[Tinyos-help] Outdoor Range with Tmote sky

[Aleksandr N. Sadkov]

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 <pal at cs.stanford.edu> 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
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