T2FD Broadband Antenna (10-40m)
The Tilted Terminated Folded Dipole (T2FD or TTFD) or Balanced Termination, Folded Dipole (BTFD) - also known as W3HH antenna - is a general-purpose shortwave antenna developed in the late 1940s by the United States Navy. It performs reasonably well over a broad frequency range, without marked dead spots in terms of either frequency, direction, or angle of radiation above the horizon.
The T2FD antenna is a classical antenna in our series of HS4 Legendary Multiband Wire Antennas. It covers 7 bands, 10-12-15-17-20-30-40m. Unlike typical antennas, this is a non-resonant, Traveling Wave antenna with a terminating load. The performance characteristics are quite outstanding. The antenna consists of two symmetrical lengths horizontal radiating elements configure like a folded dipole with a unique spacing. Most importantly, the folded element is loaded with a non-inductive resistor in the middle. The antenna is driven through a broadband Balun into a 50 Ohm coaxial cable. It is broadband antenna and has a SWR less than 1.8:1 from 7-70 MHz. The T2FD features a marginally lower gain than other legendary antennas due to partial energy absorption in the terminating load but it has excellent SWR and is insensitive element length or height above ground. It is the easiest antenna to fabricate and deploy.
This antenna never needs any antenna tuner for proper operation however a 9:1 broadband Balun is required to transform the 450 Ohm feedpoint impedance to 50 Ohm unbalanced for further coax run.. The overall gain on all bands is moderate with adequate low angle radiation for great DX. This antenna is deployed at a height of 12m (40 ft.) above average quality ground and the design accounts for ground absorption losses, antenna wire insulation dielectric losses, other structural losses, etc.
The antenna produces multiple lobes covering wide azimuth sections on most bands but it also produces several deep nulls along the azimuth. Several bands may have deep nulls in the direction of the default beam heading. Hence, the owner of this antenna will need to find the optimum direction of the radiation lobe on each band to leverage the main lobe which provides maximum gain. This may be on either side of the default beam heading. It may either be achieved by experimentation during the process of familiarizing the antenna characteristics or by referring to the exhaustive set of specifications with graphics and gain map given below... Happy DXing!