Noise margin and phone ringing

[armadillo]

I am not sure if this is a comment on phones and margins, adsl filters or surge protection nor whether this result is expected. This seems a good place to make the comment though as the OP's query has been answered.

I am using a Netgear DG834 (wired) router:

Sync        7616 kbps
Line Attenuation    32.0 db
Noise Margin    9.4 db

It is now connected to the BT master socket via one of these Commatel surge protected adsl filters

http://www.idnetters.co.uk/forums/index.php?topic=22544.msg542963#msg542963

In that thread, I said (correctly) that it had no impact on sync, noise margin, attenuation or throughput, as compared to a conventional adsl filter.

In his thread Faceplates Exposed
http://www.idnetters.co.uk/forums/index.php?topic=22687.0

g7pkf reported that the Commatel surge protector greatly affected his sync speed.

I have just noticed a behaviour with regard to phone ringing and I would welcome comments or explanation, though I do not at present regard it as a problem.

When my phone rings, my noise margin drops by about 3dB while the ringing is in progress. As soon as the ringing stops, either because I answer the call or the caller aborts the call, the noise margin returns to its previous value. The noise margin is not reduced during the speaking part of the call, only during the ringing.

This happens during the "ring" part of an incoming call even if there is no phone connected to the line. Note, there are no wired extensions. The 3dB drop in noise margin occurs even when the only equipment connected to the BT master socket is the router, plugged into the RJ11 side of the surge protected adsl filter.

If I connect a phone, the noise margin is not affected by connecting the phone, nor by making an outgoing call.

It appears that part of the incoming ring signal, or its harmonics, is getting through the filtration and being picked up as noise. I emphasise this occurs even with no phone connected.

As a comparison, I tried connecting the router via a conventional adsl filter, rather than the surge protected Commatel filter. The same thing happened: there was reduction in noise margin during the "ring", even with no phone connected. But with the conventional filter, the drop was about 1.5dB rather than 3dB.

Is it usual to get such a drop in noise margin during the ring phase? If not, then this suggests that the conventional filter I tried is either faulty or inferior. And it also suggests that the Commatel surge protected filter is considerably more susceptible to this effect. If there are certain kinds of signal that it is not good at filtering, it might explain why g7pkf reported that the Commatel surge protector greatly affected his sync speed.

I am about to post a cross reference to this post in his thread too.

Note that, if this 3dB drop during the ringing is a property of the surge protected filter, I do not have a problem with that since it does not cause my line to lose sync and I do not get many incoming calls anyway.

But I would be very interested in any explanation anyone can offer.

[Rik]

It's certainly not normal and can indicate an unusual line fault.

[davej99]

It appears that part of the incoming ring signal, or its harmonics, is getting through the filtration and being picked up as noise. I emphasise this occurs even with no phone connected.

I believe an ADSL filter provides a pass through for the ADSL signal from the incoming line to the modem. The filtration only takes place between the line and the phone. If the filter is removed and the modem is connected directly, it will work fine.

Therefore if you remove the filter and phone, connect the modem directly to the test socket with a suitable adapter and call your number you can prove a filter fault if the noise does not worsen, or prove a line or modem fault if it does. In the latter case a modem swap-out will narrow this to a line fault.

The AC ring tone adds to the standing line DC and I suggest can a produce voltage high enough to promote breakdown and noise in a leaky line, or perhaps aggravate a dry joint.

I notice the router in question is a DG834Gv3. I just upgraded to v5 and saw a large improvement in noise performance and sync.
http://www.idnetters.co.uk/forums/index.php?topic=22785.0

[g7pkf]

I agree with davej99.

but also suspect it could be something amiss with the router, have you tried a different router?

with the surge protection filter on my line my modem hated it (even with no phone connected) complaining about un-cancelled echo etc.

Dean

[armadillo]

First, thank you all three of you. Let's see if some additional info can help with an explanation before I start buying more routers or attacking wiring which seems to perform well apart from this issue.

