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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.
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.
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.
20 lis 2020 · When using a 49:1 (better for higher bands) or 64:1 (better for lower bands) coupler, you have to cut the wire for resonance to lamda/2 minus velocity factor and end effect, e.g. about 20m long for the 40m band.
The feedpoint impedance of an antenna depends on the type of antenna and where it's fed. As a result, each balun is suited for a specific purpose. 9:1 is for non-resonant wire antenna, 49:1 is for resonant wire antenna (think EFHW). Not sure about 4:1.
transformer is a step-up with an impedance ratio of 49:1, and wound on a type 43 toroid core. Both the Antenna wire and counterpoise wire are 18ga, 16 strand insulated wire.
With a 49:1 or 64:1 UNUN, no tuning is required and no antenna tuner is required (or perhaps a “touch up” tuner with up to 3:1 VSWR capability that many modern rigs have built-in.)
