Practical Evaluation of Radio Receivers (A Model)
IV.1 Factual Situation
New experiences are gained with every practical test reception with a (newly developed) radio receiver. In fact, receivers behave at times differently than expected from the pertinent characteristic parameters (Part III) specified for receiver operation (under restricted conditions).
While the performance data of receivers are very clearly described by the receiver characteristics regarding their large-signal behaviour (Section III.12) in exactly standardized radio services, this is not the case with receivers designed for applications in barely or poorly coordinated frequency bands or radio services.
For example, for a radio service operating with a fixed channel spacing any intermodulation (Section III.9) or blocking (Section III.8) can be expected only with interfering signals having at least the same frequency separation (or a multiple of this). The receiver characteristics of interest and specified can then actually describe the relevant receiving conditions.
Utterly different is the situation with equipment like search receivers (Section II.4.2) typically used in radio intelligence, short-wave receivers, or receivers for satellite communications in amateur radio service (the technical term is uncoordinated multiple access). The frequency separation between the useful signal and the interfering signal(s) can vary as much as the possible level differences. (The frequency range below 30 MHz is ...