It's certainly not normal and can indicate an unusual line fault.

Maybe we have some clue as what the unusual fault might be? (See below).

I believe an ADSL filter provides a pass through for the ADSL signal from the incoming line to the modem. The filtration only takes place between the line and the phone. If the filter is removed and the modem is connected directly, it will work fine.

I always thought that. But if it were true, then the incoming voice part of the signal would also reach the modem. If the filter provides a pass through only for the incoming adsl as opposed to incoming voice, then it is performing some filtration? I know nothing. I just ask.

Therefore if you remove the filter and phone, connect the modem directly to the test socket with a suitable adapter and call your number you can prove a filter fault if the noise does not worsen, or prove a line or modem fault if it does. In the latter case a modem swap-out will narrow this to a line fault.

My BT socket does not have a test socket inside. There is no socket behind the cover except the one that is visible when the cover is on. The socket is 50mm square and at least 30 years old.

The AC ring tone adds to the standing line DC and I suggest can a produce voltage high enough to promote breakdown and noise in a leaky line, or perhaps aggravate a dry joint.

Would a leaky line or dry joint have any other symptoms?

I notice the router in question is a DG834Gv3. I just upgraded to v5 and saw a large improvement in noise performance and sync.
http://www.idnetters.co.uk/forums/index.php?topic=22785.0

The OP's router was a DG834Gv3. Mine is a DG834v4. (Note, no "G" after the 834. It is not a wireless router. It says DG834v4 on the label).

I agree with davej99.

but also suspect it could be something amiss with the router, have you tried a different router?

with the surge protection filter on my line my modem hated it (even with no phone connected) complaining about un-cancelled echo etc.

Dean

I have not tried a different router. This one is brand new and is the first router I have used. I read what you said about the effect of the surge protection filter on your system. I did not quite understand how you connected it. I also do not know how to get details of un-cancelled echo etc. No doubt, if I need to, some kind soul will tell me how.


This is what my BT socket looks like.


I had some building work done in 2008. A lot of building work. I went away for three weeks and left the builders in the house. Part of the work involved laying laminate flooring and they removed the skirting boards and replaced them with new ones. To do that, they would have had to remove and refit the BT socket. I very much doubt that they got BT to do it for them.

The picture shows the 50mm square BT socket dwarfed behind the surge protected filter. There are three incoming wires but only two are connected. I am not sure if it was always like that. That is probably paint dropped onto the green wire. The photo is clearer than what I can see with my eye and a magnifying glass. The incoming cable comes straight in from outside where there is a round black junction box on the end of the really thick BT cable. The wire would probably originally have come through a hole in the old skirting but it seems the builders have just taken it over the top of the new skirting. The BT socket is mounted upside down.

Should I buy another DG834v4 and try it instead of the brand new one I am using now?
Should I attempt to get anyone to do anything to the wiring?
Should I just leave it alone and accept a 3dB drop in noise margin when the phone rings?

Connection Speed     7616 kbps     
Line Attenuation    32.0 db    18.0 db
Noise Margin    9.8 db    24.0 db

[sobranie]

If you google .....  dect phones causing snr drop .....
you will be amazed at the people reporting similar problems.
I haven't time to nail the probs but if you have an evening or two spare you may find
the answers to your prob.

[armadillo]

If you google .....  dect phones causing snr drop .....
you will be amazed at the people reporting similar problems.
I haven't time to nail the probs but if you have an evening or two spare you may find
the answers to your prob.

It happens with no phone connected.

[davej99]

...... the incoming voice part of the signal would also reach the modem.

This is filtered at the modem. Circuit diagrams show a total pass through to modem.

My BT socket does not have a test socket inside.

Thats OK just plug modem into the socket you have, provided there are no extentions running from it. BT might replace it for you if it looked damaged. Frankly it looks like it has been abused a bit.

Would a leaky line or dry joint have any other symptoms?

You might hear noise on a quiet line test.  Dial 17070 option 2.

