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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.
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.
antennas for HF. Transformer Construction: Assuming 49:1, I start with a good 6 feet of 18ga. enameled wire. I fold up about 7 inches of one end and place the loop created in a pair of pliers with padded jaws to protect the wire coating from scars. I then hand-twist the wire, leaving an inch or two for the short end. This is the primary winding.
This antenna, which works on 10, 15, 20, and 40 meters, has a very high impedance of around 2,500 Ohms. The kit includes the parts needed to construct a 49:1 impedance matching network, which will transform the impedance to 50 Ohms, which will suit most transceivers.
If the transformer is used with an external tuner in conjunction with a single wire antenna typically 130-135 feet in length, power should be reduced on those bands that show an SWR above 1.6 to 2:5 without the tuner.
For it's simplicity and small dimensions is very popular for portable or SOTA activities, and also as a static-mobile antenna. This Mini 49:1 UnUn can be used also as the base point of a vertical dipole antenna with its half wave length. MULTIBAND ANTENNA.
