Kenwood TK-380 Service Manual

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TK-38016CIRCUIT DESCRIPTION1. OverviewThis transceiver is UHF/FM portable transceiver designed tooperate in the frequency range of 450 to 490MHz (F1), 470 to512MHz (F2), 400 to 430MHz (F3) and an UHF/FM band EFJ LTRTMtrunked system compatible FM portable transceive that can beprogrammed to operate on both LTR and conventional systems.2. Circuit Configuration by FrequencyThe receiver is a double-conversion superheterodyne witha first intermediate frequency (IF) of 44.85MHz and a secondIF of 455kHz. Incoming signals from the antenna are mixedwith the local signal from the PLL to produce the first IF of44.85MHz.This is then mixed with the 44.395MHz second localoscillator output to produce the 455kHz second IF. This isdetected to give the demodulated signal.The transmit signal frequency is generated by the PLL VCO,and modulated by the signal from the microphone. It is thenamplified and sent to the antenna.ANTTX/RX : 450~490MHz : K, K4, M470~512MHz : K2, K5400~430MHz : K3, K6, M3ANTSWRFAMPPAAMPTXAMP1st MIX MCF44.85MHzCF455kHzFM IFSYSTEMAFAMP SP44.395MHz355.15~385.15MHz : K3, K6, M3425.15~467.15MHz : K2, K5405.15~445.15MHz : K, K4, MPLLVCO MICAMP MIC450~490MHz : K, K4, M470~512MHz : K2, K5400~430MHz : K3, K6, M3Fig. 1 Frequency configuration3. Receiver System3-1. RF unitAn incoming RF signal from the antenna terminal is passedthrough the antenna switch (D12, D14. and D15 are off) andthen the bandpass filter (L47,48,49,51,52,54,55,56). Thebandpass filter is adjusted by a variable capacitor. The inputvoltage to the variable capacitor is regulated by the voltageoutput from the D/A converter (IC8). The signal is amplified byRF amplifier Q24, and passed through the bandpass filter(L29,31,33,34,36) and band-eliminate filter (L27) to removethe spurious signal again. The resulting signal is applied to thefirst mixer (IC18), where it is mixed with the first local oscillatorsignal output from the frequency synthesizer to produce thefirst IF (44.85MHz). The 1st mixer uses the GaAs IC.3-2. IF unitThe first IF signal is passed through a four-pole monolithiccrystal filter (XF1) to remove a adjacent channel signal. Thefiltered first IF signal is amplified by the first IF amplifier (Q12)and then applied to the lF system IC (IC12). The IF system ICprovides a second mixer, second local oscillator, limitingamplifier, quadrature detector and RSSI (Received SignalStrength Indicator). The second mixer mixes the first IF signalwith the 44.395MHz of second local oscillator output (crystalunit X2) and produces the second IF signal of 455kHz.The second IF signal is passed through the ceramic filter(CF1; Wide, CF2 ; Narrow) to more remove the adjacentchannel signal. The filtered second IF signal is amplified bythe limiting amplifier and demodulated by the quadraturedetector with ceramic discriminator (CD1). The demodulatedsignal is routed to the audio circuit.3-3. Wide/Narrow changeover circuitNarrow and Wide settings can be made for each channelby switching the ceramic filters CF1 (Wide), CF2 (Narrow).The WIDE (high level) and NARROW (low level) data isoutput from IC19 (microconputer) pin 99.When a WIDE (high level) data is received, Q6 turn off andQ7 turn on. When a NARROW (low level) data is received,Q6 turn on and Q7 turn off. D5, D7 are switched to ceramicfilters when a high/low level data is received.Q9 turns on/off with the Wide/Narrow data and the IC12detector output level is changed to maintain a constant outputlevel during wide or narrow signals.Fig. 2 Receiver sectionIC12MIX, DET, IF SWQ15DMDMIC4 (2/2)AF AMP5DE-EMP MUTEEXPHPF LPF HPF BEFIC13 2 1VOLIC8IC7 (2/2)AF AMP41VC1VC2Q310SSWINT.SPEXT.SP2nd localOSCX2AF AF SWIC300AF PAANTSWL40,42,43L47,48,49,51,52,54,55,56BPFD12D14,15Q24RFAMPANTIC181st MIXQ121st IFL27BEFL29,31,33,34,36BPF XF1MCF1st LocalOSC (PLL)CF1 : WideCF2 : Narrow