ll Co-channel rejection -2dB to -2dB to -2dB to beep transducer, whose audio characteristic will have a substantial -10dB -10dB -10dB resonant peak in the 2.5kHz to 3kHz band. This peak is necessary Inter modulation >45dB >50dB >50dB to gain maximum loudness from the transducer at the beep fre- rejection quency. Transducer beep output is often a requirement in the oper- ator's specification, usually in the range 75dB to 85dB SPL measured in an anechoic chamber facing the transducer output, and at a point 30cm away. The front end r.f. noise factor using the very low voltage supply Initially it was found to be vulnerable to interference from nearby rail and minimum current, is a very important factor in the S/N ratio high power transmitters due to poor AM rejection, but now there are which finally enters the decoder, but the inefficient antennae that several techniques for minimising this affect. have to be employed largely determine the overall sensitivity. 1.5V DC LOCAL 2.2V DC OSCILLATOR PHASE QUADRATURE SIGNALS FERRITE PHASE ERROR DC TO DC BATTERY AERIAL LEAD 45 VOLTAGE CONVERTER 1.5V DC MIXER AMPLIFIER FILTER LIMITER DEMODULATED DIGITAL CODE PHASE PHASE LAG 45 DETECTOR DECODER MEMORY MIXER AMPLIFIER 32KHz LIMITER OSCILLATOR FILTER AMPLIFIER TRANSDUCER Figure 45.6 Direct conversion receivers Paging receiver design 45/13 INCOMING I.F. FROM FRONT END BOARD I.F. FILTER AMPLIFIER AMP AND DETECTOR PRE- AMP AUDIO NETWORK SPEAKER BEC SIGNAL DATA AMP FILTER DRIVER ARRAY CLOCK DRIVER BATT + LCD DRIVER EEPROM CLOCK & DISPLAY BATTERY DETECTOR CLOCK VIBRATE DRIVER Figure 45.7 Decoder and audio block diagram 45.8.3 Antennas below the level of calling and increase this level in 0.5dB stages, sending the pager's address 5 times at each stage. The generator Ferrite antennas are usually used for 25MHz to 54MHz band re- level, at which 5 successful calls out of 5 calls are sent, is deemed ceivers and sometimes in the 137MHz to 174MHz band, and are to be the sensitivity. This can be shown to be related to a theoretical wound with