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.
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
--
max four x-post groups:
uk.telecom a.c.hardware a.e.electrical sci.electronics.equipment
"Foxtrot" <foxtrot@demo.invalid> wrote in message
news:Xns9A57AA15ACE8ED712E3@127.0.0.1...
>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.
>
> 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.
--
Graham
In alt.engineering.electrical gfretwell@aol.com wrote:
| On Tue, 4 Mar 2008 19:13:07 -0000, "Graham." <me@privacy.com> 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).
--
|---------------------------------------/----------------------------------|
| Phil Howard KA9WGN (ka9wgn.ham.org) / Do not send to the address below |
| first name lower case at ipal.net / spamtrap-2008-03-04-1516@ipal.net |
|------------------------------------/-------------------------------------|
On Tue 04 Mar 2008 21:22:30, <phil-news-nospam@ipal.net> wrote:
> In alt.engineering.electrical gfretwell@aol.com wrote:
>| On Tue, 4 Mar 2008 19:13:07 -0000, "Graham." <me@privacy.com>
>| 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?
On Tue 04 Mar 2008 19:13:07, Graham. <me@privacy.com> wrote:
>
>
> "Foxtrot" <foxtrot@demo.invalid> wrote in message
> news:Xns9A57AA15ACE8ED712E3@127.0.0.1...
>>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.
>>
>> 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?
"Foxtrot" <foxtrot@demo.invalid> wrote in message
news:Xns9A57F1761E171D712E3@127.0.0.1
[snip]
: : 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?
Why would you want to do that..? The answer is very probably, so ensure
that the pair of wires you use are twisted *together*..!
Foxtrot <foxtrot@demo.invalid> wrote:
>On Tue 04 Mar 2008 21:22:30, <phil-news-nospam@ipal.net> wrote:
>> 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.
Twist the power lines all you like. You *can't*
physically twist them identically to that of a comm
cable *and* get the two pairs to snuggle up to each
other in a way that will create the problem described
above.
Regardless, it isn't "smart" to run a comm cable in
physical contact with power cabling. Even a couple of
inches separation is sufficient to significantly reduce
common mode coupling. And the fact that no hum is heard
when it is first installed is *not* sufficient reason to
accept such practice. The common mode voltage induced
on the comm cable may not be a problem at any given
time, but it means that in the future anything (such as
kinks in the cable, dampness, damaged insulation, etc)
that reduces the balance *will* cause excessive hum.
The higher the common mode induced voltage, the less
unbalance required to cause objectionable hum.
If you can avoid putting the two types of cable
together, you *should*.
>> 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).
All multipair twisted-pair cable uses different twists
for each pair. That is identically true for bundled
pairs in telephone cable. Moreover, if there are
multiple bundles the bundles are swirled within the
jacket too.
>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 is referred to as a "split pair", and yes it will
cause problems. It commonly happens with CAT5 cabling
due to the different standards for pin assignments for a
DS1 interface and for 10BaseT Ethernet. Typically a DS1
cable will work for Ethernet if the length is short, but
if used for faster than 10baseT, it won't work at all,
even for a 6 foot jumper cable.
On large telephone cables split pairs invariably have
significant crosstalk (either hum or speech from other
cables).
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
Foxtrot wrote:
>
.... snip ...
>
> 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?
Yes. The idea of twisted pairs is that an interference appears on
both lines, and thus tends to cancel itself. Separating the lines
makes it easy for unequal induction.
--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home.att.net>
Try the download section.
On Tue, 04 Mar 2008 23:44:11 GMT, Foxtrot
<foxtrot@demo.invalid> wrote:
>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?
Foxtrot wrote:
> 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.
>
> 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
Much will depend on the power and light wiring method used and the
quality of the cable used to carry your telephone circuits. What do you
mean when you say "flex". I suspect you'll be amused to learn that in
the USA that word is electricians short hand for flexible metallic
conduit. I doubt that United Kingdom "flex" is anything like Flexible
Metallic Conduit a photograph of which can be found at
<http://www.tradexpro.com/product_catalogs/machinery_electronics/cable_wire/in-commerce/product/picture_fullsize/flexible_metallic_conduit.html?env=img-106372-->.
The best way to reduce the amount of noise in telephone lines is to use
station cable that has the wire pairs continuously twisted around each
other. In this way any electro magnetic fields that might otherwise
induce an unwanted noise into the circuit is self canceling in the
twisted pair of wires. Even with good quality station cable best
practice is to maintain at least several inches of separation between
the telephone cables and the electrical power and light wiring.
--
Tom Horne
"This alternating current stuff is just a fad. It is much too dangerous
for general use." Thomas Alva Edison
Foxtrot wrote:
> On Tue 04 Mar 2008 21:22:30, <phil-news-nospam@ipal.net> wrote:
>
>> In alt.engineering.electrical gfretwell@aol.com wrote:
>> | On Tue, 4 Mar 2008 19:13:07 -0000, "Graham." <me@privacy.com>
>> | 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
Foxtrot wrote:
> On Tue 04 Mar 2008 19:13:07, Graham. <me@privacy.com> wrote:
>> "Foxtrot" <foxtrot@demo.invalid> wrote in message
>> news:Xns9A57AA15ACE8ED712E3@127.0.0.1...
