Path Loss in free space  
UNITS: 
distance in meters distance in km distance in million km distance in lightyears 

Frequency:  Input frequency  
Gain TX antenna:  Input gain TX antenna  
Gain RX antenna:  Input gain RX antenna  
Distance:  
Path loss: 
 Calculates the Path Loss (attenuation in dB) in a free field like space communications.
 Also the distance can be calculated if the Path Loss is given (in dB).
 Substract the field attenuation from the TX power in dBm to get the power in dBm at the RX input.
 Convert the TX power from watt to dBm and the RX power from dBm to uV with use of one of the calculators.
 The formula is: PATH LOSS(dB) = 32.44 + 20*log(F(MHz)) + 20*log(D(km))  Gtx(dBi)  Grx(dBi).
 The antenna gain is in dBi. A dipole has a gain of 2.14 dBi.