Kenwood TK-2302 Service Manual

Also see for TK-2302: Instruction manual Instruction manual Instruction manual

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TK-2302/2302( V ) /230691. Frequency ConfigurationThe receiver utilizes double conversion. The first IF is38.85MHz and the second IF is 450kHz. The first local oscil-lator signal is supplied from the PLL circuit.The PLL circuit in the transmitter generates the neces-sary frequencies. Fig. 1 shows the frequencies.ANTTX/RX : 136~174MHzANTSWRFAMPTXAMPRFAMP1st MIX MCF38.85MHzCF450kHzIFSYSTEMAFAMPSPRX:174.85~212.85MHzPLLVCOMICAMPMICTX: 136~174MHz38.4MHzX3multiply TCXO 12.8MHz1/2Fig. 1 Frequency configuration2. ReceiverThe frequency configuration of the receiver is shown inFig. 2.ANTANTSWBPFRCTVRF AMPQ204MIXERQ203IF AMPQ202BPFPCTV 1st LocalMCFXF201IC201IF, MIX, DETIC308AQUA-LQ2X3 multiplyX1TXCOCF2012nd Local 12.8MHzAF VOLIC309AF PA SPFig. 2 Receiver sectio■ Front End (RF AMP)The signal coming from the antenna passes through thetransmit/receive switching diode circuit, (D103, D104 andD105) passes through a BPF (L214, L216 and L213), and isamplified by the RF amplifier (Q204).The resulting signal passes through a BPF (L209 andL211) and goes to the mixer. These BPFs are adjusted byvariable capacitors (D203, D204, D205 and D202). The inputvoltage to the variable capacitor is regulated by voltage out-put from the MCU (IC306).CIRCUIT DESCRIPTION■ First MixerThe signal from the front end is mixed with the first localoscillator signal generated in the PLL circuit by Q203 to pro-duce a first IF frequency of 38.85MHz.The resulting signal passes through the XF201 MCF tocut the adjacent spurious and provide the opitimun charac-teristics, such as adjacent frequency selectivity.■ IF Amplifier CircuitThe first IF signal is passed through a four-pole monolithiccrystal filter (XF201) to remove the adjacent channel signal.The filtered first IF signal is amplified by the first IF ampli-fier (Q202) and then applied to the lF system IC (IC201).The IF system IC provides a second mixer, limiting amplifier,quadrature detector and RSSI (Received Signal Strength In-dicator). The second mixer mixes the first IF signal with the38.4MHz of the second local oscillator output (TCXO X1 andQ2) and produces the second IF signal of 450kHz.The second IF signal is passed through the ceramic filter(CF201) to remove the adjacent channel signal. The filteredsecond IF signal is amplified by the limiting amplifier anddemodulated by the quadrature detector with the ceramicdiscriminator (CD201). The demodulated signal is routed tothe audio circuit.■ Wide/Narrow Switching CircuitNarrow and Wide settings can be made for each channelby switching the demodulation level.The WIDE (low level) and NARROW (high level) data isoutput from IC306, pin 5. When a WIDE (low level) data isreceived, Q201 turn on. When a NARROW (high level) datais received, Q201 turn off.Q201 turns on/off with the Wide/Narrow data and theIC201 detector output level is switched to maintain a con-stant output level during wide or narrow signals.Q201R209R210C209CD201QUAD IFOUTIC201FM IF SYSTEMW/N(IC306) L : WideH: NarrowAFOUT Q2025RFig. 3 Wide/Narrow switching circuit■ Audio Amplifier CircuitThe demodulated signal from IC201 goes to AF amplifierthrough IC308.The signal then goes through an AF volume control , andis routed to an audio power amplifier (IC309) where it is am-plifi ed and output to the speaker.