ched on earlier but they are For land mobile radiotelephone facilities, different problems arise considered in rather more detail below. in managing spectrum. Here again a radio channelling plan is required. Channel frequencies will be re-used with geographical separation between service areas. The basic equipment type appro- 26.6.4.1 Fixed microwave links val specification will emphasise: The main elements of efficient planning for private fixed links are: 1. Excellent suppression of spurious emissions from mobile trans- mitters and receivers. Definition of radio channelling plans (such as, for example, 2. Low adjacent channel emission in transmitters and low ad- Figure 26.1) for the available frequency band. jacent channel response in receivers. Publication of technical specifications for type approval of Optimised channel bandwidth requirement, typically at present transmitting and receiving equipment, compatible with the in the range 10kHz to 25kHz, and corresponding carrier fre- radio channel plans. The specification would set standards of quency stability. such factors as antenna sidelobe response, antenna polarisation 4. Freedom from receiver blocking by powerful signals off the performance and rejection of adjacent channel interference. tuning point. These standards would be stringent if circumstances made high efficiency of spectrum utilisation necessary. However, traffic in the land mobile service typically consists of Determination of circuit noise and interference objectives. The brief conversations between pairs of users, interrupted by periods of target level for noise plus interference in channels should not silence that may be long. The key to efficient spectrum utilisation be made unnecessarily good, and the ratio of interference to lies in ensuring that a channel is not idle during the periods of noise might favour the former if efficient spectrum utilisation silence. The nature of the user's business will determine what was important. system architecture will provide efficient spectrum loading 