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    A “Milliwatt (102 Type) Test Line” is a signal generated from an Access Service Provider end office to the customer’s location for the purposes of transmission measurement, that is, testing the line quality and loss of transmission. The generated signal is a 1004 Hz tone at 0 dBm, which is the equivalent of 1 milliwatt of continuous power dissipation, hence the name.

    Milliwatt test tones are often found at NPA-NXX-0010.

    Numbers which have been reported to us as milliwatt test lines include:


    If you know of a functioning milliwatt test line, please add it in the comments.

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    1. Kirk Cross

      6 February, 2022 at 4:03 am

      Almost every exchange in the 213 and 323 NPAs have a milliwatt test at NPA-NXX-0002.

    2. Mark

      25 April, 2013 at 2:22 am

      (313)-937-9996 also seems to be a millliwatt

    3. Dave

      17 January, 2012 at 4:42 pm

      When I was a kid (1960’s), every exchange in my area (Wash DC) + 9949 gave a steady tone – probably the milliwatt test tone.  9947 gave an oscillating tone similar to a slow police siren.  What exactly were these tones used to test?

      • DanielMemetic

        29 April, 2013 at 5:21 pm

        They’re used to test line quality and loss in transmission between the service provider and you as the customer. I’ve updated the article to make it a little clearer. Thanks for the comment!

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