Evening shortpath - at the beach.

It's that time of year again when summer is drawing rapidly to a close, and the terminator lines up nicely between the UK and Australia.

Time for some beach work with WSPR!

Modelling using Proppy HF showed that 14MHz would exhibit a fairly sharp rise to a peak in propagation between the two regions, which looked like this, based on a 1/4 wave receiver and 8-ele transmitter (the maximum available from the software), beaming shortpath:

The weather was forecast to be a bit rainy, but it looked OK skywards, so off to the east-facing sandflat near high tide, and in went the 1/4 wave vertical, my standard antenna for most operations, and always for WSPR. It has two elevated sloping radials with a near-perfect match over seawater-saturated sand and glacial clay.

The model proved to be very reliable. Peak signals from Australia for me, in the far west of the UK, were at about 21:20UT, somewhat earlier than the modelled peak.

The main interest was the strength of signals over time from Ian's vast, 4x5-ele array, just outside Melbourne and beaming along the shortpath to Europe, with 5W going into the array, supplied by an Ultimate 3S transmitter.

VK3MO's world-class 14MHz array. Reproduced with consent.

With such a system, everybody hears Ian!  But not everybody hears him as well, of course. One reason is that some WSPR operators - it seems to have increased over the years - are using beam antennas. Another is that some are close to the coast, yielding enviornmental gain; this is the chosen situation for me, for example. And the other big cause of differences is local noise levels which, sadly, is far too high for all too many of us.

I've extracted all the stations that heard Ian in the time slot I was operating, and then taken a fairly large sample of those, at random, without first referencing their received signals so as to give a genuine, unbiased spread of what people could hear. This is what the plot looks like (click for larger image):

The remaining problem, one which has afflicted WSPR from its inception, is: how do we know if the best signals (other than mine, which we know is an elevated 1/4 wave), aren't simply the result of a Yagi pointing at Ian's array?  In short, we don't - because a surprising number of operators don't tell us anything about their WSPR setups. A number of those are older operators, seemingly unwilling to respond if contacted and often apt to not publish their contact details. We just have to live with this, unfortunately, or set-up our own, second identical antenna inland, in a quiet place, to run a coast/inland comparison. This is possible for me, but not until the cattle are out of the fields later in the year (cattle love destroying antennas!) I'll be doing this at some point, with a bit of luck.

Certainly, relative to the majority of UK receivers, being at the beach for this particular path at this particular time is very worthwhile, yielding maybe a 20dB gain over those, partly due to the environment and partly due to having no noise at the beach. It's reasonable to assume some of the equally good receivers to mine are using directional antennas; certainly, 2E0PYB has uses phased arrays in the past, but I don't know what his current setup is for sure.

The other take-home message is that the peak signal is generally sustained over a somewhat longer period than other stations. This may reflect access to a greater range of signal arrival angles at the beach, including exceptionally low angles not accessible to inland antennas, not even when they are large Yagis. Overall, I suspect that because there are a fair number hearing Ian at reasonably good strength, that the arrival angle on the evening shortpath is not especially low and seems likely to be perhaps in the 5-15 degrees range, at a semi-informed guess.

Next, it will be a similar test at morning long path. I already have, as many of you will know, the results for a coast/inland comparison with my own antennas, conducted during a Covid lockdown (may they never return!) and that up to 25dB environmental gain is available from the coast for this path at this time, allowing for the 6dB measured difference for this path and this time between the two antennas used for the test:

I didn't just look at VK3MO - using transmit from the beach, rather than receive, there were many stations in the far east and west that were also highly interesting, not least as I was either the only or one of only a couple of stations being heard by them. I'll cover those in another post.