Icom IC-7000 Service Manual - Page 6

SECTION 3
CIRCUIT DESCRIPTION 3-1 RECEIVER CIRCUITS 3-1-1 HF/50 MHz RF CIRCUIT (MAIN AND PA UNITS) The HF/50 MHz RF filters pass only the desired band signals and suppress undesired band signals. The HF/50 MHz RF circuit has 7 low-pass and 5 high-pass filters for specified band use. The HF/50 MHz RF signals from the [ANT1] connector, pass through one of 7 low-pass filters as below, the TX/RX switch (PA unit; RL801), low-pass filter (PA unit; L801, L802, C801 -C805) and band switch (D151), and are then applied to the MAIN unit via J101 (MAIN unit). • Used RF low-pass filter (PA unit) Frequency Control (MHz) signal 0.03-2 MHz L1 2-4 MHz L2 4-8 MHz L3 8-15 MHz L4 Entrance Frequency Control relay (MHz) signal RL881 15-22 MHz L5 RL921 22-30 MHz L6 RL841 30-60 MHz L7 RL901 Entrance relay RL941 RL821 RL861 The signals from the PA unit are applied to the RF switch (Q101) via the band switch (D113) and then passed through the 20 dB attenuator (D101, D102). The signals below 1.8 MHz are passed through the low-pass filter (L103, L104, C106, C110, C111) and then applied to the preamplifier circuit. The other band signals (1.8-60 MHz) are passed through the high-pass filter (L105, L109, L110, L116, L117, C108, C109, C114-C116) to suppress strong signals below 1.8 MHz and then applied to the low-pass and high-pass filter circuits. (1) 1.8-2 MHz The filtered signals from the high-pass filter are passed through the low-pass filter (L205, L207, C209-C213) and then applied to the preamplifier circuits. (2) 2-30 MHz The filtered signals from the high-pass filter are applied to one of 5 high-pass filters as at right above after passed through the low-pass filter (L205, L207, C209-C213) and are then applied to the preamplifier circuit. • Used RF high-pass filter (MAIN unit) Frequency Control Entrance Frequency Control Entrance (MHz) signal diode (MHz) signal diode 1.8-2 MHz B1 2-3.4 MHz B2 3.4-6.9 MHz B3 6.9-13.9 MHz B4 D204 13.9-20.9 MHz B5 D205 20.9-30 MHz B6 D208 30-60 MHz B7 D209 D210 D211 D212 (3) 30-60 MHz The filtered signals from the high-pass filter are passed through another high-pass filter (L215, L217, C228, C229, C237, C238) and then amplified at the RF amplifier (Q211). The amplified signals are applied to the preamplifier circuit. 3-1-2 VHF AND UHF RF CIRCUITS (PA UNIT) The VHF and UHF RF circuits filter and amplify only the desired band signals and suppress undesired band signals. The both RF circuits have preamplifiers and bandpass filters. • VHF RF CIRCUIT The VHF RF signals from the [ANT2] connector pass through the low-pass filters (L506, L508, L510, L601-L603, C516, C519, C521, C601, C602) and antenna switching circuit (D507-D509). The switched signals are passed through the attenuator (D551, D552) and bandpass filter (D553, D554, D556). The filtered signals are applied to the preamplifier (Q551) and then passed through another bandpass filter (D558-D560). The filtered signals are passed through the band switch (D462) and then applied to the 1st mixer circuit (MAIN unit) via J101 (MAIN unit). • UHF RF CIRCUIT The UHF RF signals from the [ANT2] connector pass through the low-pass (L601-L603, C601, C602) and highpass (L413, L414, C428, C429, C431, C433) filters and then applied to the antenna switching circuit (D408-D410). The switched signals are passed through the attenuator (D451, D452) and then amplified at the preamplifier (Q451) between the 2 bandpass filters (D453-D456). The filtered signals are amplified at another preamplifier (IC471, pins 1, 4). • RECEIVER CONSTRUCTION PA UNIT [ANT1] 0.03-60 MHz LPF [ANT2] 60-470 MHz MAIN UNIT HPF Preamp. Q301 amp. 1st LO: 124.517 MHz- 594.587 MHz FI601 2nd LO: 124.032 MHz 1st mixer IC401 Crystal filter 2nd mixer 124.487 MHz D801 (WFM; 134.732 MHz) FI901 Crystal filter 455 kHz FI1101 Crystal filter 455 kHz 3rd LO: 438.85 kHz 3rd mixer IC1101 to DSP circuit LPF BPF to WFM detector circuit (IC1401) 3 - 1