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 chodivú anténu, 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 – bolo rozhodnuté. V IARU I tried the HF Championship antenna and the result was impressive.
Princíp je v podstate veľmi jednoduchý – inverted L is a resonant quarter-wave antenna with a predominantly vertical component. This is particularly advantageous for DX operation.
Rozmery antény sú jasné z nákresu. S uvedenými rozmermi anténa rezonovala na 1850kHz. Pri využití 12,5m teleskopu bude impedancia žiariča asi 12 ohmov, celkovú impedanciu však dotvára aj impedancia zemného systému. 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. Šírka pásma pre PSV < 2 je cca. 90kHz.
Heinz-Josef veľmi dobre popísal spôsob zvýšenia účinnosti. 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.
|
|
|
|
|
|
Postaviť inverted L zvládne poľahky aj jeden človek. 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. Oba teleskopy sú v portablovom prevedení kotvené štvoricou tenkých horolezeckých laniek.
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.
V IARU HF Championship sa táto anténa podieľala 15% z celkového výsledku, pričom som na 160-ke strávil jednoznačne najmenej času. Väčšina 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!