Re: Single Cat5e for Computer Network & Telephone?

Robert Redelmeier wrote:

> James Knott <james.knott@xxxxxxxxxx> wrote:
>> If we're talking about dial pulses interfering with ethernet,
>> we're talking about harmonics.
>
> Why only harmonics? There are other kinds of interference.

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., are composed of sine waves at a fundement and harmonic
frequencies. Noise impluses consist of short duration sine waves
(sometimes called "damped" waves, in that they rapidly decay), no matter
what the pulse shape. "White" noise is simply a collection of sine waves
at many different frequencies. Can you tell me about anything, that can't
be shown to be composed of sine wave functions???

Here's something that might provide you with some idea of what's involved.

http://mathworld.wolfram.com/FourierSeries.html

> Au contraire. You see snow crackles all the time. They
> just aren't very objectionable in an analog transmission
> so long as they're not as continuous as a vacuum cleaner!
> But ethernet _IS NOT_ analog.

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, than electrical
appliances etc. However, this doesn't rule out the possibility of
interference to the TV at stages after the tuner. For example the universe
is filled with radio noise, from a variety of natural sources, including
the after effects of the big bang.

Also, while ethernet carries digital data, the signal is in fact analog, in
that a carrier is modulated by that data. 10 Mb ethernet uses Manchester
encoding and 100 Mb uses something called "multilevel threshold-3"
signalling, where there are multiple levels, depending on the data bits.
If you were to look at it with a scope, you'd see a complex analog
waveform. Also, if it wasn't an analog signal, that is some combination of
sinewaves, with equal enery above and below 0 volts, it couldn't pass
through the NIC transformers, without distortion. Incidentally, you can
take a simple modulation method, such as Manchester encoding and show that
it is composed of various sine waves.

> > A pure sine wave has no harmonics.
>
> http://en.wikipedia.org/wiki/Harmonic
>

I'm well aware of the harmonic structure of music instruments etc. However,
the fact remains that if you have a pure sine wave, it doesn't have
harmonics. Harmonics are only present, when you have a non-sinusoidal
waveform, such as square wave etc. If you can't accept that, then I
suggest you take some math courses.


> > Every other signal does. This means that everything on a
> > phone line is either a sine wave of the sum of a series of
> > sine waves. There is no other possibility.
>
> This is one way (not the only way) to deconstruct signals.
> But a perfectly square wave requires extremely high frequency
> components at very significant power to sharpen the shoulder
> and produce the very quick decay.

Where on earth did you hear that? Please read up on Fourier. He
demonstrated that *ALL* waveforms are composed of some series of sine
waves. That "perfectly square wave" is composed of a fundamental sine wave
and odd order harmonics, where the amplitude of each harmonic is inversely
proportional to it's order. Again, go back and take some math classes and
have your instructor explain it to you.

> > Every other signal does. This means that everything on a
> > phone line is either a sine wave of the sum of a series of
> > sine waves. There is no other possibility.
>
> This is one way (not the only way) to deconstruct signals.
> But a perfectly square wave requires extremely high frequency
> components at very significant power to sharpen the shoulder
> and produce the very quick decay.

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?




.

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