The search for light, easy to erect and effective HF antennas for portable use is never ending. Wire antennas have a lot of advantages as they are light, small and easily packed in a suitcase. Some years back I used a 20m dipole on the roof of a house in southern Spain and managed a few QRP contacts into northern Europe.
Recently I discovered article by AA5TB about the end fed half-wave. Not only was there a lot of technical information there were also practical instructions about making a very simple coupler to match the high impedance at the end of the half-wave to 50 ohms. (Follow the link above for full details)
Having an MFJ-259B on the shelf I decided to make a quick lash up of the coupler. The toroid is a T50-2, windings are 25T 22swg with 2.5 t of solid (pink) connecting wire, cap is ~400pf closed and ~14pf open, there was a 4.7k resistor across the tuned circuit to simulate the antenna. It worked first time.
Next the resister was replaced by 35 ft of wire and around 6 ft of counterpoise for 20M. The wire was thrown out of a first floor window and secured to a metal post use for the washing line making a ‘sloper’. The counterpoise just dangled over the end of the table. (Click image to enlarge)
First indications on the MFJ-258B were of good resonance on 20m with the variable capacitor nearly fully unmeshed. Next was a trial with my FT- 857D set at 5W. The result was perfect SWR i.e. nothing showing on the display. Power was increased to 20w and it still worked well. Then I compared signal strengths on my IC-7200 which is was connected to the main long wire tuned by an SGC-230 Smartuner. The results were very close.
The antenna analyser shows that the existing coil and cap will tune 40m, 30m and 20m. The plan is to box up the coupler and make extensions to the 20m wire so that 30m and 40m can be added when required.
Overall this has been a very satisfying experiment which has produced a good portable antenna system at very little cost. Maybe I should start making them and sell them as 3 band ‘wonder antennas’ for £50 a shot! No, make that £85 as a higher price will sell more.