Asterisk - less PSTN echo via XP100 clone or ATA?

Discussion in 'UK VOIP' started by Matt, Nov 15, 2005.

  1. Matt

    Matt Guest


    As the subject says, which of the above shold give me less echo on PSTN

    Many thanks

    Matt, Nov 15, 2005
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  2. Matt

    Matt Guest

    Sorry shold = should.

    Must use prevew option more...
    Matt, Nov 15, 2005
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  3. Matt

    Jono Guest

    Matt wrote:
    || Sorry shold = should.
    || Must use prevew option more...

    or preview, even?
    Jono, Nov 15, 2005
  4. Matt

    Jono Guest

    Matt wrote:
    || Hi,
    || As the subject says, which of the above shold give me less echo on PSTN
    || calls?
    || Many thanks
    || Matthew

    I wouldn't use the XP100 clone for anything other than testing. the call
    quality is poor. (Lots of clipping seems to occur, at least for me anyway)

    My SPA3000, acting as a SIP trunk, gives me much more flexibility and the
    sound quality is great. Obviously, with [email protected], the ZAP (XP100)
    channels can receive faxes & forward them by email. I've not sussed out how
    to do that yet, with a SIP channel.
    Jono, Nov 15, 2005
  5. Matt

    Matt Guest

    Ooops. I'll blame that on the 3 hours sleep last night, caused by a
    teething 1 yr old.

    Matt, Nov 15, 2005
  6. Matt

    PeterW Guest

    The main problem with the X100P clone is impedance matching. Most seem to
    be 600ohm US standard. In the UK this gives a lot of echo when the device
    tries to transmit to the phone line. The proper Digium card had more
    configurable impedance matching.

    PeterW, Nov 16, 2005
  7. Matt

    Sparks Guest

    Would changing a resistor on the card be an option here?

    Sparks, Nov 17, 2005
  8. Matt

    Matt Guest

    If we knew which resistor, i'd give it a try!

    Matt, Nov 17, 2005
  9. Matt

    alexd Guest

    Perhaps you could cheat, and put the resistance across/in series with the
    alexd, Nov 17, 2005
  10. Matt

    PeterW Guest

    The BT line and phone have a complex impedance (resistance/capacitance).

    The phone terminal impedance is 370 ohm + 620 ohm || 310nf. The network
    input impedance is 300 ohm + 1000 ohm || 220nf.

    I believe that UK networks are designed as 600ohm. I am not sure of how to
    match the two properly. It should be possible with the appropriate circuit,
    but I'm afraid I have forgotten my circuit theory. The problem seems to be
    mainly with echo being reflected back to the phone (ie X100P clone card)
    when it transmits to the line. It seems less noticeable the other way

    Maybe there is a good telecoms engineer out there who could come up with a
    matching circuit which could go between the card and the phone socket as
    part of the interconnecting cable?

    PeterW, Nov 18, 2005
  11. Matt

    PeterW Guest

    Oops... I mean "I believe US networks", not UK...
    PeterW, Nov 18, 2005
  12. Matt

    alexd Guest

    I've got my ATA set up as that, and it works fine.
    Hmm, google for 'vswr matching', perhaps? Also when searching google, try
    impedence and impedance as people spell it differently. Or try:
    You can't be the first person who has ever wanted to connect US-spec
    equipment to a UK line. There's probably a homebrew circuit diagram out on
    the web somewhere. Given that this is also something that applies to
    analogue telephony, maybe you could try uk.telecom?
    alexd, Nov 19, 2005
  13. Matt

    alexd Guest

    X100p cards and their clones dont appear to be configurable for impedence
    [one potential source of echo]. So probably an ATA. Another good reason for
    using an ATA is that if you're using a SIP provider for DID, you can use
    the ATA as a standalone system while taking Asterisk offline to test config
    changes etc.
    alexd, Nov 19, 2005
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