3 ms·
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.
by unixhero 5y ago
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.
- lucb1e 5y agoSameish 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!
- vvanders 5y agohttps://en.m.wikipedia.org/wiki/Radio_propagation 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.
- ac29 5y agoRain 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.
- anonymousiam 5y agoSince 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.
- jomnasi 5y agoTo 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.
- timeinput 5y agoIt'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.
- askvictor 5y agoMore specifically, a light-bulb behind a hill (no line of sight)
- tyingq 5y agoMicrowave 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.
- Zenst 5y agoMaybe a better explanation of this here: http://www.wa1mba.org/10grain.htm http://www.wa1mba.org/10grain.htm