My Own DXCC Challenge

My QTH on the outskirts of Geneva, Switzerland, is pretty much middle-of-the- line as DX locations go. On the positive side, I own my house and I have a small garden. That means that I don't have to negotiate with nosy neighbours and am free to play around with antennas as much as I want. On the negative side, it's a terribly noisy location and, especially, I am surrounded by hills and mountains. The only free takeoff I have is between 0 and 40 degrees ; in all other directions I have anything between 7 and 15 degrees of vertical obstruction. This means that at least one third of the DX spots I see on the cluster originating from central Europe - and more likely about half - I can't even hear ! Now, that's one challenge in itself… However, I have learnt that as propagation changes and income/takeoff angles vary, by waiting for the right moment I am able to work practically everything I want to work.

During the last couple of winter seasons, I have been focussing on working DXCC on 160 metres - the hardest thing I've done in my nearly 30 years of ham radio, including earning the DXCC HR and 5 Band Worked All Zones. To do that, I put up a ¼ wavelenght inverted L antenna (17 metres vertical, 23 horizontal), which has proven a very effective radiator. Having only a small lot at my disposal, I had to be creative with ground radials. The GoogleMaps picture gives you an idea of what I was able to do. With this setup, radiation resistance is decent and the antenna is a fair competitor in the pileups.

Then, as I was struggling with the vagaries of TB propagation, I happened to listen around on higher bands. To my surprise, I was to discover that – once tuned with a tuner in the shack – the antenna clearly outperformed my trusted Cushcraft R-7000. Now, I know that there are different opinions on the 7000, and I am not in for a court case on its merits. For me, it has always been an extraordinary multiband performer (for what it is), and I was truly surprised to see the inverted L work so well. In fact, in certain directions (varying depending on the band), the L sounded like a beam during A/B tests. Practically all signals on the different bands were stronger on the inverted L than on the R-7000, and in many cases the difference was between hearing and not hearing !

With an MFJ automatic tuner in the shack, the inverted L would load nicely on all bands except 17 metres, where the tuner is not able to find a proper match. Using a manual tuner, I had no problems loading properly and working plenty of DX. The RX and TX performance of this simple antenna really made me curious, and I looked around to see if anybody had modeled it and could provide some numbers. What I immediately found was no less than the work of the late L.B. Cebik, W4RNL, " Mr. Antenna " himslef. In his excellent paper " My Top Five Backyard Multi-Band Wire HF Antennas " he provides the following table - a real eye opener :

Frequency	Gain dBi	Takeoff angle (degrees)	 Feed Z (ohms)
1.8		-2.2		29				38 
3.6		3.5		84				4500
7		4		35				700
14		5.2		22				300
21		6		13				200
28		7.7		10				200

Now - lookie what we've got here. Gain - real gain at useful angles, with the exception of 80 metres, where the 160 inverted L is basically a sky burner. 4 dB on 40 is almost what you would get from a 2 element beam, and nearly 8 on 10 is what you get from a tribander! And, again with the exception of 80, a range of easily manageable feed impendence values. Cebik's numbers provided the science behind my amateur's assessment, and I was ecstatic.

I also took note of the fact that, as Cebik notes in his article, an extensive ground radial system is really necessary only on 160 metres. On higher bands, the cited gain figures are maintained even using just a few short counterpoise wires at the base of the antenna.

Since my setup has the antenna tuner at the shack end of the transmission line, I was also worried that high swr in the coax would cause big losses. There too, being aware of the problem but not exceedingly technically minded, I looked around for wisdom. Several articles available on the Web showed me that with the kind of coax I employ (30 m/100 feet of low-loss cable, better than RG 213 but not as good as hardline), losses due to SWR are not really a concern. In the worst case, I am wasting just over 1 dB heating up the cable - at the very threshold of what is discernible by the human ear. Still, as I like to experiment, I will soon add a 1 to 4 balun at the base of the 160 antenna. That should nicely lower the high impendence on the higher bands, and lower coax losses even further.

Then, having eventually nailed my 100th country on Top Band and having ran out of fun things to do, I said to myself - why don’t I start all over again, and see where can I get on the 10 DXCC challenge bands by using CW only, 1 kilowatt maximum and just low-bands inverted L antennas? I then added a quarter wavelenght wire for 80 metres to make sure to have good coverage of all bands (the 160 inverted L loads nicely on 6 metres too…), and as of January 1st, 2010, I set off for my new, very personal DXCC challenge. I do not claim to be doing anythig particularly new, or special. However, in a world where the almost mythical performances of the 43 foot radiator are celebrated everywhere (so that customers are happy to pay hundreds of Dollars for what is basically a piece of aluminum tubing !), I am glad to prove once again that 50 Dollars worth of copper wire and a reasonably tall support deliver substantial real-world DX performances.

Apart from the great fun and new enthusiasm that this new little ham adventure is producing, initial results are exactly as expected: you can work plenty of real DX with the simplest of antenna systems, including, when conditions are right, busting huge pileups. No, you don't have the performance of a stack of monobanders, but you're also thousands of Dollars better off in the bank. You will find a month-by-month update of my results by visiting my site at: www.hb9dsu.com

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