er architecture more facilities into a smaller unit without losing radio performance. In 1970 a typical size was 13cm X 6cm X 2cm but today wide area The receiver architectures that are usually employed are single tone units can be 5cm X 4cm X 1.5cm, or 5cm X 1.5cm X 1.5cm superhet, double superhet and direct conversion. The latter lends depending on the type of battery used. A numeric pager the size of itself to a high degree of integration to two or even a single multi a fountain pen has been used for several years, and a pager in a wrist p circuit, plus supporting circuitry of voltage multipliers, integral watch has now been launched. Credit card style pagers 7.5cm X antenna, alerter transducer and battery. This arrangement makes for 0.5cm X 5cm are currently available on the Hong Kong national a very small pager especially if a button cell is used as the battery. 45/12 Radio paging Table 45.6 Typical receiver specifications. On body sensitivity is dependent on code format and pager usage MIXER AMPLIFIER FILTER whilst co-channel rejection depends on code, speech and measurement techniques LOCAL Parameter 25 to 138 to 406 to OSCILLATOR 49MHz 174MHz 470MHz On body sensitivity: 8uV/m 5uV/m face-on Figure 45.5 Superhet r.f. block diagram On body sensitivity: 12uV/m 8uV/m 10uV/m 8 pos.ave Analogue processed speech is not possible using direct conversion Channel spacing 10/12.5kHz 25kHz 20/25kHz thus it is only suitable for wide area applications. Typical single or 12.5kHz superhet and direct conversion block diagrams are shown in Figure 20/25kHz 45.5 and Figure 45.6. Figure 45.7 shows the block diagram of the Adjacent channel >50dB or >65dB >65dB decoder and audio sections. A wide area decoder would omit the selectivity >60dB audio amplifier section. Speech is shown outputting to a speaker but Spurious emissions it may also be simply channelled through the beep transducer. up to 1GHz The latter allows a smaller on site pager but many customers insist on better quality and louder speech than is possible from the sma