Kenwood TK-2170 Service Manual

Also see for TK-2170 SERIES: Service manual Function reference Instruction manual Instruction manual Specifications

TK-2170231. Frequency ConfigurationThe receiver utilizes double conversion. The first IF is49.95MHz 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 necessaryfrequencies. Figure 1 shows the frequencies.The filtered first IF signal is amplified by the first IF amplifier(Q703) and then applied to the lF system IC (IC701). The IFsystem IC provides a second mixer, second local oscillator,limiting amplifier, quadrature detector and RSSI (ReceivedSignal Strength Indicator). The second mixer mixes the firstIF signal with the 50.4MHz of the second local oscillator out-put (TCXO X501) and produces the second IF signal of450kHz.The second IF signal is passed through the ceramic filter(Wide : CF701, Narrow : CF702) to remove the adjacent chan-nel signal. The filtered second IF signal is amplified by thelimiting amplifier and demodulated by the quadrature detec-tor with the ceramic discriminator (CD701). The demodu-lated signal is routed to the audio circuit.2-4. Wide/Narrow Switching CircuitWide and Narrow settings can be made for each channelby switching the ceramic filters CF701 (Wide), CF702 (Nar-row). The Wide and Narrow is output from IC4.D701 and D702 are switched to ceramic filters when aWide/Narrow level is selected.Q702 turns on/off with the Narrow and the IC701 detectoroutput level is changed to maintain a constant output levelduring wide or narrow signals.CIRCUIT DESCRIPTIONANTTX/RX : 136~174MHzANTSWRFAMPTXAMP1st MIX MCF49.95MHzCF450kHzIFSYSTEMAFAMPSP50.4MHz185.95~223.95MHzPLLVCO MICAMPMIC136~174MHzX3multiply TCXO 16.8MHzRFAMPVOLFig. 1 Frequency configuration2. Receiver SystemThe receiver system is shown in Figure 2.2-1. Front End (RF AMP)The signal coming from the antenna passes through thetransmit/receive switching diode circuit (D604, D605, D606and D608), passes through a BPF (L715 and L716), and isamplified by the RF amplifier (Q705).The resulting signal passes through a BPF (L711 and L713)and goes to the mixer. These BPFs are adjusted by variablecapacitors (D703, D704, D705 and D706). The input voltageto the variable capacitor is regulated by voltage output fromthe DC amplifier (IC19).2-2. First MixerThe signal from the front end is mixed with the first localoscillator signal generated in the PLL circuit by Q704 to pro-duce a first IF frequency of 49.95 MHz.The resulting signal passes through the XF701 MCF to cutthe adjacent spurious and provide the platinum characteris-tics, such as adjacent frequency selectivity.2-3. IF Amplifier CircuitThe first IF signal is passed through a four-pole monolithiccrystal filter (XF701) to remove the adjacent channel signal.MXOAFOUTQUADIFOUTIFI WideC702C701C708C719R705R702R701R703R706C709R708D702 D701CF701CF702IC701R719R717Q702R718 5CAFOUTNarrowNarrowCD701Fig. 2 Receiver systemFig. 3 Wide/Narrow switching circuitIC701IF, MIX, DET AQUA-LANTSWBPFQ705RFAMPQ7041st MIXQ703IF AMPANTBPF XF701MCF1st LocalTUNE TUNECF702CF701SPQ701X3 multiply2nd LocalIC10AF AMPIC18AF PAIC13 IC16X501TCXO16.8MHzVOL