Sometimes I am involved in communications outside of the ham bands. This is mainly NVIS work at frequencies within 2-10 MHz. Since my antenna park is not set up for this (I aim manly for DX in the ham bands) I had to find a suitable antenna. The standard antenna for this kind of communication is a T2FD, a terminated folded dipole. A look in eg. the Rothammel Antennenbuch shows that such an antenna should be about 30 metres long to work well on the lower frequencies. This was, initially anyway, out of the question for me.
So what should I do? Could I get away easy? The answer was, it turned out, yes! The solution was really too easy: I loaded my transmitter with a 300 watt dummy load and connected a long wire to the “hot” end of the dummy load. My thinking was that “Ok, it won’t radiate well, but the wire will get some power and emit that. Let’s hope it’s enough!”.
I took me less than five minutes to rig it up and test it. Signals were heard on all frequencies and the SWR was the dummy load’s 1:1. Would it work in real life too? In fact it did. I tried using a ground wire from the dummy’s “cold” end, but saw no change in my signals in either direction. The station has a ground anyway, so it probably does not matter. I was worried that unbalance currents would make the key “burn”, but did never notice that effect.
It worked very well as an all band antenna during the first couple of radio nets. I was happy with it but expected that to not last forever. Surely I am just lucky with the prevailing atmospheric conditions? Apparently no! I have since used this no-tuner antenna for several years at the lower end of the short wave range, both in the ham bands and outside of them, and the “antenna” works surprisingly well. Not once have I felt a need to erect a T2FD, I simply made a long wire out of the feeder to the VHD-antenna described elsewhere on this website. The feeders (about 40-50 metres) two legs are connected together with the VHD as a kind of end-capacitance (probably of no relevance, but it is easier to leave it there)!
I have not used this antenna for DX-ing, but quite a number of other European ham stations can witness that it works for inter-Europe communications, say, up to 3000 kilometres or so. Not bad considering its simplicity!
My ladder type feeder runs at approximately 4-5 metres above ground level. This is likely to be a good height for NVIS and perhaps it is this what makes the antenna tick in the first place?
The setup has an unknown efficiency. I crank out 50-100 watts into the dummy load, and apparently enough of that power finds its way out into the antenna wire. I know for sure that it communicates better than other stations having about 10-20 watts output… at least at some frequencies… and at least when the other station use a low T2FD-type antenna…
A single wire above ground has an impedance of about 1000 ohms. Depending on how long it is compared to the frequency this will show as some other impedance at the fed end. Since this is a setup for “any” frequency the resulting impedance is unknown. With a Smith-chart one could find what SWR would appear between the “hot” end of the dummy load and the antenna wire, but this changes for every used frequency, so it is hardly a meaningful excercise.
So, while no guarantees are made, this simple device has shown to work well during several years, at my QTH at least. If you need to have some signal out on a band you do not have an antenna for, then try it. If it works, it works. If not, well, the setup is cheap and not complex. What do you have to lose?