Re: Noisy Phone line when Broadband modem switched on.

On Oct 1, 8:23 pm, Paul <nos...@xxxxxxxxxx> wrote:
DontKnow wrote:
Hi All,

Many thanks for your inputs!!

I do currently have a filter fitted, (it came with the modem as a package),

What happens is that I have the telephone cable go into the filter and the
modem line goes to the modem and off to the computer and alaso there is an
output for a telephone connection.  When I insert the telephobne jack into
the filter output and listen to the dial tone , yiou can here the
interference (only when the modem is turned on). I f the modem is turned off
the interference goes away.   I don't think that it is the filter, my
thoughts are that it is the modem is creating the interference??

Do you think this is correct??
( I am thinking of purchasing a new modem)

Cheers,

"Paul" wrote:

Leythos wrote:
In article <o9Odnbp_SZZ5JlnXnZ2dnUVZ8tedn...@xxxxxxxxxxxx>,
gez...@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx says...
"Bob" <grafix...@xxxxxxxxx> wrote

You are listening to the broadband carrier.  Every normal telephone on
the system requires an filter to be inserted in the line to block it.
In practice if all your telephones meet at one point before connection
to the incoming line then a single filter at that location will do the
job.   If your broadband modem has been installed correctly then it
should be connected to the ADSL side of such a filter.  It should
therefore have an unused telephone socket on it.
Do you have the filter on the -modem- line or on the -phone- line? AFAIK,
you can't use a filter on the line coming into the modem.
Isn't this thing called a "splitter" not a "filter"?

On my system:

wall outlet >> wire >> splitter >> wire1 >> telephone
                                             >> wire2 >> modem

That is, a single wire from the outlet in the wall goes into the splitter
from which two wires emerge, one of which goes to the telephone and the
other of which goes to the modem.
DSL uses a FILTER that splits or a inline filter.

The filter has to be connected to ALL devices EXCEPT the DSL modem.

The terminology and devices tend to vary a bit from country to country..
I was hoping to find some nice pictures, of how to set up ADSL, but
couldn't find a single web site that covered the variations.

This paper, starting at PDF page 61 and figure 3, shows some examples.

http://www.uh.edu/~fzellner/adsl.pdf

For example, where I live, it is Fig.6 on PDF page 68. Each phone has
a low pass filter installed in-line with the phone wire, to cut off the
higher frequencies of ADSL. The path to the ADSL box, has no filter
in line with it, because it needs the high frequencies to work. My
ADSL kit (suitable for installation by the end user) consists of an
ADSL modem and four phone filters. That allows up to four phones to be
used.

The frequency range on the phone cable, is divided into bands. The red band
(4KHz and below) is used for telephone audio. 26KHz to 138KHz handles
uploading. 138KHz to 1104KHz handles downloading, which is why downloading
is faster (asymmetric band plan). For the lucky customers with one of
the higher speed ADSL standards installed at their phone company, the
frequencies stretch out to 2208KHz. (Mine only goes to 1104KHz.) The
phone filter is needed, so only 4KHz and below is passed to the telephone.
So the phone filter keeps the red band, and throws away the blue and green.

http://www.aaisp.net.uk/i/adslfreq.png

ADSL is distance limited, so there is a trade off between distance and
download speed. They can offer a lower speed package, and use double
the amount of wire from the telephone company. But in a lot of cases,
it is lousy house wiring (like in my house), that ruins ADSL. Corrosion
in connectors and the like, can upset it.

    Paul

The splitter concept used in Europe, seems to be the same as our in-line
filter, except the box has two output connectors.

http://adslm.dohrenburg.net/troubleshoot/splitter.php

They show a schematic of a splitter here.

http://adslm.dohrenburg.net/images/splitter-diagram.jpg

Due to the low frequencies involved on the filter circuit, the components
must be physically large. In this case, the four inductors are relatively
large coils of wire, to get a high inductance in a small space.

http://adslm.dohrenburg.net/images/inside-splitter.jpg

OK, so what could be happening ?

I'll redraw their diagram, like this. The ADSL Modem jack, has
no filtering in its path. The phone has the 4KHz LPF low pass
filter.

                            +----------------------------------+
                            |<--------- Splitter Box --------->|
                            |                                  |
     From_Phone_Company -------+------ Filter --- Phone_Jack ----- Phone
                            |  |
                            |  +----------------- ADSL_Jack ------ ADSL Modem
                            |                                  |
                            +----------------------------------+

If the filter circuit malfunctioned, then normal ADSL noise could
leak through (aliased down into voice band).

On the other hand, if the ADSL Modem malfunctioned, and *injected*
voice frequency noise (below 4KHz), the filter is fully justified
to be passing that to the phone.

So, you're right, it could be the ADSL modem that needs replacing.

I'd try these steps.

1) Make sure that the wire leading to the phone, from the splitter,
    is not twisted, coiled or bundled with the ADSL wire leading
    from the splitter. The wires should have some separation between
    them. Otherwise, there could be crosstalk coupled into the
    phone line, which is now, after the filter.
                    _______
                   /        Phone
         ---------+                  Keep wires separated!
                   \_______
                            Modem

2) Replace the splitter and try another one, on the chance that the
    super-simple and reliable filter circuit, has failed. As the
    dohrenburg.net web page indicates, no electrolytic capacitors
    are used in the circuit, so failure due to shoddy materials
    isn't likely. You could have a lightning strike that damaged
    something, but you're supposed to have lightning protection
    near the demarc (where the phone company wire ends, and your
    wiring begins).

3) Replace ADSL modem, as you've now replaced everything else.

If the noise didn't disappear when the modem was shut off, I'd
have to add other suggestions, but fortunately, that observation
allows me to stop with just three steps.

HTH,
      Paul

The filters Bellsouth sent me all acted as splitters, meaning there
were connections for adsl/phone on each of them. They recommended
plugging everything in through filters, and I never had any problem
with them.
.

Relevant Pages

  • Re: Impact of hardware with bad SNR & Attenuation
    ... > out which things the filter will mess up). ... by the bell wire of the extensions feeding back & mixing with the ADSL ... > Reading between the lines here, a good modem is better at dealing ... attempting to negotiate a connection with the exchange).. ...
    (uk.telecom.broadband)
  • Re: Noisy Phone line when Broadband modem switched on.
    ... modem line goes to the modem and off to the computer and alaso there is an ... the filter output and listen to the dial tone, ... In practice if all your telephones meet at one point before connection ...   If your broadband modem has been installed correctly then it ...
    (microsoft.public.windowsxp.hardware)
  • Re: 9-11 video: best i have seen yet
    ... This would short out the ADSL signal and cause the modem to lose sync. ... filter, but remember you would need a BT>RJ11 lead (in fact an old ... analogue modem lead) not the RJ11>RJ11 that comes with the ADSL ...
    (uk.politics.misc)
  • Re: Cable length between filter and modem
    ... > What is the maximum, sensible, cable length that can be used between an ADSL ... > filter and an ADSL modem? ... As the filter does nothing at all for the ADSL signal, ... wiring) is small enough to allow a workable signal through. ...
    (uk.telecom.broadband)
  • Re: Windows XP Fax
    ... I have a line from ADSL Modem going into splitter ... You CANNOT fax using a DSL modem. ...
    (microsoft.public.windowsxp.print_fax)
Loading