End Fed Half Wave for 40m, 20m and 10m

Shortened version of the popular tri-band end fed antenna. In order to keep the wire length relatively short a small 35 µH coil is placed towards the end of the antenna. The transformer is wound on the FT140-43 toroid with the 7:1 ratio giving the impedance reduction of 49:1. With careful tuning the antenna resonates on all three bands and can be used without a tuner. I have modified the original design slightly by adding a counterpoise connector on the side (not yet visible on the photos below). A short 0.05 wave length wire was attached during the tuning of the antenna and the results published below include this. Later tests showed that the counterpoise had little effect on the SWR as the coax takes over its role. I also made a 1:1 unun using the same toroid to accompany this antenna in case of any CM noise and RF feedback problems at above the QRP power levels. 

This is a commercially available kit but it can easily be made from the parts most hams already have in their shacks.  
I really like the portability and compact size of the antenna. One of my next projects will be a QRP version using the FT82-43 toroid. 

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