Kenwood NX-700 Service Manual

Also see for NEXEDGE NX-700 series: Brochure Function reference Instruction manual Instruction manual Specifications

NX-700/700H17CIRCUIT DESCRIPTION1. OverviewNX-700/700H is a VHF Mobile transceiver designed tooperate in the frequency range of 136 to 174MHz. The unitconsists of receiver, transmitter, phase-locked loop (PLL)frequency synthesizer, base band parts, power supply, andcontrol circuits.2. Frequency ConfigurationThe receiver is a double-conversion super heterodyneusing first intermediate frequency (IF) of 58.05MHz andsecond IF of 450kHz. Incoming signals from the antennaare mixed with the local signal from the PLL circuit to pro-duce 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 CircuitANTTX/RX: 136~174MHzMCFCF450kHz58.05MHz19.2MHz136~174MHz194.05~232.05MHzPAAMPTXAMPVCTCXOAFAMPMICAMP1st MIX SPMICFig. 1 Frequency configurationFig. 23. Receiver System3-1. RF circuitThe front-end circuit consists of former BPF (D213,D216, D217, D218),RF amplifier Q210, and latter BPF (D207,D208, D209 and D210).The BPF covers frequency ranges 136 to 174MHz.The latter BPF (D207, D208, D209 and D210) attenuatesthe unwanted signals, and sends only the necessary signalto the first mixer.3-2. First MixerThe signal from the BPF is heterodyned with the first lo-cal oscillator signal from the PLL frequency synthesizer cir-cuit at the first mixer DBM (IC204) to become a 58.05MHzfi rst intermediate frequency (IF) signal.The first IF signal is fed through a monolithic crystal filter(XF202) to further remove spurious signals.RF AMPQ210Buff AMPQ208BPFANT IF AMPQ205IF AMPQ204RXVCOBuff AMPQ10Buff AMPQ9BPF1st MIX DBMIC204D213,D216,D217,D218BPFD207~D210MCFXF202FM SYSTEM ICIC202–118dBm –120.5dBm –104dBm–114.5dBm –112.5dBm0dBm0dBm