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Hum from phone wires running next to mains?



 
 
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  #11  
Old March 5th 08, 03:58 AM posted to uk.telecom,alt.comp.hardware,alt.engineering.electrical,sci.electronics.equipment
Tom Horne
external usenet poster
 
Posts: 2
Default Hum from phone wires running next to mains?

Foxtrot wrote:
On Tue 04 Mar 2008 21:22:30, wrote:

In alt.engineering.electrical wrote:
| On Tue, 4 Mar 2008 19:13:07 -0000, "Graham."
| wrote:

|It is quite difficult to induce hum into telephone wiring.
|Use twisted pair cabling rather than the flat ready-made
|extension cables.
|
| Exactly!
| The phone company has millions of miles of cable running right
| below power lines and hundreds literally touching each other in
| the jacket of the cable. That little twist they put in the pairs
| is excellent in isolating them from crosstalk.

That twist is a great little means to ensure induced signals,
whatever they may be, are induced in equal amount on both wires, so
they do not contribute to the actual intended signal that is a
differential between those two wires.

However, a risk exists when two different pairs are present next to
each other and each pair is twisted at the same pitch. The signal
carried by one can end up being induced differentially on the
other. So don't twist those power lines, or if you do, twist them
at a pitch with a ratio to the phone line twist that is not a whole
number.

CAT5 cable is an example. It has 4 different pairs twisting along.
Each of the pairs has a different twist pitch by design (unless
you get some cheap cable not manufactured correctly).


I do not have any technical knowledge of this area.

I would like to ask about a cable which has two or more twisted pairs
in it.

Is there is a greaterlikelihood of hum if I connect a "2 wire" phone
extension by using one wire from a twisted pair and taking the second
wire from a different twisted pair?


That practice is known in the North American communications industry as
a split pair. It is usually the cause of a host of troubles of which
induced noise is only the most common.
--
Tom Horne

"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
  #12  
Old March 5th 08, 09:40 AM posted to uk.telecom,alt.comp.hardware,alt.engineering.electrical,sci.electronics.equipment
jasee
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Posts: 68
Default Hum from phone wires running next to mains?

Foxtrot wrote:
On Tue 04 Mar 2008 19:13:07, Graham. wrote:
"Foxtrot" wrote in message
...


In my situation the phone extension wires and the mains wires will
run close to one other.

There will be about four or five additional extension phone
sockets.

And in some phone sockets there will be a loose extension lead of
approx 3 metres which will be almost ontop of curled mains flex


It is quite difficult to induce hum into telephone wiring.
Use twisted pair cabling rather than the flat ready-made
extension cables.



(As you suggest, I will not get the flat ready made extension cable
which I guess is made from flexible multi-stranded wires.)

Is the sort of cable sold in the UK specifically for domestic
telephone wall sockets (wuth single stranded wires) usually made up
as "twisted pair" in the way you are recommending?


No
I don't know why it is still used as most people in the UK seem to have adsl
connections nowadays (not just phones)


  #13  
Old March 5th 08, 12:40 PM posted to uk.telecom,alt.comp.hardware,alt.engineering.electrical,sci.electronics.equipment
George[_5_]
external usenet poster
 
Posts: 1
Default Hum from phone wires running next to mains?

On Tue, 04 Mar 2008 21:22:30 +0000, phil-news-nospam wrote:

In alt.engineering.electrical wrote:
| On Tue, 4 Mar 2008 19:13:07 -0000, "Graham." wrote:

|It is quite difficult to induce hum into telephone wiring. Use twisted
|pair cabling rather than the flat ready-made extension cables.
|
| Exactly!
| The phone company has millions of miles of cable running right below
| power lines and hundreds literally touching each other in the jacket of
| the cable. That little twist they put in the pairs is excellent in
| isolating them from crosstalk.

That twist is a great little means to ensure induced signals, whatever
they may be, are induced in equal amount on both wires, so they do not
contribute to the actual intended signal that is a differential between
those two wires.

However, a risk exists when two different pairs are present next to each
other and each pair is twisted at the same pitch. The signal carried by
one can end up being induced differentially on the other. So don't twist
those power lines, or if you do, twist them at a pitch with a ratio to the
phone line twist that is not a whole number.

CAT5 cable is an example. It has 4 different pairs twisting along. Each
of the pairs has a different twist pitch by design (unless you get some
cheap cable not manufactured correctly).


Very interesting.

