SparkFun Forums

[rahikpa]

Hi all!

I wonder how can I calculate a minimum hole size to a metal shield when I have a WLAN link between two radios from which the other radio is inside that metal box. Should I calculate the hole size and the distance from the antenna to the hole using Fresnell ellipsoid? Or if I know that the hole is bigger than the radius calculated using fresnell ellipsoid, should I calculate the attenuation of RF within that hole?

I'm a bit confused because I found an old studying material for EMI protection. It says that I can calculate a how much some hole will attenuate electromagnetic field flowing through the hole. So for example I can calculate that at 2,45 GHz the diameter of the hole should be about 60 mm not to attenuate the signal. However I know that if I have a radio link I need to have free space, which I can calculate with Fresnell ellipsoid. So this doesn'n make sense. One calculation says that at 2,4 GHz the hole should be about 60 mm not to attenuate the signal. Where as using Fresnell ellipsoid everything will depend on distances between the radios and obstacles. For eaxample if distance between the radios is 1 m and distance from the antenna to the hole is 10 mm, then the diameter of the hole should be 40 mm.

So when should I use Fresnell ellipsoid and when some other calculation? Should the hole in this case be 60 mm or 40 mm?

Thanks in advance!

[stevech]

I did a lot of theoretical predictions about 2.4GHz RF propagation with transmitters (802.15.4) located within a dense stack of hundreds of ISO standard intermodal containers.

The field tests were vastly different (better) than the models predicted.