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16.6.2. Handset to Base
Circuit Operation:
The voice signal from the handset user is picked up by the microphone (MC1), voice signal passes through "Compressor"
process to reduce noise as shown in BLOCK DIAGRAM (HANDSET) (P.37). And the voice is FM-modulated by VARICAP
(DV1).
The carrier frequency is generated by TX VCO. The transmitter power transistor Q4 is turned on/off by CPU (VTX).
The carrier signal is amplified by RF AMP and sent to the handset duplexer and antenna.
The signal of 49MHz band (49.670~49.99MHz) which is input from ANT is filtered at DPX1 as shown in
BLOCK DIAGRAM (BASE UNIT) (P.36), then it is input to RF IC.
The signal input to RF IC is converted through Mixer inside of RF IC, RF filter (CF1, CF2) and Expander.
The signal is transmitted from the handset and received by the base unit antenna and amplified by RF amplifier Q1, then it is
converted to10.7 MHz and 450 KHz Intermediate by RF IC. The demodulated audio signal is output from RF IC (DET OUT) and
passed through "Expander" process to reduce noise, then voice signal is led to LINE AMP.
The signal is passed through TELEPHONE INTERFACE and Tel-line.
RX data (from Handset):
The data signal from handset (ex: Talk, ACK, COM) is also included in 49 MHz band same as the voice data. After second if
filter, the data signal is made square shape by data limiting AMP of the RF IC. RX data is output to CPU (RX Data).
16.6.3. RF signal operation/control and PLL operation (RF UNIT)
Base unit radio frequency signal received by antenna passes through duplexer (DPX1). RF signal is amplified by RF AMP.
RF signal received from RF IC is mixed with RX local frequency at Mixer to generate 10.7 MHz wide band IF. The reference
frequency is generated by X1 11.15 MHz crystal.
VC1 is the reference frequency for adjustment. The 10.7 MHz is mixed with reference and 450KHz narrow band IF is generated.
The demodulation audio signal is adjusted to the maximum at T1.
RF IC is controlled by CPU (RF_STB, DATA, CLK). The RX local frequency is generated by RXVCO.
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