Icom IC-7410 Service Manual - Page 16

3-3 FREQUENCY SYNTHESIZER (PLL UNIT) REFERENCE FREQUENCY OSCILLATOR CIRCUIT The crystal oscillator (X151) generates the 32 MHz reference frequency signal. This reference signal is applied to the Local Oscillator (LO) circuits, through the buffer (Q151) and LPF (L153, C156-158). 3RD TX LO CIRCUIT The 32 MHz reference signal from the crystal oscillator (X151) is doubled by the doubler (Q551, L551, L552), resulting in the 64 MHz reference clock signal. Using the 64 MHz reference clock signal, the 491 kHz 3rd TX LO signal is directly generated by 10-bit DDS (IC702) and D/A converter (R703-R722). The generated 491 kHz 3rd TX LO signal is passed through the LPF (L702, C713, C715), buffer (Q701), LO SW (D851), BPF (L851-L853, C851, C853, C855, C856, C858), and then applied to the MAIN UNIT. 2ND TX LO CIRCUIT The 32 MHz reference signal from the reference frequency oscillator circuit is doubled by the doubler (Q551, L551, L552) to extract the 64 MHz of 2nd harmonic component. The 64 MHz signal is applied to the MAIN UNIT as the 2nd TX LO signal, through the buffers (Q552 and Q571). The 2nd TX LO signal is amplified by the LO AMP (MAIN UNIT: IC3675), and then applied to the 2nd TX mixer (MAIN UNIT: D3671). 2ND RX LO CIRCUIT The 64 MHz reference signal from the buffer (Q552) and the 491 kHz signal from the 3rd TX LO circuit is mixed by the 2nd RX LO mixer (D951), to generate the 2nd RX LO signal. The 2nd RX LO signal is filtered by the crystal filter (FI981), and then applied to the RF-A UNIT as the 2nd RX LO signal. The 2nd RX LO signals which are 90 degrees phase-shifted from each other, is applied to the 2nd IF mixers (D1101 and D1102), through the buffers (IC1121). 1ST RX LO/TX LO CIRCUITS The 32 MHz reference signal from the reference frequency oscillator circuit is amplified by Q201, and applied to the PLL IC (IC201) as the reference frequency signal. The PLL IC (IC201) generates the 388.5 MHz master clock signal, using the applied 32 MHz reference signal as the reference. The generated 388.5 MHz master clock signal is passed through the buffer (Q301) and BPF (L301-L304, C305-C312), and then applied to the DDS IC (IC351). Using the applied DDS master clock signal as the referece, the DDS IC generates the 1st RX/TX LO signal. The generated 1st RX/TX LO signal is passed through the LPF (L381, C381, C382), MCF notch fileter (FI401), BPF (L421-L423, C421-C428 or L451-L453, C451-C458, C462; depending on the operating frequency), and amplified by the LO AMP (IC501). The amplified signal is applied to the RF-A UNIT, through the LPF (L502, L503, C504-C509), HPF (L504, C510-512). The 1st RX/TX LO signal is passed through the harmonic filter (RF-A UNIT; L868-L870, C872-C876 or L861-L864, C866-C870 or L871, C879, C880), and amplified by the LO AMP (Q811), and then applied to the 1st RX mixer (Q721-Q724) or 1st TX mixer (D651), through the LPF (L831-L833, C831-C836) and LO SW (D851, D852). • FREQUENCY SYNTHESIZER CIRCUITS RF-A UNIT 2nd RX IF mixer D1102 IC1121 BUFF 2nd RX IF mixer D1101 IC1121 BUFF 90deg IC1121 Q1141 BUFF LO ATT AMP Q301 MCLK 388.5MHz IC351 FI401 64.455MHz BUFF BPF DD S LPF ATT BRF ATT Reference frequency signal oscillator Q151 32MHz BUFF X151 LPF Q201 IC201 PLL AMP IC REF=500kHz Q251 Q271 BUFF 64.485-86.455MHz BPF 1st RX IF mixer Q721/Q722/Q723/Q724 1st RX LO Lo LPF Q811 LO AMP 1st TX LO Lo D651 1st TX IF mixer 86.455-124.455MHz IC501 BPF AM P LPF HPF LPF LPF 1st TX/RX Lo ATT Q551 KTC3880 X2 64MHz BPF Q552 IC701 KTC3880 SN74AHC1G04 BUFF AM P IC702 DDS Q901 BUFF ATT IC661 AM P Q571 BUFF IC662 P-CLK ATT LPF Q701 D/A LPF BUFF ATT 3 - 6 491kHz BPF 491kHz BPF ATT D951 PLL UNIT FI981 64.491MHz ATT XTAL ATT BPF 2nd RX Lo ATT 491kHz T3Lo 3rd TX mixer IC3621 64MHz T2LO ATT IC3675 LO AMP ATT 2nd TX mixer D3671 CODEC_CLK IC3955 AM P AM P IC3913 MCLK24M DSP_CLK24 IC3913 AM P MCLK24M MAIN UNIT