DG834G Noise Margin plummets when LAN PC connects?

I have been monitoring my noise margin recently over the past few days and
notice that when a PC on the LAN is switched on the noise margin of the
DG834G immediately plummets down from around a steady 15dB to around 3dB
(sometimes even lower, and once it went to -2). Anyone know whats going on?

What has the LAN connection got to do with the noise margin of the ADSL
connection?

Thanks

In message <(E-Mail Removed)>, Mike
<(E-Mail Removed)> writes
>I have been monitoring my noise margin recently over the past few days and
>notice that when a PC on the LAN is switched on the noise margin of the
>DG834G immediately plummets down from around a steady 15dB to around 3dB
>(sometimes even lower, and once it went to -2). Anyone know whats going on?
>
>What has the LAN connection got to do with the noise margin of the ADSL
>connection?
>
>Thanks
>
>
Probably a bad power supply in the PC generating RF noise that is being
picked up by the phone line.

Swap that PSU out, and you will potentially see an increase in ADSL
speeds (assuming you are on a Max service), but it will take some time
for the exchange to adapt.

The Max service attempts to stabilise the noise level at 6db. If it
can't it increases the noise margin in steps. Sounds like your PC has
"persuaded" the exchange you have a noisy line and the exchange has
increased the noise margin & dropped the speed.
--
Peter R Cook

"Invalid" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
> Probably a bad power supply in the PC generating RF noise that is being
> picked up by the phone line.
>
> Swap that PSU out, and you will potentially see an increase in ADSL
> speeds (assuming you are on a Max service), but it will take some time
> for the exchange to adapt.
>
> The Max service attempts to stabilise the noise level at 6db. If it
> can't it increases the noise margin in steps. Sounds like your PC has
> "persuaded" the exchange you have a noisy line and the exchange has
> increased the noise margin & dropped the speed.
> --
> Peter R Cook

The PC in question is not in close proximity to the router or the phone
line. Infact they are very much apart. The PC is connected to the router
via a 20+ metre LAN connection. Would the PC PSU have to be in close
proximity to the router for your suggestions to be vaild?

Thanks Peter
Mike

In message <(E-Mail Removed)>, Mike
<(E-Mail Removed)> writes
>
>"Invalid" <(E-Mail Removed)> wrote in message
>news:(E-Mail Removed)...
>> Probably a bad power supply in the PC generating RF noise that is being
>> picked up by the phone line.
>>
>> Swap that PSU out, and you will potentially see an increase in ADSL
>> speeds (assuming you are on a Max service), but it will take some time
>> for the exchange to adapt.
>>
>> The Max service attempts to stabilise the noise level at 6db. If it
>> can't it increases the noise margin in steps. Sounds like your PC has
>> "persuaded" the exchange you have a noisy line and the exchange has
>> increased the noise margin & dropped the speed.
>> --
>> Peter R Cook
>
>The PC in question is not in close proximity to the router or the phone
>line. Infact they are very much apart. The PC is connected to the router
>via a 20+ metre LAN connection. Would the PC PSU have to be in close
>proximity to the router for your suggestions to be vaild?
>
>Thanks Peter
>Mike
>
>
>
>
Not necessarily, high frequency RF noise is very funny stuff.

The mains, The LAN cable, or a separate telephone extension could be
acting as either a broadcast or receiving aerial, or a conductor.

I was simply working on the principle that
PC On=Low SNR - PC Off= High SNR - The PC is causing the noise
The most common source of RF noise in PC's is the switched mode PSU
Thus its likely that the PSU in the PC is the noise source.

However it COULD be almost anything. You should try moving stuff around
and experimenting. Some ideas--

If the PC is on but not connected to the LAN does the SNR drop? If so
then the LAN connection may be transferring the noise.

Is the PC properly earthed? Check the plug.

Is this the only PC on the LAN - if so does connecting the other machine
(you must have one to be monitoring the SNR with the PC off) via the
same cable have the same effect? With or without the suspect PC switched
on?

If any machine on the end of that long LAN cable causes the same
problem, then it might be the LAN cable picking up electrical noise from
somewhere else (does it pass the Christmas tree lights?) but only
transferring it to the ADSL line when the LAN port goes live.

Does shifting the LAN cable to a different port make any difference?

Does connecting via a different cable have any impact?

Is the LAN Cable a good one (6e?) Who terminated it and how?

etc. etc. etc.

Happy Hunting

--
Invalid

Invalid wrote:
> In message <(E-Mail Removed)>, Mike
> <(E-Mail Removed)> writes
>>
>> "Invalid" <(E-Mail Removed)> wrote in message
>> news:(E-Mail Removed)...
>>> Probably a bad power supply in the PC generating RF noise that is
>>> being picked up by the phone line.
>>>
>>> Swap that PSU out, and you will potentially see an increase in
>>> ADSL speeds (assuming you are on a Max service), but it will take
>>> some time for the exchange to adapt.
>>>
>>> The Max service attempts to stabilise the noise level at 6db. If
>>> it can't it increases the noise margin in steps. Sounds like your
>>> PC has "persuaded" the exchange you have a noisy line and the
>>> exchange has increased the noise margin & dropped the speed.
>>> --
>>> Peter R Cook
>>
>> The PC in question is not in close proximity to the router or the
>> phone line. Infact they are very much apart. The PC is connected
>> to the router via a 20+ metre LAN connection. Would the PC PSU
>> have to be in close proximity to the router for your suggestions
>> to be vaild? Thanks Peter
>> Mike
>>
>>
>>
>>
> Not necessarily, high frequency RF noise is very funny stuff.
>
> The mains, The LAN cable, or a separate telephone extension could be
> acting as either a broadcast or receiving aerial, or a conductor.
>
> I was simply working on the principle that
> PC On=Low SNR - PC Off= High SNR - The PC is causing the noise
> The most common source of RF noise in PC's is the switched mode PSU
> Thus its likely that the PSU in the PC is the noise source.
>
> However it COULD be almost anything. You should try moving stuff
> around and experimenting. Some ideas--
>
> If the PC is on but not connected to the LAN does the SNR drop? If
> so then the LAN connection may be transferring the noise.
>
> Is the PC properly earthed? Check the plug.
>
> Is this the only PC on the LAN - if so does connecting the other
> machine (you must have one to be monitoring the SNR with the PC
> off) via the same cable have the same effect? With or without the
> suspect PC switched on?
>
> If any machine on the end of that long LAN cable causes the same
> problem, then it might be the LAN cable picking up electrical noise
> from somewhere else (does it pass the Christmas tree lights?) but
> only transferring it to the ADSL line when the LAN port goes live.
>
> Does shifting the LAN cable to a different port make any difference?
>
> Does connecting via a different cable have any impact?
>
> Is the LAN Cable a good one (6e?) Who terminated it and how?
>
> etc. etc. etc.
>
> Happy Hunting

The one thing your forgot was it could be induced via the mains (from
the PC power supply) as well & by the way it's low frequency signals
which do the damage, lower than 1Mhz to be more accurate.

On Tue, 01 Jan 2008 14:53:58 +0000, Invalid wrote:

> I was simply working on the principle that PC On=Low SNR - PC Off= High
> SNR - The PC is causing the noise The most common source of RF noise in
> PC's is the switched mode PSU Thus its likely that the PSU in the PC is
> the noise source.
>
> However it COULD be almost anything. You should try moving stuff around
> and experimenting. Some ideas--

Another possibility is a peripheral that is only on when the suspect PC
is on.

--
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