OK. First the last few words about the 'John Loop', my poor man's homebrew of the £300 'Alex Loop' magnetic loop (coax cable) antenna.
With the loop still propped up against a chair in the kitchen, I sent 1W WSPR at 14MHz for a few hours. Whilst it was still just about working, I applied the tools of DXplorer to the results. They're pretty good.
Both these comparisons are with the stations who were reporting the largest number of spots from the UK, but both were using 5W, or 7dB more power than I was. All reports are for DX distances, in this case, beyond 4000km:
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| Here, I am 6.3dB worse than G4UGD, but he is using 7dB more power, hence I am ~1dB better at DX distances. |
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| Against G0IDE, I am 3.6dB stronger at DX distances, despite using 7dB lower power. Hence, I am actually over 10dB stronger on a Watts-adjusted basis. |
And good also against G8YPE, where the Watt-for-Watt comparison is ~3dB stronger at DX distances for my loop.
For those of you of a more gun-toting, Trump voting persuasion, remember that none of these results rely on any human involvement. I just built a coax loop, sat it in the kitchen, and let it do its thing, automatically.
And once we're finished? Just roll it up and stick it in a bag. The only thing to perfect is the support for field use. I'm thinking pipe clips of some sort to attach the capacitor to PVC tube, and maybe a ground spike. A tripod, the common solution, isn't really stable enough for windy places with such a top-heavy load.
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| It all rolls up into this small package. Ruler is 15cm. The capacitor has changed again, mostly because the vane contacts were easier to clean and maintain. |
And for a floor-mounted, tidy version, have a look at this fine construction:
Like your simple loop , how do you fix the coupling loop to the main ?
ReplyDeleteHi Franco. The coupling loop is not physically connected to the radiating loop. It's all done by induction. The small loop has to be about 1/5 the perimeter of the radiating loop. You attach one end of the small loop to the centre conductor of your coax, and the other side of the wire to the outer (sheath). Whilst it looks like you are putting energy into a tiny loop, most of that energy is of course absorbed by the radiator, provided the capacitor is set for resonance. So it works fine. There are other ways to do it if you look at this site: https://www.nonstopsystems.com/radio/frank_radio_antenna_magloop.htm
ReplyDeleteI think I will rename my loop to "Bas Loop". ;-). By the way I use a box for the capacitor which can stand on a flat surface. In storm a big stone on top will fix it. Have you considered a small field strength meter to reliable tune the loop without a SWR meter? It is also quick and simple to make. 73, Bas
ReplyDeleteSee https://www.youtube.com/watch?v=uHOoqmZruQs&feature=emb_title
ReplyDeletefor what I mean as tuning indicator...
73, Bas
Thanks for the infos, Bas! You make a much tidier antenna than I do, although things are much easier if you make the loop floor mounted. Actually, this is quite a good idea, as it is usually easy to find a wall or something, or just take a small table to raise it. I wonder how you deploy it in the field?
DeleteI wonder about that myself. I never took it out in the field....I smell a new blogpost...73, Bas
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