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An 80-10 end-fed half-wave antenna can be a very good performing part of an HF station. But its performance depends heavily on a well-designed and carefully constructed 49:1 unun, which matches the long wire impedance to within tuning range of operation. But the perfor-mance of an end-fed antenna is also very dependent on height above ground.
This project assembles a 49:1 ferrite-core (“FT”) type #43 transformer that matches 50 ohm input to 2500 ohm end fed antenna. It is optimized for 3.5/7/10/14 MHz but will work reasonably well on all amateur bands from 80 meters thru 10 meters with a 135 foot length of wire and a short connection to ground.
antenna is based on any number of parameters: specifically, the frequency or band of frequencies, location, directivity, and intended power range. This paper discusses some of the more important aspects of the End Fed Half Wave (EFHW) dipole antenna. The frequency band is HF (40 meters), and the intended power is 100 watts.
The "9:1 UNUN" are for random length wire antennas fed at the end. 49:1 or other high ratio transformers are for resonant "cut to frequency" antennas like the traditional zepp/fuchs antenna.
The end fed wire regardless of its length presents a high impedance to the feedline. If the intention is to build a ½ wave mono band antenna then it is necessary to attach a 48:1 unun at the feed point given the extremely high impedance. But if it’s a multi band antenna and is not ½ wavelength long on any of the intended bands then a 9:1 ...
Recommended wire lengths and Installation Notes for Unun models 4932, 4935, 9130, 9132 & 9135. Table shows typical SWR relative to installed wire length. SWR will vary based on topography, proximity of nearby structures, configuration of the antenna wire and choice of ground or counterpoise.
Beginning in 2015, the designer of high power MEF transformers (Multiband End Fed), Daniel “Danny” Horvat, E73M (aka N4EXA) has made number of huge advancements in designing of high ratio (49:1, 56:1, 75:1 and 81:1) UNUN (UN-balanced to UN-balanced) transformers and antennas.