>>> 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)
On Tue, 04 Mar 2008 21:22:30 +0000, phil-news-nospam wrote:
> In alt.engineering.electrical gfretwell@aol.com wrote:
> | On Tue, 4 Mar 2008 19:13:07 -0000, "Graham." <me@privacy.com> 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.
"Foxtrot" <foxtrot@demo.invalid> wrote in message
news:Xns9A57AA15ACE8ED712E3@127.0.0.1...
>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
In alt.engineering.electrical George <George@nomail.invalid> wrote:
| On Tue, 04 Mar 2008 21:22:30 +0000, phil-news-nospam wrote:
|
|> In alt.engineering.electrical gfretwell@aol.com wrote:
|> | On Tue, 4 Mar 2008 19:13:07 -0000, "Graham." <me@privacy.com> 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 / spamtrap-2008-03-05-0813@ipal.net |
|------------------------------------/-------------------------------------|
In alt.engineering.electrical Brian Cryer <brian.cryer@127.0.0.1.ntlworld.com> wrote:
| "Foxtrot" <foxtrot@demo.invalid> wrote in message
| news:Xns9A57AA15ACE8ED712E3@127.0.0.1...
|>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 / spamtrap-2008-03-05-0819@ipal.net |
|------------------------------------/-------------------------------------|
In article <fqmbgd0kd7@news3.newsguy.com>,
<phil-news-nospam@ipal.net> 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.
>| 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.
>
It depends on how old the phones, or these days with modern
electrically powered phones, cordless/etc, the REN, number
may be very low per phone. IMO, no good reason not to get a
cordless phone these days as some are dirt cheap, except
it's nice to have at least one non-electric in case the
power goes out.
> "Foxtrot" <foxtrot@demo.invalid> wrote in message
> news:Xns9A57AA15ACE8ED712E3@127.0.0.1...
> > 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.
<phil-news-nospam@ipal.net> wrote in message
news:fqma4m1ier@news3.newsguy.com
[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 Jones" <ivor@thisaddressis.invalid> wrote:
><phil-news-nospam@ipal.net> wrote in message
>news:fqma4m1ier@news3.newsguy.com
>
>[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.
All outside plant telephone cable with the exception of
the local drop cable is shielded. Inside a telephone
office equipment room, T1 and higher speed data cables
are all shielded if the cable extends between rows or
for more distance in one row than 4 racks.
STP is significantly expensive, and will not commonly be
seen anywhere that it is not absolutely required. For
example, it would make no sense to use it within a
normal customer premise area, unless there is an
equipment room with multiple rows of equipment racks.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
> What do you
> mean when you say "flex". I suspect you'll be amused to learn that in the
> USA that word is electricians short hand for flexible metallic conduit. I
> doubt that United Kingdom "flex" is anything like Flexible Metallic
> Conduit a photograph of which can be found at
> <http://www.tradexpro.com/product_catalogs/machinery_electronics/cable_wire/in-commerce/product/picture_fullsize/flexible_metallic_conduit.html?env=img-106372-->.
I believe I can help here.
Rightpondian "flex" <> Leftpondian "cord"
--
Graham
> 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.
To me, Phil's post illustrates how *similar* the our systems are,
and I strongly suspect that the reason why we don't see REN
<1 is that the approval rules specify the figure quoted should
be an integer between 1 and 4.
Powered devices like DECT base-stations and FAX machines
don't need to supply any significant ringing current from the line,
they just need to sense the AC waveform to trigger the ringing.
REN is a bit of an anathema these days IMHO.
A good get-out for the support drones.
(
For the North Americans)
What is unusual with the UK system apart from our
"special" plug and receptacle instead of an RJ11,
is the fact that we use a third wire which couples
all the ringers in parallel to a capacitor in the master
socket to which the incommer is connected.
Many modern phones do not even use this "bell wire"
and just use the A and B wires (tip & ring).
Ivor Jones wrote:
> <phil-news-nospam@ipal.net> wrote:
>
> [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.
It should deal with hum pickup on audio cables quite nicely.
However shielded twisted pairs are considerably more expensive, and
you have to be careful about generating ground-loops in the shield
grounding.
I replaced your non-standard (: :) quote markers with the normal
'>'. Please don't use thos non-standard characters. They foul up
other software.
--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home.att.net>
Try the download section.
"Graham." wrote:
>
.... snip about ringer specs on phones and lines ...
>
> For the North Americans)
> What is unusual with the UK system apart from our "special" plug
> and receptacle instead of an RJ11, is the fact that we use a
> third wire which couples all the ringers in parallel to a
> capacitor in the master socket to which the incommer is connected.
> Many modern phones do not even use this "bell wire" and just use
> the A and B wires (tip & ring).
In North America again (I don't know about elsewhere) the normal
phone uses 3 wires to connect to the two wires of the phone
circuit. The yellow wire carries the ring signal. Just disconnect
that and the phone won't ring, and the load is zero.
