Kenwood NX-300 Service Manual

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

NX-300(G)13CIRCUIT DESCRIPTION1. OverviewThe NX-300(G) is a UHF portable transceiver designedto operate in the frequency range of 450 to 520MHz (K,K3)or 400 to 470MHz (K2,K4). The unit consists of receiver,transmitter, phase-locked loop (PLL) frequency synthesizer,base band parts, power supply, and control circuits.2. Frequency ConfigurationThe receiver is a double-conversion superheterodyne us-ing the first intermediate frequency (IF) of 58.05MHz and thesecond IF of 450kHz. Incoming signals from the antenna aremixed with the local signal from the PLL circuit to producethe first IF of 58.05MHz. This is then mixed with the 57.6MHzsecond local oscillator output to produce the 450kHz secondIF. The transmit signal frequency is generated by the PLLVCO, and modulated by the signal from the DSP. It is thenamplified 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 band-pass filter (L713, L714, L715). The resulting signal is appliedto the 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). TheIF system IC provides a second mixer, AGC amplifier, andRSSI (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 operationalamplifier (IC700).IC413INAMTIC713(2/2)IC409SWSWIC701MIX, AGCEXAMTIC704 IC707IC108ASICIC719DSPIC408IC700IC412IC703AMTVOLCF701BPFIF AMPQ701MCFXF700BPFQ7002nd OSCX50019.2MHzVCTCXO x3 CF700BPFINT. SPEXT. SPRF AMPQ705LPFANTANTSW1st MIXQ703L612~L614BPFL713~L7151st PLL OSC (PLL)BPFL721,L722D606,D607D709,D711