When looking in wiki document, I’ve found some unclear information. Looking at 3DR 915 radio, its output power is 20 dBm.
With f=900MHz, d=5km, FSPL = 20log(d) + 20log(f) + 92.45 = 14 - 0.915 +92.45 = 105.51
Suppose the high loss at transmitter’s and receiver’s side Ltx = Lrx =2 dB, Ptx= 20 dBm, Lp is mainly due to polarization mismatch, if roll angle is limited to 45 degrees (for copters with no acrobatic flight) then Lp = -10*log(cos(45)*cos(45)) = 3, Tx antenna gain = Rx antenna gain = 3dBi then Prx = 20 + 3 +3 – 2 - 105.51 – 3 – 2 = -86.51 dB
If we take the typical fade margin of 10 dB then Prx > 97 dB, that is higher than the noise floor of about -100 dB and the receiver’s sensitivity of -120 dB. We can see that the communication range can easily reach 5 km distance. However, in the wiki document it’s written that the range of 3DR radio is about 500m.
The question of course is what are the real power output and the real communication range of 3DR radio?
Buy and try!