Polarization effects on water

I’d like to confirm that on the B5, chains 1 and 2 are horizontal, 3 and 4 are vertical. It turns out that they behave rather differently on an over-the-water path.

It’s well known in the microwave business that over-the-water paths are risky. All sorts of strange things can happen, especially if the path is low. Ducting effects near the surface, especially around dusk, can bend signals. And tides can move the Fresnel zone boundaries, if the link is low. It turns out that the tide effect can be really, really intense…

Someone I work with put up a whole bunch of B5 and B5c’s along the coastline (for a maritime application). In some cases the link is high enough so that it’s pretty steady. But when I chart the chains, I see two chains having shallow fades and two chains having deep fades on what looks like a tide-related basis. I am guessing that this is vertical. The one with the biggest impact is 14 miles long, mostly over the ocean. It’s actually a B5c, but I suspect chain 3 and 4 are vertical. From this chart, I may suggest that future links be configured slant 45 polarization, to avoid this.

image
The red line is total power, but only the purple, not blue, gets lost completely during what seem to be mostly tide-related events.

I think the moral is that yes, you can shoot over water, yes, it will behave weirdly, and having two chains with different polarizations is also helpful, since they don’t fade equally, but I think vertical is worse.

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Actually, my understanding is that ports 1 & 3 are vertical and 2 & 4 horizontal.

It depends on the antenna that you hook up and how you connect it.

My experience has been that using horn antennas that give you as much vertical signal width as horizontal (The physical characteristics of the signal shape, or the beam width) helps a lot with thermal inversion that happens a lot of water (or wet fields for me). Having the wider beam helps a lot especially if you have it on both sides of the link, frequently I have much more success with lower gain flat panel antennas for my CPE then higher gain very narrow beam-width dishes.

Daniel9, I was using a B5, which only has two ports or driven elements, and four chains. I’m just trying to verify which ones, on a B5, are H and which are V. Chains 1 and 2 dip one way, 3 and 4 a different way. So if 1 and 3 are both vertical, it would be a frequency thing, which sounds odd, but that’s why I hope Mimosa will answer.
My objective is to use this to gather empirical evidence about behavior of long PtP paths over water. It is most important on single-polarization licensed links, where you’d want to stick to the best polarization, but it might also impact B5 vs. B5c and the use of slant-45 on the latter for over-water paths.