Wireless NIC must use its antenna and encoding filter to keep out all unwanted RF signals and thus unwanted bits as well. Receive Sensitivity refers to the power level of an RF signal required to be successfully received by the receiver radio. Better the SNR is better the performance. SNR can be presented as a dB value or as the difference between the RSSI(signal) and the noise floor(noise). For wireless NIC to report noise,it has to receive data bits, without that NIC will report as noise variable of zero. Noise floor is the ambient or background level of radio energy on the specific channel you are analyzing. RSSI is a metric that is specified by measuring the amount of energy associated with the bits received via wireless NIC.

Received Signal Strength Indicator (RSSI)

If distance(d) in kilometers between antenna, frequency (f) in MHz then FSPL in dB FSPL=32.4 + 20log (f) + 20log(d)

If distance(d) in miles between antenna, ferequency (f) in MHz then FSPL in dB. FSPL isthe loss of signal energy caused by the natural broadening of the waves, often referred to as beam divergence.

Wifi spectrum analyser