Reflecting on The Story So Far....

 

Since acquiring my Amateur Licence in June this year, I have accumulated a few bits and bobs, and lost a few quid! It makes me wonder what it will be like a few years down the line! My (untidy) set-up can be seen above. Simple but effective. The Icom IC-7300 has many features built-in which reduces the number of accessories I need. The computer takes care of the rest. I bought a SWR / Power meter because I wanted a second opinion on the power output, but it turns out I could have saved myself some money. The readings always correlate. It will come in useful though for doing remote power readings with the dummy load. The Nano-VNA has been a good investment. It has proved very useful for testing antennas, baluns, ununs and transformers. The power supply upgrades are a triumph, giving me important feedback on power supply parameters.

I have made several antennas, but as the hobby dictates, you are never satisfied with what you have. I like to make my own gear where possible because of the learning experience. The EFHW antenna has been marvellous. I am making contacts as far away as Africa, South America, USA, Australia and New Caledonia. You soon learn that the simplest solutions are usually the best. The search for constant improvement goes on. I am enjoying the hobby so far, but the dream would be to have plenty of space to erect a tower and have an array of antennas high up. Perhaps a move to the countryside?

I think the power allowance for Foundation Licence holders at 10 Watts is too low. I mean, even users of the Free Band on 27MHz are allowed 12 Watts SSB with no licence required! It is a struggle to get a voice QSO at all! I understand that the need for reducing interference is critical, but if you cause interference, no matter how much power you are using, you are obliged to put it right. Most foundation licence holders have usually had a good grounding with CB etc. so its not like they are coming in totally green. Modern TV's and other equipment is far less prone to RFI these days anyway. It seems I am consigned to using digital for weak signals for the time being. I may look into upgrading my licence to Intermediate next year, just so I can operate with a better power level.

End Fed Half Wave (EFHW) Antenna

 

 Ever since I saw a video of someone with this antenna operating portable on 20 Watts I have been compelled to build one. He was making contacts all over the place with it just slung over a couple of trees. This is a 1/2 wave resonant antenna for 40m, but should also be good at the harmonic frequencies too, making it somewhat multiband. There are lots of resources on line about these antennas and I recommend some research is done before attempting the build. The 49:1 unun in particular needs to be studied because it isn't straight forward. The 9:1 and 16:1 ununs and transformer types I have employed before will not suffice for this project. They will be too lossy and inefficient at this ratio with a resonant antenna.  Capacitors need to be employed to improve SWR and performance on the higher bands. (counter-acting the inductance at higher frequencies)

(Diagram of 49:1 unun)

I am only using low power so just one toroid core should suffice. It seems that the higher the power, the more cores you will need, and the transformers can get hot. I have seen people opt for the FT240-31 core, but after researching the differences between type 31 and type 43, I decided to go with the recommended type 43 core. The capacitor required is a 100pF high voltage type which I found to be expensive compared to the 220pF of similar spec. I acquired some 220pF 15kV ones. If I connect two in series the capacitance will be halved and the working voltage will be doubled resulting in a 110pF at 30kV rating (belt and braces). Also, if your wallet allows, the theory is that using two toroids makes the transformer more efficient, especially at lower frequencies. Your choice. Theory also dictates that a good ground is required, however, with the right length of coax, the coax screen can act as a counterpoise because the current flow will be minimal at resonance. Some experimentation is required here. It might be that a counterpoise wire will be required on the ground connection, anything from 1m to 10m long. A good ground plane system can also be used if available. My finished project can be seen below.

I am assuming it will be good up to 50 Watts, but if the SWR drifts at higher power, this could be a sign of over-heating.

The box will have to be at least 100mm square. Mine is about 115mm square. There is a terminal post on the left for the antenna radiator. A link was made to a terminal post on the right to accomodate a ground / counterpoise connection.The two capacitors can be seen connected at the SO-239 socket, with some hot glue as a make-shift insulator on the joint.  I have left two large holes at the bottom for cooling / ventilation. I need to cover these with some kind of gauze to keep nasties out. I initially intend to house the box indoors. Just needs the 20m radiator wire erecting and we should be good to go. I want to construct a pulley and weight arrangement at the far end of the wire to maintain tension and prevent breakage in high winds.

Results and Testing

I can just fit a 20m wire from near the top of the roof to the diagonal corner of the garden. There is about 3m of radiating wire in the loft making connection to the box and counterpoise. A post was erected in the corner with the pulley attached at the top.

A piece of nylon rope was threaded through the pulley and connected to the wire.

The weight, a plastic bottle with just enough water to hold the wire tight, was tied to the rope and tension was achieved.

The theory is that any extra tension on the rope from high winds, temperature expansion / contraction or perching birds will allow the weight to rise and fall accordingly, relieving the strain on the wire. I think the antenna would perform much better if higher from the ground. At the moment it stands at about 12 feet at its lowest, rising to about 25 feet. 

Results

After experimenting with various counterpoises, 2m, 3m and longer lengths, I settled on a 1m length of wire. I really didn't know where to check the SWR for adjusting, so I decided to check at 14MHz, which is a full wavelength. The reading was about 1.5 after snipping about 6 inches off the radiating wire. Further cutting of about 2 inches caused the SWR to rise a small amount, so I decided not to trim the wire any more. I also experimented with varying the capacitance value from 220pF to 110pF, 73pF and no capcaitor at all. Some interesting and weird results were obtained. Using 220pF flattened the SWR peaks, but raised the overall SWR over the bands. 73pF raised all the readings. So I settled with the design spec of 110pF. At one point I was also getting gradually rising and falling SWR values at the higher frequencies which I couldn't explain. I guess it was something to do with changing the capacitor values, or a dodgy solder connection. The analyser results pretty much reflect the results from the radio SWR readings. Obviously, looking at the graphs, the SWR will be lowest where the impedance is 50 ohms.

