Topband, as the 160m band is also called, represents a nut in the construction of a dimensionally acceptable antenna. Therefore, many radio amateurs skip this band. For this year's CQ WW contest som sa podujal zhotoviť mobile antenna, which can be implemented even in portable conditions. The inspiration was the material DK5WL "Invisible" DX Antenna for the Low Bands. After finding out that Jirko is selling OK5IM laminate telescopes with a height of 12.5 m – it was decided. V IARU I tried the HF Championship antenna and the result was impressive.
The principle is basically very simple – inverted L is a resonant quarter-wave antenna with a predominantly vertical component. This is particularly advantageous for DX operation.
The dimensions of the antenna are clear from the drawing. With the stated dimensions, the antenna resonated at 1850kHz. When used For a 12.5m telescope, the radiator impedance will be about 12 ohms, but the total impedance is also completed by the impedance of the ground system. If we use only 2-3 radials placed on the ground, it will be possible to feed the antenna directly with a 50 ohm coaxial cable.
The efficiency of such an antenna will be only 24% compared to an ideal, lossless vertical, but no one has such a vertical, HI. However, the "poor quality" of the earth has a positive effect on the broadband of the antenna. Bandwidth for PSV < 2 is approx. 90kHz.
Heinz-Josef described very well way to increase efficiency. It is suitable for home implementation and consists in the fact that we reduce the losses by using a larger number of radials and by using a transformation circuit that transforms the lower impedance to 50 ohms. The second option is the extension of the vertical part of the antenna. We can extend the laminate telescope by inserting a duralumin tube in the base of the antenna, or we can purchase a telescope with a greater height.
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Even one person can easily build an inverted L. The joints on the telescopes are fixed with insulating tape against loosening. The wire to the telescope is also fixed with insulating tape. The termination is in a box that contains a PL-connector and clamps for connecting the radiator and radials. On top of the opposing telescope is an end insulator, in my case Teflon. Both telescopes in the portable design are anchored by four thin climbing ropes.
Setting is also possible with the PSV metro. First, we complete the antenna by changing the length of the radiator to the required frequency, where PSV should be < 2. Then by shaping, or by adding or shortening the radials, we finish the antenna so that the PSV is as low as possible at this frequency.
In the IARU HF Championship, this antenna accounted for 15% of the overall result, while I spent the least amount of time on the 160. The majority QSO one was from the EU, one from AS. Considering the location of the antenna in a built-up area, in addition near the telephone wire and other antennas - clearly a good antenna! Try it too!