Sky Hook

My next problem is how to get an antenna up a bit higher than just lying on the roof.

Now I am not a natural mountaineer, and I am not going to go clambering on the roof or shinning up chimneys; I have a bit too much metalwork in my legs for doing that. But anyway, at the moment I am thinking about simple wire antennas so all I really need is a convenient sky hook to attach wires to.

I found some 2m lengths of steel tube at the local hardware shop, which was useful as they would fit in the car. They had a number of diameters so 4 rods of 25mm, 22mm, 18mm, 12mm could be fitted inside each other, sliding about 20 cm of the smaller tube inside the larger, and drilling through for a couple of bolts. This way I had a pole of about 7 meters. I attached a pulley to the small end and put a rope through it. I am hoping this will enable me to haul up some wires when I know what I want to try.

Next, I got a 1m length of 30mm tube and with the aid of a few brackets and bolts screwed this to the wall of an out-house. Now I could drop the 7m pole in (with the aid of a friend), tighten it up and admire my new skyhook.

I took the precaution of adding a few guy strings as it can get pretty windy here, as there is not much between us and the Atlantic ocean 60km or so to the west, apart from some medium sized hills.

I am also worrying about lightning, so decided to attach a sort of "lazy" earth. I ran an earth wire from the bottom of the pole along the ground for about 10m (without insulation) and buried it a little. This is mainly to provide a leakage path for static electricity to ground and might help prevent lightning strikes. I did not want to wire it to the outdoor mains earth as the wiring is rather low grade and I think a real strike back into the house wiring might not be so good.

This is still pretty much an experiment to see how this works out. The guy ropes are basically plastic string of unknown material, so I expect the sun will have a disastrous effect. Meanwhile the general springiness of the construction should help it withstand the weather for a few months by flexing rather than breaking. After that, I will have a better idea of how to make something more permanent, and whether this location for the upright is going to be okay, both cosmetically and performance-wise. This corner of our terrace is at the edge of big drop to the west, maybe 20m, so this should help with take-off angle even though the maximum height with this arrangement is only about 9m above the ground level on the terrace.

Adding a balun

I was not happy with wiring coax directly to the centre of the dipole, so decided to make a variable balun as an experiment. I expected I would be using some twin feeder for future antennas so thought that a set of impedances might be useful.

I decided to provide 50 ohm, 200 ohm, 450 ohm and 600 ohm on the antenna side, with a 50 ohm winding for the unbalanced coax side. This is what I believe is known as a "voltage" balun. I decided on a separate winding for the radio side mainly because all the stuff I've read doesn't, so I thought I'd find out the disadvantages.

I got a ferrite 140-43 toroid off ebay (GBP 2.95) and decided on 8 turns for the 50 ohm "tap". Since I wanted a separate unbalanced winding I actually ended up with 5 windings twisted together to make a 5-filar (quintifilar?) wound transmormer. One of the winding stopped halfway at 4 turns. By wiring the antenna sides in series I got turns ratio of 1:1, 2:1, 3:1 and 3.5:1, giving impedances of 50, 200, 450 and ~600 ohms. These I wired to some 4mm sockets (does anyone call them banana plugs and sockects any more?) so I could easily try different antenna connections. The other winding went to the coax SO239 socket.

I put it in a plastic box to make the assembly easy and to make it vaguely water resistant as I intend it to be outdoors, though semi-under-cover. I decided that I was likely to get RF radiation from the twin feeder connection anyway, so hope the extra radiation from the wiring will not be significant. I am worrying a bit about what might happen if I start putting significant power down it, but since my first experiments will be QRP I am not too worried. I can rebuild it into a metal box if it ever seems necessary.

Anyway, I wired a short length of wire to the dipole (a sort of random impedance feeder), plugged it into the 50 ohm antenna side and checked out the rx. I was amazed to find that reception appeared to be much better. Difficult to quantify but I'd guess about 6dB better (1 S point). I tried different taps and got little difference, and I settled on the 200 ohm setting. I am pretty sure the QRM from the shack PC got better too, but this might just be because that's what I've been told to expect when the coax outer is not feeding interference back up to the antenna.

All in all, it was an interesting first build item. Well worth it. And I am ready for a better antenna, as I can use twin feeder to the balun outside the shack, run it through the balun and into the house on RG58 coax. 

First Antenna

My first attempt at an antenna. Two lengths of 5m, making a dipole for 20 metres. It is oriented almost exactly with the wires running N-S. 

My plan had been to hoist this up between end supports, one end at a TV antenna on the downhill side, and the other end up the hill somewhat above the house, using some nylon string. Unfortunately I discovered that the tensions got a bit high given the angles and distances, so I settled for starting with it lying on the roof, with one end raised a little.

Originally I had 50 ohm coax wired to the centre leading straight to the receiver.

This actually worked pretty well. Lots of stations in the US and Canada coming in strongly from the west and South Africa from the SE. Not only on 20m, but 40 and 80 working quite well too.

There was quite a lot of QRM from the house of course. The computer in the shack wiped out 80m and 40m mostly. I reduced that a lot by removing the Cat 5 ethernet cable and replacing it with a USB Wi-fi dongle (about 8 GBP from ebay).

My receiver

That's my trusty old HF225 receiver. Still waiting for a transmitter, but in the meantime hearing some interesting amateurs...

Not yet back on the air

I've decided to re-awaken my interest in amateur radio. After living in Portugal now for 15 years, I finally got myself a Portuguese callsign. Now how to get on the air?

I decided I don't want just to buy a transceiver and press go. I really  want to understand what is going on, so I want to build some gear. I have found that the enjoyment of using purchased equipment is nothing compared with the fun of getting something you've built yourself working.

Also it is actually about 27 years since I took my Radio Amateur's Exam in the UK. I got my UK callsign G1CWI at that time, but did not really use it. I have a lot to relearn, and I want to get on the HF bands.

I am now waiting for the Softrock RX/TX v6.3 transceiver kit I ordered to arrive. Then will start the assembly at the end of which I will have a whole 1 watt of power. 

So at the start of what I hope will be an interesting journey, I thought I'd start this blog to record the progress of an intermittent amateur. Who knows, it may even be interesting!

More to come on my early antenna ideas and my first balun...