models for simulating a dsl link

A couple of recent threads about the effects of DSL (micro)filters gave me the
idea of analysing their effect under various conditions in a simulation package.

I've got several examples of filters of varying designs here and I'd really like
to know how much difference and indeed what kind of differenc(es) they can make.

As some know from previous threads I'm a bit sceptical about how much they
affect the DSL signal itself.

Before I can do this I need some suitable 'models' for the various bits of
telecom gear involved. Can anyone point me in the right direction ?

Graham

Eeyore wrote:
>
> A couple of recent threads about the effects of DSL (micro)filters gave me the
> idea of analysing their effect under various conditions in a simulation package.
>
> I've got several examples of filters of varying designs here and I'd really like
> to know how much difference and indeed what kind of differenc(es) they can make.
>
> As some know from previous threads I'm a bit sceptical about how much they
> affect the DSL signal itself.
>
> Before I can do this I need some suitable 'models' for the various bits of
> telecom gear involved. Can anyone point me in the right direction ?

Unlike cable (DOCSIS) modems, DSL comes in many flavors with widely
varying performance specifications. Take a look at the Wikipedia article
for a start (http://en.wikipedia.org/wiki/DSL). I don't think there is
an industry standard like there is for cable broadband. Each
manufacturer has their own specs.

As far as the DSL filters go, since they are intended to be placed on
all of the other (non DSL) equipment on the shared line, their
performance might also depend on the nature of the telephone equipment
connected downstream of them.

--
Paul Hovnanian private.php?do=newpm&u=
------------------------------------------------------------------
All men are mortal. Socrates was mortal. Therefore, all men are
Socrates.
-- Woody Allen

"Paul Hovnanian P.E." wrote:

> Unlike cable (DOCSIS) modems, DSL comes in many flavors with widely
> varying performance specifications. Take a look at the Wikipedia article
> for a start (http://en.wikipedia.org/wiki/DSL). I don't think there is
> an industry standard like there is for cable broadband. Each
> manufacturer has their own specs.

That won't affect the basic physics though, which is all I want to model.


> As far as the DSL filters go, since they are intended to be placed on
> all of the other (non DSL) equipment on the shared line, their
> performance might also depend on the nature of the telephone equipment
> connected downstream of them.

That's exactly one of the things I'd like to experiment with.

Graham

"Eeyore" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...

> As some know from previous threads I'm a bit sceptical about how much they
> affect the DSL signal itself.

You can do a simple test by unplugging the filter and putting a lead from
the ADSL modem straight into the phone socket.
Although the different quality of the cable might be as important as the
filter.

They are bound to attenuate slightly.
Even a straight through extensions lead three inches long would have some
attenuation.
Whether it makes enough of a difference is the issue.


--


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Gordon Hudson wrote:

> "Eeyore" <(E-Mail Removed)> wrote in message
>
> > As some know from previous threads I'm a bit sceptical about how much they
> > affect the DSL signal itself.
>
> You can do a simple test by unplugging the filter and putting a lead from
> the ADSL modem straight into the phone socket.

Yes I know this kind of thing. It misses the point though. I want to *quantify*
in decibels of loss, frequency response etc the effect of such things using a
modern electronics simulation package.


> Although the different quality of the cable might be as important as the
> filter.

Absolutely not. If a cable wasn't twisted pair that might make a difference
though. I wouldn't call that 'quality' myself. I like to see things called by
their correct names.

Graham

If you wish to model the filters you will need to measure the inductance and
capacitance of the elements of the filter.

If you can do this you probably have the equipment to measure the real
performance so why not simply measure the performance under the conditions
you are interested in?

Alec


"Eeyore" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>A couple of recent threads about the effects of DSL (micro)filters gave me
>the
> idea of analysing their effect under various conditions in a simulation
> package.
>
> I've got several examples of filters of varying designs here and I'd
> really like
> to know how much difference and indeed what kind of differenc(es) they can
> make.
>
> As some know from previous threads I'm a bit sceptical about how much they
> affect the DSL signal itself.
>
> Before I can do this I need some suitable 'models' for the various bits of
> telecom gear involved. Can anyone point me in the right direction ?
>
> Graham
>

Alec wrote:

> If you wish to model the filters you will need to measure the inductance and
> capacitance of the elements of the filter.

Yes. The Capacitance values are printed on the caps btw.


> If you can do this you probably have the equipment to measure the real
> performance

Not from the exchange end. I don't have access to that for one thing ! The whole
entity of the line from exhange to subscriber is what I intend to simulalte.
It's quite simple as long as I can get the numbers to punch in for various
pieces of kit such as phones.