Please can you advise on how these twisted pairs compare with

1. shielded audio cable
and
2. rf coax.

In case 1 both the wanted signal and the noise are in the audio frequency
range.

In case 2 the electricity supply noise contains harmonics of similar
frequency to the wanted rf signal.




  #14  
Old March 5th 08, 02:41 PM posted to uk.telecom,alt.comp.hardware,alt.engineering.electrical,sci.electronics.equipment
Brian Cryer
external usenet poster
 
Posts: 62
Default Hum from phone wires running next to mains?

"Foxtrot" wrote in message
...
I am in the UK and want to make several phone extensions.

QUESTION: I would like to know I this will increase the level of hum.

ISTR UK phones have a transformer and some other components to
neutralise hum but would that be good enough to prevent hum from a messy
setup like mine? Some details are below.

-------------------------

In my situation the phone extension wires and the mains wires will run
close to one other.

There will be about four or five additional extension phone sockets.


Can't comment on the hum ... but it looks like others have.

One contribution I would make is that you are aware that your phone service
will support 4 REN and that each phone is normally 1 REN, meaning that you
can have a maximum of 4 phones. My parents had more of this and whilst from
their perspective it seemed to work (they could call out), it stopped people
from calling in because their phones stopped ringing.

So be aware that if you are adding four or five additional phone sockets
that you won't be able to use all of them (at the same time).
--
Brian Cryer
www.cryer.co.uk/brian


  #15  
Old March 5th 08, 03:19 PM posted to uk.telecom,alt.comp.hardware,alt.engineering.electrical,sci.electronics.equipment
[email protected]
external usenet poster
 
Posts: 134
Default Hum from phone wires running next to mains?

In alt.engineering.electrical George wrote:
| On Tue, 04 Mar 2008 21:22:30 +0000, phil-news-nospam wrote:
|
| In alt.engineering.electrical wrote:
| | On Tue, 4 Mar 2008 19:13:07 -0000, "Graham." wrote:
|
| |It is quite difficult to induce hum into telephone wiring. Use twisted
| |pair cabling rather than the flat ready-made extension cables.
| |
| | Exactly!
| | The phone company has millions of miles of cable running right below
| | power lines and hundreds literally touching each other in the jacket of
| | the cable. That little twist they put in the pairs is excellent in
| | isolating them from crosstalk.
|
| That twist is a great little means to ensure induced signals, whatever
| they may be, are induced in equal amount on both wires, so they do not
| contribute to the actual intended signal that is a differential between
| those two wires.
|
| However, a risk exists when two different pairs are present next to each
| other and each pair is twisted at the same pitch. The signal carried by
| one can end up being induced differentially on the other. So don't twist
| those power lines, or if you do, twist them at a pitch with a ratio to the
| phone line twist that is not a whole number.
|
| CAT5 cable is an example. It has 4 different pairs twisting along. Each
| of the pairs has a different twist pitch by design (unless you get some
| cheap cable not manufactured correctly).
|
| Very interesting.
|
| Please can you advise on how these twisted pairs compare with
|
| 1. shielded audio cable
| and
| 2. rf coax.
|
| In case 1 both the wanted signal and the noise are in the audio frequency
| range.
|
| In case 2 the electricity supply noise contains harmonics of similar
| frequency to the wanted rf signal.

I don't have specific data on the quality of noise immunity. I'd bet that
kind of research has been done. It most certainly would vary by quality of
construction of the cables in question.

RF coax comes in various levels of quality based on a stated shielding
percentage. I've seen lows of 60% all the way up to 100%. The latter
could be a foil, or a solid metal encapsulation (quite a variety of
different coax types with this).

I've seen cables, including CAT5, with both twisting _and_ shielding around
the whole cable assembly. I don't know how much the effectiveness works
together. I have not had a case where I would consider using it.

--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net /
|
|------------------------------------/-------------------------------------|
  #16  
Old March 5th 08, 03:42 PM posted to uk.telecom,alt.comp.hardware,alt.engineering.electrical,sci.electronics.equipment
[email protected]
external usenet poster
 
Posts: 134
Default Hum from phone wires running next to mains?

