| Author |
Message |
Robert Redelmeier
Guest
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 Posted:
Thu Sep 08, 2005 1:52 am Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
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James Knott <james.knott@rogers.com> wrote:
| Quote: | Such as??? Anything you can imagine, other than constant
DC is composed of sine waves at one or more frequencies.
Any wave form, such as square wave triangle wave, etc.,
|
Yes, I'm aware of how _regular_ waves can be built this way.
But digitial baseband transmissions are not regular.
They are a close to random pattern of ones and zeros.
| Quote: | If you're referring to the snow on a TV screen, when there's
no TV reception, you are looking at noise from other sources,
|
No, I'm refering to the effect sometimes seen of a noise
generator (vacuum cleaner) producing dropouts (snow) on a tuned
TV channel. 60 Hz interfering with MHz (transmissions) or kHz
(raster).
| Quote: | Also, while ethernet carries digital data, the signal is in
fact analog, in that a carrier is modulated by that data.
|
True for things like 10broad3. Not AFAIK in 10baseT, 100baseTX or GBE.
| Quote: | If you were to look at it with a scope, you'd see a complex
analog waveform.
|
I've seen a sorry mess that looks more digital than analog.
| Quote: | take a simple modulation method, such as Manchester encoding
and show that it is composed of various sine waves.
|
Which have to start and stop. AFAIK, the encoding is to carry
clock so there is no question "Was that 5 zero bits or 6?"
| Quote: | As I recall Maxwell's equation and the (Flemming's) left
hand rule, they relate to the relationship between a moving
magnetic field and induced current. Other than that,
what do they have to do with a waveform?
|
_EVERYTHING_! When electrons/holes move, they create magnetic
fields. When they change directions, those magnetic fields
change directions. This produces the changing magnetic field
which induces current. The waveform matters because it is
the rate of change of current that controls the rate-of-change
of magfield which controls sets the current induced.
-- Robert |
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James Knott
Guest
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| Posted:
Thu Sep 08, 2005 2:29 am Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
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Robert Redelmeier wrote:
| Quote: | James Knott <james.knott@rogers.com> wrote:
Such as??? Anything you can imagine, other than constant
DC is composed of sine waves at one or more frequencies.
Any wave form, such as square wave triangle wave, etc.,
Yes, I'm aware of how _regular_ waves can be built this way.
But digitial baseband transmissions are not regular.
They are a close to random pattern of ones and zeros.
If you're referring to the snow on a TV screen, when there's
no TV reception, you are looking at noise from other sources,
No, I'm refering to the effect sometimes seen of a noise
generator (vacuum cleaner) producing dropouts (snow) on a tuned
TV channel. 60 Hz interfering with MHz (transmissions) or kHz
(raster).
|
You must have one incredibly noisy vacuum cleaner or the interference is
entering at a later stage.
| Quote: |
Also, while ethernet carries digital data, the signal is in
fact analog, in that a carrier is modulated by that data.
True for things like 10broad3. Not AFAIK in 10baseT, 100baseTX or GBE.
If you were to look at it with a scope, you'd see a complex
analog waveform.
I've seen a sorry mess that looks more digital than analog.
take a simple modulation method, such as Manchester encoding
and show that it is composed of various sine waves.
Which have to start and stop. AFAIK, the encoding is to carry
clock so there is no question "Was that 5 zero bits or 6?"
|
Actually, with 10baseT, you have data that starts & stops with each frame
and a sync signal at the beginning of the frame. There is also a link test
signal between frames. 100baseT sends a continuous signal. The clocking is
derived from the signal and the sync signal is used to determine the bit,
within a frame.
| Quote: |
As I recall Maxwell's equation and the (Flemming's) left
hand rule, they relate to the relationship between a moving
magnetic field and induced current. Other than that,
what do they have to do with a waveform?
_EVERYTHING_! When electrons/holes move, they create magnetic
fields. When they change directions, those magnetic fields
change directions. This produces the changing magnetic field
which induces current. The waveform matters because it is
the rate of change of current that controls the rate-of-change
of magfield which controls sets the current induced.
|
Again, what about it has something specific in regards to harmonics? Does
it somehow generate harmonics? Or is it simply a method of describing the
relationship between magnetism and electricity? Yes, fields change
directions, which is the fundamental principle on which transformers,
motors etc. work. Now, you claimed, in a previous message that Maxwell
would explain the function of square waves. I haven't seen anything from
you about that. How does Maxwell (or Flemming) explain the composition of
a square wave??? Fourier certainly does. |
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Robert Redelmeier
Guest
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| Posted:
Thu Sep 08, 2005 3:56 am Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
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James Knott <james.knott@rogers.com> wrote:
| Quote: | You must have one incredibly noisy vacuum cleaner or the
interference is entering at a later stage.
|
I don't think so. I believe the TV snow from the vac cleaner
is coming radiating from the power lines and either leaking
thru the TV PSU or is picked up by the antenna/gain circuitry.
