Figure-of-eight vs. standard magnetic loop.

Many days of data are now in from WSPR transmissions from my 'Meight' (figure-of-eight) loop and a standard, square loop.

Now, the figure-of-eight loop, for reasons of not having to spend money because I had the tube to make the loop already in the shack, and for its ease of forming into shape, is made of 10mm soft copper tube.  The standard, square loop is 15mm diameter tube.

The difference in tube diameter can be expected, if both loops were the same design, to yield a +9% advantage in favour of the wider tube.

And, after many days, we do indeed find, even by eye, that the single loop significantly outperforms the figure-of-eight loop.  A comparison with MX0PHX shows that, whilst the figure-of-eight loop was running (shaded area, left), it was only very occasionally able to outperform that station.  On the switchover to the standard loop, we find MX0PHX is usually under performing the loop:

Indeed, the single loop did admirably well against the UK's typically top-performing 14MHz WSPRer, GI8YJV:

I can't say whether a figure-of-eight loop would perform better or worse than a standard square loop of essentially the same total perimeter, because the 15mm tube, compared to 10mm, does make a difference to efficiency.

But what I can say is that a 15mm square loop is considerably easier to make than a figure-of-eight loop.  My own view is that I would prefer to have a wider-bore standard loop of, say 22mm pipe in practice (the increase from 15 to 22m gives roughly +7% more efficiency).  A figure-of-eight loop in 22mm pipe might slightly outperform the single loop (but of course, I don't yet know), but it would become quite top-heavy to the point of necessitating a more substantial mounting system to tolerate strong winds.  A permanently-located, stout, treated timber mast of about 4m height would do the job well, easily and fairly cheaply.

One other thing in concluding is that I realised the figure-of-eight loop needs significantly more tuning capacitance to bring it to resonance than the standard loop.  The answer as to whether or not this affects overall antenna efficiency is something that will have to await another day. The tuning range of the single loop is also significantly different, tuning about 7MHz up, from the figure-of-eight loop, which tunes from roughly 10MHz up.