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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.

Disconnecting ringer wire question



 
 
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  #1  
Old April 23rd 12, 02:38 PM posted to uk.telecom.broadband
Tim Downie
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Posts: 13
Default Disconnecting ringer wire question

If your ADSL router/modem is plugged directly into the master socket (via
appropriate filter) and all other extensions are then supplied by the same
filter (i.e. no phones in the system connected before the modem), is there
still any advantage to disconnecting the ringer wire?

Tim

  #2  
Old April 23rd 12, 03:57 PM posted to uk.telecom.broadband
kráftéé
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Posts: 1,765
Default Disconnecting ringer wire question



"Tim Downie" wrote in message
...
If your ADSL router/modem is plugged directly into the master socket (via
appropriate filter) and all other extensions are then supplied by the same
filter (i.e. no phones in the system connected before the modem), is there
still any advantage to disconnecting the ringer wire?


If I have understood correctly no, but I can only wonder how you were
planning to disconnect the bell wire at the NTE end if it is being fed via a
plug in filter.

  #3  
Old April 23rd 12, 07:39 PM posted to uk.telecom.broadband
Denis McMahon
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Posts: 37
Default Disconnecting ringer wire question

On Mon, 23 Apr 2012 15:57:24 +0100, kraftee wrote:

"Tim Downie" wrote in message
...
If your ADSL router/modem is plugged directly into the master socket
(via appropriate filter) and all other extensions are then supplied by
the same filter (i.e. no phones in the system connected before the
modem), is there still any advantage to disconnecting the ringer wire?


If I have understood correctly no, but I can only wonder how you were
planning to disconnect the bell wire at the NTE end if it is being fed
via a plug in filter.


Presumably he's looped from the filter back into the extensions, and he's
talking about disconnecting at that point.

Or taking the microfilter apart and removing the ringing cap from it.

Personally, I think it *is* worth disconnecting the bell wire if possible.

Signals picked up on the bell wire do not get added to the a and b wire
equally - and often only get added to one of the pair in filter.

Most filters are designed to be most effective when rejecting common mode
noise, because after all, any rf picked up on the a/b pair should be
common mode noise.

If your filter attenuates by x dB, and your bell wire collects y dBmW of
noise per metre, then whatever value x is, less noise presented to the
filter means less noise ends up on the a/b pair upstream of the filter,
and the less metres of long line antenna (bell wire) you have, the less
noise you present to the filter.

Doubtless someone will be able to produce a nice mathematical proof that
shows that my gut feeling and intuition is flawed, but that's the way I
feel about removing bell wires.

Rgds

Denis McMahon
  #4  
Old April 23rd 12, 07:58 PM posted to uk.telecom.broadband
Peter Able
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Posts: 114
Default Disconnecting ringer wire question


"Tim Downie" wrote in message
...
If your ADSL router/modem is plugged directly into the master socket (via
appropriate filter) and all other extensions are then supplied by the same
filter (i.e. no phones in the system connected before the modem), is there
still any advantage to disconnecting the ringer wire?

Tim


Splitter/Filters (should) ignore the Master socket's bell wire and create a
new bell wire circuit on the phone extensions side of the filter. As such
it is somewhat isolated from the modem. Unless you've got noisy equipment
on, or likely to couple to, the extension circuits (maybe some PLT, you've
heavy, switched, electrical equipment, or you are a radio amateur) you'll
probably not have any problems if you leave the bell wire connected. On the
other hand, the less connected the less to cause problems so if it easy
(tell us) to do, disconnect it.

PA





  #5  
Old April 23rd 12, 08:13 PM posted to uk.telecom.broadband
Peter Able
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Posts: 114
Default Disconnecting ringer wire question


"Denis McMahon" wrote in message
. com...


Most filters are designed to be most effective when rejecting common mode
noise, because after all, any rf picked up on the a/b pair should be
common mode noise.


But surely the filter being discussed isn't there to deal with RF etc.
induced on the incoming line, but to prevent the phones in the house loading
the incoming line in the ADSL's passband, Denis? It is the common mode
choke in things like the i-plate that balances and so neutralises the common
mode signals - and that is in the signal path of both the modem and (not so
importantly) the phone extension circuitry.

PA


  #6  
Old April 24th 12, 02:22 AM posted to uk.telecom.broadband
Denis McMahon
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Posts: 37
Default Disconnecting ringer wire question

On Mon, 23 Apr 2012 20:13:34 +0100, Peter Able wrote:

"Denis McMahon" wrote in message
. com...


Most filters are designed to be most effective when rejecting common
mode noise, because after all, any rf picked up on the a/b pair should
be common mode noise.


But surely the filter being discussed isn't there to deal with RF etc.
induced on the incoming line, but to prevent the phones in the house
loading the incoming line in the ADSL's passband, Denis? It is the
common mode choke in things like the i-plate that balances and so
neutralises the common mode signals - and that is in the signal path of
both the modem and (not so importantly) the phone extension circuitry.


The *primary* function of the filter is to prevent the ADSL frequencies
interfering with the other consumer equipment. The signal they are trying
to block is the balanced ADSL signal on the a/b pair.

An effect, but not the design purpose of the filters, is to prevent ADSL-
band RF from the other consumer equipment interfering with the ADSL
signal.

Part of the design of such filters seems to be such that that it is
better able to do this for balanced signals. (Oops, in the earlier post I
said common mode when I meant balanced). This includes techniques such as
passing both a and b lines through the same choke but in opposite phase.

