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Author: FoxtrotFoxtrot Date: Mar 4, 2008 08:43
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
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Author: Graham.Graham. Date: Mar 4, 2008 11:13
"Foxtrot" 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
> ...
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Author: phil-news-nospamphil-news-nospam Date: Mar 4, 2008 13:22
In alt.engineering.electrical gfretwell@ aol.com wrote:
| On Tue, 4 Mar 2008 19:13:07 -0000, "Graham." 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.
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Author: FoxtrotFoxtrot Date: Mar 4, 2008 15:44
On Tue 04 Mar 2008 21:22:30, ipal.net> wrote:
> In alt.engineering.electrical gfretwell@ aol.com wrote:
>| On Tue, 4 Mar 2008 19:13:07 -0000, "Graham." privacy.com>
>| wrote:
>
>|>It is quite difficult to induce hum into telephone wiring.
>|...
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Author: FoxtrotFoxtrot Date: Mar 4, 2008 15:51
On Tue 04 Mar 2008 19:13:07, Graham. privacy.com> wrote:
>
>
> "Foxtrot" 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...
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Author: Ivor JonesIvor Jones Date: Mar 4, 2008 15:55
"Foxtrot" 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*..!
Ivor
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Author: Floyd L. DavidsonFloyd L. Davidson Date: Mar 4, 2008 16:33
Foxtrot wrote:
>On Tue 04 Mar 2008 21:22:30, 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.
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Author: konykony Date: Mar 4, 2008 17:04
On Tue, 04 Mar 2008 23:44:11 GMT, Foxtrot
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?
yes
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Author: CBFalconerCBFalconer Date: Mar 4, 2008 16:35
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.
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Author: Tom HorneTom Horne Date: Mar 4, 2008 18:53
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
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