Phone cable and networking

Discussion in 'Broadband' started by Vir Campestris, Jun 14, 2014.

  1. Vir Campestris

    Graham J Guest

    Just examined a new ADSLNation faceplate filter. The ADSL socket has 4
    contacts - in the centre - but is constructed to take a RJ45 plug. So
    plugging in a RJ-11 damages nothing.

    I've seen BT engineer installations where their cat-5 lookalike cable is
    terminated in a RJ45 plug, inserted into the ADSL socket of the
    faceplate microfilter; and the far end is terminated in a modern
    wall-mount standard BT phone socket (the type with punchdown connectors).

    The centre pair of the ADSL socket carries the unfiltered phone service,
    and the RJ45 plug is assembled with the standard colour convention, so
    pins 4/5 use the blue/blue-white pair. Only this pair is wired into the
    BT socket.
    Graham J, Jun 16, 2014
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  2. Vir Campestris

    Ian Jackson Guest

    But it almost certainly won't make proper contact (and I speak from
    Ian Jackson, Jun 17, 2014
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  3. Vir Campestris

    Graham J Guest

    However, the ADSL socket on a faceplate filter is specially constructed
    with the profile of an RJ45 socket but only 4 contacts; so one could
    describe it as 8P4C.

    I've never met an unreliability problem when using an RJ-11 plug into
    these sockets. Given that Openreach fit these faceplate microfilters I
    doubt there is a significant issue here.
    Graham J, Jun 17, 2014
  4. Vir Campestris

    Davey Guest

    Or a different approach:
    "I love work. I can sit and look at it for hours". Jerome K. Jerome,
    Three Men in a Boat.
    Davey, Jun 17, 2014
  5. Go down to Maplin, or surf the web and buy a 20m Ethernet patch cable.

    Run it through the flower beds to the shed.

    Job done for about £10.

    We connected up two sites about 75m apart using regular cat5e cable - no
    R. Mark Clayton, Jun 17, 2014
  6. Vir Campestris

    Graham. Guest

    Choose your RJ11 carefully, some seem to have more clearance than
    others and can "yaw". Having said that I haven't experienced much of
    an issue.

    There is an even more serious issue IMHO, and that's with RJ11s in
    shuttered RJ45 faceplates.

    Unless the plug is booted (comparatively rare) the shutter will spring
    down behind the connector onto the cable itself.

    To withdraw the plug you have to lift the shutter with one hand, as
    well as squeezing the retaining clip with the other.

    I think it is this that has got the RJ11 a reputation for damaging
    RJ45 sockets, and they certanly will jam if you are not aware of the
    Graham., Jun 17, 2014
  7. What's the lifetime of normal cable outdoors?

    Vir Campestris, Jun 17, 2014
  8. Vir Campestris

    grinch Guest

    I have a wifi bridge between my house and my garage through 2 11" brick
    walls.I am running 802.11g and get about 3meg when raining and about 5
    when dry. Distance between the 2 about 15 meters .

    Tried powerline which worked but the wifi gives better throughput ,but
    the powerline tech was old and got very warm so I am not sure that is
    worked too well.

    IF you take a cheap patch cable cut it in half and strip the conductors
    then connect it to the phone line at both ends making sure you connect
    the same cables together so you are effectively extending the patch cable.

    The plug the 2 rj45 plugs into appropriate ports and see if it works, if
    it does make a proper job of the connections and job done .

    Also to keep the speed down set the nic card in the computer to 10meg
    manually,his will improve your chances of it working.

    The characteristic impedance of 1308 phone cable is 600 ohms but utp is
    about 100 ohms so it should not harm your hardware.
    grinch, Jun 17, 2014
  9. Vir Campestris

    Ian Jackson Guest

    In the RF world, air-spaced 600 ohm twin feeder had the two conductors
    spaced by typically 5 inches (depends on the diameter of the
    conductors). See:
    It seems to me that it's highly unlikely that any closely-spaced twin
    cable with solid dielectric could ever be more than (say) 100 ohms - and
    most will probably be a lot less.
    Ian Jackson, Jun 17, 2014
  10. Personally, I'd expect a run of that length that to carry 100Mbps
    ethernet quite happily. I would let autoneg do its job rather than fix
    the speed at 10meg.
    Most google links suggest between 85 and 115.

