Telephone's usable bandwidth?

[Reg Edwards]

Aluminium alloys are used for ladders, jewellry, etc. Near pure
aluminium
wire is always used in phone lines. At data frequencies it has a
resistance
about 30 percent greater than copper.

Please elaborate.
--
Mike Page BEng(Hons) MIEE
===============================

Due to skin effect the resistance of both copper and aluminium wire
increases according to the squareroot of frequency. Skin effect for wire
diameters used in phone cables begins at a few tens of kilohertz, ie., at
data frequencies.

But the skin DEPTH, ie., the current-carrying cross-section of the wire,
ALSO increases according to the squareroot of wire resistivity.

So the skin depth in aluminium wire of the same diameter is greater than
that of copper. This upsets the DC resistance relationship.

The end result is that at HF, the percentage increase in resistance of
aluminium wire relative to copper is only half of the value at DC. Another
factor which at HF is halved relative to DC is the resistance-temperature
coefficient.

Cable attenuation in dB per km is directly proportional to wire HF
resistance.
----
Reg.

 

[Ian Stirling]

MikeM <trashcan@yahoo.com> wrote:

Tim Fisher wrote:
What are the upper and lower limits of frequencies that can be
transmitted over the land-based telephone network to a standard home
handset?

What are the limiting components or design factors, and is there any
way to overcome this without additional hardware on the receiving end?

Thanks,

Tim

Back in the bad old days when there was a continuous copper twisted
pair between your house, to the Telco's central office, and finally to
a buddies house across town, you could get a lot more bandwidth than
just voice freqs. Now that the central offices are digital, then you
cant play these games anymore.

Even before the exchanges all went digital, sharp filters were placed
in the voice path, to stop annoying people sending signalling tones
down them.

 

[Tam/WB2TT]

"Mike Page" <mike@SCRUBeclectic-CAPSweb.BLAMEco.SWENuk> wrote in message
news:1085000132.204847@news01.eclipse.net.uk...

John Tserkezis wrote:
Tim Fisher wrote:

Phone lines are no doubt better nowadays, but you don't know if you're
going through a pair gain, which would ultimatly reduce your available
bandwidth.

Not so recently there was a report in the UK of an entire new housing
development unable to get ADSL because all lines tested failed the
checks. The reason was aluminium wire, it was too lossy. The new
occupiers were none too happy.


--
Mike Page BEng(Hons) MIEE www.eclectic-web.co.uk

I am wondering if BT made up the Al wire story. I do not know of anybody who
manufactures, say 100 pair, Al wire. It would defeat the purpose, because to
get the same loop resistance, you need bigger wire, which would take up more
space in ducts/conduits. This is absolutely premium space. All specs as to
local loop wire that I have seen in the US refer to 19 - 26 ga Cu.

Tam

 

[Dbowey]

Ian posted:

<< MikeM <trashcan@yahoo.com> wrote:

Tim Fisher wrote:
What are the upper and lower limits of frequencies that can be
transmitted over the land-based telephone network to a standard home
handset?

What are the limiting components or design factors, and is there any
way to overcome this without additional hardware on the receiving end?

Thanks,

Tim

Back in the bad old days when there was a continuous copper twisted
pair between your house, to the Telco's central office, and finally to
a buddies house across town, you could get a lot more bandwidth than
just voice freqs. Now that the central offices are digital, then you
cant play these games anymore.

Even before the exchanges all went digital, sharp filters were placed
in the voice path, to stop annoying people sending signalling tones
down them. >>
-----

That is total nonsence. I believe you are confusing "loading" which was done
to improve voice-grade transmission on long loops, for a "sharp filter."

Filters were never placed in the voice path for the purpose you claim.

Don

 

[Dbowey]

Tam posted:

<<
"Mike Page" <mike@SCRUBeclectic-CAPSweb.BLAMEco.SWENuk> wrote in message
news:1085000132.204847@news01.eclipse.net.uk...

John Tserkezis wrote:
Tim Fisher wrote:

Phone lines are no doubt better nowadays, but you don't know if you're
going through a pair gain, which would ultimatly reduce your available
bandwidth.

