Icom IC-F4029SDR Service Manual

Also see for IC-F4029SDR: Instruction manual Instruction manual Instruction manual

Contents

The AF signal from the analog switch (IC3, pin 11) areapplied to the volume buffer amplifier (IC6, pin 9). The buffer-amplified AF signals are adjusted its level (=audio level) byvolume control pot (R315), then applied to the AF poweramplifier (IC15, pin 4) and amplified to the 0.5 W of audiooutput power (max., at 8 Ω load).The power-amplified AF signals are output from pin 10, thenapplied to the speaker (CHASSIS UNIT; SP1) or an externalspeaker via [SP] jack (J2).4-1-6 SQUELCH CIRCUITS4-1-6-1 NOISE SQUELCHThe squelch mutes the AF output signals when no RFsignals are received. By detecting noise components(around 30 kHz signals) in the demodulated AF signals,the squelch circuit toggles the mute switch and AF poweramplifier ON and OFF.A portion of the demodulated AF signals from the FM IF IC(IC9, pin 9) are applied to the D/A converter (IC12, pin 24)for level (=squelch threshold) adjustment. The level-adjustedAF signals are output from pin 23 and passed throughthe noise filter (IC9, pins 7, 8, R42, R44−R46, C69, C70,C413). The filtered noise signals are amplified the noisecomponents only at the noise amplifier.The amplified noise components are converted into the pulse-type signal at the noise detector section, and output from pin13 as the “NOIS” signal. The converted signal is applied to theCPU (IC22, pin 75). Then the “RMUTE” signal from the CPU(IC22, pin 96) to the RX mute switch (Q32, Q33) and analogswitch (IC3, pins 12, 13) becomes “Low” according to the“NOIS” signal level to cut off the AF line.At the same time, the “AFON” signal from the CPU (IC22,pin 70) to the AF amplifier controller (Q41, Q42, D21, D23)becomes “Low”, and the controller turns the AF poweramplifier (IC15) OFF.4-1-6-2 TONE SQUELCH• CTCSS/DTCSThe 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 sub audible tone is received,the tone squelch circuit mutes the AF signals even when thenoise squelch is open.A portion of the demodulated AF signals are passed throughthe active LPF (Q39) to filters CTCSS/DTCS signal. Thefiltered signal is applied to the CPU (IC22, pin 46). The CPUcompares the applied signal and the set CTCSS/DTCS, thenthe CPU controls the status (“Low” or “High") of “RMUTE” and“AFON” signals as same as “NOISE SQUELCH."• DTMFDTMF signals in the demodulated AF signals are passedthrough the LPF (IC6, pins 5, 7) to remove unwanted compo-nents (voice signals), then applied to the CPU (IC22, pin 45)and decoded.4-2 TRANSMITTER CIRCUITS4-2-1 MICROPHONE AMPLIFIER CIRCUITS(MAIN-C UNIT)The AF signals from the microphone (MIC signals) arefi ltered and level-adjusted at microphone amplifier circuits.• MIC SIGNALSMIC signals from the microphone are applied to or bypassedthe ALC (Automtic Level Control) circuit (IC24, pins 3, 5)and the A/D switch (IC25, pins 1, 7), then applied to the D/Aconverter (IC12, pin 1).In digital mode, the MIC signals are applied to the ALCcircuit which keeps the level of MIC signals constant.The level-adjusted MIC signals are output from pin 2, andpassed through the MIC mute switch (Q31), HPF (IC5, pins13, 14) and gain switch (Q34, Q35) which controls the gainof MIC amplifier (IC5) according to the Analog/Digital mode,then applied to the MIC amplifier (IC5, pin 9). The amplifiedMIC signals are output from pin 8, and passed through theanalog switch (IC3, pins 3, 4), AF mixer (IC5, pins 6, 7)where the MIC signals and tone signals are mixed with.• TONE SIGNALSThe CTCSS/DTCS signals are generated by the CPU (IC22)and output from pins 19−21. The output signals are passedthrough the 3 registers (R222–R224) to change its wave form.The wave form changed CTCSS/DTCS signals are passedthrough the LPF (IC7, pins 8, 10), tone filter switch (Q40) andD/A converter (IC12, pins 11, 12) for level adjustment. The leveladjusted CTCSS/DTCS signals are then applied to the AF mixer(IC5, pin 6).DTMF signals are generated by the CPU (IC22) and outputfrom pin 43. The output DTMF signals are passed through twoLPF’s (IC6, pins 1, 3 and pins 12, 14), then applied to the AFmixer (IC5, pin 6).The mixed AF signals are output from pin 7 of the AF mixer (IC5)and passed through the analog switch (IC3, pins 8, 9), thenapplied to another AF amplifier (IC7, pin 6). The amplifiedAF signals are output from pin 7, and applied to the D/Aconverter (IC12, pin 9) to be adjusted its level (=deviation).The level-adjusted MIC signals are then applied to themodulation circuits as the modulation signals.4-2-2 MODULATION CIRCUITSThe modulation circuits modulates the VCO oscillating signalusing the modulation signals.The modulation signals from the D/A converter (IC12, pin10) are applied to the D12 at the TX VCO (Q16, D10, D13)to modulate the VCO oscillating signal by changing thereactance of D12.The modulation signals are also applied to the referencefrequency oscillator (X2) via D/A converter (IC12, pins15, 16) and the buffer (IC7, pins 12, 14), to ensure themodulation of low frequency components of the modulationsignals.The modulated VCO output is buffer-amplified by Q15 andQ29, then applied to the transmit amplifiers as the transmitsignal via TX/RX switch (D16=ON, D17=OFF).4 - 2