In the case of a just-detectable signal, the resulting blip on the radar display may be too small or too fleeting to be recognized.
This required difference in power levels of the signal and the noise floor is known as the signal-to-noise ratio (SNR).
To establish the minimum detectable signal (MDS) of a receiver we require several factors to be known.
Confusion can arise because the level calculated above is also sometimes called the Minimum Discernable Signal (MDS).
If we need the signal to be 10 times more powerful than the noise floor the required SNR would be 10 dB.
If one assumes that the bandwidth and SNR are fixed however by the application, then one way of improving MDS is by lowering the receiver's physical temperature.
F quantifies how much the signal degrades with respect to the noise because of the presence of a noisy network.
Usable in this context then means it conveys adequate information for decoding by a person or a machine with acceptable and defined levels of error.