New multi band vertical antenna for /P

This page was originally published in 2008, the 2021 modifications are  shown at the bottom of the page.

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 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.

Modifications 2021

You can make this into a multi band antenna system very easily. These instructions are from the original 2008 page of VK7JJ. Or you can just wrap a quarter wave length of wire fo 20m onto the pole and use the tuned circuit matching as shown above.

  1. Cut the radiating wire to a length of 10.1m. This includes the wire for the coil.
  2. Cut a 30 mm length of 42mm diameter PVC pipe for the offcentre* coil former.
    – drill two 2mm diameter holes in the PVC to thread the radiating wire through. Each hole is positioned about 3mm in from each end of the PVC, the exact spacing will vary depending on the wire you use. I later re-drilled my holes closer to the coil and trimmed the PVC for a neat finish.
  3. Wind 7 turns of the radiating wire round the PVC former, poking the wire through the holes as illustrated.
    – make sure that you position the coil on the wire so that it is exactly 4.7m down from the top of the wire.
    – connect a banana plug to the bottom end of the wire.
    – tape the rawl plug to the top of the wire leaving the bottom of the rawl plug free to slide onto the top of the squid pole.
  4. The resulting length of wire + coil is used as the radiating element on all bands.
  5. Congratulations. Your squid pole is now ready for use on 40, 30 and 15m.* The centre loading coil is actually placed a little lower down the squid pole than the centre, being exactly 4,700 mm from the top of the wire.This position was calculated using MMANA modelling software to provide simultaneous resonance on 20m and 40m. The complication is because a loading coil has maximum effect at a high current point and needs more inductance the further it moves from the high current point. On the 20m half wave the current maximum is at the middle of the squid pole while on the 40m quarter wave the current maximum is at the bottom of the pole.(From http://www.perite.com/vk7jj/squidpoles.html)

The 7 turn centre loading coil* is integrated into the radiating wire.

Please note: to be strictly accurate it is only an EFHW on 20m, on other bands it is loaded vertical. That does not really matter but there is a modern tendency to talk of multiband EFHW antennas which, by definition, cannot exist.

This page is good for calculating the length of wire needed. For a simple 20n EFHW with insulated wire I will start with 10.26m.

More to come –  we build it and and try it out…