Methods are given in this section for the measurement of the electrical characteristics of frequency demodulators. Threshold aspects are not included as these are not normally required for line-of-sight radio-relay systems. Furthermore, where possible, only measurements involving the basic demodulator are considered, excluding the equipment comprising the de-emphasis network and the networks associated with sound sub-carrier signals, pilot signals and auxiliary signals. Methods of measurement for frequency modulators are given in Section Four. Measurements between the baseband terminals of modulator/demodulator assemblies are covered by various sections of Part 3 of this publication.