The interference isn't dependant on distance between TV & vac.
| Quote: | Again, what about it has something specific in regards
to harmonics? Does it somehow generate harmonics?
|
Why do you keep insisting on harmonics? They aren't
the only cause of interference.
| Quote: | Now, you claimed, in a previous message that Maxwell
would explain the function of square waves. I haven't
seen anything from you about that. How does Maxwell
(or Flemming) explain the composition of a square wave???
Fourier certainly does.
|
Fourier describes a synthetic decomposition but says nothing
about effects. Flemming describes and Maxwell quantifies
the inductive _effect_ [result] of a square edge.
-- Robert |
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James Knott
Guest
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| Posted:
Thu Sep 08, 2005 7:20 am Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
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Robert Redelmeier wrote:
| Quote: | Again, what about it has something specific in regards
to harmonics? Does it somehow generate harmonics?
Why do you keep insisting on harmonics? They aren't
the only cause of interference.
|
Perhaps because you said
"Going on/off hook (or pulse dialing)
might be, especially if there isn't parasitic capacitancy or
deliberate contact capacitors to round the shoulders. You also
have to cope with "bounce" from mechanical contacts. "
and
"Harmonics? We aren't talking carrier-wave! All it takes is
a single spike to ruin one bit, then the 12 kbit packet is shot."
and
"But an old mechanical dialer
might be a different story. I think a guy from Finland posted
with his tests."
In those comments, you implied that common activity on a phone line would
cause interference. Every desired signal on a phone line is below 4 kHz
and ethernet signaling is in the several MHz range. This means that the
only way one of those signals on a phone line could interfere with
ethernet, would be if it were to generate significant energy (harmonics) in
the frequency range that ethernet is operating in. The only way that could
conceivably happen, would be if those signals generated harmonics in the
range that ethernet is sensitive to. Your comment about "All it takes is
a single spike to ruin one bit, then the 12 kbit packet is shot." shows you
do not understand the nature of what's on the wire. What is that pulse?
If it's a square wave of very short duration, it's still composed of sine
wave components. Also, what on a phone line could generate signals in the
several MHz range? Dial pulses won't do it. Hanging up the phone won't do
it. The voice energy won't do it. Defective ADSL equipment, operating
without a filter might. Please explain how the interfering signal would be
generated and propagated, in a manner that stands up to mathematical or
electrical engineering scrutiny.
Remember, you not only have to generate such a signal on the phone line
pair, you've got to get it to couple into the ethernet pair, as a
differential mode signal, that can pass through the line transformer and
whatever filters are in the NIC. Just claiming "All it takes is a single
spike to ruin one bit, then the 12 kbit packet is shot" doesn't say much,
unless you can explain how. What does that spike look like, on the
ethernet pair? What frequency range does it occupy? What amplitude at the
ethernet receiver? Further, how could any phone device that generates such
interference get FCC approval for connection to the phone line? If it's
producing such interference to ethernet, it might also do so to various
radio services. |
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James Knott
Guest
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| Posted:
Thu Sep 08, 2005 7:29 am Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
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David Lesher wrote:
| Quote: | James Knott <james.knott@rogers.com> writes:
Because both cable and phone service entrances have grounded
protection.
Precisely. That's why sharing an ethernet cable with a protected phone
line is no more risky than having a modem connected to the computer.
Which is a major risk.... I never ever use internal {PCI bus} modems.
An external modem w/ serial port gives you an excellent sacrificial
lamb to Murphy.
Induce a large spike onto the Ethernet pair on your machine, and
hope that the standoff insulation saves your butt.
