i googled concerning calculating the the radio+antenna assembly tange and i’ve come up with this >> http://www.moxa.com/newsletter/connection/2008/03/Figure_out_transmission_distance_from_wireless_device_specs.htm
because the Tx and Rx radio are both the same, their values will be >> (http://routerboard.com/pdf/288/groove-5hn.pdf):
Tx power >> 23dBm
Rx sensitivity >> -93
NOTE: since the channel bandwidth will be around 4Mbps the radios will be able to achieve their ‘maximum’ performance
because both antennas are the same >> Tx antenna gain = Rx antenna gain = 30dBi
** means the stuff in the brackets is the exponent
so distance = 10**[(23 + 30 + 30 -(-93)) / 20] / 41.88 x 5400 = 10**( 8.8 ) / 226152 = 630957344.48019324943436013662234 / 226152 = ~2790 km ?!? 
the range seems pretty huge… am i doing something wrong or the calculations from the link are not accurate?