26.6. FM Demodulation
The receiving signal, FM signal which is despread at IC611, is input to Pin 16 of IC613. The signal of 10.24MHz output from Pin 11 of IC601 is increased by 4 times to become the 2nd local signal of 40.96MHz, and input to Pin 2 of IC613. IC613 makes the 2nd local signal of 10.8MHz from the input signals of Pin 2 and Pin 16, and outputs it from Pin 7. Then the FM demodulated signal, voice signal is output from Pin 14.
Circuit Diagram
26.7. RSSI (Receiving Signal Strength)
IC613 detects the 2nd IF signal (10.8MHz), and converts the receiving signal level to DC voltage, then outputs from Pin 10. This level modulation of RSSI indicates a level modulation of reception signal. In this system, this modulation takes a periodic of SS (PN), and returns extended signal by PN to original signal that is not extended. Output (Pin 10 )of RSSI is connected to CPU, IC702 and Q602. CPU predicts the distance between handset and base by this level change and changes transmission output. IC702 takes the periodic of SS (PN) that is referred above. Q602 controls Gain of Reception Amp between handset and base unit.
