Kenwood TK-2180 Service Manual

Also see for TK-2180: Specifications Brochure & specs Instruction manual Instruction manual Pricing and specification manual

TK-218094. Transmitter System4-1. Microphone amplifierThe signal from the internal microphone goes through themute switch (Q614).When the SP-MIC is not attached, the microphone switch-ing terminal (MSW) on the universal connector becomesHigh, and mute switch (Q614) is turned on. When the SP-MIC is attached, MSW is connected to GND at inside of SP-MIC. For this reason, Q614 is turned off, the internal micro-phone is muted, and only the input of the external micro-phone is supplied to the microphone amplifier.The signal from microphone goes through D/A converter(IC605), mute switch (Q610), and amplified by IC608 (1/2) andlimited by AGC circuit composed of D601, D602, Q606 andQ607. IC607 is composed of high-pass filter, low-pass filterand pre-emphasis/IDC circuit.The signal passes through the D/A converter (IC605) forthe maximum deviation adjustment, and enters the summingamplifier consisting of IC600 (2/2), and is mixed with the lowspeed data from the CPU (IC502).The output signal from the summing amplifier goes to theVCO modulation input. The other output signal from thesumming amplifier passes through the D/A converter (IC605)again for the BAL adjustment, and the buffer amplifier(IC602), and goes to the TCXO modulation input.4-2. VOXThe IC608 (2/2) amplify the audio signal captured in themicrophone, and then the signal is converted into the DCvoltage D603 rectifies.The DC voltage activates the CPU (IC502), and the VOXstarts.4-3. Drive and Final amplifierThe signal from the T/R switch (D100 is on) is amplified bydrive amplifier (Q101 and Q102) to +15~17dBm.The output of the drive amplifier is amplified by the RFpower amplifier (Q105) to 5.0W (1W when the power is low).The RF power amplifier is MOS FET. The output of the RFpower amplifier is then passed through the harmonic filter(LPF) and antenna switch (D106, D107 are on) and applied tothe antenna terminal.4-4. APC circuitThe APC circuit always monitors the current flowingthrough the RF power amplifier (Q105) and keeps a constantcurrent. The voltage drop at R125, R127 and R130 is causedby the current flowing through the RF power amplifier andthis voltage is applied to the differential amplifier (IC100 1/2).IC100 (2/2) compares the output voltage of IC100 (1/2)with the reference voltage from IC502, and the output ofIC100 (2/2) controls the VGG of Q101, Q102 and Q105 tomake the both voltages to same voltage.The change of power high/low is carried out by the changeof the reference voltage. Q106, Q107 and Q108 are turnedon and Q104 is turned off in transmit and the APC circuit isactive.Q614 IC605MICSWQ610SWIC608(1/2)AMPIC600(2/2)Q616(2/2)SUMAMPIC602 X1BUFFAMP TCXOVCOAGCVOLMMUTEAQUA-LIC607IC605D601,602Q606,607D/A O2I2IC605D/A O1I1LSDOUTEXT.MICMSWFromT/R SW(D100)Pre-DRIVEAMPDRIVEAMPQ101 Q102RF POWERAMPQ105ANTSW LPFD106,107ANTVDD VGGIC100(1/2)IC100(2/2)R130R127R125+BREFVOL(IC502)Fig. 7 Microphone amplifierFig. 8 Drive and final amplifier and APC circuitCIRCUIT DESCRIPTION