Re: Shielded mains cable

On Jun 3, 10:21 am, John Byrns <byr...@xxxxxxxxxxxxx> wrote:
In article <1180875605.579056.15...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Peter Wieck <p...@xxxxxxx> wrote:





On Jun 2, 9:22 pm, John Byrns <byr...@xxxxxxxxxxxxx> wrote:
In article <1180835067.111258.88...@xxxxxxxxxxxxxxxxxxxxxxxxxxxx>,
Peter Wieck <p...@xxxxxxx> wrote:

On Jun 2, 10:09 am, John Byrns <byr...@xxxxxxxxxxxxx> wrote:
In article <VMydnUz6Zu5a3_zbnZ2dnUVZ_oOkn...@xxxxxxxxxxx>,
"Arny Krueger" <a...@xxxxxxxxxx> wrote:

"John Byrns" <byr...@xxxxxxxxxxxxx> wrote in message
news:byrnsj-E233BF.11255201062007@xxxxxxxxxxxxxxxxxxxxxxxxxxxx
In article <n8GdndyQUoeItP3bnZ2dnUVZ_jGdn...@xxxxxxxxxxx>,
"Arny Krueger" <a...@xxxxxxxxxx> wrote:

"John Byrns" <byr...@xxxxxxxxxxxxx> wrote in message
news:byrnsj-D9708D.16324731052007@xxxxxxxxxxxxxxxxxxxxxxxxxxxx

I also meant to ask why DSL doesn't have the same range
as voice transmitted from the exchange over the same
pair?

AFAIK, it is becasue the higher frequencies DSL works at
have more line loss. For example, my sources say that
heavier gauge telephone wire gives greater DSL range at
a given data rate, or a higher data rate for a given
distance.

Yes, the greater loss as the frequency increases is
obvious, if that were all there was to it, logic would
say that a properly equalized amplifier would be all that
would be needed to make the range of DSL on a given cable
independent of the bit rate, so there must be more to it
than Graham is admitting to?

I don't think so. There are practical limits to what you can
accomplish
with
line equalization. The limits of practicality depend on the
application.
Trans-oceanic telephones cables used very high voltages. Cables that
run
through people's houses and backyards can't go there.

I don't know what the signal voltage used on the Trans-oceanic
telephones cables was, but I would be surprised if it was unusually
high. The high voltage you are referring to, which I think was several
thousand volts positive at one end of the cable and several thousand
volts negative at the other end of the cable, was the power source for
the repeaters of which there were a very large number. The repeaters
were powered in series like Christmas tree lights, and IIRC the power
feed was a constant current.

Cables that run through people's houses and backyards don't have to go
there, there is local power available in the house to power the
equipment.

"Bell System" lines receive no power from individual houses. Excepting
the early "Princess" phones which had separate local power for the
lighted dial, and multi-line sets with similar lighted buttons. When
these phones went modular, a very special adaptor was required (for
the princess-style).

Should I be abuse over your error?

You are welcome to if you first explain what my error is? The "OP" was
talking about ADSL, so I was referring to my AT&T DSL modem which is
powered from my home with electricity I provide for it.

And you made a blanket statement. The ADSL unit you have at home is
powered by your mains, yes. However, what gives between it and the
"switch" is 100% powered by the Company. Keep in mind that part of the
"Bell System" tariffs is that _NO_ external power sources are applied
to their lines for security and operational safety purposes. Imagine
the situation if somehow straight line-voltage found a way into the
Phone Lines.....

And exactly why I used the Princess Phone analogy. The princess had a
light which was powered from a local source, but much care was taken
to make sure that the source could not impinge on the line. The
electronics in the ADSL are local-power. The signal is "Bell System"
power.

Peter, you are playing the old internet game of putting words in
someone's mouth and then claiming they made an error because the words
you put in their mouth were in error. You are taking my statement
completely out of its original context and also trying to ascribe some
"blanket" meaning to it that it never had.

This thread was originally about "Shielded mains cable", as is typical
of internet threads, topic drift occurred and the issue of phone line
bandwidth was brought into the discussion. At that point Eeyore/Graham
commented that phone lines had a bandwidth of at least 1 MHz, citing the
example of ADSL as proof. At that point I asked what the signal to
noise ratio of a phone line was at 1 MHz, and also why the range of DSL
was less than the range of voice. Someone answered that the attenuation
of a phone line was greater at 1 MHz than at voice frequencies, so the
range of DSL less than range of voice signals, dodging the issue of
signal to noise ratio. Thinking there might be more involved than
simply attenuation, I attempted to draw out all the issues relating to
signal to noise ratio by asking the question, if attenuation were all
there was to it, wouldn't it be true that "a properly equalized
amplifier would be all that would be needed to make the range of DSL on
a given cable independent of the bit rate, so there must be more to it
than Graham is admitting to?" At that point Arny Krueger commented "I
don't think so. There are practical limits to what you can accomplish
with line equalization. The limits of practicality depend on the
application. Trans-oceanic telephones cables used very high voltages.
Cables that run through people's houses and backyards can't go there."
This raised the issue of "high voltages" running "through people's
houses and backyards" to which I responded "Cables that run through
people's houses and backyards don't have to go there, there is local
power available in the house to power the equipment." This is my
statement that you are taking exception to and calling a "blanket"
statement. I guess you could say that is a "blanket" statement in the
sense that "there is local power available in the house to power the
equipment" which is true, but notice I didn't say this "local power" was
used to power all the telephone equipment in a house, just that power
was available. I was simply pointing out that there was no need for the
telephone company to transmit high voltage power through people's back
yards and into their house to power equipment as was done with the
Trans-oceanic telephone cables. My point was that "local" power was
available in the house to power equipment like DSL modems, I made this
statement because that is how my AT&T DSL modem is powered, i.e. from
"local" power I provide, not from "high voltage" transmitted through my
backyard on the telephone cable.

What is your point, are you saying I am wrong when I stated that DSL
modems and the like are powered "locally"? Your statement that "The
signal is 'Bell System' power" is also certainly wrong, or at least half
wrong. The downstream signal may be "Bell System" power, but the
upstream signal is clearly my "local" power.

Regards,

John Byrns

--
Surf my web pages at, http://fmamradios.com/- Hide quoted text -

- Show quoted text -

John:

Your equipment, exactly as the light in the Princess Phone is locally
powered. And that is exactly as far as it goes. The ADSL Modem induces
a signal onto the "Bell System" powered line, but does not add any
power to that line from any local source. That is the point... and
with some thought, that is why it is rather obvious why a digital
signal would not have near as much range as an analog signal due to
cliff effects if nothing else.

Peter Wieck
Wyncote, PA

.

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