Telephone Experts Please - Part 2

Hi all

OK so I went round to mother's last night armed with my own cordless phone (Siemens).

The findings seemed inconsistent and were as follows:

Plugging our phone in showed similar levels of crackle-hiss noise as mother's. Unplugging the upstairs phone and filter seemed to massively reduce the noise. There was still some noise present when plugged direct into the master box rear connection (with filter included). I tried turning off fridge/freezer and heating to check that this was not the issue.

One very strange anomaly noted....

With everything plugged in: twin cordless phone and wireless modem into front connection of masterbox via splitter downstairs - and - corded phone via filter upstairs: When a call is made from the upstairs corded phone, the modem dropped its connection - then reconnected when the call was terminated.

Does this indicate a dodgy splitter? At first I thought maybe I was just unlucky and had 2 dodgy splitters. But then ISTR that they tried a cordless phone before they had broadband and gave up because of the interference.

Thanks to all

Phil

Reply to
TheScullster
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Have you got the sort of master socket where removing the faceplate disconnects the internal house wiring and leaves a single socket behind it connected to the line? If not, would be worth fitting one. Then plug an ordinary cabled phone into the line, dial one digit to get rid of the dial tone and listen to the line noise.

Reply to
Dave Plowman (News)

"Dave Plowman (News)" wrote

Thanks Dave

Yes the master has a removable faceplate. I tried this and plugged direct into the internal master socket and there was still discernible, though less I think, noise.

The one thing I may have missed though (talking to colleagues).... I was plugging the phone into the master socket with a filter attached. According to colleagues, the filter is not necessary if all other equipment (ADSL stuff in particular) is disconnected - is this correct? Therefore the problem may have still been with the filter.

Phil

Reply to
TheScullster

(In answer to you later post) I believe the ADSL side / link is only established over the line when the kit at the remote end (your ADSL modem / router) initiates it (to the DSLAM or whatever it is). So, yes, you wouldn't need the filter if the ADSL service wasn't on or if you weren't bothered about it being knocked out when you used the line.

Cheers, T i m

p.s. A mate has a BT / ADSL line and I've noticed quite a bit of 'line noise / mush' when I've used his phone. We have cable so not really that familiar with such things. ;-)

p.p.s. I was at a local shop a while back when I overheard one assistant asking the other 'if they had finished on the Internet as they wanted to use the credit card machine and that would cut the broadband off ...'.

When the customer was gone I suggested that wasn't 'right' and they replied that that was how the people who put the card machine in said it sometimes worked? I offered to check it out for them and as they knew of me (I was friends with the shop next door) they did. It turned out (as I suspected it might) that the filters / splitters were all in the wrong places and a few re-plugs got the card machine working without knocking the bb out. ;-)

Reply to
T i m

On 19/07/2011 09:11, TheScullster wrote

Yes. The filter prevents the higher frequency ADSL signals from reaching the phones, these signals are only present when you've established an ADSL connection so there's no need for any filters if you don't have an ADSL router or modem connected.

That could be a possibility.

Reply to
Mike Clarke

On mine, the filter is in the faceplate part. Remove that reveals a socket corrected direct to the line. It also disconnects the internal house wiring. If you have a noisy line then, it wants sorting.

Reply to
Dave Plowman (News)

Life would be simpler if you tried just a plain simple corded phone.

It is quite consistent with what you have experienced which is probably ADSL noise.

Or you have faulty wiring or a faulty modem/router. From what you describe you do not have interference from any external source but are hearing a high level of noise produced by the ADSL signal.

If the upstairs phone is both noisy and dropping the ADSL data then it isn't being filtered. This may be due to a faulty filter or faulty wiring. The fault may be in the filter design so if possible when testing use another brand (some cheap ADSL filters connect the pin 3 ringing signal directly through instead of using only pin 2and 5 and a separate ringing capacitor in the filter).

The ADSL filter is really a "not ADSL" filter - it filters the ADSL signal from the line to stop phones both affecting the data stream and preventing the ADSL signal producing audible noise on the phone.

As the exchange equipment will continue to send data for some time after the modem is disconnected the first check is to take a nice simple wired phone and plug it in to the test socket so that and nothing else in the house is all that is connected. If you still hear noise leave it plugged in for half an hour and check again, it will probably be quiet.

Leave the ADSL modem OFF and put the face plate back to re-instate the internal wiring. The phones should be quiet.

Switch the modem back on and within a short time the noise should return.

If this is the case use an ADSL filter in the test socket (so everything else in the house is disconnected) plug in one plain ordinary wired phone connected via an ADSL filter and the ADSL router.

If there is still noise swap the ADSL router/modem for another - I have come across two Netgear routers which, when hot, generated large amounts of ADSL noise in the audio band where an ADSL filter has no effect.

If, with two routers and a plain wired phone and using only the test socket you still have a problem it is likely to be a dry joint on the external wiring - these can act as diodes and allow the ADSL signal onto the audio part of the system.

