Hum from phone wires running next to mains?

  • Thread starter Thread starter Foxtrot
  • Start date Start date
[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
 
Ivor Jones said:
[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.
Click to expand...

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.
 
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.
Click to expand...


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 said:
[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.
Click to expand...

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.
Click to expand...

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.
 
.... 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).
Click to expand...

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.
 
: : 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.

Ivor
 
CBFalconer said:
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.
Click to expand...

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.
 
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.
Click to expand...

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 said:
: : 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.
Click to expand...

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.
 
krw said:
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.
Click to expand...

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.
 
Ivor said:
[snip]
I replaced your non-standard (: :) quote markers with
the normal '>'. Please don't use thos non-standard
characters. They foul up other software.
Click to expand...

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.
Click to expand...

Well, I said my piece. The normal method of handling it is the
casual plonk.
 
That is not a valid analysis. It is a transmission
line, not an antenna.
Click to expand...

It sure as hell is. Open up the loop and it makes a *wonderful*
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.
Click to expand...

....and open-wire transmission lines won't pick up stray noise?
 
Floyd L. Davidson said:
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.
Click to expand...

Well, it is possible that my memory is fouled. Haven't needed to
disconnect ringers for at least 20 years.
 
krw said:
It sure as hell is. Open up the loop and it makes a *wonderful*
antenna.
Click to expand...

It's a "wonderful" antenna regardless. But it's a
single conductor long wire antenna. Changing the
spacing is merely changing the effective diameter of the
single conductor. To get any other effect requires
spacing that is significant in terms of wavelength
(greater than perhaps 1/8th of a wavelength, for
example).
...and open-wire transmission lines won't pick up stray noise?
Click to expand...

It picks up as much, or as little, as unshielded twisted
pair of smaller gauge and closer spacing. That's the
point... there isn't any difference. In either case
what you have is a single conductor longwire antenna, not
a loop antenna, until the spacing is a significant fraction
of a wavelength.
 
Ivor said:
: : 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.

Ivor
Click to expand...

Non-standard usage can make your posts harder to understand,
and more difficult for others. Apparently, you don't care.
I'm just adding one more response to let you know that your
non-standard usage is not appreciated.

Ed
 
: : : : : : : : 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...

Which part..? The part where I say I use non-standard quotes for a reason,
or the part where I said nobdy has so far complained..?

: : 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?

Both.

: : 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.

So why, in my 10+ years of Usenet use, is this the first complaint..?

: : What your formatting style does, is tell the reader what
: : your priorities are, and that your ability to comprehend
: : the effect is apparently impaired.

Your ability to comprehend my reply appears to be impaired also.

<plonk>

Ivor
 
[snip]

: : Non-standard usage can make your posts harder to
: : understand, and more difficult for others. Apparently,
: : you don't care. I'm just adding one more response to
: : let you know that your non-standard usage is not
: : appreciated.

Ok, you're the *second* complaint in 10+ years. When that figure gets to a
noticable percentage, I might sit up and take notice.

Ivor

: :
: : Ed
 
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