    This BT Cables PDF for multi-pair outdoor cable (which is what the OP
    says he has) specifies a resistance (not impedance) of 97 ohms.
    The characteristic impedance of CatX cable is specified at 100 ohms.
    Mike Tomlinson, Jun 18, 2014
  11. Vir Campestris

    grinch Guest

    Might I politely suggest you learn the difference between the two,they
    are totally different things . An rough approximation Zo is usually the
    square root of L/C

    The Zo of most twisted pair cables is quoted as 600ohms ish I made no
    mention of the resistance which is normally given as Ohms/Kilometre for
    1308 type phone cable.

    Try googleing Zo and maximum power transfer and transmission line theory
    grinch, Jun 18, 2014
  12. I know the difference, which is why I took care to point them out.

    Wind your neck in. Prat.
    Mike Tomlinson, Jun 18, 2014
  13. Vir Campestris

    Ian Jackson Guest

    In message <lnspll$sq6$>, grinch
    As I have already said, for the Zo to be 600 ohms, the conductors would
    normally have to be several inches apart (depending on their diameter).
    For thin twin cable to be 600 ohms, the diameters of the conductors
    would have to be exceedingly small indeed.
    Ian Jackson, Jun 18, 2014
  14. +1 IIRC twisted pair is around 1-200 ohm

    600 ohm is an audio only spec.

    And was never the characteristic cable impedance.


    (in-ep-toc’-ra-cy) – a system of government where the least capable to
    lead are elected by the least capable of producing, and where the
    members of society least likely to sustain themselves or succeed, are
    rewarded with goods and services paid for by the confiscated wealth of a
    diminishing number of producers.
    The Natural Philosopher, Jun 18, 2014
  15. Vir Campestris

    Jim Guest

    Then how does a telephone line achieve an
    impedance of 600 Ohms (as I understand it to be) ?
    Jim, Jun 19, 2014
  16. Vir Campestris

    Ian Jackson Guest

    I suspect that the wide spacing of the old (very old) fashioned multiple
    open telephone wires (bare, each carried on its own of insulators) gave
    around 600 ohms.
    However, I simply can't see how anything resembling twin flex could be
    anything like 600 ohms.
    Ian Jackson, Jun 19, 2014
  17. Vir Campestris

    grinch Guest

    try reading this you might learn something

    As I said 600ohms is the normal quoted Zo for telephone circuits .
    grinch, Jun 19, 2014
  18. Appalling things, technically illegal under European EMC law, but the
    government refuses to do anything about them.

    Brian Gregory, Jun 20, 2014
  19. It doesn't.

    That's what its rated as for audio purposes. Its not its impedance..


    (in-ep-toc’-ra-cy) – a system of government where the least capable to
    lead are elected by the least capable of producing, and where the
    members of society least likely to sustain themselves or succeed, are
    rewarded with goods and services paid for by the confiscated wealth of a
    diminishing number of producers.
    The Natural Philosopher, Jun 20, 2014
  20. Vir Campestris

    NY Guest

    Is it *all* PLTs that are bad, or just the ones that use the whole frequency
    band instead of leaving gaps for the most commonly-used amateur radio

    It's a shame that a less invasive form of PLT can't be devised, because they
    are sometimes the best way of getting Ethernet from one room to another, if
    there are thick walls that attenuate wifi or if it would mean drilling holes
    through walls or running cables along skirting boards and around doorways -
    using existing mains wiring is so much easier. But it's no joke if it
    interferes with radio hams.

    What's the situation with ADSL and VDSL? When that first started there were
    fears that the xDSL signal would be radiated from telegraph poles and even
    through street lights via interference into adjacent mains wiring that ran
    next to the phone cables (I never understood how the latter caused
    interference). Have there been any problems with xDSL harmonics causing
    radio ham interference?

    What about other mains wiring devices like baby alarms? I remember seeing
    (presumably analogue) intercoms and baby alarms as far back as the 1960s.
    Did they cause radio ham interference or were different freqencies used for
    that - or was the AM/FM less intrusive than the modulation used for carrying
    the digital signal in PLTs?
    NY, Jun 20, 2014
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