[Tinyos-help] Behaviour of a CTP network for low signal paths.

[Pedro Almeida]

Benjamin;

Thanks a lot for the thorough explanation! It seems very difficult to
achieve ideal conditions, and i'm afraid i did the test not knowing all
those facts. However, the real situation is never ideal, and the nodes are
all scattered in a large variety of orientations and positionings, so in
terms of "average" transmission, i hope the test was more or less helpful...
except for the human factor of course.
It would be really hard to suspend nodes in an open environment... maybe a
tree I guess.
However, indoors i got better ranges, probably due to all the reflections
(it was a long garage filled with cars). Shouldn't the metal hurt the range?

Thank you for your input!

On 7/13/07, Benjamin Madore <bcmadore at cs.pitt.edu> wrote:
>
>
> On Thu, July 5, 2007 7:24 pm, Pedro Almeida said:
> > Hello, Phillip, thanks for your reply;
> >
> > I thought the antenna to be omni-directional, the orientation to be
> > unimportant. I had a friend holding the mote from a distance, no concern
> of
> > orientation. I guess the test went kind of buggy, then...
>
> I would like to add: The antenna itself is "omni-directional", but the PCB
> imparts some direction on it.
>
> Remember, the PCB is unshielded, and the antenna connector is essentially
> a
> very small directional antenna. Using some of my Mica 2s I can easily see
> the directionality without antennas, and notice some even with them on.
>
> Added to the fact is that having someone hold a transmitter is the best
> way
> to make funny things happen. The human body reacts to radio waves mostly
> because of capacitance, but can also shield and reflect signals.
>
> If you want proof, simply tune an AM or FM radio to a weak station, then
> touch the antenna. Depending on the position of the antenna, frequency,
> other transmitters in the area, and probably the phase of the moon, the
> signal can get stronger or weaker.
>
> Cartoons where someone is standing on the TV with an aluminum foil hat in
> a
> strange pose are not hyperbole, but may in fact get someone a weak signal!
> It's funny not because it is absurd, but because it's true.
>
> So, when you test, keep track of orientation. Keep your motes as far away
> from metal as possible. Keep them away from water, as water is a conductor
> (the human body is mostly water). Do not place them on a floor or table,
> but
> suspend them at least a foot (330 cm) above or below a flat surface. There
> is a surface effect around most items due to ferric impurities and
> moisture.
>
> A small plastic or wooden stand is the best course of action. Small sticks
> of balsa wood and superglue are common in most hobby stores around here,
> and
> very cheap.
>
> I'm not an expert on routing, especially in TOS 2, so I can't help you
> there.
>
> -Ben
>
> --
> The difference between the right word and the almost right word is really
> a
> large matter- it's the difference between a lightning bug and the
> lightning.
> -Twain
>
>
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