Communication Path Calculator (RF Link Budget)

This calculator determines the amount of transmitted power received and delivered to the input of a radio receiver in a RF communication link that has signal dissipation losses in the transmitter and receiver hardware as well as signal attenuation as the RF signal energy travels and disperses along its propagation path. The transmitted power received together with the receiver sensitivity determines if the communication link is successful or fails.

Transmit distance (d):   km
Transmit frequency (f):   GHz
Transmit power (Pt):   watts
Transmitter misc. losses (Ltm):   dB
Transmitter cable losses (Lct):   dB
Transmitter antenna gain (Gt):   dBi
FSPLi (calculated):  
Receiver antenna gain (Gr):   dBi
Receiver cable losses (Lcr):   dB
Receiver misc. losses (Lrm):   dB
Receiver sensitivity (Sr):    (dBm values below one mW are negative)
Receiver impedance (Zr):   Ω (needed if specifying receiver sensitivity in µV)
Pin:   (power delivered to receiver input)
Receiver sensitivity (Sr, from above):  
SNR (Pin - Sr):  

Free space propagation of the signal outside of the earth's atmosphere is subjected to dispersion losses only no attenuation occurs due to dissipative losses in the free space propagation path.

f = frequency of the transmitted signal in GHz

c = free space propagation velocity of an electromagnetic wave = 299 792 458 m/s EXACTLY

d = distance between transmit and receive antennas in km

Pt = transmitter output power in Watts feeding the transmission line cable going to the transmit antenna
Gt and Gr = transmit and receive antenna gains expressed in dBi (db above an isotropic radiator)
Lct and Lcr = losses in dB of the transmission line cable that feeds the transmit and receive antennas
Ltm and Lrm = miscellaneous losses in the transmission and receiver sections of the communication link

Sr = Receiver sensitivity expressed as

dBm [ watts above (+) or below (-) one mW ]
v (microvolt)
If receiver sensitivity is expressed in v, then the impedance level of the receiver system, Zr, needs to be specified. The default impedance level is 50.
Sr(dBm) = 20 Log Sr(v) - 10 Log Zr - 90

FSPLi = free space path loss due to 1/R dispersion as a signal propagates from an isotropic radiator out into free space
FSPLi = 20 Log(d) + 20 Log(f) + 20 Log(4 π/c) + 240 dB = 20 Log(d) + 20 Log(f) + 92.448 dB

FSPL = FSPLi corrected for the transmit and receive antenna gains = FSPLi - Gt - Gr

Pin = Received power from the transmitter delivered to the receiver input = Pt - Ltm - Lct + Gt - FSPLi + Gr - Lcr - Lrm
    = Pt + Gt + Gr - FSPLi - (Lct + Lcr + Ltm + Lrm)

The Signal to Noise Ratio (SNR) is the received power in dBm less the receiver sensitivity in dBm.

4:42 PM Sat 1/25/2020 SNR = Pin(dBm) - Sr(dBm)

A positive number indicates the received signal power exceeds the detectable power of the receiver electronics (sensitivity) and successful communication is possible. A negative number means the signal is below the receiver noise level and may not be detectable unless other signal processing steps are taken.

Version 1.0 (2020.1.25)
Script by Quartus [ please report any problems with this page to George Hnatiuk ]