Kenwood NX-800 Service Manual

Also see for NEXEDGE NX-800 series: Brochure Function reference Instruction manual Instruction manual Specifications

NX-800183. Receiver System3-1. RF circuitThe front-end circuit consists of former BPF (D212, D213),RF amplifier Q210, and latter BPF (D207, D208, D209 andD210).The BPF covers frequency ranges 450 to 520MHz.The latter BPF (D207, D208, D209 and D210) attenuatesthe unwanted signals, and sends only the necessary signal tothe first mixer.1. OverviewNX-800 is a UHF Mobile transceiver designed to operate inthe frequency range of 450 to 520MHz. The unit consists ofreceiver, transmitter, phase-locked loop (PLL) frequency syn-thesizer, base band parts, power supply, and control circuits.2. Frequency ConfigurationThe receiver is a double-conversion super heterodyneusing first intermediate frequency (IF) of 58.05MHz and sec-ond 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 the57.6MHz second local oscillator output to produce the450kHz second IF. The transmit signal frequency isgenerated by the PLL VCO, and modulated by the signal fromthe DSP. It is then amplified and fed to the antenna.CIRCUIT DESCRIPTIONFig. 1 Frequency configurationx357.6MHzANTSWRFAMPMIXIF AMPPLLVCOBase band CircuitANTTX/RX:450~520MHzMCFCF450kHz58.05MHz19.2MHz450~520MHz391.95~461.95MHzPAAMPTXAMPVCTCXOAFAMPMICAMP1st MIX SPMIC3-2. First MixerThe signal from the BPF is heterodyned with the first localoscillator signal from the PLL frequency synthesizer circuit atthe first mixer DBM (IC204) to become a 58.05MHz firstintermediate frequency(IF) signal.The first IF signal is fed through a monolithic crystalfilter(XF202) to further remove spurious signals.RF AMPQ210Buff AMPQ208BPFANT IF AMPQ205IF AMPQ204RXVCOBuff AMPQ10Buff AMPQ9BPF1st MIX DBMIC204D212,D213BPFD207~D210MCFXF202FM SYSTEM ICIC202-118dBm -120.5dBm -104dBm-114.5dBm -112.5dBm0dBm0dBmFig. 2