Kenwood TKR-840 Service Manual

Also see for TKR-840: Brochure & specs Instruction manual

TKR-840 CIRCUIT DESCRIPTION1.0utlineThe TKR-840 is a UHF-band repeater operating in the 400-430MHz and 450-512MHz frequency ranges. It has thefollowing features:• High-performance model with enhanced features.• 32 channel radio with 16 QT / DQT.• Remote control functions for use by base stations.• Fine frequency steps using Direct Digital Synthesizer (DDS).• Signaling decoding and AF processing using Digital SignalProcessor (DSP).CN101 C00SC1C201CRIPI)I2.Transmitter UnitThe transmitter unit (X56-305 A/3) consists of the followingcircuits: (1) internal/external reference circuit, (2) transmitterreference PLL circuit, (3) transmitter DDS circuit, (4) transmittermain PLL circuit, (5) driver circuit, (6) modulation leveladjustment circuit, and (7) other circuits.2.1 Internal/external reference circuitThe internal/external reference circuit switches betweenthe internal +/-1.0ppm/20MHz TCXO (X101) and the 10MHzexternal reference automatically. If there is no externalreference signal applied to the unit, the internal TCXO is usedas the reference frequency. When an external reference(10MHz/-10dBm or higher) is applied, the external referenceis automatically used as the reference frequency. The circuitconsists of 0102, 0106, XF210, 0109, D101, D103, 015,X101, 0205, D205, 0206, IC204, 0110, 0114, 0112, 0113,0108, XF211, and 0115....•c!XT RI" IH24I=-�· N.• (BUFFER AMP I ; DlOl 0103Q109IRF AMPISCR207IC204Ll03 RUOQ110 �I DC SWtTCHI -0101. 103jRF swjCN3(1XR)CH102t-------ilt-+�-.---t0J REF OUTFig.1 Internal/external reference circuit2.2 Transmitter reference PLL circuitThe transmitter reference PLL circuit generates thereference frequency signal (19.2MHz) for the transmitter DDSand modulates the low-frequency components of QT and DOT.This circuit consists of IC201, X201, 0201, and 0202. TheVCO consists of 0201, X201, D203, D201, and D202.The signal generated by the VCO is fed to buffer amplifier0202 and unwanted harmonics are removed with an LPF. Theresulting signal goes to the PLL IC (IC201) and its phase iscompared with that of the reference frequency using thecomparison frequency of 200 kHz. The phase difference signalis converted to a DC voltage by a lag-lead type loop filter. Thecapacitance of D201 and D204 are varied by the DC voltageto keep the VCO oscillator frequency at 19.2MHz. The 19.2MHzoscillator signal is fed to 0241 and used as the referencefrequency signal for the transmitter DDS.