Kenwood TK-2200 Service Manual

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TK-220085) Audio Amplifier CircuitThe demodulated signal from IC201 goes to AF amplifierthrough IC301.The signal then goes through an AF volume control , andis routed to an audio power amplifier (IC302) where it isamplified and output to the speaker.Fig. 3 Wide/Narrow switching circuitCIRCUIT DESCRIPTION1. Frequency ConfigurationThe receiver utilizes double conversion. The first IF is 38.85MHz and the second IF is 450 kHz. The first local oscillatorsignal is supplied from the PLL circuit.The PLL circuit in the transmitter generates the necessaryfrequencies. Fig. 1 shows the frequencies.Fig. 1 Frequency configuration1) Front End (RF AMP)The signal coming from the antenna passes through thetransmit/receive switching diode circuit, (D103,D104,D105and D106) passes through a BPF (L214 and L213), and isamplified by the RF amplifier (Q205).The resulting signal passes through a BPF (L209 and L211)and goes to the mixer. These BPFs are adjusted by variablecapacitors (D203,D204,D205 and D206). The input voltageto the variable capacitor is regulated by voltage output fromthe microprocessor (IC405).2) First MixerThe signal from the front end is mixed with the first localoscillator signal generated in the PLL circuit by Q1 toproduce a first IF frequency of 38.85 MHz.The resulting signal passes through the XF201 MCF to cutthe adjacent spurious and provide the opitimuncharacteristics, such as adjacent frequency selectivity.Fig. 2 Receiver section2. ReceiverThe frequency configuration of the receiver is shown in Fig. 2.3) 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 amplifier(Q203) and then applied to the lF system IC (IC201). TheIF system IC provides a second mixer, second localoscillator, limiting amplifier, quadrature detector and RSSI(Received Signal Strength Indicator). The second mixermixes the first IF signal with the 38.4MHz of the secondlocal oscillator output (TCXO X1) and produces the secondIF 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 routedto the audio circuit.4) 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 IC405, pin 45.When a WIDE (low level) data is received, Q202 turn on.When a NARROW (high level) data is received, Q202 turn off.Q202 turns on/off with the Wide/Narrow data and theIC201 detector output level is switched to maintain aconstant output level during wide or narrow signals.SPBPFIC301 IC302AF PAIC201IF,MIX,DETANTAQUACF201TCXOTUNEQ1X3 multiplyTUNEANT SWBPFMCF1st LocalRF AMPQ205 MIXERQ204 XF201 IF AMPQ203AF VOLX112.8MHz2nd LocalQ202L : WideH : NarrowC214RX_W/N(IC405)R211R213 CD201QUADIC201FM IF SYSTEM5RAFOUTQ203IFOUTSPTX: 150 ~ 174MHzPLLVCOIF SYSTEMANTTCXOX3 multiply38.85MHzMCFAFAMPMICMICAMPTXAMP RFAMP38.4MHzCF450kHzRX: 188.85 ~ 212.85MHzTX/RX: 150 ~ 174MHz12.8MHzRFAMPANT SW1/ 2