Évaluations - 3, GPA: 3.7 ( )

Fabricant : Icom Taille : 3.71 mb Nom Fichier : Langue d'enseignement:

The amplified MIC signals are output from pin 8, and passed through the analog switch (IC3, pins 4, 3), AF mixer (IC5, pins 6, 7) where the MIC signals and tone signals are mixed with. * TONE SIGNALS The CTCSS/DTCS signals are generated by the CPU (IC22) and output from pins 19-21. The output signals are passed through the 3 resistors (R222-R224) to change its waveform. The waveform changed CTCSS/DTCS signals are passed through the LPF (IC7, pins 10, 8), tone filter switch (Q40) and D/A converter (IC12, pins 12, 11) for level adjustment. The level adjusted CTCSS/DTCS signals are then applied to the AF mixer (IC5, pin 6). DTMF signals are generated by the CPU (IC22) and output from pin 43. The output DTMF signals are passed through two LPFs (IC6, pins 3, 1 and pins 12, 14), then applied to the AF mixer (IC5, pin 6). The mixed AF signals are output from pin 7 of the AF mixer (IC5) and passed through the analog switch (IC3, pins 9, 8), then applied to the AF amplifier (IC7, pin 6). The amplified AF signals are output from pin 7, and applied to the D/A converter (IC12, pin 9) to be adjusted its level (= deviation). The level-adjusted MIC signals are then applied to the modulation circuits as the modulation signals. 5-2-2 MODULATION CIRCUITS (MAIN UNIT) The modulation circuits modulate the VCO oscillating signal using the modulation signals. The modulation signals from the D/A converter (IC12, pin 10) are applied to the D12 at the TX VCO (Q16, D10, D13, D34) to modulate the VCO oscillating signal by changing the reactance of D12. The modulation signals are also applied to the reference frequency oscillator (X2) via D/A converter (IC12, pins 16, 15) and the buffer (IC7, pins 12, 14), to ensure the modulation of lower frequency components of the modulation signals. The modulated VCO output is buffer-amplified by Q15 and Q29, then applied to the transmit amplifiers as the transmit signal via TX/RX switches (D16 is ON, D17 is OFF). 5 - 2 5-2-3 TRANSMIT AMPLIFIERS (PA UNIT) The transmit signal from the VCO is amplified to the transmit output level by the transmit amplifiers. The transmit signal from the TX/RX switches (MAIN UNIT; D16 is ON, D17 is OFF) is amplified by the pre-drive amplifier (Q704), drive amplifier (Q702) and power amplifier (Q701) in sequence to obtain 5 W (approx.) of transmit output power. The power-amplified transmit signal is passed through the antenna switch (D701), then applied to the antenna via the LPF (ANT UNIT; L801, L802, C802, C803, C807). 5-2-4 APC CIRCUIT (PA UNIT) The APC (Automatic Power Control) circuit prevents the transition of the transmit output power level which is caused by load mismatching or heat effect, etc. A portion of transmit signal is detected by the transmit power detectors (D702, D703) to produce DC voltage corresponding to the transmit output power level. The detected voltage is applied to the APC amplifier (IC701, pin 3). The transmit power setting voltage “APC (T1)” from the D/A converter (MAIN UNIT; IC23, pin 1) 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 “APCV” is output from pin 4. The voltage “APCV” controls the bias of the pre-drive (Q704), drive (Q702) and power (Q701) amplifiers to reduce/increase the gain of these amplifiers for stable transmit output power. The transmit power muting is carried out by the TX mute switch (MAIN UNIT; Q46), using the “TMUT” signal from the CPU (MAIN UNIT; IC22, pin 35). 5-2-5 OVER CURRENT DETECTION CIRCUIT (PA UNIT) The driving current of the drive (Q702) and power (Q701) amplifiers is detected at the current detector (Q705, Q706) by detecting the difference of voltage between both terminals of R714. The detected voltage “ISENS” is applied to the CPU (MAIN UNIT; IC22, pin 47). In case of the over current is detected, the CPU outputs “TMUT” signal from pin 35 to TX mute switch (MAIN UNIT; Q46) to stop the transmitting to protect the transmit amplifiers (Q701, Q702, Q704). • APC CIRCUIT Q705, Q706 5 - 3 5-3 PLL CIRCUITS 5-3-1 VOLTAGE CONTROLLED OSCILLATORS (VCOs; MAIN UNIT) VCO is an oscillator whose oscillating frequency is controlled by adding voltage (lock voltage). This transceiver has 2 VCOs RX VCO (Q17, D9, D11, D33) and TX VCO (Q16, D10, D13, D34). The RX VCO oscillates the 1st LO signals, and the TX VCO oscillates the transmit signal. •RXVCO The output signals are amplified by the buffer amplifiers (Q15, Q29), and applied to the 1st mixer (Q6) via TX/RX switches (D16 is OFF, D17 is ON) and LPF (L46, C396, C397), to be mixed with the received signals to produce the 46.35 MHz 1st IF signal. • TX VCO The output signal is applied to the transmit amplifiers via the buffer amplifiers (Q15, Q29) and TX/RX switches (D16 is ON, D17 is OFF). A portion of each VCO output is applied to the PLL IC (IC2, pin 8) via the buffer amplifier (Q15), doubler (Q14), BPF (D31, D32...

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