David,

Barker & Williamson "BWD-90" T2FD Antenna provides full coverage
of the Shortwave Bands from 1.8 MHz to 30 MHz and is 90 Feet long.
http://www.bwantennas.com/ama/fdipole.ama.htm
http://www.universal-radio.com/catal...wire/0872.html

Idealy at 90 Feet long this "BWD-90" T2FD Antenna would
require a 64 Feet elevation difference between the Tip-Ends
of the Antenna.

Practically speaking the BWD-90 T2FD Antenna at 90 Feet long
would only need a 45 Feet elevation difference between the
Tip-Ends of the Antenna. This would require a High Mounting
Rigging Point of 60 Feet and a Low Mounting Rigging Point of
15 Feet.

iane ~ RHF