Kenwood NXR-800 Service Manual

Also see for NEXEDGE NXR-800: Brochure Instruction manual Instruction manual Instruction manual Instruction manual

Contents

NXR-80092-3. Transmitter modulation 19.2MHz PLL circuitThe transmitter modulation 19.2MHz PLL circuit producesthe reference frequency signal for the Transmitter DDS cir-cuit and modulates the low-frequency components.The circuit consists of IC302, IC303, IC305, IC306, X301,Q304, Q305, and Q307.The signal generated by the VCXO (X301) is fed to thebuffer amplifier Q307.The VCXO (X301) signal enters buffer amplifi er Q307 andis amplified by Q305. The higher harmonic wave is attenu-ated by the LPF and returns to IC303. Its phase is com-pared with that of the reference frequency 5kHz.The phase difference signal produced by the comparingphase is converted to a DC voltage by a lag-lead type loopfilter. This DC voltage is input to the IC305 invert amplifier(B/2) and is synthesized with the modulating signal. ThisDC voltage is input to the X301 control voltage terminal forcontrolling the VCXO oscillating frequency 19.2MHz.The DC voltage passes through the IC306 operational am-plifier, and is output as a voltage signal (CVT-MOD) for moni-toring the modulating 19.2MHz PLL circuit lock voltage.The 19.2MHz oscillating signal is fed to the Q307 bufferamplifier and is amplified by Q304. The higher harmonicwave is attenuated by the LPF, fed to IC307, and is used asthe reference frequency signal of the transmitter DDS cir-cuit.Q415Internal/ExternalRef circuit1/R1/NPDFref.=19.2MHzR=1920Fpd=10kHz8V #2Q417X4018V #2IC4075V #3Q4165V #1Q4015V #2Q4025V #2Q4125V #18V #25V #35V #319.2MHz 19.2MHzIC401OP-AMP2865.99MHzor10MHzIC404PLL ICCVT-REFTX Mod19.2MHzPLL circuitRX unitControlunitCN40619.2MHzCN40519.2MHzFig. 2 Transmitter reference 19.2MHz PLL circuitQ305TX Ref19.2MHzPLL circuit1/R1/NPDFref.=19.2MHzR=3840Fpd=5kHz8V #2Q307X301IC3025V #2IC3055V #2 8V #2 8V #28V #25V #219.2MHzIC306OP-AMPQ3045V #228619.2MHzIC303PLL ICCVT-MODTX DDScircuit19.2MHzMod signalFig. 3 Transmitter modulation 19.2MHz PLL circuitCIRCUIT DESCRIPTION