2% performance (guesstimate based on some limited examples).

However such a low figure is arguable well within the margin of error (i.e. most broadband lines naturally fluctuate by that much or more) and thus you might be forgiven for not noticing any difference, unless you monitor intensely over a longer period of time (both before and after the cable change). On the other hand you might notice a slight improvement in your connection stats and fewer line errors, which while not huge are still a benefit.

At the end of the day this is really all about being prudent and giving your broadband connection the best possible chance to deliver a good and stable service. After all, it’s cheap to buy a proper cable, so why skimp?

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11 Responses
  1. Jim

    We have an Infinity 2 service and are lucky to be approx 100m from the cabinet. I just installed a half metre twisted pair cable on Saturday to our HH5. Before our download speed was averaging a pretty consistent 73.5Mbps and with the new cable it has gone up to 74.3Mbps. Not a big leap, but an improvement never the less.

    • Indeed it is easier to spot a change on lines that are already quite stable, which usually means they’re at the faster end of performance too. Conversely it might be harder to spot a difference on lines that are slower and fluctuate a lot, although people may still benefit without realising (a longer period of checking and review will often reveal a small difference).

    • Hypocrite State

      More than likely nothing to do with the cable and within reasonable expectation for a variation in sync speed (NO connection will constantly sync at the exact same rate… 1Mb or so variation is entirely normal). You are more likely to gain or lose more syncing at specific times of day or during differing weather.

  2. Just a small point… :-)

    There is nothing in the quote from Mr Bell about the wires being twisted, merely that they should run alongside each other (as is the case for a straight cable). Indeed, for a long time (overhead) telephone lines were not twisted.

    Here is an extract from wikipedia:

    “The first application for balanced lines was for telephone lines. Interference that was of little consequence on a telegraph system (which is in essence digital) could be very disturbing for a telephone user. The initial format was to take two single-wire unbalanced telegraph lines and use them as a pair. This proved insufficient, however, with the growth of electric power transmission which tended to use the same routes. A telephone line running alongside a power line for many miles will inevitably have more interference induced in one leg than the other since one of them will be nearer to the power line. This issue was addressed by swapping the positions of the two legs every few hundred yards with a cross-over, thus ensuring that both legs had equal interference induced and allowing common-mode rejection to do its work. As the telephone system grew, it became preferable to use cable rather than open wires to save space, and also to avoid poor performance during bad weather. The cable construction used for balanced telephone cables was twisted pair, however, this did not become widespread until repeater amplifiers became available. For an unamplified telephone line, a twisted pair cable could only manage a maximum distance of 30 km. Open wires, on the other hand, with their lower capacitance had been used for enormous distances – the longest was the 1500 km from New York to Chicago built in 1893. Loading coils were used to improve the distance achievable with cable but the problem was not finally overcome until amplifiers started to be installed in 1912.[2] Twisted pair balanced lines are still widely used for the telephone subscribers local end.[3]”

    http://en.wikipedia.org/wiki/Balanced_line

  3. Hypocrite State

    Nice story pity BT internal wiring is not twisted pair in the first place. Ah you say that is why you should use the master socket. Oh i say but some old drop wires are not twisted pair either so having a twisted RJ11 would highly unlikely make any difference.

    Even if it is twisted if you use a external filter rather than a filtered faceplate the wire in that is not twisted pair so interference can affect that anyway.

    Same for your phone if you have one of them plugged into your faceplate or filter and that wire is not twisted pair that is another potential source of EMI. In fact a situation like that can still happen with DECT phones or Sky, Virgin, BT or any other TV box that wants to use the phone line. Lets also not forget alarm systems and much more.

    Just replacing the RJ11 modem cable in most modern homes will basically make no difference.

    • AlexAtkinUK

      The whole point of a filter is to block any frequency other than voice from getting through. So if you DO induce noise on a telephone cable, it should only affect voice quality not the broadband.

      Yes its possible it can get in via an external filter, but the cable on those is usually only a couple of inches so its not as likely.

      The whole point is, it doesn’t hurt to minimise it wherever possible.

  4. Somerset

    This is what you need – http://www.belkin.com/uk/p/P-F3L900/

    The Belkin High Speed Internet Modem cable attaches your modem or home phone to your telephone wall jack and transmits 10 times faster than any normal telephone cable for a clean, and clear transmission.

    Discuss.

    • DTMark

      I’d hate to use it when ringing the local Chinese takeaway.

      They have a woman who can already speak 50% faster than most people can listen.

    • “transmits 10 times faster than any normal telephone cable”.

      Right.. marketing gone a little crazy.

    • Matthew Williams

      Just brought that myself [waiting on delivery] to replace the standard Home Hub 5 cable doubt I will get much difference like people have said but for how cheap they are might as well try and eliminate as noise as possible.

  5. AlexAtkinUK

    I hard wired a pair taken from a CAT5 cable into the back of my face plate filter and then crimped my own RJ11 connector on that. (it was hard, CAT5 is much thicker than phone line grade cabling)

    Not sure if it made any difference but I do seem to have the most stable broadband of anyone I know. Then again I also have a vastly overpowered router which keeps the pings down, so its probably more down to that.

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