Will connecting the phone line directly without the splitter cause any harm to my ADSL router?

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?

obviously not.. and I suppose the question would apply to what americans use too, DSL. If it did damage, then there'd be some results on google about it, anyhow, people don't use adsl much anymore.. as they use eg fibre.. on my fibre connection my device is apparently a VDSL router!

i'd add that you should put a DSL filter in every socket. My ISP told me that and so does this link here greedhead.net/do-i-need-an-adsl-filter-on-every-socket

6 Answers 6

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.

He subject asked if it'd damage his router, the answer is NO. It's good to address all the things that he asked.

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

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.

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.

@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.

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.

The main purpose of an ADSL filter is to filter the phone from the line, which isolates the effects of the phone from the line and hence the modem, and also filters modem traffic out of the phone

ADSL filters consist of:

1. The female BS6312 port on it is connected to a low pass filter, which is connected to the line via the male BS6312 exuding from it.
2. There is often a secondary RJ11 port for connecting a modem, and it's just directly to the line without filtering.
3. Some ADSL filters high pass filter the ADSL frequencies on the RJ11 port as well, but the assumption is typically that there is a high pass filter built into the modem, so this is uncommon I think, and doesn't happen on the filters I've used.

The effect of 1. (the main function) is:

• you don't get frequencies outside of 4khz making a noise on the phone
• more power in the frequencies outside of 4khz is delivered to the modem rather than to the phone, because it is a parallel path, and the low pass filter presents more impedance in the phone path, so more power is dissipated over the smaller modem impedance, meaning greater SNR per DMT bin. The filter reduces the length of the bridge tap effect of the phone attached to the line to a fraction of a wavelength, rather than having power loss due to reflections because the reflections will now all be superimposed. Less signal travels down the phone cable and reflects off of the phone because there is a high impedance of the low pass filter that reflects most of the power in the way.
• the phone impedance transiently changes from time to time; for example, taking the phone off the hook can see the impedance drop to 600Ω from several mega ohms, this would interfere with the DMT subchannels and would likely cause a modem retrain, which can take up to 10 seconds without fast retrain mode. When you use the filter there is now a low pass filter in series, the change in power delivered to the modem due to the alternate phone path opening at that moment will be much smaller as there is already a high impedance on the phone path.

The last 2 points demonstrate how even though POTS and ADSL are in different frequency bands, and are spectrally compatible, interference still occurs due to the impedance response of the phone and the modem outside of their respective bands of interest.

For this type of filter above (consisting of function 1. and 2.), it can be used as a simple adapter for a DSL cable phone, for connecting a RJ11 male to BS6312 female, by plugging the phone in the DSL socket, but does not perform the filtering. It can also be used to connect an RJ11 male coming from the line to a BS6312 male coming from the phone, and the BS6312 male coming from the adaptor is left hanging unconnected – in this case it does filter the phone from the line. You need to filter all phones from the line regardless of whether the modem is there or not – the DSL connection is just a regular handy socket attached to the side providing a direct connection to the line that appears on some filters. You get filters just for the phone without this extra socket.