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I've connected the phone line (RJ11) directly into my D-link ADSL router. But the ADSL LED on the router is not glowing, the router is not detecting any ADSL, so dialing doesn't connect. I'm not going to use the phone for voice, so I don't need a splitter as such. Will the ADSL router work like, this? Or I have to have splitter in between?

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up vote 3 down vote accepted

As far as I'm aware without the filter when anyone makes a phone call your internet connection will drop. As you;re not planning on making Voice calls on the line there shouldn't be a problem at all.

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There is no problem connecting the DSL modem directly to the wall jack. I ran for years like this.

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From DSL filter/splitter :

Typical installation for an existing home involves installing DSL filters on every telephone, fax machine, voiceband modem, and other voiceband device in the home, leaving the DSL modem as the only unfiltered device.

Doing so will avoid connection cuts upon incoming calls.

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A DSL filter/Splitter is an analog low-pass filter installed between analog devices (such as telephones or analog modems) and a plain old telephone service (POTS) line, in order to prevent interference between such devices and a digital subscriber line (DSL) service operating on the same line. Without DSL filters, signals or echoes from analog devices at the top of their frequency range can result in reduced performance and connection problems with DSL service, while those from the DSL service at the bottom of its range can result in line noise and other issues for analog devices.

The important things to remember are:

The Filter/Splitter (and your ADSL modem) needs to be connected DIRECTLY to the incoming exchange line and must NOT pass through an In-Line Filter first. All analogue devices/telephones are connected via an In-line Filter.

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Welcome to Superuser! This is a yes-or-no question. Your answer contains much useful information, but does not specifically address the question: will a direct connection harm the modem. – Isaac Rabinovitch Feb 16 '13 at 7:56
@IsaacRabinovitch I agree that he does not simply say yes or no, but he does address it. The modem must be directly connected without any filter in place for it to work. In the splitter that the OP is referring to: the modem side is unfiltered and is a direct pass through, the other side of the filter helps keep the analog equipment from interfering with the DSL connection. – Scott Chamberlain Feb 16 '13 at 9:09

A phone line splitter only needs to be used if you connect a telephone to the same wall jack as your DSL modem/router. No phone to be connected to this same jack? No splitter needed; no filter should be used; no harm done.

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