Kenwood NX-300 Service Manual

Also see for NEXEDGE NX-300: Brochure Instruction manual Instruction manual Instruction manual Instruction manual

NX-30011CIRCUIT DESCRIPTION1. OverviewThe NX-300 is a UHF portable transceiver designed tooperate in the frequency range of 450 to 520MHz (K,K3) or400 to 470MHz (K2,K4). The unit consists of receiver, trans-mitter, phase-locked loop (PLL) frequency synthesizer, baseband parts, power supply, and control circuits.2. Frequency ConfigurationThe receiver is a double-conversion superheterodyneusing the first intermediate frequency (IF) of 58.05MHzand the second IF of 450kHz. Incoming signals from theantenna are mixed with the local signal from the PLL circuitto produce the first IF of 58.05MHz. This is then mixed withthe 57.6MHz second local oscillator output to produce the450kHz second IF. The transmit signal frequency is gener-ated by the PLL VCO, and modulated by the signal from theDSP. It is then amplified and fed to the antenna.x357.6MHzANTSWRFAMPMIXIF AMPPLLVCOBase band circuitANT TX/RX: 450~520MHz (K,K3)TX/RX: 400~470MHz (K2,K4)450~520MHz (K,K3)400~470MHz (K2,K4)MCFCF450kHz58.05MHz19.2MHz391.95~461.95MHz (K,K3)341.95~411.95MHz (K2,K4)PAAMPTXAMPVCTCXOAFAMPMICAMP1st MIX SPMICFig. 1 Frequency configurationFig. 2 RF and IF circuit3. Receiver System3-1. RF CircuitAn incoming RF signal from the antenna terminal ispassed through the antenna switch (D606, D607, D709,D711) and then the bandpass filter (L721, L722). The band-pass filter is adjusted by a variable capacitor. The input volt-age to the variable capacitor is regulated by the voltage out-put from the D/A converter (IC703). The signal is amplifiedby an RF amplifier (Q705), and passed through the bandpassfilter (L713, L714, L715). The resulting signal is applied tothe first mixer (Q703), where it is mixed with the first localoscillator signal output from the frequency synthesizer toproduce the first IF (58.05MHz).3-2. IF CircuitThe first IF signal is passed through a four-pole mono-lithic crystal filter (XF700) to reject adjacent channel signals.The filtered first IF signal is amplified by the first IF amplifier(Q701) and then applied to the lF system IC (IC701). The IFsystem IC provides a second mixer, AGC amplifier, and RSSI(Received Signal Strength Indicator).The second mixer mixes the first IF signal with the57.6MHz of second local oscillator output and produces thesecond IF signal of 450kHz.The second IF signal is passed through the ceramic filter(CF700) to reject the adjacent channel signal. The filteredsecond IF signal is amplified by the AGC amplifier.The signal from the AGC amplifier is input to the ASIC(IC108) through the ceramic filter (CF701) and operationalamplifi er (IC700).IC413INAMTIC713(2/2)IC409SWSWIC701MIX, AGCEXAMTIC704 IC707IC108ASICIC102DSPIC408IC700IC412IC703AMTVOLCF701BPFIF AMPQ701MCFXF700BPFQ7002nd OSCX50019.2MHzVCTCXO x3 CF700BPFINT. SPEXT. SPRF AMPQ705LPFANTANTSW1st MIXQ703L612~L614BPFL713~L7151st PLL OSC (PLL)BPFL721,L722D606,D607D709,D711