Magloop experiment time!

Fine, calm weather came to rest over North Wales today, so off we went to the coast with the 'John (Cheap) Loop'.  Or maybe it's the 'Cheap John Loop'!

Final test at 14MHz with horizontal polarisation (perpendicular to loop, out to sea).

 

Vertical polarisation testing with WSPR, 14MHz.

The main aim of the experiment was not to see how the coast enhanced reception (the site had a limited sea horizon to North America, for example), but to look at why the changes in received signal strength with loop height occur.  Overall, the loop performed identically (actually +0.25dB better) than the delta loop back home, but with the strong caveat that the NW horizon, from which most US stations are arriving, was not a clear sea one at the coast.  Even so, for a tiny loop, that's pretty good!

VK3YE compared signals with a loop being wafted around in height and orientation.  He reached conclusions about the loop based on what he could hear - but not on the real reason why the changes in signal strength were taking place.  Have a look:

I slowly reached the conclusion that it wasn't height per se that was responsible, but the way in which the antenna couples to the ground with height.

I made a GIF of two analyser screengrabs, which nicely shows the dramatic shift in matched frequency as the antenna is changed in height.  Remember, this is an extremely high Q antenna type, so shifts in matching like this massively detune from the desired frequency. 

Conclusion?  The received signal strength with height will change depending on the height at which you first tune it.  If you look and listen again at the VK video carefully, you will see that, contrary to the "not much difference at all" claim, there is actually a big difference with changing position in the vertical plane: it's strongest at about waist/chest height - probably the height it was first tuned, and drops off sharply with any increase or decrease in height from that position.  

With VK3YE's loop held horizontally at ground level in the opening sequences, the coupling to ground would of course be very strong, and the tuning, which I'll bet my bottom dollar was done when he was standing up, would be very much further off than in my example above. And in any case, nobody would realistically use a loop flat, almost on the ground.

I'm afraid we will have to wait for another day before I can start answering the question whether the loop, when properly matched at all heights, works better at some height, rather than others.  Very short daylight hours also lead to rapid propagation changes at this time of year, so it's actually a tough experiment to gather enough data for.