Kenwood NXR-710 Service Manual

Also see for NEXEDGE NXR-710: Instruction manual Instruction manual Instruction manual Instruction manual Instruction manual

NXR-71091. OutlineThe NXR-710 is a VHF repeater operating in the 136~174MHz frequency range.2. TX-RX unitTX-RX unit (X57-7940-10) consists of the following cir-cuit.(1) Internal/external reference circuit(2) Transmitter reference 16.8MHz PLL circuit(3) Transmitter main PLL circuit(4) Modulation level adjustment circuit(5) Front-end circuit(6) 1st-Mixer circuit(7) IF circuit(8) Receiver PLL circuits(9) AVR circuits(10) Other circuits2-1. Internal/External reference circuitThe internal reference circuit consists of X500, Q502,Q504 and D505. The output of 19.2MHz VCTCXO (X500) isfed to buffer amplifier Q502. The higher harmonic wave isattenuated by the LPF. This reference signal is fed to IF IC(IC304) as the 2nd Local signal through the Tripler.The internal reference signal is amplified by Q504 toachieve the needed level for PLL ICs. That signal is dividedby a Wilkinson divider. The divided signal is fed to the PLLIC for the receiver. Another signal is fed to the transmitterreference 16.8MHz PLL IC through PIN diode switch (D505)which switches the Internal or external reference.The external reference circuit consists of CN500, Q501,Q503, IC500, IC501, D503 and D504. The external refer-ence signal (10MHz/0dBm) input from CN500 is fed to buf-fer amplifier Q501 and is amplified by Q503. Q503 is a dualgate MOS-FET. The output of amplifier (Q503) is detectedby D503 and that DC voltage is amplified by IC500 (B/2).The amplifi ed DC voltage is compared to the reference volt-age by IC500 (A/2). The difference of voltages is amplifiedby IC500 (A/2) and is fed to the gate-2 terminal of Q503. Thevoltage of the Q503 gate-2 terminal is controlled automati-cally to constantly maintain the power output of amplifier(Q503). The output of amplifier (Q503) is fed to the transmit-ter reference 16.8MHz PLL IC through the PIN diode switch(D504) which switches the Internal or External reference.The PIN diode switches (D504, D505) are controlled bythe I/O expander IC (IC805 Pin15). The I/O expander IC iscontrolled by the MCU which is in the Control unit (X53-449).If internal reference is selected by FPU, the I/O expander ICoutputs an “H” status. This signal sets power switch Q506to ON. Then D505 is activated.If external reference is selected, the I/O expander IC out-puts an “L” status. This signal sets power switch Q500 toON. Then D504 is activated.CIRCUIT DESCRIPTION10MHz or19.2MHzDetectorRX VCO/PLL1dBATT1dBATTX58-5070-102nd LoREFAMPQ504AMPQ502AGC AMPQ503BufferQ501SWX3Q202LPFLPFCN500LPFD503AMPIC500(B/2)AMPIC500(A/2)X500OSC19.2MHzD504,D505 EXT_IN10MHzFig. 1 Internal/external reference circuit2-2. Transmitter reference 16.8MHz PLL circuitThe transmitter reference 16.8MHz PLL circuit producesthe reference frequency signal for the Transmitter Main PLLcircuit and modulates the low-frequency components.The circuit consists of IC600, IC601, IC602, IC603,IC604, Q601, Q602, Q603, and X600.The VCXO (X600) signal enters the buffer amplifier Q603and is amplified by Q602. The higher harmonic wave is at-tenuated by the LPF and returns to IC602. 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 loopfi lter. This DC voltage is input to the IC604 invert amplifierand is synthesized with the modulating signal. This DC volt-age is input to the X600 control voltage terminal for control-ling the VCXO oscillating frequency 16.8MHz.The 16.8MHz oscillating signal is fed to the Q603 bufferamplifi er. The output signal of the buffer amplifier is used asthe reference frequency signal of the transmitter main PLLcircuit.