Kenwood TK-7180 Service Manual

Also see for TK-7180: Modification Information Function reference Brochure & specs Specification Instruction manual

TK-7180172-5. Squelch CircuitThe output signal from IC172 enters FM IC again, thenpassed through a band-pass filter.The noise component output from IC172 is amplified byQ175 and rectified by D173 to produce a DC Voltage corre-sponding to the noise level. The DC voltage is sent to theanalog port of the CPU (IC404).IC172 outputs a DC voltage (RSSI) corresponding to theinput of the IF amplifier.3. Transmitter CircuitThe transmitter circuit consists of the following circuits : 3-1 microphone circuit, 3-2 modulation level adjustment circuit,3-3 driver and final power amplifier circuit, and 3-4 automaticpower control circuit.3-1. Microphone CircuitThe audio signal from the microphone goes into TX-RXunit (X57-698) from the display unit (X54-348) and passesthrough the mute switch (Q416). The audio signal is ampli-fied by the microphone amplifier (IC414) and is input into theTXIN terminal of the audio processor (IC415) after passingthrough the multiplexer (IC413).The input audio signal is output from the MOD terminal ofthe audio processor (IC415) and is amplified by the audio fre-quency amplifier (IC412) after passing through the electricvolume (IC410).3-2. Modulation Level Adjustment CircuitThe audio signal amplified by the audio frequency ampli-fier (IC412) is added to the low speed data LSD passedthrough the low pass filter (IC409). The combined signals issupplied to the VCO (voltage controlled oscillator) and theVCXO (voltage controlled crystal oscillator) X301, respec-tively.3-3. Driver and Final Power Amplifier CircuitThe transmit signal obtained from the TX VCO buffer am-plifier Q311, is amplified to approximately +17dBm by thedriver amplifiers Q313, Q1 and Q2. This amplified signal ispassed to the power amplifier module (power module) IC1,which consists of a MOS-FET amplifier and is capable oftransmission output power.3-4. Automatic Power Control CircuitThe automatic transmission power control (APC) circuitstabilizes the transmitter output power at a predeterminedlevel by detecting the power module output with a diodesD6, D7 and D8. Diodes D6, D7 and D8 apply a voltage to DCamplifier IC72 (A/2). IC72 (B/2) compares the APC controlvoltage (PC) generated by microprocessor IC404 and DC am-plifier IC71 (A/2, B/2) with the detection output voltagefrom IC72 (A/2) to control the Vgg pin of IC1, and stabilizestransmission output.The APC circuit is configured to protect over-current of thepower module due to fluctuations of the load at the antennaend and to stabilize transmission output at voltage and tem-perature variations.AMPSWSWIC414Q416Q417AMPDCAMPIC408LPFIC409IC410 IC412IC415D-SUBMI2AQUA-LMODD-SUBDIDACMB(for VCXO)MOD(for VCO)MICJ901MojularjackDISPLAY UNIT(X54-348) TX-RX UNIT (X57-698)IC413Multi-plexer TXINLSDOTX VCOVCXO16.8MHzQ307Q313DriveAMPQ311BuffAMPQ1DriveAMPQ2DriveAMPIC1FinalAMPX301MODMB DCAMPDCAMPPCMPSWD2~D4DET DETD6 D7DETD8ANTGatebiasIC71 IC72CIRCUIT DESCRIPTIONFig. 2 Microphone and modultion level adjustment circuitFig. 3 Drive and Final power amplifier and automatic power control circuit