In addition, setting in series the cages increases the insulation voltage which makes it possible to use the variable capacitor of an old BCL in transmit (while keeping reasonable powers anyway but one can go up to 30 or 40 watts in CW on 40 m which is well beyond the necessary specifications in QRP !). As always with magnetic loops, in order to limit the losses, it is necessary to avoid going through a frictional contact in the variable capacitor so the best is to put in series the two cages of a double cages variable capacitor (the ideal is the butterfly type – quite difficult to find – but a classic double-cage variable capacitor is just as good). As a result, coaxial cable using multi-wire cores are unusable so I opted for the POPE H100 that I had on hand (quite light and single wire core).įor the coupling loop (diameter 1/5 of the main loop, so 20 cm in this case), the RG58 is quite suitable.Īccording to my Excel spreadsheet, to cover the bands from 10 m to 40 m, the variable capacitor must be able to cover from 10 to 170 pF. The compromise between a good performance and a good compactness oriented me on a main loop with a diameter of 1 meter (more modestly, let’s say that I agree with the choice of Alex, PY1AHD :-)), that I made with a coaxial with outer shield diameter of 9 mm which should theoretically provides efficiencies of 91% on 10 m, 78% on 15m, 46% on 20 m, 21% on 30m and 7% on 40m (calculations done using from my personal spreadsheet).įor the outer loop, to avoid adding an horizontal support, the coaxial cable must be rigid enough to maintain its circle shape by its own. Opting for operating during the day, I set as specifications to cover the bands from 40 to 10 meters. So I decided to resume my experiments of magnetic loops that I conducted several years ago and here is the version that I built this summer.
Multiple commercial versions exist, especially the famous “Alex Loop” of a very simple design, so quite easy to reproduce. However, a magnetic loop still represents a good candidate in terms of compactness, as far as designed to be folded for easy carrying. Sometimes, light wire antennas can be easily erected when natural supports are available around such as trees or when carrying light fiber pole. Operating QRP requires to select an efficient antenna. Personally, I do not like to carry too much equipment so I find the QRP approach quite appropriate to me.
#RG58 MAGNETIC LOOP PORTABLE#
When summer is back, I often like to go outside for HF portable operations.
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