I have not tried a different router. This one is brand new and is the first router I have used.

Fine, may be it is OK. Do the test and see what happens.

[davej99]

Sorry, just realised we had got crossed topics here and my last post is not addressing tehidyman's issue. Ignore my ramblings. 

[armadillo]

This is filtered at the modem. Circuit diagrams show a total pass through to modem.

OK.

Thats OK just plug modem into the socket you have, provided there are no extentions running from it. BT might replace it for you if it looked damaged. Frankly it looks like it has been abused a bit.

No extensions. There is nothing wired to the BT socket except the incoming signal.

I just tried connecting the router direct to the BT socket without any filter or surge protector. I used a BT plug to RJ11 connector with about 3 inches of cable between them. The router did not achieve sync at all (the DSL light did not light up).

I know that this connector works because, until recently, it was connecting a different surge protector that I used to use with a modem instead of a router.

So I connected up again via the surge protected filter. Connection fine with a 9.5dB noise margin.

Repeated the test of calling my home number with my mobile.
During ringing, noise margin dropped 1.5dB (like it had done with an ordinary adsl filter).
After ringing stopped, margin recovered to 9.5dB.
Immediately rang my number again.
This time, noise margin dropped 3dB and recovered to 9.5dB immediately after ringing stopped.
Immediately rang my number a third time.
Margin dropped to zero and the router lost sync.
Came back up with noise margin 9.6dB.
Waited 5 mins and called my number again.
This time a 2dB drop.
Waited 2 mins and called agian.
2dB drop
Waited 2 mins and called again.
2dB drop.

Margin is now a steady 9.6dB.

So it looks like there is a cumulative effect if there are several rings in a very short time but a 2 minute gap between calls is enough to allow recovery time to whatever needs it.

Either that or the drop to zero margin was a fluke.
I would rather not provoke loss of sync if I can avoid it. I do not want to end up causing the problem I am trying to avoid (reduction of profile).

This is what those noise margin reductions look like

You might hear noise on a quiet line test.  Dial 17070 option 2.

Neat! It was totally quiet except for the voice saying "quiet line test" every now and then.







I also took this from dmt before torturing the line by ringing it. It will mean more to you than it does to me.

Sorry, just realised we had got crossed topics here and my last post is not addressing tehidyman's issue. Ignore my ramblings. 

Not sure what you mean there. (a) I might be rambling but you are not. (b) I think tehidyman's issue was resolved and I have hijacked the thread! BTW, if a moderator would rather separate this out as a new thread, I would be perfectly happy. Perhaps I should have posted it as "Noise margin and ringing".

[Rik]

I always thought that. But if it were true, then the incoming voice part of the signal would also reach the modem. If the filter provides a pass through only for the incoming adsl as opposed to incoming voice, then it is performing some filtration? I know nothing. I just ask.

The voice is passed through, but I suspect that routers/modems may have a high pass filter. It certainly does not, in itself, affect ADSL, though it will if you trying using an unfiltered phone on the line.

Would a leaky line or dry joint have any other symptoms?

Not necessarily.

I also do not know how to get details of un-cancelled echo etc. No doubt, if I need to, some kind soul will tell me how.

I don't think the Netgear reports that.

The picture shows the 50mm square BT socket dwarfed behind the surge protected filter. There are three incoming wires but only two are connected. I am not sure if it was always like that. That is probably paint dropped onto the green wire. The photo is clearer than what I can see with my eye and a magnifying glass. The incoming cable comes straight in from outside where there is a round black junction box on the end of the really thick BT cable. The wire would probably originally have come through a hole in the old skirting but it seems the builders have just taken it over the top of the new skirting. The BT socket is mounted upside down.

Only two wires are needed. The third wire, if it exists, runs from the master socket to extensions, and this is called the ring wire. If you have any extensions, and it doesn't look like you have from what I can see, remove the faceplate and check if anything is connected to terminal 3. If there is, disconnect it at every socket.

