What is noise floor?

In signal theory, the noise floor is the measure of the signal created from the sum of all the noise sources and unwanted signals within a measurement system.
The first is the minimum equivalent input noise for the receiver. This can be calculated from the following formula:
P =  k T B
P is the power in watts
K is Boltzmann's constant (1.38 x 10-23 J/K)
B is the bandwidth in Hertz
Using this formula it is possible to determine that the minimum equivalent input noise for a receiver at room temperature (290K) is 10log(kT*1000) = 10log(1.38×10-23×1000×290) = -174 dBm / Hz.
Noise floor     =     -174   +   NF +   10 log Bandwidth
Where NF is the noise figure 
The noise figure (NF) is defined as the ratio of the output noise power of a device to the portion thereof attributable to Thermal noise in the input termination at standard noise temperature (usually 290 K). The noise figure is thus the ratio of actual output noise to that which would remain if the device itself did not introduce noise.


It will be right that Noise figure is expressed in dB. Smaller numbers correspond to lower noise and a greater ability to detect weak signals.