Short HF Multiband Vertical Antenna M0CVO

 So what do we need to do to get the length of an antenna down? Well it needs to be coil loaded. This build was originally published by M0CVO who apparently made this antenna, the HFC3015-V, commercially in the past. It is supposed to be good for 7MHz through to 28MHz with the help of an ATU. I have put my own 'spin' on it here and there though. It reminds me of the Firestick and DX27 antennas we used back in the CB days. We will need a 4:1 unun for this project and I stood by my tried and tested KISS Balun type of auto transformer. You can make your own unun or purchase one if preferred. You will also need 13.6m of 1.5mm insulated stranded copper wire. To create the coils I cut two  pieces of 41mm O.D. plastic pipe - top coil = 230mm long and bottom coil = 80mm long. Then drill 3mm holes in the pipe at the correct spacings - 220mm for top coil and 70mm for bottom. The wire can be passed through these holes to maintain the correct spacings and secure the wire in place. Keep all the coil turns in the same direction. For the main supporting tube I used a couple of fat sections of fishing pole to make about a 2m long piece. The pole sections were selected to fit the 41mm pipe pieces over and reduced the total weight as opposed to using 41mm pipe straight through because the type I had was quite heavy. You could just use a full length of lightweight 41mm pipe or any other support pole you have. They were a bit slack on the pole but the ubiquitous hot glue gun was called into action and the sections were glued together in the right places. The recommendations for the ground connection is unclear and varies from ground rod, counterpoise and/or radials from 4ft long to 30ft long. This may be where we have to experiment a bit. I initially made this antenna and stood it up at an awkward angle in the loft next to all kinds of stuff. Not an ideal situation, however the SWR readings looked promising. This is why I decided to proceed with the build. 

Testing

(The HFC3015-V, mounted and in use)

The antenna was erected outdoors on the gable wall about 10 to 12 feet high. The feed line was RG-8 Mini coax about 10m long, up to the loft and into my shack which is upstairs in my home (not ideal). The SWR readings can be seen below:

1.8MHz - >10:1 (useless)

3.5MHz - > 10:1 (useless)

7.0MHz - 1.4:1

10.1MHz - 1.2:1

14MHz - > 2.8:1 (ATU)

18.07MHz - 2.2:1 (ATU)

21.0MHz - 1.8:1 (ATU)

24.9MHz - 2.7:1 (ATU)

28.0MHz - 1.6:1 (ATU)

50.0MHz - 1.1:1

Conclusions

After experimenting with various ground plane wires, I couldn't get a decent SWR across these bands without grounding it to the water pipes, since creating a separate isolated ground would be too far away. Please don't use this grounding method as a long term solution as you could get stray currents flowing into your household appliances and RFI problems. This antenna only claims to cover 7 to 28MHz. Maybe with lots of messing about you can get it better than me, especially if you make the transformer a different way. I did make some contacts across Europe, but no real long distance as yet. My signal is being seen as far away as Australia though! On the plus side, the antenna is very compact at only 2m high, and is quite discrete when erected. It's quite easy to construct, cost effective and it works. Your experience of building this antenna could result in better outcomes. I intend to come back to this project to see if it can be improved. Below you can see spot reports generated by GridTracker that shows my signal reach for my antennas for comparison. I realise this is not a definitive test because of varying propagation, frequencies and conditions, but I just wanted to get an idea of the directions and reach of the antennas.

(Long Meander Wire Spots Report - seems to be greater East & West coverage)

(14MHz Inverted V Spots Report - seems to be greater West coverage)

(Multiband Short Vertical Spots Report - someone heard me in Australia?)

I cannot draw any definite conclusions from these spot reports really. I just wanted to compare a vertical with an IV and horizontal. Antennas are a mysterious and wonderful thing!

                                        (Oops! There's that Ozzy connection again. Interesting...)