This is a reprint of the original post to my site in 2011. There are no photographs as they were not archived.
20m vertical end fed half wave
Looking around for a quick and easy 20m antenna for forthcoming portable operation I found an article by VK7JJ where he describes using 9m ‘squid poles’, fibreglass fishing rods or roach poles as antenna supports. There are designs for 80m, 40m, 30m 20m, 17m and 15m. The same centre loaded wire is used for all bands and matching for 80m and 20m achieved by changing the base coil arrangement. On other bands and an ATU is used.
What attracted me was the matching on 20m as it is identical to the other EFHW designs around which I know work well. I used the basic design in the article removing the top section, the thin whippy bit, off a 10m pole and attaching the wire by poking it into tube. I also slipped the centre matching coil over the pole while winding the wire to form a helical antenna. See the VK7JJ article for full details of the wire and centre loading coil.
The matching coil is 12 turns of 18SWG enamelled copper wire on 40mm plastic drain pipe with a 2 turn coupling winding over the earthy end. The coil is tuned to resonance with a 30pf beehive trimmer that has been in the ‘junk box’ for over 30 years. Any air spaced trimmer of similar value should do the job.
I tried several different lengths of counterpoise and found that around 7.6m of wire produced the best results. This goes against the advice from Steve Yates AA5TB who suggests that 0.05 of a wavelength works best for horizontal EFHW wires. All I can say is that I get a near perfect match with the 7.6m counterpoise.
I setup the antenna on a homebrew drive over mount next to the house. After adjusting the beehive trimmer for resonance the Small Wonder SW+ 20 was attached and a CQ on the QRP calling frequency produced an immediate response from another QRP station in Sicily, a distance of 1350 miles on 2w. I also heard many other stations in the south and east of Europe on a day when conditions were not good and the SFI was in the mid 70s.