I switched on the other evening and heard a very quiet DX caller on 7.142. It was YC0LOU from Indonesia and I could only pick up parts of his call. He called and called and had no takers. In fairness, he was extremely quiet but as the sun was gradually moving around the sky, he finally became audible and it was worth giving him a shout. 400w off my inverted V at 7m height got his attention but I needed a few blasts for him to get my call right. I put him on the cluster and he had a pile up.
Now, the point is, had I had more gain, I’d have not only heard him better, but he’d have heard me quicker too.
So I could add more height to my Inverted V but the difference between 7m and 10m isn’t actually that much at 5 degrees off the horizon – not even a db. Hardly worth writing home about.
Anyway, this was the QSO that made me sit up and take stock of what I could do. I was seriously considering phased verticals for DX when I thought up the idea of having a switchable wire yagi. Either firing East or firing West.
Like me, you may already have an inverted V dipole up for 40m, all you need to is build another one about a quarterwave in front – or behind your existing dipole but out of a single wire. You don’t need to feed this with coax, it’s a parasitic element, like a 2 element yagi.
The A3S is 14Kg (That’s 30 pounds in US money )
I was worried that the combined weight of a Create Rotator an aluminium pole *and* an A3S Cushcraft might be too much for my little lighting rig.
To test it out, I fitted the Create Rotator to the mast and added a 20Kg dumb-bell weight and started the motor.
It lifted without an issue so I’ll go ahead and plan to use the A3S for next field day.
How mad is that? !
Essentially, this is a single 1/4 wave vertical antenna with ground radials, complimented by a pair of parasitic verticals; a reflector and a director. It will deliver around 6db of additional gain over a standard vertical with a beamwidth of around 70 degrees. I have built mine pointing 300 degrees so that I can work the US easily at night.
I call this the M0MCX VPA (Vertical Parasitic Array).
Hours of planning and modelling with MMANA has finally produced an excellent and extremely economical method of producing gain in one direction, although the front-to-back ratio isn’t superb, it still has some rejection. Continue reading
A few years ago, I bought a 6m yagi from Moonraker and James and I used it on one of our private field days. We found it difficult to get a great match but I thought I’d resurrect the project earlier this year to enter some random Saturday contest that was taking place on 6m.
Unfortunately, for love nor money, although I managed to assemble most of the bits, I couldn’t find the gamma match arrangement in all my Tesco boxes. I needed this because unfortunately the impedance of a three element yagi is well under 50 ohms so unless I went for just a two element beam, I would have to re-engineer things. I recall that a loop had a higher impedance, about 100 ohms. Using a closed loop system with a reflector and a director would bring the loop impedance down, probably by about half (according to the modelling) to achieve 50 ohms. I modelled it and things looked very promising. Wide bandwidth and pretty good gain.
Our 17 element Tonna is up for a test tonight, to ensure that everything will be working for VHF NFD event this weekend. Initial results are proving that its an extremely capable antenna and at 30 feet high, it’s just sitting over the rooftops, giving me a clear run across Warwickshire to the continent.
Fingers crossed for a bit of a lift tonight since it’s the 2m activity contest and James is popping over for some practice. I’ll write up a small report later.
In case you are wondering, yes that’s a Yaesu rotator bearing that I’m guying to at the 9.5 meter mark. It’s not holding the mast up, just taking the horizontal strain off the rotator.
41 QSOs in tonight’s contest and 12 square multipliers. Not a big score but jolly good fun and at least we seemed to be ini the top third in terms of score. Longest DX was GM3UCI for 398 Km.
Last night, we finally fitted the rotator housing and G450 Yaesu Rotator to the tower and tested it out with a small VHF ZL Special which we’ll use for VHF NFD in July (being at 1,000 feet means that we might be able to get away without high-gain antenna arrays, time will tell).
Barry (M0DGQ) is working on designs for a hinged rotator cage which means we will be able to use a 20 foot aluminium pole at ground level. Maybe next year..?
Anyway, we can now claim the record for putting up a 35 foot antenna: 20 seconds with a hydraulic switch
I needed to get an antenna higher for the kids computer room but a quarter wave vertical didn’t seem to have the gain I wanted, in fact from the kids room I couldn’t even see the network. I hunted for a Pringle can to make a “Can-Tenna” (see http://www.m0mcx.co.uk/?p=17) but apparently we were out of stock(!). A small yagi was the answer:
I made the driven element directly out of the lossy RG58 coax so that the centre conductor became one side of the driven element and the braid became the other. I used solder to give the wires some strength.
A good test but don’t be fooled. The standard 5/8th antenna shipped with most routers are probably just as good. This yagi needs to be a 5 or maybe 8 element to work better.
I also built a quarter wave last night directly from Westflex W-103, no other components – and although it compared well to the shipped vertical, it only started to match the retail antenna when I gave it some height. Another good (but failed!) experiment!