Kenwood TK-3148 Service Manual

Also see for TK-3148: Service manual

Contents

TK-3148113-2. IF unitThe first IF signal is passed through a crystal filter (XF200)to remove a adjacent channel signal. The filtered first IF signalis amplified by the first IF amplifier (Q205) and then applied tothe lF system IC (IC200). The IF system IC provides a secondmixer, second local oscillator, limiting amplifier, quadraturedetector and RSSI (Received Signal Strength Indicator). Thesecond mixer mixes the first IF signal with the 44.395MHz ofsecond local oscillator output (crystal unit X200) and producesthe second IF signal of 455kHz.The second IF signal is passedthrough the ceramic filter (CF200; Wide,CF201; Narrow) to more remove theadjacent channel signal. The filteredsecond IF signal is amplified by thelimiting amplifier and demodulated bythe quadrature detector with ceramicdiscriminator (CD200). The demodulatedsignal is routed to the audio circuit.Fig. 2 Receiver section / 图２接受部构成CIRCUIT DESCRIPTION / 电路说明Fig. 3 Wide/Narrow changeover circuit图３宽／窄转换电路IC200MIX, DET, IF SWQ204DMDMIC300 (2/2)AF AMP5DE-EMP MUTEEXPHPF LPF HPF BEFIC500 2 1VOLIC307IC305 (2/2)AF AMP41VC1VC2Q308SSWINT.SPEXT.SP2nd localOSCX200AF AF SWIC313AF PAANTSWL110~112 L215,217BPFD102~105Q207RFAMPANTQ2061st MIXQ2051st IFL209~211BPF XF200MCF1st LocalOSC (PLL)CF1 : WideCF2 : NarrowQ201IC200Q202AFOUT5RR213R210CF201CF200 D202 D203R208R216R211C206C210MIXOUTAFOUTQUADIFOUTIFIN C221R255R221CD200R264R256W/N5CNSR2223-2．中频单元第一中频信号通过晶体滤波器（XF200）消除邻道的信号。经滤波的第一中频信号被第一中频放大器（Q205）放大并进入中频系统芯片（IC200）。中频系统芯片提供第二混频器，第二本振信号，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44.395MHz的第二本振信号输出（晶体单元 X200）进行混频，并生成 455kHz 的第二中频信号。第二中频信号通过陶瓷滤波器（CF200∶宽，CF201∶窄）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（CD200）的正交鉴频器进行解调。解调后的信号进入音频电路。3-3. Wide/Narrow changeover circuitNarrow and Wide settings can be made for each channelby switching the ceramic filters CF200 (Wide), CF201 (Narrow).The WIDE (high level) and NARROW (low level) data isoutput from IC311 (microcomputer) pin 14.Regardless of NARROW or WIDE band selection, signalsalways pass through the filter, CF200.When the WIDE band is selected, Q201 is turned ON, thenD202 and D203 are turned OFF.So, the signal does not pass through the filter CF201. Whenthe NARROW band is selected, Q201 is turned OFF, then D202and D203 are turned ON. So, the signal passes through thefilters, CF200 and CF201.Q202 turns on/off with the Wide/Narrow data and the IC200detector output level is changed to maintain a constant outputlevel during wide or narrow signals.3-3．宽 / 窄转换电路可以通过开启陶瓷滤波器 CF200（宽），CF201（窄）对每一个信道进行窄宽设定。IC311（微电脑）的管脚 14 输出宽（高电平）和窄（低电平）信号。无论选用宽还是窄带，信号都要通过滤波器 CF200。当选用 WIDE 带宽时，D202 和 D203 关断。因此，信号不通过滤波器 CF201。当选用 NARROW 带宽时，Q201 关断，D202 和 D203 打开。因此，信号通过滤波器 CF200和 CF201。Q202 伴随着宽 / 窄数据而接通 / 断开，IC200 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。