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Hello!
I'm trying to model a cable in ltspice. I read some articles and everybody talk about the implementation of the ABCD matrix in spice. I will do the same but i don't understand how can i do...

Somebody can help me?

Thank you,
desi

In message <ksu4kg+9r5j@...>, dated Fri, 26 Jul 2013, desi2209 <desi0985@...> writes:

I'm trying to model a cable in ltspice. I read some articles and everybody talk about the implementation of the ABCD matrix in spice. I will do the same but i don't understand how can i do...

There is a good article about 2-port networks and the ABCD matrix at:



but the 'ABCD matrix' is a very general concept and in order to do simulations you have to decide which particular matrix you want to use, h, k, z, y, a, b or s. If it's a high-frequency cable, you probably want to use the s-matrix.

You need to search Files => Tables of Contents => All Files on the list's web site for 's-parameters', using your browser's search or 'Find' facility.
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OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Why is the stapler always empty just when you want it?

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

I need to simulate the cable behaviour between 90 kHz and 150 kHz. For these reason I think is always cited the abcd matrix and no others.

How I have to go on if I choose to work with the a matrix?
My teacher said that it is possible to define a new component in ltspice with the required matrix but I didn't find no hint in the web about it.

thank you,
desi

Instead of a matrix representation, you can use the normal transmission
line that is built into LTspice. At those low frequencies, it should work
well.

So I'm wondering what sort of "cable" you need to model, and why an
ordinary transmission line isn't what those articles were using?

Andy

i'm working with power line communication systems.
The articles explain the trasmission line theory for cable modelling, but then start to talk about abcd matrix and the advantage to describe the cable with this element, because on power line cable there are several branches and a complex topology to describe and the abcd matrix permitts to evaluate the total transfer function simply with matrix multiplications.

What i need is a way to define different elements of the line (segment of cable, different types of branches) in order to have a database to use to display the desired network topology and analyze the signal behaviour through the line.

In message <ksud7b+n6i9@...>, dated Fri, 26 Jul 2013, desi2209 <desi0985@...> writes:

What i need is a way to define different elements of the line (segment of cable, different types of branches) in order to have a database to use to display the desired network topology and analyze the signal behaviour through the line.

This can be an exceedingly complex matter. I think you need much more guidance from your tutor.

In your previous post you said:

I need to simulate the cable behaviour between 90 kHz and 150 kHz. For these reason I think is always cited the abcd matrix and no others.

How I have to go on if I choose to work with the a matrix?

Now you say 'a-matrix'. That is NOT the same as ABCD matrix, it's one specific example of the general concept.

My teacher said that it is possible to define a new component in ltspice with the required matrix but I didn't find no hint in the web about it.

It's a black box with four terminals. It has input voltage and current and output voltage and current; these are four variables. It also has a feedback path and a feed-forward path, but being passive, these have equal properties.

The a-matrix gives you two equations. The left sides are input and output quantities, while the right sides connect the four variables with these quantities, the coefficients being the elements of the 2 x 2 a-matrix.

You need to make one of these 'black boxes' for each cable type and length.

Does that help? I have to say that the a-matrix is, as far as I know, not often used.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Why is the stapler always empty just when you want it?

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

In message <6iHTSlOY3r8RFwLH@...>, dated Fri, 26 Jul 2013, John Woodgate <jmw@...> writes:

What i need is a way to define different elements of the line (segment
of cable, different types of branches) in order to have a database to
use to display the desired network topology and analyze the signal
behaviour through the line.

This can be an exceedingly complex matter. I think you need much more guidance from your tutor.

I found another Wikipedia page that specifically explains a-parameters:



You need to scroll down quite a bit.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Why is the stapler always empty just when you want it?

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK

--- In LTspice@..., "desi2209" <desi0985@...> wrote:

i'm working with power line communication systems.
The articles explain the trasmission line theory for cable modelling, but then start to talk about abcd matrix and the advantage to describe the cable with this element, because on power line cable there are several branches and a complex topology to describe and the abcd matrix permitts to evaluate the total transfer function simply with matrix multiplications.

What i need is a way to define different elements of the line (segment of cable, different types of branches) in order to have a database to use to display the desired network topology and analyze the signal behaviour through the line.

Let me save you a lot a trouble. The domestic ring main is not a high speed data circuit. If you take data at 1Mbps then 1 data bit is just 1 micro second duration.
This is very short compared to any electrical spikes, surges, or noise on a domestic ring main. It's also the reason why powerlines are inferior to ethernet or wireless. I've seen very poor and erratic throughputs on power line adapters always ending up loosing be50 and 90% of the original speed.
Don't let this put you off, but you will need to explain in your simulation how the power line overcomes data dropouts, e.g. 25ms contact bounce from a switch and even longer noise periods from heavy loads like kettles or devices containing motors.

hal8000b wrote:

Let me save you a lot a trouble. The domestic ring main is not a high speed

data circuit. If you take data at 1Mbps then 1 data bit is just 1 micro
second duration.
...

I have mixed feelings about this.

First, it is a homework assignment. She cannot "save herself the trouble"
by telling the teacher that the assignment was wrong because the method is
inferior to running brand new copper or fiber. Sometimes it is impractical
to do that and you need to work with what you have.

Note that the signal range is 90-150 kHz, so it is not very high speed and
the symbol rate can't be anything close to 1Mbps. It also isn't the "BPL"
that floods the power lines with 2-50 MHz, used for Internet access, and a
major source of interference.

Power line communications have been used for close to a century, by the
power utilities themselves to monitor their own circuits without having to
run additional wires. The signaling rate might be as low as 1 to 10bps
(bps, not Mbps). I'm sure the power companies understand the difficulty of
carrying data signals in a noisy environment.

I am puzzled about the choice of a matrix representation for the lines. It
seems to me that gives you two major hurdles: how to generate the matrices
for typical power lines, and how to use it in a simulator. It would be one
thing if you were handed the matrices and instructed to use them. If
instead all you have is a physical description of the lines and topologies,
then SPICE's standard transmission line element might be the best choice.

Be aware that some things in SPICE work nicely in the frequency domain (.ac
analysis) but not the time domain (.tran analysis) or vice-versa.
(Transmission line models work correctly in both.)

Regards,
Andy

In message <CALBs-Ti+aoOcfQycr1TTkGEM_rctOP6+uArGyOTTS=YT=xJhsA@...>, dated Sun, 28 Jul 2013, Andy <Andrew.Ingraham@...> writes:

If instead all you have is a physical description of the lines and topologies, then SPICE's standard transmission line element might be the best choice.

One significant effect in PLC is mode conversion; the signal is launched differentially but mode conversion to common-mode occurs at discontinuities in the cables, such as Y-junctions, switches etc. The cables have three conductors and should be treated as 3-wire transmission lines (which is written-up in the literature). So a 3-wire 'cell', used with LTspice's 'array' feature is more appropriate than the standard transmission line.
--
OOO - Own Opinions Only. With best wishes. See www.jmwa.demon.co.uk
Why is the stapler always empty just when you want it?

John Woodgate, J M Woodgate and Associates, Rayleigh, Essex UK