Just out of curiosity, if anybody happens to know this,( I'm sure someone does), what exactly determines the characteristic impedance in coax? I understand that the shielding plays a role; but is it the material of the shielding or the distance of the shielding from the core, plus the dielectric constant of the jacket? If it's a combination of distance and dielectric constant, then it would seem to me to be impedance that is capacitive in nature. Thanks!