Should I buy another DG834v4 and try it instead of the brand new one I am using now?
Should I attempt to get anyone to do anything to the wiring?
Should I just leave it alone and accept a 3dB drop in noise margin when the phone rings?

Try and borrow a different router to eliminate yours. If that fails, then check for the ring wire. If neither help, and the drop causes no problems, I'd live with it, otherwise contact IDNet.

[davej99]

Thanks for sorting out my posts, Moderators. I was completely lost and forgot who I was talking to. Happens all the time!!

[Rik]

NP, I should have split the thread earlier, Dave.

[armadillo]

The voice is passed through, but I suspect that routers/modems may have a high pass filter. It certainly does not, in itself, affect ADSL, though it will if you trying using an unfiltered phone on the line.

Now that is something I can understand - a high pass filter in the modem.

If Netgear does not report uncancelled echo, then fair enough.

Only two wires are needed. The third wire, if it exists, runs from the master socket to extensions, and this is called the ring wire. If you have any extensions, and it doesn't look like you have from what I can see, remove the faceplate and check if anything is connected to terminal 3. If there is, disconnect it at every socket.

Beautifully clear. No, there are no extensions. I should have remembered that the third wire is the redundant ring wire.

Try and borrow a different router to eliminate yours. If that fails, then check for the ring wire. If neither help, and the drop causes no problems, I'd live with it, otherwise contact IDNet.

Also very clear guidance. Thanks. I have nobody to borrow a router from. Most of my friends are in the internet dark ages. I could buy another router though and then keep it as a spare. Would be specially useful for all those times when someone says "Have you tried another router?" 

In view of what you say, I think I shall shall just live with the drop. If I get no loss of sync over the next month despite incoming phone calls, there is probably no cause for concern. If I have bought a spare router, I could try it after a month or so and then see if it makes any difference.

Thank you for separating out the thread. I should have posted it separately to begin with.

[Rik]

NP.

The third wire is part of a 4-core drop wire from BT. The cable then allows two separate physical lines to be connected from the exchange.

Whereabouts are you in the country?

[armadillo]

Oh, so it is not the ring wire. Never mind. I do not need two phone lines!

I am in Tadcaster, North Yorkshire (a few miles west of York).

[Rik]

I'm wondering if we'd got anyone in the area who could pop round with a spare router? Volunteers anyone?

[Steve]

Has Tadcaster still got the Sam Smiths and the John Smiths breweries?

[Rik]

Thinking of a day trip, Steve?

[Steve]

 

I remember the smell as a child as we used to pass through on the way to the east coast.

[Rik]

Smell, it evokes so many memories doesn't it.

[Glenn]

The yellow sulphur ladened smoke from the chimney at Bridgewater, the memories. 

[Tacitus]

Jut seen a post further up by Armadillo in which 'uncancelled echo' is referred to.  Can someone tell me exactly what that is, what is its significance and, if necessary how do I get rid of it?

My 2700 reports an uncancelled echo of -9.1dB which it says is OK.

[armadillo]

Has Tadcaster still got the Sam Smiths and the John Smiths breweries?

Yes. The ironic thing is that I don't drink alcohol! The smell rarely seems to be upwind of my end of the town but sometimes is very strong.

[Rik]

Jut seen a post further up by Armadillo in which 'uncancelled echo' is referred to.  Can someone tell me exactly what that is, what is its significance and, if necessary how do I get rid of it?

My 2700 reports an uncancelled echo of -9.1dB which it says is OK.

Typically when you see this uncancelled echo entry it's usually a problem with something inside the house. I always suggest that people simplify their setup when troubleshooting so unplug everything from all of the phone sockets except the router. Go back into the diagnostic page (or refresh it) and look to see if the uncancelled echo error goes away. If it did you can start plugging things back in one at a time and refresh that page each time. You'll be able to determine which device was the culprit when the error returns. It may also be the filter on that device so either replace the filter or use a filter from another socket to test with.