Kenwood TK-3148 Service Manual

Also see for TK-3148: Service manual

Contents

TK-314810CIRCUIT DESCRIPTION / 电路说明1. OverviewThis transceiver is UHF/FM portable transceiver designedto operate in the frequency range of 350 to 390MHz (C).2. Circuit Configuration by FrequencyThe receiver is a double-conversion superheterodynewith a first intermediate frequency (IF) of 44.85MHz and asecond IF of 455kHz. Incoming signals from the antenna aremixed with the local signal from the PLL to produce the firstIF of 44.85MHz.This is then mixed with the 44.395MHz second localoscillator output to produce the 455kHz second IF. This isdetected to give the demodulated signal.The transmit signal frequency is generated by the PLLVCO, and modulated by the signal from the microphone. Itis then amplifi ed and sent to the antenna.3. Receiver System3-1. RF unitAn incoming RF signal from the antenna terminal ispassed through the antenna switch (D102, D103, D104 andD105 are off) and then the bandpass filter (L215 and L217).High pass filter HPF (L219) the 1st image response improve.And the bandpass fi lter is adjusted by a variable capacitor.The input voltage to the variable capacitor is regulated bythe voltage output from the D/A converter (IC307). The sig-nal is amplified by RF amplifier Q207, and passed throughthe bandpass filter (L209, L210 and L211). The resultingsignal is applied to the first mixer (Q206), where it is mixedwith the first local oscillator signal output from the frequen-cy synthesizer to produce the fi rst IF (44.85MHz).3-2. IF unitThe first IF signal is passed through a crystal filter (XF200)to remove a adjacent channel signal. The filtered first IF sig-nal is amplified by the first IF amplifier (Q205) and then ap-plied to the lF system IC (IC200). The IF system IC providesa second mixer, second local oscillator, limiting amplifier,quadrature detector and RSSI (Received Signal StrengthIndicator). The second mixer mixes the first IF signal withthe 44.395MHz of second local oscillator output (crystal unitX200) and produces the second IF signal of 455kHz.1. 综述本对讲机是在 350 到 390MHz(C) 的频率范围内工作的 UHF/FM 对讲机设备。2. 电路的频率构成接收部采用 44.85M H z 的第一中频和 455k H z 的第二中频的二次变频超外差方式。通过天线接收到的信号与来自于锁相环电路的本振信号混频生成 44.85MHz 的第一中频。然后与 44.395MHz 的第二本振信号混频生成 455kHz 的第二中频。此频率被检测并产生解调信号。锁相环压控振荡器生成发射信号频率，并且被来自于麦克风的信号调制。然后被放大并发送到天线。3. 接收部系统3-1. 射频单元由天线接收到的射频信号进入天线开关 (D102，D103，D104和 D105 截止 )，然后通过带通滤波器 ( L215 和 L217)。高通滤波器 H P F ( L219)，抑制镜像信号。带通滤波器由可变电容进行调整。向可变电容输出的电压通过来自于数 / 模转换器 ( I C307)的电压输出进行调节。信号被射频放大器 Q207 放大，并通过带通滤波器 ( L209，L210 和 L211) 生成的信号进入第一混频器 ( Q206)，并且与来自于频率合成器的第一本振信号混频生成第一中频 (44.85MHz)。3-2. 中频单元第一中频信号通过晶体滤波器 ( X F200) 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 R S S I ( 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。ANTTX/RX: 350~390MHz (C)ANTSWRFAMPPAAMPTXAMP1st MIX MCF44.85MHzCF455kHzFM IFSYSTEMAFAMP SP44.395MHz305.15~345.15MHz (C)PLLVCO MICAMP MIC350~390MHz (C)Fig. 1 Frequency configuration / 图 1 频率构成