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(Svante) wrote in message

Thank you for the offer, but I am the (perhaps silly) type of guy that
tries to understand things and make my own computer programs. I know
it is slower, but I feel that I learn from doing this.

I do that too, and I feel the same way. The program I was refering to
was one I wrote about 20 years ago. (My, how time flys.) Write your
own program, have fun, enjoy. :-)

Well, another way would be to take an ohm-meter and measure it's
resistance. That would be another aspect, that is VERY relevant. And
at least in my mind that is an easier measurement than the delay
measurement.

No, delay is the easiest to measure. All you need is a ruler. Measure
how long the cable is. The wave in cable travels at 66% to 90% of the
velocity of light, depending on the dialectric material.

Hmmm... So what is the typical XL/R ratio for audio frequencies? :-)
If that is a prerequisite, IS the transmission line model really valid
for audio frequencies?

As a rule of thumb, the XL should be 10 times higher than R. For 12
gage cable, XL/R starts getting too low below 10 KHz.

Even in the case where the series resistance dominates, and the load
varies with frequency?

In that case, the transmission line numbers become such a small part
of the answer you can forget about them. At that point, you can use
Ohms law to calculate the cable loss.

...and this you do for one frequency at a time, right? I mean, if you
want to do this for another frequency, you go through this process
again?

That is right! As far as the computer is concerned, each frequency has
a different cable, one with it's own loss and phase shift
characteristics. Each frequency also has a different termination
impedance. The computer calculates a new cable and a new load at each
frequency. It's a lot of work to do it that way, but the the computer
never complains.

OK, but then I would argue that we are no longer talking about a
resistor, but a model of a real physical resistor, that contains other
elements as well. OK, I'm picky again.

I agree. An ideal resistor is a simpler circuit. Still the
transmission line is a fairly simpler entry into the matrix. No long
equations needed. Just convert the cable S-parameters into
Y-parameters, and pop them into the matix, at four places.

I'll have to think a bit about this to understand it. I have written
programs that reduced passive circuits down to 4-poles, but it was
some time ago.

The easiest way to program a computer to do circuit analysis, is to
write the circuit conductances into a large matrix. The conductance
(y-parameter) is entered at the row and column that correspond to the
circuit node the conductance is across. This is much easier than
trying to use different equations for every different circuit
topology. The matrix is reduced to one number, and that number is the
voltage at the output node.

There were four types, G, Y, H and Z, was it? The H one
is often used to describe transistors, and the Y would be one of those
that you describe, right?

H, Y, Z, G, and S parameters can be converted from one to the other.
You can measure a two-port device using whatever parameters suit your
test equipment the best, then convert them to any other type of
parameters.

Y, Z and H parameters require open or short circuits on the port
during measurement. A lot of devices object of having their inputs or
outputs short circuited, so S-parameters have become very popular.(
S-parameters are measure with a load on the output.)

Bob Stanton