Helically wound 40m vertical

Helically Wound 40m verticalChris (G0EYO) kindly modelled my 40 meter vertical with loading coil (http://www.m0mcx.co.uk/?p=44) and mentioned that he felt the take off angle may be higher than I would like it.. He suggested experimenting with a helically wound vertical. Chris recalls a team event last year where they needed to get on 40m fast so a fishing pole and about 10 meters of wire were produced along with 2 elevated radials. The problem was that the fishing pole was only about 7 meters long. The team simply wound the 10 meters of wire on to the fishing pole and hit the TUNE button on the rig to swallow up any mismatch.

I tried the same experiment with my 8 meter fishing pole and 10.6 meters of wire. Why 10.6 meters? Simply because I cut the wire a bit long intentionally. Using 4 elevated radials, I found the resonant 1:1 frequency with a near 50 ohm match was 7.7 Mhz. Way above my requirement however the SWR bandwidth curve was very strange with a flat 2:1 SWR all the way from 7.2 Mhz right up to 7.6 Mhz. Indeed, the TUNE button easily swallowed the incorrect size of this antenna for the whole of the 40m band. I needed to make this longer though so I could run high power in a comfortable manner.

Stripping off the 10.6 length, I found a 100 meter roll of 6 core telephone wire and chopped 15 meters off it. I wound this on to the fishing pole which gave me 6.8 Mhz. A couple of attempts later and about 50cms of wire short, the vertical tuned in to 7.05 Mhz with a very large bandwidth, certainly better than the loading coil version.

Later in the evening I heard VE1KF managing a European pile up from his QTH in Nova Scotia. My vertical broke the pile in one shout. He emailed me later, “Your signal was a nice strong 59“. Thanks for the report Brent.

I give a thumbs up to this antenna; I believe I am getting a lower angle of radiation. It’s the best 40 meter vertical I’ve made yet but remember – these only work from about 1,000 miles upwards. If you want lots of QSOs, you’ll need a dipole or a loop to compliment this.

More pics: http://www.m0mcx.co.uk/gallery/index.php?/category/40

Postscript: I recommend using a 1:1 choke balun on this design to stop the feedline radiating and to ensure that all the RF goes where it should. See here http://www.hamuniverse.com/balun.html for some regular designs.

73, Callum.