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uk.telecom.broadband (UK broadband) (uk.telecom.broadband) Discussion of broadband services, technology and equipment as provided in the UK. Discussions of specific services based on ADSL, cable modems or other broadband technology are also on-topic. Advertising is not allowed.

Noise margin question



 
 
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  #1  
Old July 29th 06, 04:48 PM posted to uk.telecom.broadband
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Default Noise margin question

I have basic 512 ADSL and am using a Belkin wireless modem/router plugged
into the BT master socket via the DSL outlet a standard two-way splitter
(filter) with all house wiring connected via the BT-type outlet socket of
the same splitter. Am hoping to upgrade to ADSL MAX and thought I'd check
the line statistics via the Belkin software.

Very surprising result is that the downstream 'noise margin' indicated when
the house wiring is connected is a fairly good 21.5 or 22 dB (varies
slightly) but when I unplug the house wiring from the splitter the 'noise
margin' indicated by the Belkin status page goes down to about 14 dB
(upstream stays at 20 and attenuations stays at 59 or 60 dB).

I would have thought that unplugging the house wiring would have either no
effect at all OR a slightly beneficial effect upon the noise margin (same
thing as SNR, I assume - bigger the better)?

Can anyone suggest a possible explanation for this strange phenomenon
(disconnecting house wiring makes the noise margin WORSE and not, as one
would expect, BETTER).

If anyone has any thoughts on the matter I'd be extremely grateful.

Yours very puzzled.
--
Paul



  #2  
Old July 29th 06, 10:04 PM posted to uk.telecom.broadband
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Default Noise margin question

In an earlier contribution to this discussion,
paul paul wrote:

I have basic 512 ADSL and am using a Belkin wireless modem/router
plugged into the BT master socket via the DSL outlet a standard
two-way splitter (filter) with all house wiring connected via the
BT-type outlet socket of the same splitter. Am hoping to upgrade to
ADSL MAX and thought I'd check the line statistics via the Belkin
software.
Very surprising result is that the downstream 'noise margin'
indicated when the house wiring is connected is a fairly good 21.5 or
22 dB (varies slightly) but when I unplug the house wiring from the
splitter the 'noise margin' indicated by the Belkin status page goes
down to about 14 dB (upstream stays at 20 and attenuations stays at
59 or 60 dB).
I would have thought that unplugging the house wiring would have
either no effect at all OR a slightly beneficial effect upon the
noise margin (same thing as SNR, I assume - bigger the better)?

Can anyone suggest a possible explanation for this strange phenomenon
(disconnecting house wiring makes the noise margin WORSE and not, as
one would expect, BETTER).

If anyone has any thoughts on the matter I'd be extremely grateful.

Yours very puzzled.


Strange! Have you connected and disconnected the house wiring several times,
and is this a consistent result - or could it be just a one-off effect?

What happens when you do away with the filter/splitter, remove the faceplate
from the master socket, and plug the router directly into the test socket?
[You'll need a lead with a BT plug one end and an RJ11 the other end to do
this. A lead from an old analog modem will do.]
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!


  #3  
Old July 29th 06, 10:39 PM posted to uk.telecom.broadband
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Posts: n/a
Default Noise margin question


"Roger Mills" wrote in message
...
In an earlier contribution to this discussion,
paul paul wrote:

I have basic 512 ADSL and am using a Belkin wireless modem/router
plugged into the BT master socket via the DSL outlet a standard
two-way splitter (filter) with all house wiring connected via the
BT-type outlet socket of the same splitter. Am hoping to upgrade to
ADSL MAX and thought I'd check the line statistics via the Belkin
software.
Very surprising result is that the downstream 'noise margin'
indicated when the house wiring is connected is a fairly good 21.5 or
22 dB (varies slightly) but when I unplug the house wiring from the
splitter the 'noise margin' indicated by the Belkin status page goes
down to about 14 dB (upstream stays at 20 and attenuations stays at
59 or 60 dB).
I would have thought that unplugging the house wiring would have
either no effect at all OR a slightly beneficial effect upon the
noise margin (same thing as SNR, I assume - bigger the better)?

Can anyone suggest a possible explanation for this strange phenomenon
(disconnecting house wiring makes the noise margin WORSE and not, as
one would expect, BETTER).

If anyone has any thoughts on the matter I'd be extremely grateful.

Yours very puzzled.


Strange! Have you connected and disconnected the house wiring several
times, and is this a consistent result - or could it be just a one-off
effect?

What happens when you do away with the filter/splitter, remove the
faceplate from the master socket, and plug the router directly into the
test socket? [You'll need a lead with a BT plug one end and an RJ11 the
other end to do this. A lead from an old analog modem will do.]
--
Cheers,
Roger
______
Email address maintained for newsgroup use only, and not regularly
monitored.. Messages sent to it may not be read for several weeks.
PLEASE REPLY TO NEWSGROUP!


Many thanks Roger.

Yes - consistent result (done it a couple of times at least).

Old fashioned master socket (no removable faceplate) - but I will do as you
suggest and try bypassing the filter. Will also try swapping filters.

Watch this space!

Regards,

Paul



  #4  
Old July 29th 06, 11:32 PM posted to uk.telecom.broadband
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Posts: n/a
Default Noise margin question

Many thanks Roger.

Yes - consistent result (done it a couple of times at least).

Old fashioned master socket (no removable faceplate) - but I will do as
you suggest and try bypassing the filter. Will also try swapping filters.

Watch this space!

Regards,

Paul



Further installment:

Plugging lead from router into master socket directly (into non-detachable
faceplace - house wiring entirely disconnected) restores previous relatively
good noise margin reading of 22.5 (with attenuation 60).

Reverting to same splitter, but with house wiring still disconnected now
gives 23.5 (up from 22.5) and attenuation 59 (down from 60)! Can only think
the previous phenomenon was something to do with dirty contacts, which have
now been cleaned by repeated removal/reinsertion(?)

House wiring back on line - no change!!

Think the moral must be 'disconnect and reconnect your cables now and again
to be sure they are making good good contact'!

Thanks again for your help.

Paul





  #5  
Old July 30th 06, 08:37 AM posted to uk.telecom.broadband
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Default Noise margin question

That does sound pretty weird, could it be that it was actually
reporting the actual Noise ratio rather than the Signal to Noise Ratio?

I seem to remember that the Belkin had an issue with the download
figures that you have to swap the results from the upstream to the
downstream, as this was somehow setup the wrong way around, possibly
this could be somehow related?

Warmest regards,
Jay Best

  #6  
Old July 31st 06, 12:25 AM posted to uk.telecom.broadband
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Posts: n/a
Default Noise margin question


"jaybest" wrote in message
ups.com...
That does sound pretty weird, could it be that it was actually
reporting the actual Noise ratio rather than the Signal to Noise Ratio?

I seem to remember that the Belkin had an issue with the download
figures that you have to swap the results from the upstream to the
downstream, as this was somehow setup the wrong way around, possibly
this could be somehow related?

Warmest regards,
Jay Best


Many thanks Jay,

Interesting observation about Belkin. It does say noise margin.

My current figures are below - do you think they are the wrong way round?!

Comments appreciated.

Best wishes,


Paul

BELKIN STATS:

Noise Margin: (upstream) 20 (downstream) 23
Output Power: 11.5 dBm 17 dBm
Attenuation: 31.5 59






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