In alt.engineering.electrical Brian Cryer wrote:
| "Foxtrot" wrote in message
| ...
|I am in the UK and want to make several phone extensions.
|
| QUESTION: I would like to know I this will increase the level of hum.
|
| ISTR UK phones have a transformer and some other components to
| neutralise hum but would that be good enough to prevent hum from a messy
| setup like mine? Some details are below.
|
| -------------------------
|
| In my situation the phone extension wires and the mains wires will run
| close to one other.
|
| There will be about four or five additional extension phone sockets.
|
| Can't comment on the hum ... but it looks like others have.
|
| One contribution I would make is that you are aware that your phone service
| will support 4 REN and that each phone is normally 1 REN, meaning that you
| can have a maximum of 4 phones. My parents had more of this and whilst from
| their perspective it seemed to work (they could call out), it stopped people
| from calling in because their phones stopped ringing.

I used to see phones rated in terms of their "ringer equivalence" here in
the USA. These numbers were, for some phones, as low as 0.2. I do not
recall ever seeing one about 0.9. That would suggest to me that you could
readily have more than 4 phones on such a phone circuit. I never had any
reason to actually do a scientific test of this.


| So be aware that if you are adding four or five additional phone sockets
| that you won't be able to use all of them (at the same time).

Or check your phone specs for an REN or ringer equivalence number.

If you want to put DSL on your phone line, I also suggest a splitter at
the entrance of the phone line and a separate NON-branching higher grade
(e.g. twisted pair) wire for the run from the DSL side of the splitter
to the intended connection.

--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / |
|------------------------------------/-------------------------------------|
  #17  
Old March 5th 08, 04:25 PM posted to uk.telecom,alt.comp.hardware,alt.engineering.electrical,sci.electronics.equipment
charles
external usenet poster
 
Posts: 4
Default Hum from phone wires running next to mains?

In article ,
wrote:

I used to see phones rated in terms of their "ringer equivalence" here in
the USA. These numbers were, for some phones, as low as 0.2. I do not
recall ever seeing one about 0.9. That would suggest to me that you could
readily have more than 4 phones on such a phone circuit. I never had any
reason to actually do a scientific test of this.


There is obviously a significant difference in the phone systems in the two
countries. Our phones have the bells in parallel and if thee are too many
the wrong impedance is presented to the exchange, and no ringing voltage
will get sent. I have never seen a UK approved phone with a REN less than
1, but there were plenty of 2s & 3s about at one time.

You can buy a REN booster ( a mains powered device) which allows many more
phones.

--
From KT24 - in "Leafy Surrey"

Using a RISC OS computer running v5.11

  #19  
Old March 5th 08, 07:06 PM posted to uk.telecom,alt.comp.hardware,alt.engineering.electrical,sci.electronics.equipment
Ryan Weihl
external usenet poster
 
Posts: 1
Default Hum from phone wires running next to mains?

Brian Cryer wrote:

"Foxtrot" wrote in message
...
I am in the UK and want to make several phone extensions.

QUESTION: I would like to know I this will increase the level of
hum.

ISTR UK phones have a transformer and some other components to
neutralise hum but would that be good enough to prevent hum from a
messy setup like mine? Some details are below.

-------------------------

In my situation the phone extension wires and the mains wires will
run close to one other.

There will be about four or five additional extension phone sockets.


Can't comment on the hum ... but it looks like others have.

One contribution I would make is that you are aware that your phone
service will support 4 REN and that each phone is normally 1 REN,
meaning that you can have a maximum of 4 phones. My parents had more
of this and whilst from their perspective it seemed to work (they
could call out), it stopped people from calling in because their
phones stopped ringing.

So be aware that if you are adding four or five additional phone
sockets that you won't be able to use all of them (at the same time).


I just looked at my phoneset, a wireless extension by Uniden.
the base is rated at 0.08 REN. We have a regular phone and 2 of these
wireless base stations with 2 sets each, so everyone has a set handy
and the neighbors can listen in too.


--

  #20  
Old March 5th 08, 07:22 PM posted to uk.telecom,alt.comp.hardware,alt.engineering.electrical,sci.electronics.equipment
Ivor Jones[_2_]
external usenet poster
 
Posts: 34
Default Hum from phone wires running next to mains?

wrote in message


[snip]

: : I've seen cables, including CAT5, with both twisting
: : _and_ shielding around the whole cable assembly. I
: : don't know how much the effectiveness works together.
: : I have not had a case where I would consider using it.

That's STP (shielded twisted pair) and is not really worth it for most
applications. There is a military spec. for it somewhere, I believe.

It's also a different impedance to UTP so may not work correctly with all
equipment.


Ivor


 




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