It's an interesting study and exploits one of the biggest advantages of NDBs: they are always on. In principle, one can do more with an automated WSPR data taking and analysis system but the problem in this part of the world is that it's hard to be be sure what the relatively few 630 m transmitting stations on the other side of the Australian continent (and beyond) are up to on a given night. Still, looking at some ensemble characteristics, and comparing WSPR reception at a number of, for example, VK6 stations, makes it clear than there are some interesting short-timescale temporal and moderate scale spatial characteristics that would be missed in studies such as the QST one. And, in fact, looking at the receiver bandscope also shows quite large amplitude structure on timescales shorter than the WSPR integration window. But, notwithstanding all that, I found the QST conclusions as they relate to the biggest picture to be very interesting.
One thing that I did wonder about was the nature of the (manual?) data taking. Reading the relevant section a few times I assume that it involved the same human listening on the same equipment, with some sort of implicit signal to noise threshold. I guess that threshold related to be being able to read the station ident, but whether there was any other s/n or signal strength information, or rough classification, logged is not clear. The data-taking cadence is also a bit unclear and I'd have liked a few more details on the collection process before launching into the statistics. I doubt any of these reservations upset the broadest conclusions but they may be relevant if further analysis is undertaken.
With my own recent and very limited 630 m data taken in what's "high season" for us, I can't yet see evidence of a local pre-dawn enhancement of the magnitude mentioned in the article, notwithstanding many international reports of comparable MW broadcast DX behaviour. There's certainly a big effect around sunset, with some broadly repeatable structure. But the QST commentary is a motivation to get more data and look harder at our local conditions, and that's a good thing. Along with all this we hope to get some VK6 amateur MW transmitting stations on the air soon, so the reciprocal reports will also be interesting.
73, Peter.