T2FD antenna

Although inferior in terms of efficiency[3] (at least 30% of the RF power is lost as heat in the resistor [3][4]) to antennas specifically designed for given frequency bands, or optimized for directionality, its all-around performance, relatively modest size, low cost, and the fact that it does not require any complicated matching to operate with a standard shortwave transmitter, have made it popular in professional shortwave communications where ERP or gain are not a concern.

[1][2] It was a popular antenna design during the middle of the 20th century, but fell out of common use during the latter part of the century with the growing popularity of upper HF and VHF frequencies, which needed dipoles with more feasible lengths – only 16 foot (4.9 m) or smaller, as opposed to 70 foot (21 m) quarter-wave antennas needed for the lower "short"-wave bands.

Another factor contributing to its fall in popularity was the increasing use of low-impedance 50 Ω antenna feedline, which requires impedance matching at the T²FD feedpoint.

There have also been disputed claims that this antenna is comparatively insensitive to man-made radio interference; if true, that would make the design useful in urban environments, where a low noise floor is often more beneficial than high received signal strength.

[citation needed] A typical T²FD is built as follows,[5] out of two parallel-wire conductors: The commercially available B&W AC3-30 and B&W DS1.8-30 antennas[6] vary from the above to cover 3–30 MHz using a 90 foot length with an 18 inch spacing of the wires.

If such long spans cannot be accommodated, smaller antennas will still give adequate receive-only performance down to about half of their lowest design frequency.

At shortwave frequencies, a dipole cut for the longest used wavelength, fed with ladder line and matched with an antenna tuner, would make better use of the applied power than the T²FD.