Not so recently there was a report in the UK of an entire new housing
development unable to get ADSL because all lines tested failed the
checks. The reason was aluminium wire, it was too lossy. The new
occupiers were none too happy.


--
Mike Page BEng(Hons) MIEE www.eclectic-web.co.uk

I am wondering if BT made up the Al wire story. I do not know of anybody who
manufactures, say 100 pair, Al wire. It would defeat the purpose, because to
get the same loop resistance, you need bigger wire, which would take up more
space in ducts/conduits. This is absolutely premium space. All specs as to
local loop wire that I have seen in the US refer to 19 - 26 ga Cu.

------

Unfortunately, in the early 70s there was a push to use aluminum cable in the
US. I don't recall the magnitude of usage, but I do recall a lot was hung. At
the time, I was a Plant Manager in eastern Oregon and it was used there for a
while. As I recall 17 g aluminum was used where 19 g copper would have been
used. It's first cost was cheaper, but, when wet, fell apart fast.

Don

 

[Roy McCammon]

Dbowey wrote:

I am wondering if BT made up the Al wire story.

I haven't heard of AL for telco use either,
but there is steel wire used for aerial drop
and it is lossy at high freq.


--
local optimization seldom leads to global optimization

my e-mail address is: <my first name> <my last name> AT mmm DOT com

 

[Tam/WB2TT]

"Dbowey" <dbowey@aol.com> wrote in message
news:20040521120848.23183.00001268@mb-m24.aol.com...
...........................

Unfortunately, in the early 70s there was a push to use aluminum cable in
the
US. I don't recall the magnitude of usage, but I do recall a lot was
hung. At
the time, I was a Plant Manager in eastern Oregon and it was used there
for a
while. As I recall 17 g aluminum was used where 19 g copper would have
been
used. It's first cost was cheaper, but, when wet, fell apart fast.

Don

Don,
Were these open wire lines? Bell System or GTE? I could see stringing #17
wire off pole insulators, but not pulling it through ducts. Can you wire
wrap Al?

Tam

 

[Joel Kolstad]

Dbowey <dbowey@aol.com> wrote:

That is total nonsence. I believe you are confusing "loading" which was
done to improve voice-grade transmission on long loops, for a "sharp
filter."

I have heard that people used to be able to order up always connected
(physically patched together) 'alarm monitoring' lines between themselves
and another party, and that often they could manage to just use the line for
direct digital communications and could send, say, a variant of RS-232 over
the pair at some hundreds of kilobits per second...

 

[Dbowey]

Joel posted:

<< Dbowey <dbowey@aol.com> wrote:

That is total nonsence. I believe you are confusing "loading" which was
done to improve voice-grade transmission on long loops, for a "sharp
filter."

I have heard that people used to be able to order up always connected
(physically patched together) 'alarm monitoring' lines between themselves
and another party, and that often they could manage to just use the line for
direct digital communications and could send, say, a variant of RS-232 over
the pair at some hundreds of kilobits per second... >>

--

Those channels are called "dedicated" lines or "Private" lines. Some types
were only for voiceband use, and had repeaters in the transmission path.
Others were for the transmission of DC signals and had no Central Office
equipment on them.

Over time, some of the more knowledgable customers ordered the DC channels
(called "signal channels"), which were quite inexpensive, and used them for
wider-bandwidth service, including 1.544 Mbit/s, which requires a 772 kbit/s
channel (each 1/2 cycle is a digital bit, using a unique line-code).

This has become complex to impossible, because not all customer premises are
served by copper. Today, many telcos offer signal channel service, but the DC
capability is provided by a converter at the customer premises and transport is
by copper or pair-gain by the telco. Consequently, if you order one of these
channels you can't use it at a rate faster than about 20 baud.

Don

 

[Dbowey]

Tam posted:

<< "Dbowey" <dbowey@aol.com> wrote in message
news:20040521120848.23183.00001268@mb-m24.aol.com...
...........................

Unfortunately, in the early 70s there was a push to use aluminum cable in
the
US. I don't recall the magnitude of usage, but I do recall a lot was
hung. At
the time, I was a Plant Manager in eastern Oregon and it was used there
for a
while. As I recall 17 g aluminum was used where 19 g copper would have
been
used. It's first cost was cheaper, but, when wet, fell apart fast.

