radio wave polarization over water

If I have understood fresnel zones correctly, a horizontally polarized tx&rx antenna system is less likely to have out-of-phase signal issues over a flat plane (water) that a vertically polarized one.

If I haven't - or if the difference is in practice inconsequential - would someone say so before I start building?

ps I know this is a mostly radio question but all (those) groups are full of whackos and I have filters for this one, not for them.

Reply to
unk
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It is best to use circular polarisation, because reflections off a flat surface will have the opposite sense of polarisation and thus will not interfere with the direct signal and cause nulls.

Reply to
Rob

On May 5, 2018, unk wrote (in article ):

Look into Brewster?s Angle over water:.

Circularly polarized light will become linearly polarized upon replection at Brewster?s angle.

Practical naval fire control radars since the 1970s use vertical polarization, to mitigate multipath from the echo from the target reflecting off the sea surface. With verical polarization, there is very little reflection.

.

Joe Gwinn

Reply to
Joseph Gwinn

Sorta. It's like polarized sunglasses. The sun produces randomly polarized light. When the light bounces off the ground, road, or water, it becomes mostly horizontally polarized, especially at low angles of elevation. The Polaroid sunglasses pass vertically polarized light, thus blocking most of the horizontally polarized glare. The same thing happens with RF. Random polarized RF that bounces off the water is mostly horizontally polarized.

In the distant past (1970's), I worked for a marine radio manufacturer designing various contrivances including several VHF radio direction finders:

One of the many problems with doppler type direction finders is that they produce erroneous output trying to resolve multiple signals coming from multiple directions. That includes reflections. Our antenna was essentially a vertically polarized ground plane antenna, so we just extended the ground radials to raise the antenna pattern above the horizon, which eliminated most reflections. As long as the vessel wasn't pitching and rolling and the antenna remained reasonably vertical, reflections were not a problem.

For the navy, the preferred polarization for conventional RADAR is vertical. This has little to do with sea clutter and reflections, but rather because the highest part of the vessel is the mast, which produces a strong reflection with vertically polarized RF, but reflects far less with horizontally polarized RF.

I have no way to answer that. You haven't supplied any numbers with which one could obtain a clue as to what you're attempting to accomplish, what frequency you're using, and how Fresnel zones fit into your problem. Presumably, your frequency of operation is low that the RF path intersects the Fresnel zone at the water line: You'll get a much better answer to your question if you would kindly disclose what you're trying to accomplish and what you have to work with. Extra credit for providing numbers.

By your evaluation, I'm defined as a whacko because I read those evil radio newsgroups. If you want useful answers, it's considered useful not to insult your readers.

--
Jeff Liebermann     jeffl@cruzio.com 
150 Felker St #D    http://www.LearnByDestroying.com 
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Reply to
Jeff Liebermann

** The OP contains a few clues that suggest the question could be related to radio control of model boats. A theory that does the rounds is that signal level at the model from a transmitter on the bank can fade out dues to a water reflection being out of phase with the direct signal.

Polarisation of the antennas in use is held by some to be a possible fix as the reflected signal becomes reverse polarised.

Frequencies used range from 29MHz to 75MHz at distances up to 150 metres and water incidence angles of a few degrees.

IME, the issue is mostly bunkum.

.... Phil

Reply to
Phil Allison

Correct.

Could also be 400-ish mHz, &or 2.4gHz, &or 5.8gHz. I don't have a lot of antenna height on the boat to work with. I'm hoping for >1000m tx and rx both ways.

Control station antenna can be directional, model must (obviously) be ommni.

Reply to
unk

unk wrote

** At 1000m, a model boat is virtually invisible. 2.4 & 5.8 GHz R/C model radios use "spread spectrum".

Small antennas with high gain have to use GHz frequencies.

Good luck....

... Phil

Reply to
Phil Allison

Yup.

It'll be waypoint programmed; but would like telemetry (forgot that freq:

900-ish mHz) & video downlink and if I can get that why not control as well.
Reply to
unk

In vertical polarization there's an E field antinode at the surface of a conductor.

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

I only know optics, where I use the linoleum floor and some far away light source to check the angle of linear polarizers. (checking that the setting isn't off 90 degrees, polarized sunglasses for fishing and stuff use the same trick, let you look into the water, block surface reflections.

It's finally spring, I can think about trout fishing. :^)

George H.

Reply to
George Herold

It's not at all clear you aren't asking for help in blowing up the crusader's navy. You might want to clarify that to reduce the spooks interest in you.

Reply to
Clifford Heath

On May 7, 2018, Phil Hobbs wrote (in article ):

Yes. Lloyd?s Mirror:

.

Joe Gwinn

Reply to
Joseph Gwinn

Which is Young's slits using the one-sided Laplace transform. ;)

Cheers

Phil Hobbs

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Dr Philip C D Hobbs 
Principal Consultant 
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Reply to
Phil Hobbs

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