If you think the protector the telco provides will save your Ethernet;
keep spares around. Using the same cable is like painting a bullseye
on your butt and going to Pamplona. It works, and you may be luckly
for a long time...but...
|
Most computers are connected to a power line and phone or cable TV line or
both. Any of those three connections can bring hazardous voltages to the
computer. My point has always been that simply sharing a cable, with no
electrical connection between the phone and ethernet pairs, is not likely
to create a significant increase in risk. Any harmful voltage or current
on the phone pair, has to be coupled into the ethernet pair, which will
result in significant attenuation of that harmful voltage or current,
simply because twisted pair is designed to avoid such coupling. Then it
has to overcome the protective circuits of the NIC, such as the ethernet
line transformers etc., to get to a point where it can cause damage. |
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David Lesher
Guest
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| Posted:
Thu Sep 08, 2005 12:57 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
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James Knott <james.knott@rogers.com> writes:
| Quote: | Most computers are [here I shall add "DIRECTLY"] connected to a
power line and phone or cable TV line or both.
|
True on the power; true for some modems [internal vs external; shared
vs. separate power supply, etc] and never true for cable -- the
cable talks to an external cable modem {in every case I have seem..}
and it uses Ethernet to talk to the PC.
| Quote: | Any of those three connections can bring hazardous voltages to the
computer. My point has always been that simply sharing a cable, with no
electrical connection between the phone and ethernet pairs, is not likely
to create a significant increase in risk.
|
And that's where we disagree. Yes, it's separate pairs, but in CLOSE
proximity to each other, esp. at each jack. And yes, the telco has
a protector, one whose original function was to keep them from being
sued over folks who were on the phone when the pair took a hit; NOT
to protect IC's in end-use equipment.
And the 1500v isolation of a NIC transformer is a joke when you talk
lightning-induced surges.
As I said, you can likely get away with it.....but...
--
A host is a host from coast to coast.................wb8foz@nrk.com
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433 |
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Robert Redelmeier
Guest
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| Posted:
Thu Sep 08, 2005 4:20 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
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James Knott <james.knott@rogers.com> wrote:
| Quote: | Every desired signal on a phone line is below 4 kHz and
ethernet signaling is in the several MHz range. This means
that the only way one of those signals on a phone line could
interfere with ethernet, would be if it were to generate
significant energy (harmonics) in the frequency range
that ethernet is operating in.
|
Harmonics aren't the only way to generate energy. As a
rule, harmonics allow energy levels to build by reflection
and reinforcement.
My overall point is that the effects of noise are different on
digital and analog signals. Digital is _NOT_ immune to noise.
It just tolerates low levels continuously with impunity.
Bug digital is vulnerable to spikes/high noise levels, even
if fairly rare. Analog rides these through but is vulnerable
to continuous low levels.
| Quote: | Your comment about "All it takes is a single spike to ruin
one bit, then the 12 kbit packet is shot." shows you do
not understand the nature of what's on the wire
|
Baseband signalling voltage levels. No carrier wave.
| Quote: | What is that pulse? If it's a square wave of very short
duration, it's still composed of sine wave components.
Also, what on a phone line could generate signals in the
several MHz range?
|
Then why snow on TV from running vacuums? Any sharp edge
has lots of UHF components.
| Quote: | Dial pulses won't do it. Hanging up the phone won't do it.
|
Both of these may be mechanical contacts that produce
very sharp edges (and bounces).
| Quote: | Please explain how the interfering signal would be generated
and propagated, in a manner that stands up to mathematical
or electrical engineering scrutiny.
|
OK. You have a set of POTS contacts (either pulse dialer or
on-hook) that are open but have voltage across them. Then they are
mechanically closed (and probably bounce open & closed a few times
in a ms or so). Current suddnly starts to flow, rapidly building
a magnetic field. This change in magnetic field induces a current
on all nearby conductors. Twisted pair is good because the two
conductors are balanced (both generating and receiving pairs),
but it isn't perfect, and magnetics follow an inverse square law.
If this generated current is sufficiently high (differential)
and long, the ethernet tranceiver transformer will register
the noise, not the data. This ruins the bit, and the packet.
| Quote: | Further, how could any phone device that generates such
interference get FCC approval for connection to the phone
line? If it's producing such interference to ethernet,
it might also do so to various radio services.
|
Extremely easily. I'm talking about intermittant noise,
not continuous interference. Hard to detect transients,
especially in analog signals.
-- Robert |
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James Knott
Guest
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| Posted:
Thu Sep 08, 2005 9:44 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
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Robert Redelmeier wrote:
| Quote: | My overall point is that the effects of noise are different on
digital and analog signals. Digital is NOT immune to noise.
It just tolerates low levels continuously with impunity.
Bug digital is vulnerable to spikes/high noise levels, even
if fairly rare. Analog rides these through but is vulnerable
to continuous low levels.