Let me put it another way. Right now I'm looking for phone schematics so I can
make a model of them. Can you point me in the direction of any ?


> so why not simply measure the performance under the conditions
> you are interested in?

Because I want to simulate any number of generalised (and specific) conditions
and measure the effect of individual changes.

Measuring performance the wayyou suggest is so passe these days and hoplessly
time consuming.

Graham

"Eeyore" <(E-Mail Removed)> wrote in message
news:(E-Mail Removed)...
>
>
> Alec wrote:
>
>> If you wish to model the filters you will need to measure the inductance
>> and
>> capacitance of the elements of the filter.
>
> Yes. The Capacitance values are printed on the caps btw.
>
>
>> If you can do this you probably have the equipment to measure the real
>> performance
>
> Not from the exchange end. I don't have access to that for one thing ! The
> whole
> entity of the line from exhange to subscriber is what I intend to
> simulalte.
> It's quite simple as long as I can get the numbers to punch in for various
> pieces of kit such as phones.
>
> Let me put it another way. Right now I'm looking for phone schematics so I
> can
> make a model of them. Can you point me in the direction of any ?

Try looking on http://www.telephonesuk.co.uk/ There's wiring diagrams and
schematics on there, I believe (not looked myself so don't shout at me if
there isn't )

John

On 25-May-2007, "Alec" <(E-Mail Removed)> wrote:

> If you wish to model the filters you will need to measure the inductance and
> capacitance of the elements of the filter.
>
> If you can do this you probably have the equipment to measure the real
> performance so why not simply measure the performance under the conditions
> you are interested in?

You can measure the physical parameters R, L and C and put these
into an analysis package to get the passband, attenuation, phase shift
and other parameters, expressed in compatible units such as db.

This won't be much help because the filter assumes input and
output impedance parameters that are laboratory design concepts,
that don't match real life, so your analysis package graphs won't
match real life. In fact you may find that what appears to be a
cheapo sub-standard filter gives better results because it creates
a better match between the incoming lines impedance, and the
modems input impedance.

Like a lot of HF electronic design you can impedance match (often with
difficulty) at a specific frequency, but the match rarely holds over
a range of frequencies where the source and load are complex,
and frequency dependent, numbers.
Complex numbers in this sense are numbers/vectors with real and
imaginary components, where you get into hyperbolic functions.

Like your TV antenna should be 75 ohms across its frequency range,
and your TV's antenna socket should be 75 ohms across the
full range of TV channel frequencies, it's a pie in the sky concept.
In the heyday of CB radio it was all about matching, many and
various, were the weird and wonderful combinations of coils and
capacitors, pie, half pie, etc.

(E-Mail Removed) wrote:

> "Alec" <(E-Mail Removed)> wrote:
>
> > If you wish to model the filters you will need to measure the inductance and
> > capacitance of the elements of the filter.
> >
> > If you can do this you probably have the equipment to measure the real
> > performance so why not simply measure the performance under the conditions
> > you are interested in?
>
> You can measure the physical parameters R, L and C and put these
> into an analysis package to get the passband, attenuation, phase shift
> and other parameters, expressed in compatible units such as db.

Correct.


> This won't be much help because the filter assumes input and
> output impedance parameters that are laboratory design concepts,
> that don't match real life, so your analysis package graphs won't
> match real life. In fact you may find that what appears to be a
> cheapo sub-standard filter gives better results because it creates
> a better match between the incoming lines impedance, and the
> modems input impedance.

But *does* the filter (did the filter designer) assume that ? It certainly doesn't
have to be that way. That's why I fancy simulating some.


> Like a lot of HF electronic design you can impedance match (often with
> difficulty) at a specific frequency, but the match rarely holds over
> a range of frequencies where the source and load are complex,
> and frequency dependent, numbers.
> Complex numbers in this sense are numbers/vectors with real and
> imaginary components, where you get into hyperbolic functions.
>
> Like your TV antenna should be 75 ohms across its frequency range,
> and your TV's antenna socket should be 75 ohms across the
> full range of TV channel frequencies, it's a pie in the sky concept.
> In the heyday of CB radio it was all about matching, many and
> various, were the weird and wonderful combinations of coils and
> capacitors, pie, half pie, etc.

At the lowish frequencies used for ADSL I'm not clear how much that 'matching' is
relevant. It certainly won't be a big issue at ~ 30kHz for example, rather more of
one at 300kHz and 1MHz..

Graham