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(Bob-Stanton) wrote in message
So... The precision would be +/- 15%. My ohm meter is within the
percent, I think, and I know where it is. I always have to look for
the ruler... :-)

Velocity factor of a given cable can be known to within a small
fraction
of one percent. When I said 66% to 90% I was refering to different
types of
cable. For example, 300 twin lead has a velocity factor of 66%, while
coax
such as RG59 has a velocity factor of 80%.

Yes, I probably would have thought that was the case. Anyway, my
multimeter is still easier to find than my ruler (I wonder what that
says about me... :-) ).
Also, the multimeter will tell me directly how many ohms there is in
the cable. My ruler tells me how many centimeters there are, not how
many (nano-)seconds.
So to get the delay I need a ruler AND a calculator. But let's not
argue about this... :-)

So, how do the equations look, how do I get from delay & loss to
Y-parameters?

Here is a model for 40 feet of 12 gage speaker wi

! 12 gage "speaker cable

# HZ DB S R 100

! S11 S21 S12 S22

19 -120 0 -6.95e-3 278.2e-6 -6.95e-3 278.2e-6 -120 0
20 -120 0 -6.95e-3 292.8e-6 -6.95e-3 292.8e-6 -120 0
21 -120 0 -6.95e-3 307.2e-6 -6.95e-3 307.5e-6 -120 0

The file above is an S-parameter, two-port file.

The first line is a comment.
The second line discribes the file: Frequency = "HZ", mag in "dB",
parameter type "S", reference impedance 100 Ohms.

The third line is a comment.

The 20 Hz line, completely models 12 gage cable (at 20 Hz).

It is much simpler to model a cable with one line of code, than with a
bunch
of resistors, capacitors and inductors.

Now, you need to convert line 20, into Y-parameters.

In the book "Solid State Radio Engineering" by Herbert L. Krauss and
Charles W. Bostian, on page 110 is a conversion formula:

dS =(S11*S22)-(S21*S12)

Yin = (S22-S11-dS/S22+S11) * (1/Z)
Yf = (-2*S21/S22+S11+dS) * (1/Z)
Yr = (-2*S12/S22+S11+dS) * (1/Z)
Yo = (S11-S22-dS/S22+S11+ds)* (1/Z)

From the Y-paramerters, you can find: delay, loss, impedance,
inductance, resistance/capacitance and phase shift of the cable. This
model will work with *any* source impedance, and with *any* load.

Now we're talking, these were the nuts and bolts I wanted to see. I
don't know if I think that this is easier than the RLC implementation,
but I guess that would depend on the computer implementation that is
available. One thing in the above explanation that seems akward is
that it seems like you have to have a TABLE of the s-parameters for
each and every frequency? In the RLC model it is easy to calculate the
impedances for ANY frequency. Is there any method to CALCULATE the
S-parameters, rather than having a large table?
Another clarification, the S-parameters above are they given as
magnitude/phase pairs? I assume that the two numbers that appear for
each S-parameter in some sense describe real and imaginary parts, or
amplitude/phase if you wish, is that correct?