Figure of Eight Magnetic Loop

This week has seen a flurry of yet more magnetic loop experiments, using some spare 10mm microbore copper tube I had in the attic.

I started out with a parallel, double loop array for 20m.  This ran on 14MHz WSPR for a couple of days, and turned out to be a perfectly good performer for its size, simplicity and cost.

Parallel loop array with homebrew remote tuning and pseudo-gamma matching system.

Here's how the simple distance graph looked, when compared against a full-sized dipole that is known to be one of the best on the bands.  Disregard the second day of comparison, because it has been affected adversely by a battery supply that had exhausted:

Parallel, two-loop array at 14MHz.

The smaller bore tube works fine at 14MHz, although some extra height above the ~1.5m base height I used would make a positive difference.

I decided then to recycle the parallel loop array into a figure-of-eight loop.  I've long wanted to build one of these, but never got round to it.  One thing I found with my construction was that the loop, having a bit of a twist at the 'waist', introduces some considerable stiffness to the whole thing.  This makes it very mechanically stable, and so eliminates changes in the tuning due to strong winds.  With an exceptionally high-Q antenna like this, mechanical and electrical stability is essential.

My figure-of-eight loop in 10mm microbore tube.  Plum wine and axe in the kitchen are optional!

The weather is Arctic cold today, with moderate winds direct from the North Pole.  It has remained drier than forecast, though, so I am now active (pm, 26/10/2018) on 14 MHz WSPR.  The matching is extremely good, at 1.05:1 SWR.

Now in action on 14MHz WSPR!

For now, what I can say is that I have, in essence, saved myself almost all the astonishing £502 that the commercial version of this antenna is now selling for!  A useful RadCom write-up, including an EZNEC model, can be found here.  There's no doubt at all that those corrosion-prone compression fittings on the commercial model should be replaced with soldered connections, and reduced in number through using formed pipe.