Magnetic loop - 40m WSPR results

Well, nobody can claim I am not thorough!  After a very favourable outcome at 14MHz for my car-portable magnetic loop mounted at 2.5m base height, I had a similarly successful result at 10MHz.

How would this small loop, 3.9m total perimeter, in 15mm pipe, do on 7MHz?  A loop of somewhat larger perimeter and 28mm pipe has done extremely well here in the past, but I didn't expect so much from a loop primarily designed to fit in a car.

Matching is via my usual pseudo-gamma ('wire up one leg') system, which provides a combination of induction, direct coupling and loop mode energising of the main loop.  It all goes through a 4:1 balun, although a 2:1 or 1:1 balun - or no balun - will usually also work.  SWR at resonance was 1.05:1, done with a SARK 110 analyser.

A lot smaller, and infinitely easier to deploy than a wire antenna at 7MHz.

Well, I always choose to put my antennas to the test against the best-performing WSPR stations to be found in the UK.  At 7MHz, M0PAI was the comparison station.

Here's the distance plot for both stations.  Note the very clear dips at post-sunset and pre-sunrise grey line periods.  I've never seen such a clear example before, which was aided by some of the quietest geomagnetic conditions, even at high latitudes, I've seen for a while:

Across all distances, the magnetic loop is only 8dB down on what I think is a full-sized G5RV at 7MHz:

This difference reduces to just 6dB when looking at DX distances, noting there were not many simultaneous DX spots.

Also note that the DX situation is an average.  Looking at the plot of spots, the highlighted station was, at that moment, hearing my loop 1dB above M0PAI:

Once again, the message is clear: magnetic loops work, and can compare very favourably for their size and ease of deployment, against full-sized wire antennas.  This is especially true when one can deploy a loop in a high quality environment.

It's also interesting to note that, even though it makes no allowance for environment, the 6-8dB difference is exactly in line with the efficiency of the loop predicted by this online calculator, which yields a 7.5dB reduction from 100% efficiency, yielding an overall efficiency for the loop of 18%.  This is not the same comparison as testing the antenna itself, of course, as there are various radiation pattern effects and environmental gain to take into account for both the loop and wire antenna.

IMAGES - ESPECIALLY FOR PE4BAS!