The latest 'crazy idea' to hit my head has been earth loop antennas for 160m. Initially, I thought these would be good only for receive, but then found transmitting was a very real possibility.
If you've never heard of these, take a look at a July 1985 edition of New Scientist (link removed 2024 - no longer available), all about earth antennas and submarine communications. If you click on a page number, you get full pages to read.
It's all very simple in theory. The schematic below summaries my set-up: two copper pipe electrodes about 30m apart, where the AC current takes a loop-like path through the ground between them. This effectively yields a vertical loop antenna in the ground that is ~ 4 x the distance between the electrodes. High soil conductivity might yield a shorter path and thus shorter antenna than lower conductivity ground.
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| A ground loop antenna for 160m. |
Before you say this couldn't possibly work, then have a look at this 39 second-long video of a UK long wave commercial radio transmission being received by one of my sloper antennas (hint, it's the weaker signal by far), and the ground loop antenna:
Early results on 160m are just as astonishing. I've never seen such strong signals as the ground loop antenna produces. Here's a minute or two's worth of FT8 'CQ' reports received of my ~35W output; very happy to get a good signal report soon after sunset here into far eastern Russia at 6555km. As sunset approached Japan, the antenna confidently managed to cross the 10,000km, which is absolutely amazing, when you think the antenna is, deployment-wise only a transmission line and two copper electrodes. Note that it is necessary to operate during low Kp in order to see good results at 160m.
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| Well, no other antenna I'e tried at 160m managed this kind of DX, just one hour after sunset here! |
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| Later, close to 10,000km! |
8 comments:
Next step, try Japan on FT8 at their sunrise. They transmit on 1908 and listen on 1840. Good luck, 73, Bas
Thanks, Bas - now two-way at about -14dB to JA!
John, how did you construct the antenna. Do you have pictures? I see it does use a 6:1 transformer. How did you construct it? I made something similair for the beverage experiment but it is only for receive. I would like to transmit on it as well. I've asked G3XBM a while ago about the contruction but he couldn't give me the details I want. Hopefully you can....73, Bas
Hi Bas. You don't need a 6:1; I only used it because it was the first to fall out of the overcrowded 'junk cupboard'! A 4:1 or even a 1:1 is probably going to be fine. If you do want a 6:1, then have a look at: https://mw1cfnradio.blogspot.com/2016/03/delta-loop-balun.html
My assumption is the antenna is fairly narrow banded. Like, Bas, do you have any details on the construction such as depth of electrodes and interconnecting wire. Have plenty of room for 160 but I like the idea of the earth loop due to it being simple. 73, Don
Hi Don. Electrodes are about 12"-18" deep (15mm copper pipe). Perhaps in lower conductivity soil (mine is extremely high), deeper or greater surface area pipes may be needed. Yes, the bandwidth is fairly narrow, but not excessively so; certainly easily encompassing the 1.840/1.908 split commonly used for DX.
Ok John, with this information you have now in the post and in your answers I can experiment with something. I understand if I place the electrodes 15m apart it would be theoretically interesting for the 60m band. I wonder how that would go with such a electrode based antenna. 73, Bas
I don't know how well it will work at 60m. Mine will match OK on 80m, but it's not an effective antenna there. I haven't tried 60m. I'm still evaluating 160m. Still, it's cheaper than buying a low band magnetic loop!
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