A split capacitance-tuning band of a nuclear magnetic resonance (NMR) distributed-capacitance radio-frequency (RF) coil includes a fixed band and a longitudinally-movable (sliding) band, both disposed to overlap a central coil structure. The fixed band is situated along the boundary of the RF coil window. The movable band can move between a proximal position abutting the fixed band and various distal positions. The fixed band provides an RF current path close to the RF coil window, while the movable band allows tuning the coil capacitance and resonance frequency by varying the area of overlap between the movable band and the central coil structure. A longitudinal coupling member is attached to the movable band and to an actuator piston disposed under a probe lower insulator. A chip capacitor is connected between the coupling member and the actuator piston, to provide RF insulation for the movable capacitance band.