Your comment about "All it takes is a single spike to ruin
one bit, then the 12 kbit packet is shot." shows you do
not understand the nature of what's on the wire
Baseband signalling voltage levels. No carrier wave.
|
Any signal carrying intelligence involves changing some aspect, such as
voltage, frequency or phase. If you have a digital square wave on a wire,
you will have a sine wave, at the frequency of the square wave or
fundemental frequency, along with another at 3 times the the fundemental
frequency and 1/3 the amplitude and another at 5 times the fundemental at
1/5 the amplitude, etc to infinity (assuming infinite bandwidth). While
you may have a digial circuit, you have a lot of analog signals. You can
then take a square wave at, for example 1 kHz. You will see the various
sine waves, as described above, at 1 kHz, 3 kHz, 5 kHz etc. If you then
pass that square wave through a perfect low pass filter, with the cut off
frequency somewhere between 1 kHz and 3 kHz, you will remove all the
harmonics and have only a 1 kHz sine wave left. Further, since ethernet
NICs are connected to the cable via a transformer, the signal must be
analog.
Ethernet uses modulation to create a signal that can transit the cable, NIC
transformers etc. Please read up on Manchester encoding, as used in
10baseT. Incidentally, to pass a signal through a transformer, without
distortion, you need a signal that is balance, with equal energy above and
below 0V. If there is any DC bias in that signal, it will be lost. For
mathematical proof of this, read up on differential calculus.
| Quote: | Dial pulses won't do it. Hanging up the phone won't do it.
Both of these may be mechanical contacts that produce
very sharp edges (and bounces).
Please explain how the interfering signal would be generated
and propagated, in a manner that stands up to mathematical
or electrical engineering scrutiny.
OK. You have a set of POTS contacts (either pulse dialer or
on-hook) that are open but have voltage across them. Then they are
mechanically closed (and probably bounce open & closed a few times
in a ms or so). Current suddnly starts to flow, rapidly building
a magnetic field. This change in magnetic field induces a current
on all nearby conductors. Twisted pair is good because the two
conductors are balanced (both generating and receiving pairs),
but it isn't perfect, and magnetics follow an inverse square law.
|
I'll describe pulse dialing, as it's a simpler case than the hook switch,
because it's a periodic function. With pulse dialing (assuming 50 % duty
cycle for simplicity), you will typically have a 10 pulse per second, or 10
Hz, square wave. That square wave, as I have described before, is composed
of a sine wave at 10 Hz and a series of harmonics. This is a fundamental
fact, proven both mathematically and in experiment. And again, as has been
irrefutably proven over the years, the amplitude decreases in proportion to
harmonic order. There is absolutely no way, for a square wave at 10 Hz, to
generate significant energy levels at ethernet frequencies. It is
physically impossible. Now when you take the hook switch contacts
operating, you have a similar situation WRT Fourier analasys, but since
it's not a periodic function, the calculations become more complex.
So, yes, contacts can generate noise at higher frequencies, but by the time
you get to ethernet frequencies, there is simply not sufficient energy to
cause interference. In order for such pulsing to have sufficient energy in
the range of frequencies used by ethernet, it would have to be of extremely
short duration. You will then find circuit capacitance and inductance will
not permit sufficient bandwidth for such a pulse to exist. That pulse will
then be much broader and lower amplitude, due to the low pass filtering,
caused by that capacitance and inductance.
| Quote: | Further, how could any phone device that generates such
interference get FCC approval for connection to the phone
line? If it's producing such interference to ethernet,
it might also do so to various radio services.
Extremely easily. I'm talking about intermittant noise,
not continuous interference. Hard to detect transients,
especially in analog signals.
|
Situations such as dialing and hook switch operation are very easy to
repeat. Either the phone creates such interference or it doesn't. Again,
if the phone managed to produce signals capable of interfering with
internet are produced, they won't get far, due to the low pass filter
effect, that exists in every circuit.
You have yet to describe any source of such interference. If you still
believe that pulse dialing or hook switch operation can, you're proving
that you don't know what the hell you're talking about. |
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James Knott
Guest
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| Posted:
Thu Sep 08, 2005 9:59 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
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Robert Redelmeier wrote:
| Quote: | James Knott <james.knott@rogers.com> wrote:
Every desired signal on a phone line is below 4 kHz and
ethernet signaling is in the several MHz range. This means
that the only way one of those signals on a phone line could
interfere with ethernet, would be if it were to generate
significant energy (harmonics) in the frequency range
that ethernet is operating in.
Harmonics aren't the only way to generate energy. As a
rule, harmonics allow energy levels to build by reflection
and reinforcement.
|
???
What do you mean by " reflection and reinforcement"? If you're referring to
standing waves, they don't change the frequency of the signal. What they
will do is create voltage (or current) maximum and minimum nodes at
periodic intervals along a transmission line and then only if the line is
not properly terminated.
Please explain how a cable can generate energy. Last I heard, you can't
create or destroy energy, except in a nuclear reaction.
