Beach vs Lake at 10MHz

Because my 30m vertical is currently working 200mW WSPR at a lakeside location, I decided this week would be a good opporunity to compare with an identical antenna at the beach.

The beach 10MHz vertical.

At the time of the test, the tide was about 1km out, but the sand surrounding the antenna is wet, with seawater at only about 2 feet below ground (this is a sandflat, with an extremely shallow gradient; land further out is slightly higher than the antenna's position - which is why people often get surrounded by an incoming tide here).

So, let's delve into the results!

First, the DX I was interested in: short path to Australia - in this case, to top-WSPR receiver, VK5ARG.  No real surprises here, though the relatively small difference of 6dB in favour of the beach location is encouraging to those who can't get to the coast but can find a lake. I've thrown-in G0PKT, the top-performing coastal station, as a baseline. MW1CFN is the seaside antenna.

Reception at VK5ARG, short path.

Why does G0PKT not do especially well in relation to my coastal location?  Partly, it's because that club station's antenna, whilst extremely effective and always at the top of the beaconing list, is based over land and so doesn't benefit from the full ground loss reduction effect of being over water or damp sand. And partly it's because the shortpath to Australia is in the landward direction, where the environmental gain reduces significantly.

The lake vertical, with WSPRlite and battery in the bag.

 

Whilst the difference at any given moment between sea and lake is not constant, the median value works out as exactly 6dB in favour of the beach.

Perhaps more importantly, there were nine receptions of the beach transmissions at VK6PK (median of -27dB) in the roughly 100-minute test, whilst the lake vertical was not heard at all.  The same was true at VK7ZAB (one spot from the beach antenna, at -27dB, none from the lake). A QSO you can make is a lot better than one you can't!

Let's look at SA2LLL, a much closer station, but in the seaward direction from my beach location:

RX at SA2LLL

The beach antenna achieves a median received signal of -25dB, whereas the lake vertical is heard only once, at -28dB. Perhaps a surprising result for the relatively short distance of 1995km.

Over at SM7KHA, we obtained a more informative plot, where the median difference is only 2dB in favour of the beach vertical. At the end of the run, the situation seems to be reversing, probably reflecting the changing propagation after sunset:

RX at SM7KHA

Let's look at a much closer station: GB7BI, near Inverness (450km):

RX at GB7BI

This is more complex! Overall, as a median, the two locations come out within 0.5dB of each other (-7.5dB for the beach, -8dB for the lake). But, you can see the situation changes over time, with periods where there is both a much larger positive and negative difference for the lake antenna. This probably reflects changing propagation angle changes as sunset approaches (around 17:55UT).

In my landward direction, out towards the south and EA8/DF4UE (2854km), the result was again in favour of the beach vertical:

RX at EA8/DF4UE

There's a significant, 5dB benefit to the beach location in this case - noting that the difference is sometimes very much less, or even zero. The sharp drop in signal strength between roughly 17:45 and 18:05UT is interesting - and much more pronounced for the lake vertical. The dip is coincident with my sunset period.

Out at UA3245SWL (2695km), a seaward direction for my beach vertical, the result is again in favour of the beach:

RX at UA3245SWL

I don't draw connecting lines in the above plot, as there is a lot going on, and lines tend to give a false picture in this case. The median difference is more useful, but amounts to only 2dB in favour of the beach antenna.

Finally, at OZ4JJ, the difference turned out to be 6dB - equivalent to what we saw to VK-land, despite the distance being only 1013km - but the period of reception is shorter from the lake vertical, even when the signal from the beach is strongest:

RX at OZ4JJ