In theory Rain doesn't affect on Path Loss at 2.4GHz, for example (http://www.radionet.com/_FileRoot/318040.pdf)
But I have measured great drop in RSSI during the rain, I guess it's due to antenna effects. Regards, Sadkov Aleksandr. > > A few rules of thumb... > The lower the frequency, the more likely the signal will "curve" > or diffract around obstacles. > The bigger and more conductive the obstruction, the more it will > absorb. > Microwaves at 2.4 GHz are used to heat food because water absorbs > at that frequency, thus 802.11b,g and CC2420's don't work so well > when it's raining below sea level... > > MS > > David Gay wrote: > > On 2/20/07, Philip Levis <[EMAIL PROTECTED]> wrote: > >> On Feb 20, 2007, at 10:42 AM, Jacob Sorber wrote: > >> > >> > You are asking for a simple answer where none exists. Wireless > >> > channels are tricky. While line-of-sight is straightforward, "not > >> > in line of sight" could mean a lot of things. What is obstructing > >> > the signal? A building? A person? A hill of dirt and rock? Is > >> > it raining? What is the humidity? I have yet to find a radio that > >> > is immune to obstructions. If you find one, I would love to see > >> > it. My experience has been that the 2.5Ghz radios are usually more > >> > robust to obstructions than the CC1000 radios on the Mica2/Mica2Dot > >> > motes, but not always. When one mote is a meter under water the > >> > CC1000 seems to do much better than the CC2420, though neither work > >> > very well in that situation. Also a rain storm can reduce the > >> > range some. The best thing to do is to program two motes and take > >> > them outside and see. It will only take a few minutes. If you > >> > need a more technical explanation for why node A can't hear node B, > >> > then you need to do some reading in the wireless comm literature. > >> > This might be a good place to start ( www.eecs.berkeley.edu/~dtse/ > >> > cu_day1.ppt). > >> > > >> > >> My understanding is that the waves which are really resistant to > >> obstructions are extremely low frequency (ELF) ones: think < 100Hz. > >> That's what submarines use to communicate when submerged, for example > >> [1]. > > > > Lower frequencies propagate better through water (which is why a > > CC1000 at 400 or 900MHz is better than a CC2420 at 2.4GHz). And > > propagation through fresh water is significantly better than through > > salt water (if I remember the numbers correctly, salt water == > > essentially no range at the frequencies under discussion, while fresh > > water might get a few meters). > > > > Lots more detail on all this is available if you look up electrical > > engineering source materials rather than sensor network ones... (i.e., > > tinyos-help is probably not the best place to find out about this, try > > finding a friendly professor with RF knowledge). > > > > David Gay > > _______________________________________________ > > Tinyos-help mailing list > > [email protected] > > https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos- > help > _______________________________________________ _______________________________________________ Tinyos-help mailing list [email protected] https://mail.millennium.berkeley.edu/cgi-bin/mailman/listinfo/tinyos-help
