The relationship between the three characteristics is more imaginary
than real. It amounts to little more than an old-wives' tale.

The reason attenuation is usually smaller for twin line than coax is
because the twin line conductors are usually of greater diameter than
the coax inner conductor.

And the reason twin line usually has a greater velocity is because the
conductors are spaced further apart and usually there's less
insulating material between them.

But it's quite easy to reverse the situation by obtaining large
diameter, high impedance coax and flimsy close-together twin line.
----
Reg, G4FGQ

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"Hal Rosser" wrote in message
. ..
I've noticed, (but have not studied), some loose relationships in
transmission line characteristics (and I guess waveguides fit in
here).
From an observer's point of view, it seems that a high
characteristic
impedence line (like 400-ohm or 600-ohm ladder line) also is usually
a
lower-loss line, and has a higher velocity factor.
It also seems that some coax may have a low VF and high loss.

Is there a real cause for the relationship of these 3
characteristics of
transmission lines ? Is it something we can generalize ?
It makes some sense to say that the faster a signal gets through the
line,
the less loss it will have - and that gives some credence to the
relationship in VF and loss being inversely associated.