Bill:

[snip]
Being an RF guy, mostly, I am interested in
complex Z0 values of low loss lines, where
Imag(Z0) is no more than a few percent of
Real(Z0). I use exact equations in a Mathcad
program to get detailed answers. I find this
interesting and useful. The "classical" formula
for rho is quite satisfactory, for me.

Bill W0IYH
[snip]

That's the same approach most xDSL experts take
to complex Zo lines. Mathematical simulations
using say MatLab and such are used for designs.

The telephone twisted pair plant certainly has a
very complex Zo although it has extremely
high loss compared to most RF applications which
I know of.

Typically most lines world wide start out with
an approximate 1500 Ohm design basis. That
is the DC resistance of the lines are aimed at
no more than a DC resistance of 1500 Ohms
end to end. The R, L, C, and G primary parameters
of the line vary quite widely. Especially when
one considers there may be one or more
un removeable bridged taps [transmission line stubs]
floating across the line at unknown locations having
resonances directly in band!

A typical xDSL transceiver has a terminating
resistance of 100 Ohms... thus the transmitters
are attempting to transmit energy into a 100 Ohm
load at the end of 1500 Ohms of DC and even
higher at higher frequencies of loss!

Should the transmitter really be adjusted for
maximum power transfer, i.e. a conjugate
match into the local driving point impedance,
when most of the transmit power will be lost
heating up the line and never reach the load?

How will the poor suffering receiver be able to
copy weak signals from the far end of such
a line in the presence of the enormous QRM
from it's own transmitter blasting away on
the same pair it is listening on?

What kinds of line equalizers [tuners?] are used?
What kinds of echo cancellers are used?
What kinds of modulation are used?
What kinds of coding are used?
What is the bandwidth [bps/Hz] efficiency obtained?

Is any of this advanced technology
applicable to amateur radio of the future?

Is anyone interested?

What?

--
Peter K1PO
Indialantic By-the-Sea, FL.