Can ADSL noise come from the exchange

I have two ADSL connections to my office on two separate phone lines. Both have faceplate microfilters supplied by BT. Both ADSL connections are working fine. However, one of the two phone lines is very noisy. On that line, if I unplug the ADSL side, the line stays noisy for 5-10 seconds and then it goes quiet.

I have switched the two faceplates over and the problem stays with the line. The other line is quiet whichever faceplate is connected to it. From this I deduce that the faceplate ADSL microfilters are ok.

I have unplugged the phone equipment from both lines, the problem remains. From this I deduce that the phone equipment attached to the master socket is also not the issue.

I have switched the ADSL modem wires and routers over, again the problem does not move. The other phone line does not become noisy when the equipment form the first is used on it. From this I deduce that the ADSL equipment is not being overly noisy.

The reason I am asking the question about the problem being outside the house, is the 5-10 seconds of line noise that remains *after* the ADSL modem lead is unplugged. The ADSL equipment in the office cannot be the cause of the noise if it is not plugged in.

Am I right in thinking that there is a microfilter component at the other end of the line, at the exchange? If so, could it be this component that has broken down, allowing ADSL chatter to cause audible noise on the phone line.

Cheers

Andy M

In reply to:

---

I have unplugged the phone equipment from both lines, the problem remains.

---

How do you know ? Is that not like trying to see if the fridge light is on with the door closed

The 10s hangover may be the time taken for the DSLAM to stop transmitting after it loses contact with your kit. Once the ADSL signal is off the line the audio noise goes away ?

The noise will remain for 5 to 10 seconds after you have disconnected ADSL, because the exchange will continue to send the ADSL signal until it notices that the ADSL equipment at the subscriber end has been disconnected, which takes 5 to 10 seconds.

> How do you know ? Is that not like trying to see if the fridge light is on with the door closed

A tested, known good phone is still plugged in .. so no

>The 10s hangover may be the time taken for the DSLAM to stop transmitting after it loses
> contact with your kit.

This was the point I was trying to make. It cannot be a badly modulated signal from my end, because it is no longer conected.

> Once the ADSL signal is off the line the audio noise goes away ?

Yes.

As I have verified the effectiveness of the microfilter my end by switching it with a known good and have disconnected the ADSL equipment; the noise can only be coming from the other end or the middle.

If my microfilter was misbehaving, it could still have been the ADSL signal from the exchange end leaking though my microfilter. As my microfilter is ok, where is the noise leaking over?

Andy M

if your filter is inadequate the ADSL signal can generate audible noise from your telephone kit. Two filters in series can help in some cases. Similar things can arise from a line fault.

How do you know your microfilter and phone are good - have you tested them on a different line without audible noise ?

Hi

I've read similar things before. From memory it went something like it is caused by a high resistance connection somewhere along the telephone line that acts like a diode or something similar and causes part of the high frequency ADSL signal to change frequency into the audible part, so getting through the filters.

In otherwords a fault on the line.

> if your filter is inadequate the ADSL signal can generate audible noise from your telephone kit.

> Two filters in series can help in some cases.

I have already tried this .. it makes no difference. It doesn't even make the noise quieter.

>Similar things can arise from a line fault.

This is what I was wondering about and has now been confirmed as a posibility in two replies.

> How do you know your microfilter and phone are good - have you tested them on a different
> line without audible noise ?

Yes I have.

I have two ADSL connections and have switched all the equipment around, including the faceplate microfilter. The noise level does not change on the line in question and the other line remains clear.