## [kismac] Re: Net Area Power Interpolation

• From: Andreas Rossbacher <andreas.rossbacher@xxxxxxx>
• To: kismac@xxxxxxxxxxxxx
• Date: Thu, 12 Jun 2003 18:51:45 +0200

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Michael Rossberg wrote:

>
> result=1/this.getDistance(x,y,i) * Math.sqrt((rField/(4 * Math.PI)) *
> scatterPoint[i].getValue());
> result=result / scatterPoint[i].getValue();
>
> how should this work? if this derived from the surface area of a
> sphere, then should this be not  decline = rField / ( distance^2 * 4 *
> Pi ). why did you take the square root?
> and what about correction to dbm?

I used the calculation for a E-Field using the scatterPoint as an
"virutal" antenna and the measured signal strength there as its
power.
To calculate the E-Field your use:

E = 1/r sqrt( (Z_0 / (4 PI) ) P_rad)

better to visualize in TeX:
$E = \frac{1}{r} \sqrt{\frac{Z_{0}}{4\pi}\cdot P_{rad}}$

Z_0 is the field wave resistance of empty space which shall
be 377 Ohm. P_rad is the radiatin power which is set equal
to the measured data at the scatter point.

So if i have the Power in mW at the scatter points i can
calculate the decline factor here.

You can easyly convert dbm to mW by:

mW = 10^(dbm/10)

Anyway, this is not my realm. :-) If i did something stupidly wrong,
hit me! *g*

After finishing my decline algorithm i though thougt it might be
much to difficult cause the radiation simply declines with the square
over the distance. But that is cause of it having to spread a much
wider area on the surface of the sphere of the antenna. No normal
field wave resistance is used then.
- --
bye Andreas
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