Icom IC-7410 Service Manual - Page 15

TX AMPLIFIER CIRCUITS (PA-A UNITS) The TX signal from the BPF UNIT is sequentially amplified by the pre-drive AMP (Q201), drive AMP (Q221, Q222), and power AMP (Q241, Q242). The amplified TX signal is applied to the TX filter circuits. TX FILTER CIRCUITS (PA-A UNIT) The amplified TX signal from the power AMP (Q241, Q242) is passed through one of LPFs, depending on the transmitting frequency, to remove harmonic components contained in the TX signal. The filtered TX signal is applied to the CTRL UNIT. • TX AMPLIFIER AND TX FILTER CIRCUITS HF ANT1 HF ANT2 RL501 D401 CURRENT DET IC431 IC701 AMP ANTI RL351 1.8 MHz RL801 RL802 LPF 3.5/3.8/4.63 MHz RL501 RL502 LPF RL601 5/7 MHz RL602 LPF 10/14 MHz RL1001 RL1002 LPF 18/21 MHz RL1101 RL1102 LPF 24/28 MHz RL901 RL902 LPF From the BPF circuits Q201 PRE DRIVE Q221/Q222 Q241/Q242 DRIVE PWR AMP AMP 50 MHz RL701 LPF RL702 PA-A UNIT NETWORK UNIT TUNING NETWORK TUNER CPU RL301 D251 D151 D152 IC171 RESIST DET R AMP PHASE DET IC171 P AMP IC31 SWR FOR/REF AMP DET D11/D12 CTRL UNIT ANTENNA TUNING AND SWITCHING CIRCUITS (CTRL UNIT) The TX signal from the PA-A UNIT is passed through 4 detection circuits on the CTRL UNIT, before being applied to the antenna connector [ANT1] or [ANT2]. Refering to the detected parameters, the tuner CPU (IC701) controls the tuning networks on the NETWORK UNIT, to match the transceiver and connected antenna. SWR DETECTION CIRCUIT The forward wave is rectified by D12 at the current detect transformer (L11). The rectified voltage is amplified by the DC AMP (IC41), and then applied to the A/D port of the tuner CPU (IC701). The reflected wave is rectified by D11 at the current detect transformer (L11). The rectified voltage is amplified by the DC AMP (IC41), and then applied to the A/D port of the tuner CPU (IC701). REACTANCE DETECTION CIRCUIT The TX signal which is picked up at the current detect transformer (L101), and the TX signal which is picked up by C101, C105 and R105, are rectified by D102 and D101, and amplified by C-MOS IC (IC111). The amplified signal is applied to IC131, through the buffer (IC121) for phase comparison. The resulting signal of phase comparison is rectified by D131 and D132, and composed and amplified by IC51, then applied to the A/D port of the tuner CPU (IC171). RESISTANCE DETECTION CIRCUIT A portion of the TX signal is picked up by L151 and C152, and rectified by D152 to be converted into DC voltage. Another portion of the TX signal is rectified by D151 to be converted into DC voltage too. And these voltages are the same when the connected load (=antenna) is matched to 50 Ω. Thus the difference of these voltages represents the resistance components. By comparing the difference of these voltages, the transceiver detects the resistance components. The detected resistance components are buffered by Q151 and amplified by IC171, and then applied to the A/D port of the tuner CPU (IC701). CURRENT DETECTION CIRCUIT A portion of the TX signal is picked up by L401, rectified by D401, and applied to IC431 to be level-compared with the voltage from the SWR detection circuit. When the resistance of connected load (=antenna) is less than 10 Ω, the TX signal is bypassed the NETWORK UNIT, through the tuner compulsorily switches (RL301 and RL351), to protect the circuit on the NETWORK UNIT from reflected waves. 3 - 5