Rain Backscatter on 10 GHz | Hacker News Reader

Rain Backscatter on 10 GHz

destevez.net

88 pointsparsecs33 comments

The site is still having troubles but Bing has got a cached result now:

https://cc.bingj.com/cache.aspx?q=10GHz+rain+backscatter&d=7...

Maybe not on the 3cm (10GHz) band but on 13cm (2.3/2.4GHz) and even 70cm (430/440mhz) there’s quite a lot of activity with aircraft scatter.

I’m still in awe that you can bounce a signal off a plane and get a useful and predictable bounce off it.

http://www.airscout.eu/screenshots.html

Meteor scatter is also a popular amateur radio mode. Brief VHF/UHF contacts are possible by reflecting off the ionized meteor trails during any of the 30 or so meteor showers per year.

https://en.wikipedia.org/wiki/Meteor_burst_communications

https://www.electronics-notes.com/articles/ham_radio/amateur...

Hopefully the mass production of X-Ka band phased array antennas for Starlink and Kepler will bring the costs down for general purpose equipment. It would be really cool to be able to ’see’ the signal bouncing off of clouds and whatnot in the form of a raster image vs 2d fft.

s/Kepler/Kuiper/

This was cool, but I have no idea of what was achieved or what the significance of it was. Other than it was possible to receive a signal during heavy rain.

It's probably not super "significant", but it's neat. Someone has a light bulb (the omni-directional beacon) 40 km away, and completely invisible if you go looking for it (from his ground station location).

The author pointed a telescope (his directional ground station antenna) straight up and on a rainy day and could see the light bulb turn on and off.

More specifically, a light-bulb behind a hill (no line of sight)

Microwave reflections/refraction off of the rain made the otherwise blocked line-of-sight signal temporarily not blocked.

This is also how "troposcatter" shots work with microwave radios. If the distance between two stations is too far for line-of-sight (due to earth curvature effectively being a "hill" in the way), you can bounce the signal off of the troposphere.

Sameish here. I get the significance, like, it's cool in general to be able to receive other things when the rain somehow scatters it, but I understand very little about why rain makes it possible. Isn't rain supposed to block 2.4GHz and nearby frequencies? Is 10GHz also affected? Why doesn't it block but reflect? Does the moving of the rain have anything to do with it, is that why they're seeing a 20m/s doppler effect? Speed of light in water is maybe different, does it refract and then come out on the other side after having moved down? If someone could give a "Too Dumb; Didn't Understand" version of the article, I'd be interested!

https://en.m.wikipedia.org/wiki/Radio_propagation covers it a little bit. The short answer is that wavelength(aka frequency) vs raindrop size causes signals to scatter instead of attenuate and you can pick up a fraction of the original signal.

To add to what others have said, it's a common misunderstanding that water somehow has a peak absorbtion of radio waves at 2.4GHz because microwave ovens use that frequency. There is, however, nothing special about 2.4 GHz and in general attenuation of radio waves in water increases with frequency.

Since nobody else answered you, yes, the falling rain creates the observed Doppler frequency shift. This guy must have some pretty good instrumentation to be able to accurately detect a 700Hz shift in an X-band carrier.

Rain itself doesn't "block" 2.4GHz signals per se, though any obstruction will cause some degree of radio wave attenuation. Attenuation is higher at 10GHz and above, since the wavelength is shorter: higher frequency = shorter wavelength, and shorter wavelengths are obstructed by smaller objects.

That being said, wet trees are more effective at attenuating non line of sight radio signals than dry ones, even at 2.4Ghz and below. So while the raindrops themselves have minimal effect for sub-10GHz signals, you can see signal fade in wet conditions.

Maybe a better explanation of this here: http://www.wa1mba.org/10grain.htm

Is this like the ham radio site? http://www.wa1mba.org/10grain.htm

Yes, just linked that in another thread, then scrolled down a few more and can only concur it's the best of the offerings having a quick dig about. Nicely explains things.

Yes, the experiment conducted on the submitted website looks a lot like the "Storm 1" example situation in Figure 3 on the page you linked to.

Does the scatter volume have to be kept small so that when the signal gets scattered at different positions, the path lengths and thereby the delay of the scattered signals do not diverge too much? If they did, the received signal would be "blurred" by receiving the signal overlayed by itself but with different delays. Is this the correct explanation here?

I think it probably has more to do with path loss than the multi-path effects that the rain drops would have. That is the reflection from water in the cloud only has to travel through a smaller amount of rain than it might if you were doing it over a terrestrial network, but I definitely don't know all the ins and outs of CW transmission.

Link to Tweet: https://twitter.com/ea4gpz/status/1401598857478279173

I guess the site got fried

Something is wrong with the database, it's a PHP site...

It's WordPress, and the database can't be connected to because it's probably maxing out the number of MySQL connections.

If you're the owner of the site: Get some caching installed. I like WP Super Cache and Autoptimize, they're a great combo.

For reference: My WordPress site got hugged on the front page of HN yesterday, didn't bat an eye.

Kind of boggles the mind that some form of these aren’t yet the defaults / built-in after all these years.. is it just too hard to integrate into the core out of box install for some reason?

Many different kinds of server environments where cache configuration isn't the same and many kinds of sites where some things really shouldn't be cached (shopping carts, admin panels).

I don't know, Wordpress had like what, 1 billion years to wrap it's connection manager to do auto-caching for anonymous users - I mean a 15 second cache internally managed by files on the disk in the temp folder would have instantly made Wordpress be fault tolerant during a hug of death.

I get the criticism but looking at the history of caching plugins' security issues and the commonality of screwed up caching, it's obvious there isn't a one-size-fit-all solution.

Rather than dynamic caching, most users wanting to survive getting hugged on a simple blog would probably best be served by one of the static site generators for Wordpress. Takes out the main bottlenecks and leaves a lot more flexibility in how to serve it.

One of WordPress' primary strengths is that it's extensible and does not do anything big by default. One of its weaknesses is that its so easy to use. No difficult configuration is necessary and most web hosts have an auto-installer for it that configures it with default settings. The web host I work for does have a plugin that fixes a lot of these things (caching, wp-cron, basic security issues, etc) but it's not a panacea. There just isn't one.

Ease of use is a weakness?

Technologically speaking, yes. The default configuration works but there are problems when the site becomes busier that show up.

For example: WordPress has its own scheduler called wp-cron.php. Part of the ease of setup is that you don't need to create a cron job. It will just run wp-cron.php every time there is a page load. While that makes it very convenient it doesn't scale well and so when a site becomes busy it starts to fall over. So in that sense it's ease of use is also a downfall at times.

I think they meant that not having to think about anything makes people not think about anything.

> Kind of boggles the mind that some form of these aren’t yet the defaults / built-in after all these years.. is it just too hard to integrate into the core out of box install for some reason?

Because not all hosting providers compatible with Wordpress are compatible with these caching addons, it's as simple as that. Wordpress runs on the lowest sane PHP+Apache+Mysql environment.

Now I can't access this website but it looks like it doesn't need to run on PHP, it should be using a static site generator.

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