Why WSPR is no guide to propagation.

Have you ever tried WSPR?  It's a great way to test propagation and compare antenna performance.

Or, that's how the story goes.

The testing of propagation is central to WSPR - the 'P' stands for 'propagation'.  But is WSPR actually any good at revealing propagation in real time?

Well, yes.  And no!

First of all, the distribution of WSPR stations strongly reflects economic development.  So it's no surprise to find that there are few or no WSPR stations in remote, poor and otherwise undeveloped areas of the world.  This amounts to a large fraction of the planet from where no WSPR stations operate.

All 14MHz WSPR spots at 08:00UT, 07/01/2017.  A very 'western world'-dominated distribution.

So WSPR won't tend to reveal if propagation is open to Antarctica, Nepal, Svalbard of the Cooke Islands on most days, because there are no stations there.  But that there are no WSPR stations doesn't always mean there are no stations at all.  Maybe, over on SSB or JT65, there will be activity.

But there's another issue that I've repeatedly recognised with WSPR, and that is it will often show no spots being heard or received, especially on the higher bands, when another mode - say JT65 or FT8 -  will be turning 'real' QSOs in at quite a rate.

I'm not entirely sure why this phenomenon exists.  There is some explanation in that most WSPR stations tends to be simple vertical or other wire antennas with no gain over an essentially omnidirectional pattern.  With 'real' QSO modes, especially on the higher bands where antennas are smaller and easier to install, directional antennas are possibly more common.

Then again, WSPR is sensitive down to 1000 times (30dB) below the noise floor, so even simple antennas should reveal propagation openings, even accounting for different noise floor levels (which are commonly very high).

Relying on WSPR to show you band openings is therefore not a very good way to use time effectively, in my experience. It is much more effective, especially now that the very fast and fairly sensitive FT8 has arrived, to simply send a 'CQ' or three and see if someone responds.  Indeed, what FT8 has revealed to me on 12m is some very brief (often of just a few minutes) but strong openings to various, often far-flung places that an intermittent-transmission mode like WSPR often fails to identify altogether.

So WSPR certainly has its place.  But I would suggest that its principal usefulness is not in testing propagation, but in comparing antennas and all that is attached to them.