Don

Don,
Were these open wire lines? Bell System or GTE? I could see stringing #17
wire off pole insulators, but not pulling it through ducts. Can you wire
wrap Al? >>

I was with Bell. These were large aerial and underground cables. There was a
large set of special hardware for splicing aluminum cable, because of the need
to avoid dissimilar metal connection problems. I don't recall any use of
aluminum in open-wire plant.

Don

 

[Le Chaud Lapin]

"Tam/WB2TT" <t-tammaru@c0mca$t.net> wrote in message news:<QZSdncq5N9DvHDDdRVn-hw@comcast.com>...

If it is the wire from the telephone unit to the face plate, that
would not be the same as for the cat-3 wire inside the house, where
you can actually get ethernet speeds under certain circumstances. (I
once got almost 1Mb/s by butchering some cat-3 cable tied in with
Coax). If you mean the wire from the house's point of demarcation to
central office, assuming local loop length of over 20,000 ft, you can
expect DSL to attempt to use the entire 1.1MHz, starting at 4KHz,
using quadrature or other techniques to maximize spectral efficiency.

Perhaps one should ask what is the maximum expected bit rate from
demarcation to CO since it is quite possible to use frequencies well
beyond 1.1MHz if one is willing to tolerate a corresponding reduction
in througput and symbol delay.

-Chaud Lapin-

This all assumes you have a metallic connection to the CO.

What would be the alternative?

-Chaud Lapin-

 

[Richard Henry]

"Le Chaud Lapin" <unoriginal_username@yahoo.com> wrote in message
news:fc2e0ade.0405210958.5da2b2e8@posting.google.com...

"Tam/WB2TT" <t-tammaru@c0mca$t.net> wrote in message
news:<QZSdncq5N9DvHDDdRVn-hw@comcast.com>...
If it is the wire from the telephone unit to the face plate, that
would not be the same as for the cat-3 wire inside the house, where
you can actually get ethernet speeds under certain circumstances. (I
once got almost 1Mb/s by butchering some cat-3 cable tied in with
Coax). If you mean the wire from the house's point of demarcation to
central office, assuming local loop length of over 20,000 ft, you can
expect DSL to attempt to use the entire 1.1MHz, starting at 4KHz,
using quadrature or other techniques to maximize spectral efficiency.

Perhaps one should ask what is the maximum expected bit rate from
demarcation to CO since it is quite possible to use frequencies well
beyond 1.1MHz if one is willing to tolerate a corresponding reduction
in througput and symbol delay.

-Chaud Lapin-

This all assumes you have a metallic connection to the CO.

What would be the alternative?

Optical fiber.

 

[Tam/WB2TT]

"Le Chaud Lapin" <unoriginal_username@yahoo.com> wrote in message
news:fc2e0ade.0405210958.5da2b2e8@posting.google.com...

"Tam/WB2TT" <t-tammaru@c0mca$t.net> wrote in message
news:<QZSdncq5N9DvHDDdRVn-hw@comcast.com>...
If it is the wire from the telephone unit to the face plate, that
would not be the same as for the cat-3 wire inside the house, where
you can actually get ethernet speeds under certain circumstances. (I
once got almost 1Mb/s by butchering some cat-3 cable tied in with
Coax). If you mean the wire from the house's point of demarcation to
central office, assuming local loop length of over 20,000 ft, you can
expect DSL to attempt to use the entire 1.1MHz, starting at 4KHz,
using quadrature or other techniques to maximize spectral efficiency.

Perhaps one should ask what is the maximum expected bit rate from
demarcation to CO since it is quite possible to use frequencies well
beyond 1.1MHz if one is willing to tolerate a corresponding reduction
in througput and symbol delay.

-Chaud Lapin-

This all assumes you have a metallic connection to the CO.

What would be the alternative?

Some sort of Digital Subscriber Line Multiplexer. In the UK that would mean
30 or 31 (can't remember which) customers on 2 pairs of wires, 23 in the US.
A whole lot cheaper than pulling new wire.

