Asimov wrote:

You are right there is a connection between wire diameter and spacing.
It has to do with the self inductance and resistive losses of two
conductors in proximity. By contrast a balanced line has a wider
spacing and also allows part of the energy to travel unhindered, so to
speak.

Conductors don't "hinder" the traveling of energy. Energy travels just
as well along close spaced conductors as it does along wide spaced ones.
In fact, loss due to radiation is greater with wider spacing than narrow
(although it's still negligible with the lines typically used).

It helps if the balanced line is designed to be close to the
theoretical impedance of free space.

Please explain in what way it "helps". No equation, formula or
theoretical treatment I'm aware of shows any advantage, change, or
anomaly in tranmission line behavior at a value equal to or near the
characteristic impedance of free space. (As has been pointed out many
times before in this newsgroup, the impedance of free space is the ratio
of E/H fields in a plane wave; the impedance of a transmission line is
the ratio of voltage to current of a traveling wave. Although they have
the same unit of measure, they're different things -- like foot-pounds
of work and foot-pounds of torque.)

The price to pay is that it is
more susceptible to the environment.

Do you mean that lines of approximately 377 ohms impedance are more
susceptible to the environment than 200 or 600 ohm lines? In what ways? Why?

The loss in coax is a trade off
to achieve stability.

Coax is more stable than open wire line? Does open wire line drift in
some way?


A*s*i*m*o*v

... "Beware of all enterprises that require new clothes." -- THOREAU

Roy Lewallen, W7EL