Telephone wetting current.

Discussion in 'Broadband' started by The Natural Philosopher, Oct 27, 2010.

  1. Someone remarked here once that if there are any dodgy joints on a
    telephone line, drawing a bit of current off it improved it..i.e. the
    'on hook' current is beneficial to broadband.

    I have no telephones connected: Only a PABX which draws almost no on
    hook..or does it?

    I am wondering if a resistors might not improve line quality slightly.

    Where can I find chapter and verse on this?
     
    The Natural Philosopher, Oct 27, 2010
    #1
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  2. You PABX looks like a normal phone to the exchange, when your make or
    recieve a call it goes "off hook" and draws current just like a
    normal phone.

    A slightly iffy joint might be improved by this current but ringing
    has more power. TBH I doubt it will make any difference to your ADSL.
    In fact depending on why a joint is iffy it might make things worse,
    damp dissimilar metals plus current = more corrosion...
     
    Dave Liquorice, Oct 27, 2010
    #2
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  3. Oh well..thanks for that anyway.
     
    The Natural Philosopher, Oct 27, 2010
    #3
  4. The Natural Philosopher

    Bob Eager Guest

    Used copies on Amazon...that's where I got mine.
     
    Bob Eager, Oct 27, 2010
    #4
  5. The Natural Philosopher

    Gaius Guest


    Answers to the current possible are in SIN351 - find it at :
    http://www.sinet.bt.com/index.htm

    You can draw up to 4mA from the line before it may be recognised as a
    "Seize". A 15K resistor across the line will draw 3mA. Try it and see -
    it works well for me.

    The actual physics of wetted contacts is well understood, but that said,
    I've no idea where to find definitve data. It's probably in some very
    specialised (expensive) textbooks on contact phenomena. To reliably
    carry small signals with no superimposed DC current usually requires
    platinum contacts. It's the oxide layer on other contact materials which
    does the damage. We're only speaking about a layer a few atoms thick, so
    a milliamp or so wetting current is usually sufficient to punch through
    this.
     
    Gaius, Oct 27, 2010
    #5
  6. Is this any use?
    http://www.clare.com/Products/DCTermination.htm

    George
     
    George Weston, Oct 27, 2010
    #6

  7. Try an old GPO phone bell and ring the phone. The bells are ooften on
    Ebay.
     
    brightside S9, Oct 28, 2010
    #7
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