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Phone noise

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Phone noise

Hi

I'm fairly new to broadband at home, and having insalled my PCI modem a week ago I have a problem with noise on the phone while the computer is off.

My BT connection is via a two-port extension box. The phone and fax are plugged into a filter on one side and the ADSL is plugged straight into the box on the other. While the PC is on the phone line is fine, but as soon as the PC is switched off the noise on the line arrives. The noise stops when the ADSL cable is unplugged from the box.

A friend who is also on PlusNet has suggested it's likely that the ADSL signal voltage is lower with the PC on because the modem is drawing a current that would cause it to drop, and rising when the PC is switched off, causing the interference. Can anyone suggest how I can solve this problem? Any help is grateful appreciated.

Best wishes
Peter
15 REPLIES
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Phone noise

Your modem may not require a filter, check with supplier or supplied documentation.
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Re: Phone noise

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A friend who is also on PlusNet has suggested it's likely that the ADSL signal voltage is lower with the PC on because the modem is drawing a current that would cause it to drop, and rising when the PC is switched off, causing the interference.


The modem draws no power off the DSL signal. In fact there has to be power isolation between the PC and the DSL line to avoid the voltages present within a PC getting into the phone system.

You should have the modem plugged into the correct RJ11 socket on the filter and not separately into the wall socket, this will balance the impedance.
I have to ask the question, how did you manage to plug the modem directly into a BT socket ??, you must have used an old 56K dial-up modem cable, these can be wired incorrectly for specific DSL modems with regard to earth paths.
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Re: phone noise

I have tried the connection with no filters at all and it doesn't help.

I was using my old 56k phone cable simply to avoid having to fish out loads of wiring and disturb a whole load of other wiring stuffed behind the computer! Lazy, I know, but it's a jungle back there. I've now replaced the old cable with the RJ11. This goes into the filter on one side of the phone box, while the telephone and fax go into a second filter on the other side of the box (its a double-socket phone box).

When the PC is turned off the noise isn't so bad, but there's still a high-pitched whine on the line. I wasn't sent the type of filter shown in the diagram on my paperwork (a kind of square box with a 5cm lead and a connector at the end of it), instead, mine looks more like an ordinary telephone splitter, but with a label on the side which says "Linkcom LAF0026". I was sent two of these and am using them both.
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Phone noise

And to confirm, the noise goes away when you unplug the ADSL modem?
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Re: phone noise

Yes, the noise goes away when the ADSL is unplugged from the telephone box, and also when the PC is switched on (to start booting up, not when ADSL connects), and is fine until the PC shuts down.
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Phone noise

I wonder if the PCI modem is configured as LAN and has "wake up on LAN" configured ??

With everything connected, switch of the PC and unplug the PC from the mains and see if the noise is still there (this will romove any possibility of "standby" being at fault.)
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Re: phone noise

Hmmm. That's strange. I did switch off and unplug the PC, and the phone line sounded normal. Then I plugged the PC back in and the phone still sounded normal. The only noise was a bit of background mush which I get on my cordless phone. I'll try it again to be sure, but it looks promising.
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Re: phone noise

It did the same again. The second the PC powered down the same high-pitched whistle was back on the phone line. I unplugged the PC and the whistle was gone, and stayed gone when I plugged the PC back in.
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Phone noise

If your getting noise while the modem is off, have you tried using a corded phone to check for noise, in the master socket?

I had the same problem and it turned out to be a wiring fault at the local green box.
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Phone noise

Did your green box have doors on it?
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Phone noise

This would appear to be something related to the "standby" state that modern PC's are in while supposed turned off.
Check in the BIOS to see if there is a Wake on LAN (WOL) or Wake on Modem Ring and turn these off. Similarly check if there is similar in the PCI modems manual.
Niether WOL or WOR should really have any effect on a DSL modem, however, it is work a look.
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Re: phone noise

I don't have a corded phone to test with, just the cordless phone. My neighbour is a BT engineer, and he's done a few basic line tests for me with no problems found. Also, he's on broadband too, and we use the same overhead telephone wires to the nearest junction.


I've checked the BIOS but I can't find a Wake on LAN, WOL, or Modem setting. Anything that does have "Wake" in the title is disabled.

The modem, supplied by PlusNet, didn't come with a manual but there is one relating to ADSL set-up on the accompanying CD. I don't have the Bridge driver installed, and I don't know if this would make a difference. Also my Network Connection TCP/IP settings are obtaining both IP address and DNS server address automatically, just in case this effects anything.
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Re: phone noise

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I don't have the Bridge driver installed, and I don't know if this would make a difference. Also my Network Connection TCP/IP settings are obtaining both IP address and DNS server address automatically, just in case this effects anything.


These settings will have no effect on the noise you get on the line when the PC is off.
Also, a line fault is extremely unlikely.
It is almost certainly something to do with way modern ATX machines always have power to the motherboard and some cards to allow auto wakeup functions. The fault would appear to lie within your PC.
How to stop the noise when the PC is off, I havn't a clue - use a switched plug and turn off all power or change to a modem router.
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Phone noise

The standby current is only used to supply power for S3, suspend to ram. Check in BIOS, and change to S1 if S3 is selected (it is unlikely you will use str). This is usually the top of the list in advanced power management. This will not stop standby current, this is present all the time power is present to your PSU, but if S3 is consuming this current, it may explain the noise. A better quality PSU may help.