In this section are described selected methods of measurement applicable to the electrical characteristics of terrestrial radio-relay-system receivers excluding any r.f. branching and switching networks. The block diagram of Figure 1, page 22 is a functional representation of such a receiver, but in practice the actual diagram may differ in detail, for example some stages, such as the r.f. amplifier, may be omitted. The noise of the local oscillator, although an important parameter of a receiver, is not usually measured on the receiver itself but rather between baseband terminals in the radiorelay system. This parameter, which results in path-loss-independent baseband noise, is not therefore considered in this section.