The formulas for calculating T2FD dimensions are given. The length of each leg ("A'') from the center is equal to 50,000 divided by the lowest desired operating frequency (in kHz) and then multiplied by 3.28. The answer is in feet.
http://www.hard-core-dx.com/nordicdx/antenna/wire/t2design.html
Performs excellently. Compact in size it gives great signal gain, wide frequency coverage, and exceptionally low noise characteristics
http://www.hard-core-dx.com/nordicdx/antenna/wire/index.html
A discussion.
http://www.hard-core-dx.com/nordicdx/antenna/wire/t2fdfeed.html
Comparison with other antennas with T2FD.
http://www.hard-core-dx.com/nordicdx/antenna/wire/t2fdcomp.html
The T2FD is essentially a closed loop design with the element ends folded back and joined by a noninductive resistor. The feed line can be 300 to 600 ohm twinlead or open line.
http://www.hard-core-dx.com/nordicdx/antenna/wire/t2fd.html