Sunday, 19 February 2017

More WSPRlite Testing: Single vs. Triple Magnetic Loop

G3JKF runs probably the definitive magnetic loop on WSPR across many bands.  He and I have exchanged thoughts many times, and continue to do so.

I encouraged Ken to buy a WSPRlite last week, and we had a brief meeting on 30m where his triple loop array could run against my single loop.  Ken's construction is very careful and considered, as he has a long career in electronics enginnering.

This is how the loops, running 200mW, compared.  My single turn, 28mm copper pipe loop is in blue, Ken's triple, 15mm pipe loop in red:

In terms of the average distance achieved, the two loops were identical, coming in on that day at 6.6% of the maximum possible (antipodan) distance.  Ken's loop managed a greater distance periodically.

Overall, there isn't an awful lot to choose between the two loops, but it's clearly worth adding a bit more metal if you can manage it.

The question of whether a loop is any good and can keep up with full-sized antennas is one that is dominated by each antenna's environment.

For example, here's the week-long loop run against a doublet end fed wire run by the WSPRlite maker:

Clearly, the loop does better than this particular doublet by all measures during the whole run.  Notably, the loop keeps going through the night, whereas the doublet EF wire drops out for long periods.

Here's a comparison with an inverted-L, tuned at the base:

The loop is not quite as good as the inverted-L, but it does very well, nevertheless, especially when one considers the difference in physical size and the simplicity with which a loop can be installed.

And, finally, few people have anything bad to say about a loft dipole.  Yet, many criticise magnetic loops as just 'dummy loads'.  Here's why that view is utterly misguided:

Again, and whilst the loft dipole wasn't running some of the time, the magnetic loop does better at all points.

So the message is always the same: a well-made magnetic loop in a good, clear environment can do as well as or better than full-sized wire antennas in many cases.


  1. Interesting analysis but can I correct one assumption? I am not using a doublet on 10MHz. The antenna is a low poorly sited 10m endfed wire! 73 Richard G3CWI

    1. Thanks Richard. Readers can adjust their understanding accordingly. Tough to keep track of everyone's set-ups, which also change!