Tam

-Chaud Lapin-

 

[Dbowey]

RE:
<< Some sort of Digital Subscriber Line Multiplexer. In the UK that would mean
30 or 31 (can't remember which) customers on 2 pairs of wires, 23 in the US.
A whole lot cheaper than pulling new wire. >>

------

The UK uses 2.048 Mbit/s as the E1 rate. That provides 32 channels of 64
kbit/s of which 30 channels are available for customer services. The US uses
1.544 Mbit/s as the DS1 rate, providing 24 channels of 64 kbit/s each, all
usable for customer services.

Don

 

[Mike Page]

Reg Edwards wrote:

Aluminium alloys are used for ladders, jewellry, etc. Near pure

aluminium

wire is always used in phone lines. At data frequencies it has a

resistance

about 30 percent greater than copper.

Please elaborate.
--
Mike Page BEng(Hons) MIEE

===============================

Due to skin effect the resistance of both copper and aluminium wire
increases according to the squareroot of frequency. Skin effect for wire
diameters used in phone cables begins at a few tens of kilohertz, ie., at
data frequencies.

But the skin DEPTH, ie., the current-carrying cross-section of the wire,
ALSO increases according to the squareroot of wire resistivity.

So the skin depth in aluminium wire of the same diameter is greater than
that of copper. This upsets the DC resistance relationship.

The end result is that at HF, the percentage increase in resistance of
aluminium wire relative to copper is only half of the value at DC. Another
factor which at HF is halved relative to DC is the resistance-temperature
coefficient.

Cable attenuation in dB per km is directly proportional to wire HF
resistance.
----
Reg.

Quite so. It's useful to spell out the physics and givens (data
frequency and wire diameter), because Al does have a bad reputation.
Clearly through *correct* wire gauge compensation this effect can be
mitigated.

However, the sum of field experience suggests BT (or its agents) didn't
bother. There are also questions of Cu-Al joints and Al corrosion, but
since BT don't easily pronounce on anything so commercially sensitive,
and I have a perfectly decent ADSL connection, I lose interest.

Mike.

--
Mike Page BEng(Hons) MIEE www.eclectic-web.co.uk
^^^^^^^^^^^^^^^^^
does my bum look big in this ???

 

[Doug Goncz]

For example, will it do subaudio down to a few Hz and how much energy
could be dumped at this frequency?

To make up a transmissible "phone bomb" I used a wave I made up in Mathcad. It
was based on sin(x) / x. It filled the available channel completely from
300-3000 Hz. I still have the worksheet. I don't have an energy rating in
joules.

I got it from the bong tone used on telephone card in the 1980s. They may still
use that. It's not the same thing.

Hold on, let me get Fourier Analysis by R.D. Stuart... Damn, it's packed away.
Let me get my worksheet.

I can't find it.

Would one of you expound on the spectrum of sin(x) / x? As I recall, it is a
block of noise extending upward from the fundamental. No harmonics. Then you
combine it with a block of noise extending downward from 3000 Hz, and there it
is.

You see, merely gating a blast of band-filtered noise, that is, ramping it up
to full power and down, generates a spectrum of its own. It changes the
spectrum of the noise. This one was designed to sneak past the gating circuits
and blow the receiver out of the handset.

I'm not saying it ever did.

Subaudio, no. The ringer will absorb anything near subaudio.




Yours,

Doug Goncz ( ftp://users.aol.com/DGoncz/ )

Read about my physics project at NVCC:
http://groups.google.com/groups?q=dgoncz&scoring=d plus
"bicycle", "fluorescent", "inverter", "flywheel", "ultracapacitor", etc.
in the search box

 

[Bob Martin]

You see, merely gating a blast of band-filtered noise, that is, ramping it up
to full power and down, generates a spectrum of its own. It changes the
spectrum of the noise. This one was designed to sneak past the gating circuits
and blow the receiver out of the handset.

I'm not saying it ever did.

Subaudio, no. The ringer will absorb anything near subaudio.

Doug Goncz ( ftp://users.aol.com/DGoncz/ )

Is there any way to apply subaudio to the headset coil by using
destructive phasing of higher frequencies or a similar technique?

Bob