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Manafacture: Icom File size: 3.69 mb File name: 6f123e2a-dc51-445a-a408-0048952ee449.pdf Language of manual:

The amplitude-limited MIC signals are output from pin 5, then applied to the base band IC (IC5, pin 3). The applied MIC signals are amplified at the amplifier (TXA1), and level adjusted at the volume controller (VR1). The level adjusted MIC signals are applied or bypassed the compressor section, pre-emphasis section, TX/RX HPF, de-scrambler, limiter, splatter, in sequence, then applied to another volume controller. The compressor compresses the MIC signals to provide high S/N ratio for receive side, and the pre-emphasis obtains +6 dB/oct audio characteristics. The TX/RX HPF filters out 250 Hz and lower audio signals, the limiter limits its level and the splatter filters out 3 kHz and higher audio signals. The filtered MIC signals are level adjusted at another volume controller (VR2), and then output from pin 7 via smoothing filter (SMF). BASE BAND IC (IC5) Limiter Splatter VR2 SMF 0 Expander 7 MOD VR4 RXA2 20 SIGNAL 5 - 2 The output AF signals are then passed through the Digital/ Analog switch (IC14, pins 12, 14) and applied to the AF mixer (IC9, pin 6) where the MIC signals and Tone signals are mixed with (while CTCSS/DTCS are in use) via the PM/FM switch (IC13, pins 12, 14). The CTCSS and DTCS signals are generated by the CPU (IC18) and output from pins 89-91. The output signals are passed through the 3 registers (R263-R265) to change its wave form. The wave form changed CTCSS/DTCS signals are passed through the LPF (IC17, pins 1, 3) and the D/A converter (IC4, pins 21, 22) for level adjustment. The level adjusted CTCSS/ DTCS signals are then applied to the AF mixer (IC9, pin 6). 2/5 tone and DTMF signals are generated by the CPU (IC18) and output from pin 43. The output signals are passed through two LpF's (IC17, pins 8, 10 and pins 5, 7), then applied to the AF mixer (IC9, pin 6). The mixed AF signals are output from pin 7 of the AF mixer (IC9) and passed through the D/A converter (IC4, pins 3, 4) for level adjustment (=deviation adjustment), then applied to the modulation circuit (D9) as the modulation signals. The modulation signals are also applied to the reference frequency oscillator (X1) via D/A converter (IC4, pins 11, 12) and AF amplifier (IC21, pins 1, 4). 5-2-2 MODULATION CIRCUIT (MAIN UNIT) The modulation signals from the microphone amplifier circuits are applied to the D9, and modulate the VCO oscillating signal by changing the reactance of D9. The modulated VCO output signal is buffer-amplified by Q4 and Q6, then applied to transmit amplifiers as a transmit signal via the TX/RX switch (D14 is ON, D15 is OFF). 5-2-3 TRANSMIT AMPLIFIERS (RF UNIT) The transmit signal from the TX/RX switch (MAIN UNIT; D14 is ON, D15 is OFF) is amplified to the transmit output level by pre-driver (Q603), driver (Q602) and power (Q601) amplifiers. The power-amplified transmit signal is passed through the two LPF’s (L607, L608, C620, C622-C624, C664 and L606, C615-617) to filter off the harmonic components in the transmit signal. The filtered transmit signal is passed through the antenna switching circuit (D601 and D603 are ON), then applied to the antenna connector (CHASSIS; J1) via another LPF (L601-L603, C601, C602, C604-C606, C608, C609, C663). 5-2-4 APC CIRCUIT (RF UNIT) The APC (Automatic Power Control) circuit stabilizes transmit output power to prevent the transition of the transmit output power level which is caused by load mismatching or heat effect, etc. The APC circuit also selects transmit output power from high, middle and low power. A portion of the transmit signal is detected by the transmit power detector (D604, D605) to produce a DC voltage corresponding to the transmit output power level. 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 U...

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