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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.
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.
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.
All antennas work better when height or distance from ground or object is equal or larger than antenna Reactive Near Field or 0.159 wavelength. Just as the mantra is in the Real Estate business: “location, location, location”, the mantra for antennas is: “Height, Height, Height”.
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.
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
The lenght of the wire for 40M band should be around 20.7m or 67.9ft. MAIN FEATURES: - lightweight (only 50g) - small dimensions (fits into your pocket) - max. input power up to 50W. - easy and quick installation. - no counterpoise. - external tuner is on some bands required. Buy it now for: 50€ (Shipping is not included.
