À moins que... Oui, ce sont les méchants Gremlins magiques qui branchent à la masse l'armature métallique de l'immeuble quand une onde wifi de longueur 12cm arrive, mais qui la débranche très vite dès que c'est une onde GSM de longueur 17cm ou 34cm !
Vous n'avez jamais vu de béton armé, vous, c'est ça ? Ou vous faites exprès de ne pas comprendre ce que j'essaye de vous expliquer ?...
Si si, j'ai déjà vu du béton armé.
Ce que je n'ai pas vu c'est votre explication quant au phénomène surnaturel qui permettrait à un treillis métallique donné de stopper des ondes d'une longueur de 34cm (le GSM) mais de laisser passer des ondes d'une longueur de 12cm (le wifi).
http://www.microdaq.com/maxstream/application_notes/900v24.phpRange of 9XStream (900 MHz) and 24XStream (2.4 GHz) Modules
A link budget analysis can mathematically predict the system range based on the power output, receiver sensitivity, antenna gains, path loss, and fading margin. The path loss equation represents path loss (signal attenuation) as a function of distance between the receiver and transmitter and the wavelength of the operating frequency. This equation is derived from the Friis transmission equation and is given by:
Path Loss = 20* log(4*p*r/λ) dB (Eq. 1), where
r = distance between transmitter and receiver
& = wavelength
The Friis transmission equation can be used to represent the path loss as the sum of the other system factors leading to the following equation:
Path Loss = P(t) + G(t) + G(r) - R(s) - F(s) dB (Eq. 2), where
P(t) = transmitted power
G(t) = gain of transmit antenna
G(r) = gain of receive antenna
R(s) = sensitivity of receiver
F(s) = fading margin, (experimentally determined to be 22dBm)
These two equations can be used to compare the maximum range of the 9XStream and 24XStream modules.
1. Consider the range of the 9XStream module:
= 0.33 meters (for f=900 MHz)
(Eq. 1) Path Loss = 113 dB = 20 * log(4*p*r/?)
(Eq. 2) Path Loss = 21dBm + 2dB + 2dB - (-110dBm) - 22dBm= 113 dB
By setting these equal to each other, a little computation reveals that r=11848 meters, or a little over 7 miles.
2. Now consider the 24XStream module:
= 0.125 meters (for f=2.4 GHz)
(Eq. 1) Path Loss = 105 dB = 20 * log(4*p*r/?)
(Eq. 2) Link Budget = 18dBm + 2dB + 2dB - (-105dBm) - 22dBm = 105 dB
Once again, setting these equations equal leads to r=1768 meters, or just over 1 mile.
[g]From this example, it is shown that operating at 900 MHz exhibits a significantly longer range than is possible at 2.4 GHz.[/g]
Le 2.4GHz s'aténue beaucoup plus vite que le 900 MHz dans un environnement idéal, si ça réponds partiellement à ta question. Maintenant faut voir ce que ça donne en environnement perturbé, mais le 2.4 a l'air mal barré.