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...)

End Fed Random Wire Antenna for HF

 After my successful build of the BBTD antenna, I started to wonder if the terminator resistor was actually needed, and if perhaps using a matching transformer would allow a lot of latitude when designing other antennas. I started to experiment and researched other antennas, in particular the Rybakov 806 design. This antenna is based on a length of wire (7.6m) that, as far as I know, is not resonant on any of the desired frequencies and is erected vertically using a matching transformer at the base. The Rybakov needs radials to perform well.

I do not profess to know exactly what or why I am doing these experiments, but that's exactly what they are to me - experiments!

My experiments used the 9:1 matching auto-transformer of the KISS Balun type. It is technically not a balun but an impedance matching auto-transformer. The transformer can be constructed using two ferrite beads large enough to pass the wire windings through. I used 1.5mm stranded wire so the holes need to be about 6 to 8mm diameter. Bind the two ferrite beads together with tape and/or cable ties to form a 'binocular' style ferrite. A better solution for the core would probably be a FT240-43 toroid and wound accordingly for a 9:1 ratio. I attached a completely random length of wire which meanders all over the place through the garden on the fence (approx 140 feet long) which is horizontal for most of its length. The ground connection was made via approximately 33 feet of wire (later shortened to about 8 feet) connected to a cold water feed pipe. Although using this method of grounding is frowned upon, it was the most convenient earth at the time. 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. I didn't think for a minute that it would work with any usefulness, but you know, you have to get these ideas out of your head! The SWR readings can be seen below:

1.8MHz - >10:1 (useless)

3.5MHz - 3:1 (ATU)

7.0MHz - 1.3:1

10.1MHz - 1.4:1

14MHz - 1:1

18.07MHz - 1.8:1 (ATU)

21.0MHz - 1:1

24.9MHz - 1.1:1

28.0MHz - 1.6:1

50.0MHz - 1:1

So the SWR readings are not all that bad. As we all know that's not the full story. The length of the radiating wire doesn't seem critical, but as long as possible is best. If it can be laid out in a straight line and also as high as possible, this also helps, but is also not critical to the SWR. But does it perform? Yes and no. I can make contacts on it all over the place, again on FT8. I can't seem to make any voice contacts at the moment, no matter which antenna I use. Listening to most of the SSB conversations though they are all mainly using very high power and multi element beam antennas compared to my menial 10 Watts on a homebrew! Some of them are on anything from 400 to 1000 Watts. I can't compete with that!

One conclusion I have come to, after making some comparisons, is that these wire antennas with matching transformers are a 'Jack of All Trades but Master of None'. They cannot perform as well as a proper tuned antenna for a specific band, for example the 14MHz 'Inverted V' I have on my gable wall, but they do get the job done for people with limited space and resources. If the antennas were installed at a decent height above ground I'm sure the performance would improve dramatically, but I have no provision for that here. On to the next project which will be another antenna - vertical this time. I understand that verticals tend to give you a better 'take-off' angle for DX when propagation allows. It will be a shortened antenna because I can't have a 60 foot monstrosity in my garden! 

(Update - I tried the antenna with a 16:1 transformer but made it with isolation between primary and secondary. I then shortened the radiating wire length by about 8 feet. Arguably it is working a bit better than before. The SWR hasn't changed much, if anything it has improved.)

Power Supply Make-over

 A while ago, I built my own 30 Amp power supply after seeing how much they cost these days. It has performed flawlessly since, so I thought it was time for a make-over. The heart of the unit is an 'off the shelf' 30 Amp switch mode power supply module, cheap as chips from Amazon. At first I ordered a couple of cheap Amp and Volt meters for indication. Problem was that after a while they started to stick, especially in the hot weather, and I also couldn't get a definite reading from them. Originally, the DC terminal posts were at the front where you would normally expect to see them. I wanted them at the back out of the way for neatness, so I re-routed those. I re-hashed the box to accomodate a 20x4 LCD display and programmed a micro controller to do the work. A DS18B20 temperature sensor was also installed close to the electronics. I used an ACS712 - 30A as the current sensor. This sensor has received quite a lot of bad reviews, but I don't seem to have a problem with it. The main concerns are that the terminal connections are incapable of carrying the 30 Amps that it's rated at. Some say that it got extremely hot when passing only 5 Amps. Well I must concurr that the connections do seem a little 'puny' but I managed to get a significant sized conductor into the terminal block after prising it open a bit with a small screwdriver. I have been testing this unit for a few days now and with an intermittent current of about 10 Amps, I haven't witnessed any overheating issues. The temperature sensor will alert me to this. After a bit of messing with the calibration routines for the voltage and current, it was looking good. A couple of days of testing and tweaking, and a coat of matt black paint, now it takes pride of place in my shack. Very pleased with it!

(Update - After experiencing an accidental short circuit on the PSU, I have decided that I need to have some physical protection on the output, like a fuse. The unit itself has short circuit protection but I don't trust it. My monitor registered a maximum current of 35.8 Amps, if even only very briefly. This could be dangerous and a fire hazard. I intend to install a fuse to be sure, ASAP).