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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.
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.
Table shows typical SWR relative to installed wire length. SWR will vary based on topography, antenna wire configuration and use of ground or counterpoise. For best results, use the longest wire shown on the table that will fit your installation constraints.
ratio (49:1, 56:1, 75:1 and 81:1) UNUN (UN-balanced to UN-balanced) transformers and antennas. The efficiency- Insertion loss of the transformers continues to be unmatched by any copycat or competitor products on the market.
High Impedance UNUN for EHFW antenna The UNUN has a high impedance ratio (49:1 to 64:1) – not feasible to use transmission line transformers whose practical limit is about 16:1. It is a conventional transformer. Uses a ferrite toroidal core or cores (usually Type 43 or type 52 material). Most 1:4 and 1:9
