A flexible drive cable comprises a flexible cable body, a pair of electrically insulated wires disposed through an axial lumen of the cable body, and a resilient support tube disposed over the wire pair. The resilient support tube provides support for the wire pair to help the wire pair recover from bending and deformation which may occur during storage or use of the drive cable. The support tube is usually liquid impermeable to maintain an air gap around the wire pair. The air gap improves shielding and maintains a constant overall impedance across the drive cable. The drive cable may be combined with an ultrasonic transducer at its distal end to form an ultrasonic transmission core.