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DAA specifications

Discussion in 'Electronic Basics' started by Watson A.Name - Watt Sun, Dark Remover, Dec 27, 2003.

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  1. Long ago I wondered why the phones and then modems were made the way
    they were, why transformers had the word HIPOT on them, and other
    mysterious things. Then I found out about FCC Part 68, and its
    requirements. Later, I saw some designs that were seriously
    deficient, mainly because they were made cheap to sell cheap. Many
    cheap phones don't even have a transformer. As for the DAA using the
    solid state relay, they don't get into that in this doc.

    I found a document that explains some of the circuits and reasoning
    behind them. Unfortunately this document doesn't go into designing a
    DAA that minimizes RFI, which so often becomes a real problem around
    larger installations. In the circuit shown, I would have made the
    relay dual contacts so that both sides of the DAA are disconnected
    from the line during on hook. This minimizes the unbalance of the
    line. Anyway, now I've learned how to calculate REN, always wondered
    how they figured that. All I knew was that with the usual cap and
    coil, the impedance was several kohms at the ringing freq. Enjoy.
    http://www.web-ee.com/primers/files/AN812_1.pdf

    ~~So Happy Holidays~~

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  2. The answer to your question lies in the telecom safety issues of each
    country.

    The basic safety for telephone equipment is there MUST BE an isolation
    (insulation) barrier between the
    telecom circuits (which have telecom network voltages TNV on them) and those
    circuits which
    which the user may touch (safe extra low voltage circuits- SELV)

    For a simple telephone the isolation is the plastic of the hand peice and
    the plastic of the outer casing of the base.
    Plastic offers insulation ! (thus the whole internal telephone circuit can
    be at TNV potential).

    For a modem the serial port connection is something that the user can touch
    and the users equipment connects to
    (thus most modems have an isolation barrier at the DAA). The transformer and
    opto-couplers offer this isolation.

    The HI-POT test is a High Potential test to test the breakdown of the
    isolation barrier - regaardless if it is a modem transformer
    or the plastic insulation of a standard telephone....

    Telephone safety standards EN60950 (Europe), UL1950 (USA), CSA950 (Canada)


    If you do a search on EN60950 and Transformer ... I am sure you will find
    lots of transformers that are compliant to this standrd.

    JG
     
  3. I asked a question????

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    ###Got a Question about ELECTRONICS? Check HERE First:###
    http://users.pandora.be/educypedia/electronics/databank.htm
    My email address is whitelisted. *All* email sent to it
    goes directly to the trash unless you add NOSPAM in the
    Subject: line with other stuff. alondra101 <at> hotmail.com
    Don't be ripped off by the big book dealers. Go to the URL
    that will give you a choice and save you money(up to half).
    http://www.everybookstore.com You'll be glad you did!
    Just when you thought you had all this figured out, the gov't
    changed it: http://physics.nist.gov/cuu/Units/binary.html
    @@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@[email protected]@[email protected]@@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@[email protected]@@
     
  4. John Smith

    John Smith Guest


    No, you didn't. But thanks for the link you provided.
     
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