Cette page était sur le site de G3YCC; mais le lien ayant disparu, j'ai reproduit ici l'article que j'avais conservé. (F5AD)



An End Fed Half Wave Antenna

Useful for portable work

This end fed type of antenna was marketted in the UK and is a useful system for the portable set-up. Being a half wave, no radials or counterpose wires are needed.

As the impedance will be high at the end of the wire, some form of matching unit is needed and a simple parallel tuned circuit housed in a plastic film container is fine (figure 1). A hole in the container allows for tuning, by adjusting the ferrite core in the coil for maximum reading on a field strength meter nearby.

The inner of the coax goes to a tap about 1/4 of the way from the earthy end of the winding, to which the braid of the coax is soldered.

As a rough guide, a capacitor of 50pf across a winding of say 30 turns is a starting point for 40m. Some experimenting with turns and tapping point is necessary. The coil former used was about 1/4 inches in diameter as found in old IF transformers.

The antenna wire (1/2 wave long) is soldered to the top of the coil as shown in figure 2.

The drawings illustrate the set up, I hope.

For portable use, throw the wire into a tree or whatever, using thin cord or rope onto the insulator (figure 1), tune for best filed strength reading and off you go!

Try it - it works!

Want to work two bands? Use a slightly bigger container with two tuned circuits which have some sort of terminal each, to which one of their respective wires can be connected.

Rough lengths of half wave wires:

80m - 132 feet, 40m - 66 feet, 20m - 33 feet.

Enjoy your portable working and how about telling me what you thought of the above idea - when you have used it?


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