If that works OK you need to work your way through the house wiring. Start by unplugging everything from telephone sockets in the house and plugging your test phone and modem into the NTE5 faceplate. If there is no noise re-instate everything one item at a time making sure each device has an ADSL filter.

If it was an analogue phone that is completely irrelevant.

Reply to
Peter Parry

"Peter Parry" wrote

Peter

Thanks for detailed diagnostic.

If the router is not "in use" (i. e. there are no PCs communicating/surfing) is it still generating some form of ADSL signal that will create noise?

Phil

Reply to
TheScullster

I once had crackling noise, very variable, which was traced by a BT engineer's standing wave gizmo to the overhead twin cable from my eves to a communal telegraph pole across the street. The copper wire was found to be corroded through in 6 places. This was before ADSL so only 40 kbps, but it was a bit intermittant on the modem.

Is this anything like your external connection.

rusty

Reply to
therustyone

Yes, the radio frequency ADSL signal is present if the router is connected, even when no computer is being used.

Reply to
Peter Parry

To clarify, different phones will draw a different static current (AIUI) and affect the conductivity of moist copper verdigris in a broken cable. So the cordless phone is probably a different loading to the original phone and could show different fault conditions.

rusty

Reply to
therustyone

As long as it is synched, the carrier signals are there.

Reply to
The Natural Philosopher

Phones are required to reject spurious RF signals. If they don't, broadcast radio (which is in the same band as ADSL) will interfere with the phone.

It may return but it sure as hell shouldn't return. Something is faulty if it does and it isn't normal to have "ADSL noise". If you have working phones you should not get noise from the ADSL even without the filters.

They may well have been faulty and generated noise but to call it ADSL noise is at best misleading.

You would get noise induced from broadcast radio too. The ADSL router would be reporting poor signal quality and throughput would be lower than expected. It may be consistent with the ADSL dropping when the upstairs phone is used as dry joints behave differently when there is DC flowing.

Has the OP tried the upstairs phone in the BT line socket behind the face plate to see what happens?

Reply to
dennis

Oh dear dennis.

It IS normal to have ADSL noise.

Because no wire and no connection is perfect, and down conversions into the audio band are absolutely inevitable.

Reply to
The Natural Philosopher

Don't talk rubbish. The ADSL filters would have no effect on them as they are audio signals and you would get them all the time on every line and ADSL would never have been useable.

You really do talk cr@p.

Reply to
dennis

Phones are very simple devices with a low impedance at RF and relatively high signal levels. They are inherently well protected against RF. ADSL however is not a spurious signal but one coming in on a balanced line.

To get significant noise something has to turn that RF into AF - this can be a faulty joint or faulty equipment.

It will return if the fault is still there. This is a process called "fault finding", a systematic identification of cause to determine the cure.

correct

correct

Wrong. The upstream channel starts at 25kHz and ends above 1MHz. The signal level is sufficiently high to cause some demodulation within the phone so some level of ADSL noise and speech distortion is usual if no ADSL filter is installed. The filter has two purposes, one is to prevent the phone, which has a very low impedance at RF, shorting out the line at RF preventing ADSL from working, the other is to remove the RF from the audio channel.

Not normally you wouldn't, the balanced line reduces most of that to insignificant levels. The ADSL signal is at a much higher level than induced interference.

Reply to
Peter Parry

I disagree, there is no reason why a phone should demodulate the ADSL signal. There is a big gap between the top of the audio and the start of the ADSL channels. There are phones that will and they should be consigned to scrap. There is more chance that the joints in the aluminium cable will demodulate it, which is why aluminium cable is a real pain for ADSL.

I assume you mean the short bit of cable between the line and the phone, it doesn't remove it from the line.

That would be entirely dependent on the line.

Reply to
dennis

Have you never tried plugging a cable phone into a line with an ADSL carrier sans filter? I have. You get very audible constant 'noise'.

Reply to
Dave Plowman (News)

There are a few options here. A broken or missing splitter can result in a hiss being detected in some handsets. In theory the handset ought not be worried by the ADSL signal since its well out of its bandwidth, however in reality you do find a few that will have a problem.

With a phone plugged into the internal test socket on the BT master (i.e. take the bottom bit of the faceplate off to disconnect the extension wiring (which should be wired to the faceplate) and leave the internal socket exposed), do a "quite line" test by dialing 17070 and selecting it from the menu. You should then be able to hear basically nothing except the normal side tone on the phone - no his or crackle etc. If you get noise here, then report it as a line fault.

Reply to
John Rumm

This is correct. They don't, and you do.

and ADSL would never

They are 50dB or more down on baseband signal levels. That does not make the phone unusable. Just hissy.

It has no effect on the ADSL usability at all.

NO, that's you dennis.

Reply to
The Natural Philosopher

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