Icom IC-V85 Service Manual

Also see for IC-V85: Step-by-Step Programming Guide Instruction manual Service manual Instruction manual

Contents

4 - 2• SQUELCH CIRCUIT (RF AND LOGIC UNITS)- NOISE SQUELCH -The noise squelch mutes the AF output when no RF signalsare received. By detecting noise components (around 30 kHzsignals) in the demodulated AF signals, the squelch circuittoggles the mute switch and AF power amplifier ON and OFF.A portion of the AF signals from the IF IC (RF UNIT; IC2,pin 9) are passed through the D/A converter (RF UNIT;IC10, pins 23, 24) for level adjustment. The level adjustedAF signals are applied to the noise filter section (RF UNIT;IC2, pins 7, 8; R86−R88, C121, C122) which allows onlynoise components to pass. The filtered noise componentsare amplified at the noise amplifier section, and rectifiedinto the DC voltage which is proportional to the noise signallevel, at the noise detector section, then output from pin 13as the “NOIS” signal.The “NOIS” signal is applied to the CPU (LOGIC UNIT; IC8,pin 17), and the CPU compares the “NOISE” signal and setreference level (squelch threshold level). When the input“NOIS” signal is higher than reference level, the CPU cutsoff “AFON” signal (from pin 4) to the AF power amplifiercontrol circuit (LOGIC UNIT; Q14−Q16) to deactivate the AFpower amplifier (LOGIC UNIT; IC23).- TONE SQUELCH -The tone squelch circuit detects tone signals and opens thesquelch only when receiving a signal containing a matchedsub audible tone. When the tone squelch is in use, and asignal with a mismatched or no subaudible tone is received,the tone squelch circuit mutes the AF signals even when thenoise squelch is open.A portion of the demodulated AF signals is passed throughthe LPF (LOGIC UNIT; Q53) to filters CTCSS/DTCS signal.The filtered signal is applied to the CPU (LOGIC UNIT; IC8,pin 93). The CPU compares the applied signal and the setCTCSS/DTCS, then the CPU controls the status (“Low” or“High”) of “AFON” signal as “• NOISE SQUELCH.”HPFLPFPre-emph.1610 87IC3IC3IC4“MMUTE”“RMUTE”• AF and MIC amp. CIRCUITSDemodulated AF signalsFrom IF IC (IC2, pin 9)From the microphoneAF signals“MICS”RF UNITLOGIC UNIT“AFON”D/AconverterIC4IC10IC3AMP4112210IC23SP24 31013 141112219 8 VCO4-2 TRANSMITTER CIRCUITS• MICROPHONE AMPLIFIER CIRCUITS (LOGIC UNIT)The AF signals from the microphone (MIC signals) arefi ltered and level-adjusted at microphone amplifi er circuits.Audio signals from the microphone (MC1) are applied to IC3(pin 10) which combines a microphone amplifier and pre-emphasis circuit. The MIC signals are amplified and filteredto obtain +6 dB/oct of frequency characteristic by IC3.The amplified and emphasized MIC signals are outputfrom the pin 8, and passed through the splatter filter (IC3,pins 13, 14) which suppresses 3 kHz and higher audiocomponents, via the TX/RX switch (IC4, pins 3, 4; 8, 9).The filtered MIC signals are then applied to the modulationcircuit.• MODULATION CIRCUITS (RF UNIT)- MIC SIGNALS -The modulation circuits modulates the VCO oscillating signalusing the modulation signals.The MIC signals from AF circuits are passed throughthe D/A converter (IC10, pins 21, 22) for level (deviation)adjustment. The level adjusted MIC signals are applied tothe variable capacitor (D61) in the VCO (Q76, D59−D61),and modulate the VCO oscillating signal by changing thereactance of D61. The modulated VCO output are buffer-amplified by Q75 and Q74, then applied to the transmitamplifier as a transmit signal.- TONE SIGNALS -CTCSS/DTCS signals are output from CPU (LOGIC UNIT;IC8, pin 2) and passed through the LPF (R224, R227,C219), then applied to the LPF (as the AF mixeRF UNIT;IC3, pin 13) to be mixed with MIC signals. The mixedCTCSS/DTCS signals are applied to modulation circuits as“• MIC SIGNALS.”• TRANSMIT AMPLIFIERS (RF UNIT)The transmit signal from the buffer amplifier (Q74) is amplifiedto the transmit output level by the transmit amplifi ers.The buffer-amplified VCO output signal is amplified bytransmit amplifiers; pre-drive (Q3), drive (Q2) and power(Q1) amplifiers in sequence, after being passed through theTX/RX switch (D3).The power-amplified transmit signal is passed through thepower detector (D32, D33), antenna switch (D1) and LPF(as a harmonic filter ; L1, L2, C1−C5), before being emittedfrom the antenna.