Abstract: The drive coupling for an antenna having a shorting assembly traveling along a helix to tune the antenna includes a metal rotating drive shaft extending concentrically through the shorting assembly with flutes on the drive shaft in the region of the helix. A metal shielding cylinder is disposed coaxial to and spaced from the outer surface of the drive shaft and provides an outer member of the shorting assembly. A drive bearing of dielectric material is disposed to engage the flutes and the shielding cylinder so that rotation of the drive shaft rotates the shielding cylinder to cause the shielding assembly to travel along the helix. A guide bearing of dielectric material is disposed to engage the shielding cylinder and the end of the drive shaft remote from the flutes.

Abstract: The structure includes a tunable high power MF/HF transmitting antenna having a vertical axis and a shorting assembly driven along the vertical axis to tune the high power antenna. A hollow rotating drive shaft is disposed coaxially of the vertical axis within and coupled to the shorting assembly to drive the shorting assembly. A plurality of additional antennas are disposed in a vertical stacked arrangment above the high power antenna. A plurality of service conductors each coupled to a different one of the plurality of additional antennas are enclosed in a conduit disposed coaxially of the vertical axis and within the drive shaft. A tunable ferrite isolator is disposed below the drive shaft and includes the conduit to enable the conduit and the service conductors to pass through the high power antenna with a minimum of modification to the performance of the high power antenna.