--
[mail]: Chuck F (cbfalconer at maineline dot net)
[page]: <http://cbfalconer.home.att.net>
Try the download section.
"CBFalconer" <cbfalconer@yahoo.com> wrote in message
news:47CF3D42.810AA5C9@yahoo.com
: : Ivor Jones wrote:
[snip]
: : I replaced your non-standard (: :) quote markers with
: : the normal '>'. Please don't use thos non-standard
: : characters. They foul up other software.
With respect, and without wishing to start a row, that's *your* problem. I
use non-standard quote marks for a purpose. If your system can't cope with
that, then it's up to *you* to do something about it. I have been using
the quote marks I use for several years and you are the first to complain.
CBFalconer <cbfalconer@yahoo.com> wrote:
>In North America again (I don't know about elsewhere) the normal
>phone uses 3 wires to connect to the two wires of the phone
>circuit. The yellow wire carries the ring signal. Just disconnect
>that and the phone won't ring, and the load is zero.
I don't recall any system in North America that put ring
voltage on a separate wire. The yellow wire is
generally not connected unless one 4-wire cable is used
for two separate telephone lines.
In North America the "normal" line uses only 2 wires.
The audio signal is applied between the "tip" and the
"ring" of a single pair. "Ring Current" and "Loop
Current" are also applied between the Tip and the Ring
of the same pair.
Commonly used drop cable has four wires: Green is the
Tip and Red is the Ring (positive and negative,
repectively for the DC loop current), while the Yellow
and the Black wires are not used. (Note that the DC
voltages used by telephone companies are negative with
respect to ground, hence for DC the Tip wire is at
ground potential, and the Ring wire has a negative
potential. But the Tip is not at ground potential for
Ring Current or for the audio signal.)
One configuration often seen includes a second line on
the same cable, using Yellow and Black as Tip and Ring.
Historically the Yellow wire was, for a few years, used
for a small AC voltage (nominally 6.8 volts) to power a
lamp circuit on some telephone set models.
Another historical use had the Yellow wire as a ground
for party line service from the old style mechanical
switching systems (such as the Step or Stroeger
switching systems once used by the Bell System and by
Automatic Electric). On those systems the ring current
was applied between either Tip or Ring and ground, which
was supplied to the telephone set on the Yellow wire.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
In article <47CDEAD6.2D67BCF3@yahoo.com>, cbfalconer@yahoo.com
says...
> Foxtrot wrote:
> >
> ... snip ...
> >
> > 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?
>
> Yes. The idea of twisted pairs is that an interference appears on
> both lines, and thus tends to cancel itself. Separating the lines
> makes it easy for unequal induction.
Twisting also makes the loop area low (average over a long stretch
is nil). Separating them makes a large loop, increasing the size of
the antenna.
"Ivor Jones" <ivor@thisaddressis.invalid> wrote:
>"CBFalconer" <cbfalconer@yahoo.com> wrote in message
>news:47CF3D42.810AA5C9@yahoo.com
>: : Ivor Jones wrote:
>
>[snip]
>
>: : I replaced your non-standard (: :) quote markers with
>: : the normal '>'. Please don't use thos non-standard
>: : characters. They foul up other software.
>
>With respect, and without wishing to start a row, that's *your* problem. I
>use non-standard quote marks for a purpose. If your system can't cope with
>that, then it's up to *you* to do something about it. I have been using
>the quote marks I use for several years and you are the first to complain.
Consider for a bit just how absurd that statement is...
Are you posting your articles for your personal
edification, or are they intended to be read by an
audience? Who should you format them for, yourself or
the audience?
Your non-standard quote characters are *not* appreciated
by the audience, and indeed the more sophisticated
members that you might want to appeal to the most are
the ones most likely to make use of software options
based on the quote marks.
What your formatting style does, is tell the reader what
your priorities are, and that your ability to comprehend
the effect is apparently impaired.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
krw <krw@att.bizzzzzzzzzz> wrote:
>In article <47CDEAD6.2D67BCF3@yahoo.com>, cbfalconer@yahoo.com
>says...
>> Foxtrot wrote:
>> >
>> ... snip ...
>> >
>> > 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?
>>
>> Yes. The idea of twisted pairs is that an interference appears on
>> both lines, and thus tends to cancel itself. Separating the lines
>> makes it easy for unequal induction.
>
>Twisting also makes the loop area low (average over a long stretch
>is nil). Separating them makes a large loop, increasing the size of
>the antenna.
That is not a valid analysis. It is a transmission
line, not an antenna.
Consider that the effect, both for relatively small
gauge cables, such as the ubiquitous 26 gauge used
today, is *exactly* the same as the effect on the open
wire lines used in the 30's and 40's with several inches
of separate between a pair of much larger copperclad
steel wires. And while the twist on some cable is
measured per inch, on typical telephone cable it is
measured in many inches per twist, and on those old open
wire lines it was in hundreds of yards per twist.
--
Floyd L. Davidson <http://www.apaflo.com/floyd_davidson>
Ukpeagvik (Barrow, Alaska) floyd@apaflo.com
Hum from phone wires running next to mains? 
Linear Mode
