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VOIP to analogue phone adapter.

Discussion in 'General Electronics Discussion' started by tmetford, Jun 10, 2013.

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  1. tmetford

    tmetford

    16
    1
    Apr 14, 2011
    I would like to know if a DSL/analogue phone filter/splitter (the small box with a DSL and phone socket that is usually supplied with the router when you buy a contract for BroadBand), be adapted to enable an analogue telephone to be used on a VOIP phone socket (i.e. the VOIP socket that's available on the back of my fibreoptic Broadband router)?

    I was thinking that by replacing the ordinary BT - type phone jack on the splitter with an RJ11 jack, you could then plug that into the VOIP phone socket and then plug the analogue phone into the BT - type phone socket in the splitter.

    May be it's a case of try it out, unless there's some good reason not to meddle with it in an attempt to save myself £40 or so buying a VOIP to analogue adapter.

    Best wishes
    Tim
     
  2. poor mystic

    poor mystic

    1,071
    33
    Apr 8, 2011
    I think your main problem will be that your telephone is a 2 wire device whereas you have a 4 wire signal.

    In other words the telephone is designed to separate the send and receive signals from the 2 wire line, while in VOIP there's no reason to go 2 wire - the signals are never mixed onto a single pair of wires in the first place.

    It might be possible to design a simple resistive "hybrid" to convert between 2W and 4W. This would require some knowledge of the output and input impedances (let's quite reasonably hope they're resistive) of the soundcard. The telephone itself will work satisfactorily with 600 Ohms.

    Perhaps you could read up and tell us how good your understanding of the problem is, and whether you'll be able to determine the impedances I mentioned. Although the article pointed to by this link (http://en.wikipedia.org/wiki/Telephone_hybrid) doesn't go into resistive hybrids (which are too lossy for the big world network) it describes the problem and some less lossy solutions.

    Resistive hybrids have 1 huge advantage: simplicity. Only 4 resistors are required.

    This idea I've proposed is not a long shot, but I haven't actually tried it, either. If you're interested I'll draw and explain the circuit.

    :) Mark
     
  3. tmetford

    tmetford

    16
    1
    Apr 14, 2011
    Thank you for your help.

    Hi Mark, and thanks for your insight into the problem. I shall read up on the matter and, if I think I can get to grips with it i'll get back to you.
    Kind regards
    Tim
     
  4. poor mystic

    poor mystic

    1,071
    33
    Apr 8, 2011
    The theory can look very scary - lots of new big words. I would have drawn the circuit and explained it already (you'll be surprised at how simple it is) but that I'm tired.
     
  5. Raven Luni

    Raven Luni

    798
    8
    Oct 15, 2011
    VOIP (voice over IP) is an internet protocol, there is nothing physical about it. I used to write VOIP software for a living. A VOIP phone can be in the form of an application that runs on your computer, or you can have a physical (dedicated) device. These are what you most commonly find in office phone systems. They use an ethernet connection and plug directly into a router. So basically that socket on your router youre talking about is an ethernet port (or a dumbed down version of one anyway depending on the router's firmware).

    A DSL splitter is a different thing, and nothing to do with VOIP. The job of these is essentially to multiplex your phone line. They separate the audio band (about 4K or less) used for voice calls from the data band used for internet. Without one of these devices, a normal phone call would disrupt your internet connection.
     
  6. poor mystic

    poor mystic

    1,071
    33
    Apr 8, 2011
    Ahh, thanks Raven.
    I might have been fooled by lack of familiarity with modern connector names. My post is all about how to deal with the analogue side, and as far as that goes I stand by it.
    I never imagined that the OP might believe he could plug a phone into his digital stream, but it's a mistake that somebody will make sooner or later u guess.
     
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