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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