I'm also a ham and a one-time violist, as well as an amateur
instrument-maker.

Jon Teske wrote:
The only time both sides of a
stopped string vibrate is when we play what we
call a "harmonic" and there are several of them on violin strings. A
harmonic is when the violinist lightly touches the string so that the
unexcited side (e.g. not the bowed side) can also vibrate

In particular, you have to touch lightly enough that some energy
can couple into the other half of the string. Some of the energy
is transferred through up-down motion and some through the bending-
stiffness of the string itself. You could see the finger as a series
capacitor to ground, attached to each half of the string by a pair
of resisters bypassed by another capacitor. You can tweak the values
by the way you touch.

I don't think I have ever also considered my violins strings to have
impedance, or reactance, and I haven't quite considered the feedline
problem.

Mechanical impedance/reactance is a widely used idea in mechanical
and civil engineering. The dynamic motion of bridges and buildings
is sometimes even modelled using electronic circuit modelling tools
amongst other methods.

Clifford Heath.