Icom IC-F2610 Service Manual

Also see for IC-F2610: Instruction manual Service manual Service manual

Contents

Icom IC-F2610 Service Manual Manual pdf 9 page image

4 - 2The N/W switches (D501, D502) select a ceramic filter (FI3or bypass), and the other N/W switch (Q61) adjusts the inputlevel of the FM IF IC (IC1, pin 8) to switch the bandwidthdepending on the NWC signal from the CPU (IC20, pin 57).When NWC signal becomes high level, bandwidth setting iswide.4-1-5 AF AMPLIFIER CIRCUIT (MAIN UNIT)The AF amplifier circuit amplifies the demodulated AF sig-nals to drive a speaker.The AF signals from the FM IF IC (IC1, pin 9) are amplifiedat the AF amplifier (IC2), and are then applied to the high-path filter circuit (IC3a/b). The high-pass filter characteristicsare controlled by the HFSW signal from the CPU (IC20, pin60). When HFSW signal becomes high level, the cut-off fre-quency is shifted higher to remove CTCSS or DTCS signals.The filtered AF signals from the high-pass filter (IC3, pin 1)are passed through the de-emphasis circuit (R68, C74) withfrequency characteristics of –6 dB/octave, and are thenapplied to the electronic volume controller (IC7, pin 2) viathe AF mute switch (Q6).The output AF signals from the electronic volume controller(IC7, pin 9) are applied to the AF power amplifier (IC8) todrive the speaker.4-1-6 RECEIVE MUTE CIRCUITS (MAIN UNIT)• NOISE SQUELCHA squelch circuit cuts out AF signals when no RF signals arereceived. By detecting noise components in the AF signals,the squelch circuit switches the AF mute switch.Some noise components in the AF signals from the FM IF IC(IC1, pin 9) are passed through the active filter section in theIC (pins 10, 11). The N/W switch (Q62) adjusts the inputnoise level to the IC between wide and narrow bandwidth.When NWC signal which is applied to Q62 becomes highlevel, bandwidth setting is wide.The noise signals from the FM IF IC (IC1, pin 11) are passedthrough the level controller (IC5, pins 21, 22) and are thenconverted into the pulse-type signals (NOIS) at the noisedetector circuit (Q9, Q10).The NOIS signal from the noise detector (Q10) is applied tothe CPU (IC20, pin 32). The CPU then analyzes the noisecondition and controls the AMUT (pin 56) and SP (pin 79)ports to toggle the AF mute switches (Q6, Q7).• CTCSS AND DTCSThe tone squelch circuit detects AF signals and opens thesquelch only when receiving a signal containing a matchingsubaudible tone (CTCSS or DTCS). When tone squelch is inuse, and a signal with a mismatched or no subaudible toneis received, the tone squelch circuit mutes the AF signalseven when noise squelch is open.A portion of the AF signals from the AF amplifier (IC2) passthrough the low-pass filter (Q503) and are then applied tothe CTCSS decoder inside the CPU (IC20, pin 43) via theCDEC line to control the AMUT and SP ports.4-2 TRANSMITTER CIRCUITS4-2-1 MICROPHONE AMPLIFIER CIRCUIT(FRONT AND MAIN UNITS)The microphone amplifier circuit amplifies audio signalsfrom the microphone, within +6 dB/octave pre-emphasischaracteristics, to a level needed for the modulation circuit.AF signals (MIC) from the FRONT unit via J5 (pin 10) areapplied to the audio switch (IC25). While transmitting, theMCON signal from the CPU is high and the AF signals ispassed through IC25 to the microphone amplifier circuit.The AF signals from IC25 are applied to the microphoneamplifier (IC22) via the pre-amplifier (IC21b). The amplifiedsignals are applied to the limiter amplifier in IC22.The entered signals are pre-emphasized with +6dB/octaveat a limiter amplifier, then passed through a splatter filtersection in IC22. The output signals from pin 8 pass throughthe level controller (IC5, pins 4, 3) via the buffer amplifier(IC503), and are then applied to the modulation circuit(D46).SpeakerAMUTE SPVolume control signalAmp.AF muteswitch AF muteswitch AF poweramp.Q6 Q7IC7IC2IC92 9AF signalfrom IC1 HPFHFSWIC3IC22IC511478613165121415 HPFLimiterMICSplatterQ65W/NswitchIC502 W/N switch/NWCDTMFSIGOUTAMODRef./NWCTx dev.DTCS bal.Tone dev.BeepSQL1413211222TX PO 111429103ModulatorcircuitRef.osc.• MICROPHONE AMPLIFIER CIRCUIT• AF CIRCUIT