Digital Subscriber Line Why is there a DSL jack on a DSL filter?

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Subject Author Date
Why is there a DSL jack on a DSL filter? John Smith 11-12-05
Posted by John Smith on November 12, 2005, 12:28 pm
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I assume a DSL filter filters off the DSL signal. Is that correct?

I just switched to DSL from cable. The kit I got includes three
DSL filters. One end of the filter plugs into a phone jack, the
other end has two jacks, one labeled DSL, the other phone.

If the purpose of a DSL filter is to filter off the DSL signal,
why is there a DSL jack on a DSL filter? (I assume this DSL jack
has unfiltered signal. Is that correct?) Why not just plug in to
the wall jack?

A separate question. The phone box on the outside of the house has
a test jack. What does it do? I plan to plug a DSL filter to the
test jack and have all phone lines connected to the phone jack on
the DSL filter and have the DSL line which is a separate line
connected to the two screws to which the current phone lines are
connected. Is that a good idea? Or should I leave the test jack
alone and cut the wire of the DSL filter and connect the red and
green wires to the screws?

Posted by Clark W. Griswold, Jr. on November 12, 2005, 11:19 am
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>I assume a DSL filter filters off the DSL signal. Is that correct?
>

Yes. DSL uses frequencies higher than those required for voice calls, but some
phones don't handle those frequencies very well, thus infiltered it results in a
"hiss" for voice calls.

>I just switched to DSL from cable. The kit I got includes three
>DSL filters. One end of the filter plugs into a phone jack, the
>other end has two jacks, one labeled DSL, the other phone.
>
>If the purpose of a DSL filter is to filter off the DSL signal,
>why is there a DSL jack on a DSL filter? (I assume this DSL jack
>has unfiltered signal. Is that correct?) Why not just plug in to
>the wall jack?
>

Flexibility. You put the splitter filter near your computer so that the DSL
modem is near your router and plugs into the unfiltered side. The other filters
go by phones, which plug into the filtered side.


>A separate question. The phone box on the outside of the house has
>a test jack. What does it do?

If you are having problems with your voice phone line, you take a known working
phone to that jack and plug it in. If you can make calls, the problem is within
your house (either wiring or phones). If you still have problems, you call the
phone company.

>I plan to plug a DSL filter to the
>test jack and have all phone lines connected to the phone jack on
>the DSL filter and have the DSL line which is a separate line
>connected to the two screws to which the current phone lines are
>connected. Is that a good idea? Or should I leave the test jack
>alone and cut the wire of the DSL filter and connect the red and
>green wires to the screws?

Why on earth are you doing either of those? Just hook the DSL modem at a
convenient point inside the house.

Posted by David Schwartz on November 12, 2005, 11:02 am
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>>I plan to plug a DSL filter to the
>>test jack and have all phone lines connected to the phone jack on
>>the DSL filter and have the DSL line which is a separate line
>>connected to the two screws to which the current phone lines are
>>connected. Is that a good idea?

Yes, just make sure you get a splitter designed for that,

>> Or should I leave the test jack
>>alone and cut the wire of the DSL filter and connect the red and
>>green wires to the screws?

Get a splitter and connect it properly.

> Why on earth are you doing either of those? Just hook the DSL modem at a
> convenient point inside the house.

That has a lot of downsides, and I only recommend it if four things are
true:

1) You aren't a hardcore user who wants every bit of performance out of
your DSL connection.

2) You don't have or plan to add devices like alarm systems to your
phone line.

3) You rarely if ever change around your phone wiring. (For example, you
don't have a fax machine that you sometimes connect to one phone line,
sometimes to the other, and most of the time it's in a closet.)

4) It just happens to work for you, that is, you get the fastest DSL
speed available for your service class, see few if any data errors, and
almost never lose sync.

The problems with using cheapo filters are many:

1) If you have a jack anywhere in your house that you don't use that's
in poor condition, it will degrade your DSL quality.

2) If you have or add an obscure device somewhere that you forgot about
(satellite receiver, alarm system, answering machine), it can degrade your
DSL quality.

3) When you add new devices, you need to add new splitters.

4) If any of the wiring in your house is low quality and/or goes past a
source of noise, it will reduce your DSL speed or cause you to lose sync
intermittently.

DS



Posted by Ken Abrams on November 12, 2005, 6:16 pm
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> If the purpose of a DSL filter is to filter off the DSL signal,
> why is there a DSL jack on a DSL filter? (I assume this DSL jack
> has unfiltered signal. Is that correct?) Why not just plug in to
> the wall jack?
>

It is a matter of convenience.
They assume that at one location you will want to connect your DSL modem to
the same jack where you have a phone. If that is not the case and all you
will connect to that jack is the modem, then no, you don't need a filter
there.

> A separate question. The phone box on the outside of the house has
> a test jack. What does it do? I plan to plug a DSL filter to the
> test jack and have all phone lines connected to the phone jack on
> the DSL filter and have the DSL line which is a separate line
> connected to the two screws to which the current phone lines are
> connected. Is that a good idea? Or should I leave the test jack
> alone and cut the wire of the DSL filter and connect the red and
> green wires to the screws?

If the DSL really comes in on a "separate line" then this whole discussion
is moot and you don't need any filters at all. Connect your DSL line
directly to the modem (only) and you are done.




Posted by John Smith on November 12, 2005, 1:59 pm
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Ken Abrams wrote:
>
> If the DSL really comes in on a "separate line" then this whole discussion
> is moot and you don't need any filters at all. Connect your DSL line
> directly to the modem (only) and you are done.
>

Thanks to all those who replied to my question.

Sorry that I did not make myself clear. I only have one telephone
number but there are five lines going into my house from the phone
box. One of the lines is dedicated for DSL. That line only goes to
one jack. That's what I meant by "a separate line". Now I see the
term has a totally different meaning to other people. Oops!

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