Kenwood TK-2317 Service Manual

Also see for TK-2317: Service manual Specification Instruction manual Instruction manual

Contents

TK-2317222-2. First MixerThe signal from the front end is mixed with the first localoscillator signal generated in the PLL circuit by Q406 to pro-duce a fi rst IF frequency of 49.95MHz.The resulting signal passes through the XF401 MCF tocut the adjacent spurious and provide the optimum charac-teristics, such as adjacent frequency selectivity.CIRCUIT DESCRIPTION / 电路说明2-3. IF Amplifier CircuitThe first IF signal is passed through a four-pole mono-lithic crystal filter (XF401) to remove the adjacent channelsignal. The filtered first IF signal is amplified by the first IFamplifier (Q405) and is then applied to the IF system IC(IC401).The IF system IC provides a second mixer, limitingamplifier, quadrature detector and RSSI (Received SignalStrength Indicator). The second mixer mixes the fi rst IF sig-nal with the 50.4MHz signal of the second local oscillatoroutput (Q403) and produces the second IF signal of 450kHz.The second IF signal is passed through the ceramic fil-ter (Wide: CF402, Narrow: CF401) to remove the adjacentchannel signal. The filtered second IF signal is amplified bythe limiting amplifier and demodulated by the quadrature de-tector with the ceramic discriminator (CD401). 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 fi lters CF401 (narrow).The second IF signal always passes the ceramic filtersCF402 (Wide).The wide and narrow switching data is output from theMCU (IC820).D401 and D402 are switched to ceramic filters when anarrow mode is selected.Q404 turns on/off with the Narrow and the IC401 detectoroutput level is changed to maintain a constant output levelduring wide or narrow signals.IC401WID/NARD401IFOUTMXOIFI QUADAFOUTC404R406C402C414R408R411R415D402CF401CF402 C424R423 R424Q401R426 50CAFOUTCD401Q404R409IC402+ -R471Fig. 3 Wide/Narrow switching circuit /2-2. 第一混频器前端的信号与 PLL 电路产生的第一本振信号在 Q406 混频，生成 49.95MHz 频率的第一中频信号。生成的信号通过晶体滤波器 (XF401)。2-3. 中频放大电路第一中频信号通过晶体滤波器 (XF401) 消除相邻信道的信号。经滤波的第一中频信号被第一中频放大器 (Q405) 放大并进入中频系统芯片 (IC401)。中频系统芯片提供第二混频器、限幅放大器、正交检测器和 RSSI( 接收信号强度指示器 )。第二混频器将第一中频信号与 50.4MHz 的第二本振信号输出 (Q403) 进行混频，并生成 450kHz 的第二中频信号。第二中频信号通过陶瓷滤波器 ( 宽 :CF402、窄 :CF401) 继续消除相邻信道的信号。经滤波的第二中频信号被限幅放大器放大并被带有陶瓷鉴频器 (CD401) 的正交检测器解调。经解调的信号进入音频电路。2-4. 宽 / 窄切换电路通过切换陶瓷滤波器 CF402( 宽 )、CF401( 窄 ) 可以对每一信道进行宽，窄 ¬ 设置。第二中频信号通过陶瓷滤波器 CF402( 宽 )。宽、窄控制信号从 IC820 输出。选择宽 / 窄电平时，将 D401 和 D402 切换到陶瓷滤波器。Q404 伴随着宽 / 窄数据而接通 / 断开，IC401 检测器输出电平经常变化用来维持宽或窄信号过程中的恒定输出电平。图 3 宽 / 窄切换电路