Hi,
I made the tests, mentioned in my posting below. The capacitance, added
by attaching a thin wire (0.4mm) to the topload, works out to around
6pF/m, resp. 1.8pF/foot. That's in fair agreement with Udo's calculation
from the wikipedia formulas, and with Terry Fritz's 1.5 pF/foot, of his
proven simple leader model ...but in not so good agreement with
Antonio's elegant calculation (11pF/m). Perhaps the 1uH/m inductance of
the transmissionline in the model could be a bit different? From the
experiments, the Fres detuning of the secondary system, by adding a thin
wire, is quite remarkable. I "think", only the low overall Q of a
sparking TC (~10), is making it feasible, to tune to zero detuning, and
observing acceptable sparks anyway. Primary detuning to lower Fres seems
indicated, indeed, while not possible excessively, in order not to
hinder breakout. - Well: thin wires are not yet real sparks!
Following, the original results of my tests. Hope the tables appear not
scrambled. They are written with Font "calibri 12", and copied from my
Excel, which I can mail you, if desired (including 2 graphs). Pic's of
the experiment setup also exsist.