How does a cable take a signal below 4 kHz, and convert it to something in
the range of several MHz? |
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Watson A.Name - \"Watt Su
Guest
|
| Posted:
Sat Sep 10, 2005 10:30 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
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|
"James Knott" <james.knott@rogers.com> wrote in message
news:FLudnZ2dnZ2xOp30nZ2dnUnwvd6dnZ2dRVn-yJ2dnZ0@rogers.com...
| Quote: | Robert Redelmeier wrote:
James Knott <james.knott@rogers.com> wrote:
Every desired signal on a phone line is below 4 kHz and
ethernet signaling is in the several MHz range. This means
that the only way one of those signals on a phone line could
interfere with ethernet, would be if it were to generate
significant energy (harmonics) in the frequency range
that ethernet is operating in.
Harmonics aren't the only way to generate energy. As a
rule, harmonics allow energy levels to build by reflection
and reinforcement.
???
What do you mean by " reflection and reinforcement"? If you're
referring to
standing waves, they don't change the frequency of the signal. What
they
will do is create voltage (or current) maximum and minimum nodes at
periodic intervals along a transmission line and then only if the line
is
not properly terminated.
Please explain how a cable can generate energy. Last I heard, you
can't
create or destroy energy, except in a nuclear reaction.
How does a cable take a signal below 4 kHz, and convert it to
something in
the range of several MHz?
|
The last time I checked, the cable creates its own energy by acting as
an antenna. Nearby radio stations can induce signals that are strong
enough to interfere with data signals. This is less true for well
balanced cables, but it can still happen. The world's not perfect,
unfortunately, as theory would have you believe.
Corrosion and/or rust on a contact can cause rectification and detection
of signals, making them mix and/or change frequency. Again, the world's
not perfect, unfortunately, as theory would have you believe. |
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James Knott
Guest
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| Posted:
Sat Sep 10, 2005 11:27 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
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Watson A.Name - "Watt Sun, the Dark Remover" wrote:
| Quote: | How does a cable take a signal below 4 kHz, and convert it to
something in
the range of several MHz?
The last time I checked, the cable creates its own energy by acting as
an antenna. Nearby radio stations can induce signals that are strong
enough to interfere with data signals. This is less true for well
balanced cables, but it can still happen. The world's not perfect,
unfortunately, as theory would have you believe.
|
That's not creating energy. It's merely conducting energy from another
source, such as a radio station. Then again, if that was a problem, it
wouldn't likely require the presence of a phone line in the CAT5 cable to
make it one.
| Quote: |
Corrosion and/or rust on a contact can cause rectification and detection
of signals, making them mix and/or change frequency. Again, the world's
not perfect, unfortunately, as theory would have you believe.
|
Yes, as I mentioned earlier, corroded connections can generate harmonics,
but they still cannot create energy. It can, through the generation of
harmonics, affect the frequency distribution of the energy, but not create
more than there was to begin with. And again, the harmonics will have
reduced amplitude with harmonic order. It's been a long time since I've
looked at the harmonic distribution of a perfect half wave rectifier (the
best you can get with a perfect diode), so I don't recall the exact
details. However, here's some info about harmonic distribution, in both
full and half wave rectifiers. Don't forget, corrosion is not likely to
form a "perfect" rectifier, so the amount of harmonic energy will be even
less.
http://www.dranetz-bmi.com/pdf/harmonicspart3.pdf
I've never claimed a perfect world, but some people seem to be making some
extraordinary claims about potential problems, without examining the real
world facts, that must follow the laws of physics. Incidentally, a phone
line that generates significant levels of harmonics, does so by creating
significant levels of distortion in the desired signal. Such a line would
not go unnoticed for long. |
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Jack Masters
Guest
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| Posted:
Sun Sep 11, 2005 9:50 pm Post subject:
Re: Single Cat5e for Computer Network & Telephone? |
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James Knott wrote:
| Quote: |
As for your area, what have they got against grounding? Lightning induced
surges are generally common mode, which a protector across the pair won't
protect against.
Exactly. Pure lazyness on the part of the phone company; in this country |
the phone company is a 100% pure monopoly (hopefully not for much longer
though), so they can get away with anything. The typical installation is
'drop a line from the nearest pole, run it through the nearest
ventilation duct (saves the trouble of having to drill a hole through
the wall), and terminate it in a little plastic box with 3 surge
protectors and a telephone jack.
Finding (or creating) a decent ground point is way too much trouble.
Besides, the exchanges are properly protected, all that will break is
CPE, which they don't care about. |
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