Medium Wave Sky Loop Antenna

This page describes my experiences with a sky loop antenna, which I now use for medium wave DXing. The idea for the antenna came from Rik van Riel, he describes his experiences with his HF loop antenna here.

Rik wanted an antenna that performed reasonably well on the HF ham bands. In my case, I was interested in the MW band, and would be for reception only, not transmitting, so SWR was relatively unimportant. I also wanted something that would be fairly easy to put up, so I would actually build it. Perfection is the enemy of progress.

The antenna is approximately 635 feet of #16 insulated stranded wire. Why that choice of wire? Because I had a spool of it. And I figure the insulation might help in cases where the antenna wire rests against trees or leaves (it certainly won't hurt). It is roughly square-ish in shape about 170 ft on three sides and 125 ft on the fourth. Because that's where the trees are. It varies between about 20 and 40 ft in height, again, because that is what was convenient. I hope to get it up a bit higher in the future, which should help improve the low elevation pattern.

I've got a rather large (2 acre) lot, with a lot of trees, especially around the sides. So I decided to put several of the dogbone antenna insulators up in the corners of the intended antenna location, as well as a few along the sides, for extra support. The wires run roughly N-S and E-W, but that was luck not planning.

The antenna is fed with a 16:1 balun (because I had one handy) feeding 100 ft of RG-6 coax. Yes, 75 ohm RG-6, not 50 ohm RG-8/etc. Why? Because I... well, you can guess why... :-)

Modelling with MININEC suggests that the feedpoint impedance is very roughly in the 1200 ohm range (with a lot of variation from frequency to frequency of course, until about 4 MHz). So the use of a 16:1 balun and 75 ohm coax isn't too bad actually. Some spot checks with a noise bridge show that the model approaches reality.

So... how does it work? Very well. Signal levels are quite strong, as expected. The nearest local MW station, WHVR 1280, is about S9+60 dB. WWVB on 60 kHz is S6 during the daytime. My previous antenna, a 132 ft T2FD, produced very weak signals below the upper end of the MW band. I can't wait to try it out next winter on longwave. (Well, winter itself I can wait for) I've bagged quite a few new stations with it in just a few weeks.

It also works quite well on HF. Being a loop, it is much less noisy than dipoles or random wires, but noiser than the T2FD, which I still use also.

In fact, what is really working out great is using both the sky loop and T2FD at the same time, with a phasing unit. But that's another story.

I decided to see how the loop works on HF for transmitting. Here are my results.

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Updated June 11, 2010