Sensitivity and noise factor are the conventional parameters which describe the, capability of a system to process weak signals. The noise factor is particularly important, since it characterises not only the system as a whole but also its modules (such as HF preamplifiers, mixers, or IF amplifiers). By making a careful selection of the noise factor and the amplification of individual stages, the designer can optimise the noise factor and the dynamics of the system as a whole. With a known noise factor, the system sensitivity can be easily estimated from the system bandwidth.