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The detected voltage is applied to the APC amplifier (IC601, pin 3). The transmit power setting voltage “T2” from the D/A converter (MAIN UNIT; IC20, pin 2) is applied to another input terminal (pin 1) as the reference voltage. The APC amplifier compares the detected voltage and reference voltage, and the difference of the voltage is output from pin 4. The output voltage controls the bias of the drive (Q602) and power (Q601) amplifiers to reduce/increase the gain of these amplifiers for stable transmit output power. The change of transmit output power is carried out by the change of reference voltage "T2," and the transmit power muting is carried out by the TX mute switch (Q606), using the “TMUT” signal from the CPU (IC18, pin 13). 5-2-4 OVER CURRENT DETECTION CIRCUIT (RF UNIT) The driving current of the drive (Q602) and power (Q601) amplifiers is detected at the current detector (Q604, Q605) by detecting the difference of voltage between both terminals of R623. The detected voltage "ISENS" is applied to the CPU (IC18, pin 47). In case of the over current, the CPU outputs "TMUT" signal from pin 13 to TX mute switch (Q606) to stop the transmitting for protection of transmit amplifiers (Q601, Q602). 5-3 PLL CIRCUITS 5-3-1 VCO (Voltage Controlled Oscillator) CIRCUITS (MAIN UNIT) A VCO is a oscillator which its oscillating frequency is controlled by adding voltage (lock voltage). This transceiver has 3 VCO’s; RX VCO1 (Q1, D1-D4), RX VCO2 (Q2, D5-D8) and TX VCO (Q3, D10-D12). The RX VCO1 oscillates the 1st LO signals for 155 MHz and higher, and the RX VCO2 oscillates the 1st LO signals for 155 MHz and lower frequencies. And the TX VCO oscillates the transmit output signal. • RX VCO1 and RX VCO2 The RX VCO1/RX VCO2 (Q1, D1-D4/Q2, D5-D8) oscillates the 1st LO signals. The output signals are amplified by the buffer amplifiers (Q4, Q6), and applied to the 1st mixer (Q37) via TX/rX switch (D14 is OFF, D15 is ON) and LPF (L38, L39, C161-C164, C383, C384), to be mixed with the received signals to produce the 46.35 MHz 1st IF signal. • TX VCO The TX VCO (Q3, D10-D12) oscillates the transmit signal. The output signal is applied to the transmit amplifiers via the buffer amplifiers (Q4, Q6) and TX/RX switch (D14 is ON, D15 is OFF). • APC CIRCUIT 5 - 3 A portion of the each VCO output is applied to the PLL IC (IC1, pin 6) via the buffer amplifiers (Q4, Q5) and the tunable BPF (D30, D31, L40, C170-C174). 5-3-2 PLL CIRCUIT (MAIN UNIT) The PLL circuit provides stable oscillation of the transmit frequency and receive 1st LO frequency. The PLL output frequency is controlled by the divided ratio (N-data) from the CPU. The buffer-amplified VCO output signals from the tunable BPF (D30, D31, L40, C170-C174) are applied to the PLL IC (IC1, pin 6). The applied signals are divided at the prescaler and programmable counter according to the “SSO” signal from the CPU (IC18, pin 10). The divided signal is phase-compared with • PLL CIRCUIT the reference frequency signal from the reference frequency oscillator (X1), at the phase detector. The phase difference is output from pin 4 as a pulse type signal after being passed through the internal charge pump. The output signal is converted into the DC voltage (lock voltage) by passing through the loop filter (R7, R9, R12, C17, C18, C20). The lock voltage is applied to the variable capacitors (D1 and D2 of RX VCO1, D7 and D8 of RX VCO2, D11 and D12 of TX VCO) and locked to keep the VCO frequency constant. If the oscillated signal drifts, its phase changes from that of the reference frequency, causing a lock voltage change to compensate for the drift in the VCO oscillating frequency. 5-4 POWER SUPPLY CIRCUITS (MAIN UNIT) Voltage from the attached battery pack is routed to whole of the circuit in the transceiver via switches and regulators. Q30, Q31 Q16 5 - 4 5-5 PORT ALLOCATIONS 5-5-1 CPU (MAIN UNIT; IC18) Pin No. Port Name Description 1 DSDA Outputs serial data to the D/A converter (IC20, pin 6). 2 DAST Outputs strobe signal to the D/A converter (IC4, pin 6). 3 SIDE3 Input port for [Side3] key (S4). "Low"=When the key is pushed. 4-7 CBI0-3 Input ports for [ROTARY SELECTOR] (VR UNIT; S701). 10 SSO Outputs serial data to the PLL IC (IC1, pin 15), D/A converter (IC4, pin 8). 11 SCK Outputs serial crock signal to the PLL IC (IC1, pin 14), D/A converter (IC4, pin 8). 13 PLST Outputs PLL strobe signal to the PLL IC (RF UNIT; IC1, pin 16). 15 DASW Outputs mode (Digital/Analog) switching signal to the D/A converter (IC14, pins 10, 11). 17 TMUT Outputs transmit mute signal to the transmit mute switch (RF UNIT; Q606). 18 NWC2 Outputs Narrow/Wide mode switching signal to the bandwidth switches (Q26, D32, D33). 19 NWC1 Outputs Narrow/Wide mode switching signal to the bandwidth switches (Q27, Q41, Q42, D34, D35). 20 DDSD Outputs serial data to the DTMF decode IC (IC10, pin 9). 21 DDAC Outputs serial clock signal to the DTMF decode IC (IC10, pin 11). 26 T5C Outputs T...

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