This does mean that when faced with an unbalanced signal, such as the rf
injection from a bell wire, they may be less efficient at blocking it
than they are at blocking such balanced signals.

In addition, the shorter the bell wire, the less signal it is likely to
pick up, and assuming less than perfect attenuation and thus that some
signal will make it through the filters, the less unwanted signal you
start off with downstream of the filters, the less unwanted signal you
end up with upstream of the filters (my second point).

Rgds

Denis McMahon
  #7  
Old April 24th 12, 03:33 AM posted to uk.telecom.broadband
The Natural Philosopher
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Posts: 2,728
Default Disconnecting ringer wire question

Denis McMahon wrote:
On Mon, 23 Apr 2012 20:13:34 +0100, Peter Able wrote:

"Denis McMahon" wrote in message
. com...


Most filters are designed to be most effective when rejecting common
mode noise, because after all, any rf picked up on the a/b pair should
be common mode noise.


But surely the filter being discussed isn't there to deal with RF etc.
induced on the incoming line, but to prevent the phones in the house
loading the incoming line in the ADSL's passband, Denis? It is the
common mode choke in things like the i-plate that balances and so
neutralises the common mode signals - and that is in the signal path of
both the modem and (not so importantly) the phone extension circuitry.


The *primary* function of the filter is to prevent the ADSL frequencies
interfering with the other consumer equipment. The signal they are trying
to block is the balanced ADSL signal on the a/b pair.


No. the primary function of the ADSL filter is to STOP other equipment
SHORTING OUT the ADSL signal


An effect, but not the design purpose of the filters, is to prevent ADSL-
band RF from the other consumer equipment interfering with the ADSL
signal.


that much is correct at least.


Part of the design of such filters seems to be such that that it is
better able to do this for balanced signals. (Oops, in the earlier post I
said common mode when I meant balanced). This includes techniques such as
passing both a and b lines through the same choke but in opposite phase.


Golly. O level physics.

This does mean that when faced with an unbalanced signal, such as the rf
injection from a bell wire, they may be less efficient at blocking it
than they are at blocking such balanced signals.

er..no.

In addition, the shorter the bell wire, the less signal it is likely to
pick up, and assuming less than perfect attenuation and thus that some
signal will make it through the filters, the less unwanted signal you
start off with downstream of the filters, the less unwanted signal you
end up with upstream of the filters (my second point).

blimey.

Rgds

Denis McMahon



--
To people who know nothing, anything is possible.
To people who know too much, it is a sad fact
that they know how little is really possible -
and how hard it is to achieve it.
  #8  
Old April 24th 12, 08:45 AM posted to uk.telecom.broadband
Peter Able
external usenet poster
 
Posts: 114
Default Disconnecting ringer wire question


"Denis McMahon" wrote in message
. com...
On Mon, 23 Apr 2012 20:13:34 +0100, Peter Able wrote:

The *primary* function of the filter is to prevent the ADSL frequencies
interfering with the other consumer equipment. The signal they are trying
to block is the balanced ADSL signal on the a/b pair.


No, absolutely not so. Consider which service get borked if the filter is
absent.


PA


  #9  
Old April 24th 12, 10:05 AM posted to uk.telecom.broadband
Denis McMahon
external usenet poster
 
Posts: 37
Default Disconnecting ringer wire question

On Tue, 24 Apr 2012 08:45:32 +0100, Peter Able wrote:

"Denis McMahon" wrote in message
. com...
On Mon, 23 Apr 2012 20:13:34 +0100, Peter Able wrote:


The *primary* function of the filter is to prevent the ADSL frequencies
interfering with the other consumer equipment. The signal they are
trying to block is the balanced ADSL signal on the a/b pair.


No, absolutely not so. Consider which service get borked if the filter
is absent.


Yes, because the ADSL signals cause the other equipment to generate noise
that then interferes with the ADSL equipment.

If the other equipment was not affected by the ADSL signals, they
wouldn't need to be blocked from it, because the signals wouldn't then
cause them to create noise in that band.

Normally audio telephony frequencies do not interfere with the ADSL
equipment.

Rgds

Denis McMahon
  #10  
Old April 24th 12, 10:10 AM posted to uk.telecom.broadband
Bob Eager
external usenet poster
 
Posts: 177
Default Disconnecting ringer wire question

On Tue, 24 Apr 2012 09:05:27 +0000, Denis McMahon wrote:

On Tue, 24 Apr 2012 08:45:32 +0100, Peter Able wrote:

"Denis McMahon" wrote in message
. com...
On Mon, 23 Apr 2012 20:13:34 +0100, Peter Able wrote:


The *primary* function of the filter is to prevent the ADSL
frequencies interfering with the other consumer equipment. The signal
they are trying to block is the balanced ADSL signal on the a/b pair.


No, absolutely not so. Consider which service get borked if the filter
is absent.


Yes, because the ADSL signals cause the other equipment to generate
noise that then interferes with the ADSL equipment.

If the other equipment was not affected by the ADSL signals, they
wouldn't need to be blocked from it, because the signals wouldn't then
cause them to create noise in that band.

Normally audio telephony frequencies do not interfere with the ADSL
equipment.


But lifting the receiver often does - and that isn't triggered by the
ADSL signal...!

--
Use the BIG mirror service in the UK:
http://www.mirrorservice.org

*lightning protection* - a w_tom conductor
 




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