It is not quite perfect, but under the circumstances an acceptable compromise. I am a bit handicapped in that I have a flat roof with about 4x12m area - which is unfortunately almost completely covered by a tin roof. So what I did now was putting a relatively short radiator on one side, basically already sticking a bit into the neighbouring house's area.

I had long worried about how to mount this radiator, until BV7GA came up with a very simple solution. The radiator is not stainless spring steel (dreaming...), just regular 4mm steel, 2.5m long. You see it already started to rust, and should there be indeed very strong winds it might even bend. But until then, I will gladly use it.

Above you can see how the feeding is done. So far I am not using an unun, the bottle on that beam is just a choke. I still had a piece of aluminum on my bench, so it was put to good use. The holes were drilled free hand, without measuring, so they are not especially aligned. You may see that I only use seven radials, and that they are not insulated.

The reason is simple: First of all, I did not find other suitable wire, and secondly I have to pull those radials along the tin roof, I can not just put them on the ground. I had hoped originally that I could put this tin roof to good use as either antenna or ground, but I was disappointed both times. Since there is not much space where I could lay the radials, I only used seven so far. There is however one thing the roof does: It shield slots of noise.

I hope that what I deducted from antenna radiation patterns is correct, as I could find only one article somehow dealing with the influence of radials to the radiation pattern. In theory (and if that theory is correct), a radial seems to improve antenna performance opposite to it. That means Europe and also Japan should be somehow OK now. Unfortunately I did not have much chance to confirm this, as I was busy hunting ZL8X (opposite direction) these days - with quite a bit of success I think I can say...

So, time to go hunting now...

Before I talk about the antenna, I need to show you my roof. OK, you can see the antenna here already, because there is not much space. The house is about four metres wide. When I took this photo, I was standing on the stairs of which you see the handrail, leading from fifth floor to the roof. As you can see, the fifth floor veranda is mostly covered by a tin roof that extends from the neighbouring house to the (less than one metre wide) stairs. In the front, there is less than one metre left until the front facade creates a rather sudden and significant drop in height.

Houses in Taiwan usually have a flat roof and this one is no exception. Unfortunately, here too the landlord has set up another tin roof, this time covering the whole width and extending almost to the edge of the lower roof. The distance between both is slightly more than two metres. While the landlord allows me to set up antennas, I had to realize that there is nearly no place where I could actually do so - at least with "regular" antennas. Enter the quick JAIG antenna...

In case you do not know JAIG , the acronym stands for "Japanese Amateurs In Germany". It is a group originally founded by a few Japanese (and one German - yes Bertin, I remember the photo) hams in Germany, later included German hams who had been in Japan or had relations with it and then generally everyone who had an interest in either Japan or Germany or both. There is a weekly JAIG net on 21MHz, which I had joined whenever I was able to.

I was not able to do so for the last 11 years, due to many reasons, one being the law here in Taiwan not allowing me to operate as easily as in other countries. But I took the exam recently, got a local call and now I wanted to see if I could join the JAIG net again, so I needed an antenna.

Due to the limited space available I had to come up with a shortened antenna, and the only solution I could think of was a groundplane of about two metres height, done in wire and hung from the upper tin roof. I know, I would love to get something above that tin roof, among others to get rid of the noise created by all the electronics around here, but I would not be able to secure such antenna.

I was lazy this time, I admit it. I did not do any manual calculations. I used one of the online calculators for dipoles, since a quarter-wave GP is just half a half-wave vertical dipole. Those calculators are not very precise though, they only give integer values for the coil, and the result I got was a 2uH coil that should match the two metres of wire on 21MHz.

Did I mention I was lazy? This time I also did not calculate the coil, but instead used my AADE LC meter to wind the coil to the correct value. I found an empty one-litre Cola bottle and cut the top (or now bottom) off. (That was a mistake, the next version will feature a complete bottle.) Unfortunately, the plastic bottles here in Taiwan are pretty crappy, made of very thin and soft plastic, quite different to the sturdy PE bottle in Germany.

Nevertheless, since the wire goes all around the bottle, it is relatively stable. There is a hole at the top for the antenna wire. The coil then uses 1mm enamel copper wire. I applied three strips of double-sided tape to keep the windings in place. I actually had to adjust them later, because the resonant frequency was above 22MHz (and the coil had less than two microhenry). Now the l/d ratio is not 1:1 any longer, but it still works. SWR is about 1.3 on the desired frequency, because resonance is still at bit high, at 21.8MHz.

I will use a complete bottle next time because then I can put the connector into the cap. Now it is just dangling there. Looking at the coil picture, the word "radial" may perhaps come to your mind. A groundplane antenna usually needs a ground pane, a counterpoise. Many vertical antennas employ radials, often of the longer kind. I do not have the space for that, but you may have noticed a few tin roofs and some more metallic structure on my photos.

This is probably the only good thing about these tin roofs: I can use them instead of radials. So far it seems to work rather well. Japan is at about 25 degrees from my location, which is opposite to the tin roof radial. Conditions were pretty good when I tried the antenna, and although there was (sometimes heavy) QSB, the continuous reports I received from both JM2HBO and JR0DLU were S5 at least, with a S9+60dB (Yes, JM2HBO said that.) peak, but usually around S7 with about 50W blown into this contraption on my side.

Such a short antenna does of course have its drawbacks, and a significant one is reception. I may be able to burn lots of RF energy, but only two metres of wire do not receive a lot. I was lucky both stations I tested with had Yagi antennas. But when I listened in to the JAIG net last Sunday, I could barely hear the net control, which currently is unfortunately not JA1DKN with his enormous antennas. But I will try again next week.

If you expect very specific data to replicate this antenna - sorry. But I may perhaps even calculate the coil next time, so that I can present some data for it other than the volume of a bottle. (and about four windings) I also thought about making this multiband, but while 1uH should do the job on 28MHz (only about 50cm of wire missing), 14MHz would require 7uH. But all this is "TBD"...

Oh, btw, this antenna did leave me with a new problem: I only have one coax cable going up to the roof, so I had to take down my 2m spoke antenna to get this one working. So, I guess next on my workbench are two duplexers...

After getting a local call sign, I hoped to get in touch with local hams on VHF (no UHF equipment currently), so I assembled a simple 2m GP from a UHF case socket and a few bicycle spokes.

I did not want to spend too much effort on an antenna that may not be up for too long - fortunately. This is a very quick solution. I used that UHF socket because it had four small holes for screws in which the spokes fitted just nicely. They did not accept the solder, but are covered in it anyway, so they should conduct. The radiator is screwed into the small tube where usually the inner coax conductor gets soldered. This contraption is put onto the top of a PVC pipe with the coax cable hanging inside, so the cable's weight keeps the antenna in place.

I am glad I did not put more effort into this, because after putting it up, all I heard between 144 and 146MHz are truck drivers, house wives and whatever else, but no amateur radio call sign. Time to find a solution for an HF antenna...