(Analyser results - 1.8MHz to 30MHz sweep)

Final SWR Readings

1.8MHz = 2.9

3.5MHz = >10 (useless)

  7MHz  = 1.9

10MHz  = 1.6

14MHz  = 2.1

18MHz  = >10 (useless)

21MHz  = 2.2

24MHz  = 3

28MHz  = 1.7

Conclusions

The final results I obtained are far from perfect with respect to SWR, but the antenna is very effective when used with the internal ATU. It was immediately apparent that the received signals sounded much better and clearer compared to my other antennas. It would also seem that the antenna works better at long distances rather than closer to home, judging by the signal reports. Contacts with USA for example, are much easier to get now, but I can still make contacts across the UK. I will have to do without the 3.5 and 18MHz bands for now until I come up with a solution. The problems must lie with the transformer build. I might try a different approach in the future. Generally very impressed with this antenna, once again proving that the simplest methods are usually the best. 

 

 

Update - September 2023

Just for the hell of it I decided to take apart the 49:1 unun and add another ferrite core to see if there would be any difference. Apart from a possible increase in power handling ability, its hard to see any real improvement with performance. No improvement with the higher SWR readings on the lower frequencies. However, I can now tune the 18Mhz band. I found a small improvement by disconnecting the counterpoise. I also noticed that after moving things around in the loft, there was a change in readings. This reinforces the fact that you shouldn't have any objects close to your antenna. My situation isn't ideal because part of my antenna is in the loft! On the positive side, all the frequency bands above 3.5MHz fall below the 3:1 threshold. This is still my best performing antenna. So my advice would be that if you are only running up to about 50 Watts, then I think you would be OK with just one ferrite. Above this, you probably need two. Below is the full band sweep from the antenna analyser.

Dummy Load 50 Ohm 50 Watts

I thought it would be useful to have a dummy load to take power measurements. Rather than buy one I decided to make my own (as usual!) I purchased 10 x 470 Ohm 5 Watt Metal Oxide Film resistors. They are low inductance which is very important at RF. My power is limited but I decided to make it rated for 50 Watts. 10 x 470 Ohm in parallel gives 47 Ohms nominally. Parallel connection means that the power rating becomes 10 x 5 = 50 Watts nominally. (I read one article online which stated 4 x 100 Watt resistors in series gave him 400 Watts. This is incorrect! A common mistake.) The main problem I find with most projects is the hardware, in particular, cases and enclosures. Mooching around, I found this sewing tin with a hinged lid. Using a metal enclosure ensures good screening and prevents any transmissions radiating from the unit. A quick inspection found that the SO-239 socket would just fit on the side, provided I cut the lid away to allow it to close. The metal is very thin, so care is needed when drilling the holes. Sharp drill bits and proper support whilst drilling is the key. When assembled I measured the DC resistance with a multimeter at 47 Ohms. I'm not sure how accurate my multimeter is.

                                        

I assembled the project in about 2 hours. The tin made for a neat compact unit. everything just fit inside really snug. Total cost was about £6.00. A lot cheaper than the commercial ones and it is rated at 50 Watts.

The resistors were all soldered onto 2 pieces of solid copper wire and covered with heat shrink sleeving. A bit of hot glue secured everything in place. The hot glue you can see on top is covering the centre feed wire to the SO-239 to prevent any accidental short circuits. The ground wire was attached via a small crimp-lug and bolted to the holding screw. On reflection, I could have put some sleeving over the wires. I've tested it up to 20 Watts on all HF frequencies and the SWR reading does not change from 1:1. If operating at higher powers, the tin could be filled with dry sifted sand to dissipate heat, and then sealed up.

Update:

I did fill it with sand and seal it up because I noticed that it got quite warm when testing up to 25 Watts. Hopefully, problem solved.

14MHz Coil Shortened Dipole

 After a multitude of antenna builds using other people's designs, I thought it was time I designed my own from scratch. I decided a single frequency would be best to start with so I chose 14MHz because of the amount of traffic on this band. I think it's so popular because the antenna size is not too large to construct especially in a confined area. I looked at trap dipoles and the like and the art of shortening using coils. My final design would be a 6 metre long dipole so that it could be formed into an Inverted V to join my nest of dipoles in the loft. The coils were calculated for a 20mm former and came out at 6.68uH - 25 turns of 1.13mm diameter insulated solid copper wire, at 14.15MHz centre frequency. I decided to centre load the elements.

Testing

14MHz = 1.1:1

Bonus: 50MHz = 1.7:1(ATU) 

I had to add about 100mm to each end to get the SWR down. This means the calculations, or the interpretation of them, was in error. The measurements were made to the centre of the coils which is probably incorrect. When tested at 50Mhz, it was found that the SWR was a useable 1.7:1. I suppose the antenna has a tuneable harmonic.

Contacts made:

Croatia -6dB    Poland -15dB    Germany -11dB    Belarus -12dB    France -12dB

Hungary -17dB    Croatia(2) -13dB    Hungary(2) -11dB  (All on FT8)

Spot Reports for 14.074MHz FT8:

Conclusions

The SWR readings achieved were to be expected. This is a single frequency antenna with a comparatively narrow bandwidth. The Inverted V angle was very large, probably greater than 120 degrees. If this antenna was erected outdoors, the performance would be much better. Loft antennas tend to perform a lot worse. It seems to be working very well though and I will keep this antenna on-line for using on a regular basis.

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).