Icom IC-PCR100 Service Manual

Also see for COMMUNICATION RECEIVER IC PCR100: Instruction manual

Contents

SECTION 4 CIRCUIT DESCRIPTION4 - 14-1 RECEIVER CIRCUITS4-1-1 RF ATTENUATOR CIRCUITThe attenuator circuit attenuates the signal strength toapprox. 20 dB to protect the RF amplifier from distortionwhen excessively strong signals are received.The RF signals from the antenna connector are passedthrough or bypass the “L” type attenuator (R1, R3). The sig-nals are then applied to the RF filter circuit.4-1-2 RF FILTER CIRCUITThe applied signals pass through either the low-pass filter orthe high-pass filter circuits via the band switching diodes.• RF signals below 50 MHzThe RF signals below 50 MHz are passed through the low-pass filter (L1, L2, C7–C11) via the band switching diode(D2). The filtered signals are applied to the HF RF circuit.• RF signals above 50 MHzThe RF signals above 50 MHz are applied to the high-passfilter (L172, C477, C478) after passing through the bandswitching diode (D4). The filtered signals are then applied tothe VHF/UHF RF circuit.4-1-3 HF RF CIRCUITThe HF RF circuit amplifies the received signals within therange 0.01–50 MHz and filters out-of-band signals.The HF RF circuit consists of three low-pass filters, threehigh-pass filters and one RF amplifier.The filtered signals below 1.8 MHz from the RF filter circuitare passed through the low-pass filter (L3, L4, C14–C16)between the band swithing diodes (D6, D35), and are thenapplied to the 1st mixer circuit (IC4) directly.The 1.8–14.999 MHz signals pass through the low-pass fil-ter (L6, L7, C21–C25) and high-pass filter (L8, L9,C26–C30) between the band switching diodes (D3, D7), andare then applied to the 1st mixer circuit after being amplifiedat the RF amplifier (Q12).The 15–29.999 MHz signals pass through the low-pass filter(L10, L11, C33–C37) and high-pass filter (L11, L12,C38–C42) between the band switching diodes (D90, D91),and are then applied to the 1st mixer circuit via the RF ampli-fier circuit (Q12).The 30–49.999 MHz signals pass through the high-pass fil-ter (L14, L15, C45–C49) between the band switching diodes(D8, D5), and are then applied to the 1st mixer circuit via theRF amplifier circuit (Q12).• Filters4-1-4 VHF/UHF RF CIRCUITThe VHF/UHF RF circuit amplifies the received signals with-in the range 50–1300 MHz and filters out-of-band signals.The VHF/UHF RF circuit consists of 4 bands of filter circuitswith an RF amplifier for each.The 50–149.999 MHz signals from the RF filter pass throughhigh-pass filter (D11, L17, C53–C55, D12, D82, D83, L18,C57) via the band switching diode (D10), and are thenamplified at the RF amplifier (Q8) between the tunablebandpass filters (D13, D80, L19–L21, D14, D81, L23–L25).The filtered signals are applied to the 1st mixer circuit (IC4)via the band switching diode (D15).For improving the characteristic of the bandpass filter circuit,the shift switch (Q31) shifts the cut off frequency of the high-pass filter (D12, D82, D83, L18, C57). The shift switch (Q31)is controlled by the VCO 1 signal from the CPU (IC21).Receive freq. SW diode Filter select Components(MHz) signal0.01–1.7991.8–14.99915.0–29.99930.0–49.999D6, D35D3, D7D90, D91D8, D5B0B1B2B3L3–L5, C14–C17L6–L9, C21–C30L10–L13, C33–C42L14, L15, C45–C49• RF filter and amplifier circuits0.01–50 MHz50–150 MHz150–350 MHz350–700 MHz700–1300 MHz50–1300 MHz1.8–15 MHz15–30 MHz0.01–1.8 MHz30–50 MHzTunedBPFATT AGCTunedBPFTunedBPFTunedBPFHPFTunedBPFTunedBPFTunedBPFTunedBPFHPFHPFLPFLPFLPFHPFRF Amp.RF Amp.To 1st mixer circuitRF Amp.LPFRF Amp.RF Amp.Q12Q8Q9Q10Q11