On Mon, 23 Jul 2012 00:08:53 +0000, foxbrain
wrote:

BTW i'm making a project for my own not any kind of homework.

Ok, you're off the hook.

i have one more question : if i wanted to make my device have a bigger
range like 500-1000meters should i put an amplifer before the antenna?
i should change the antenna in to yagi shouldn't i?

FCC 15.209
http://louise.hallikainen.org/FCC/FccRules/2012/15/209/
200 uv/meter maximum, measured at 3 meters. That works out to about
-46dBm ERP or about 12 milliwatts into a unity gain antenna.

This should explain how it all works:
http://transition.fcc.gov/Bureaus/Engineering_Technology/Documents/bulletins/oet63/oet63rev.pdf
See the calcs on Pg 29.

Claims 500 meters:
http://www.sparkfun.com/products/155
At 10mw, this is close to maximum legal. Anything more than that and
you're going to start interfering with wireless weather stations, car
alarms, etc.

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558