Kenwood NX-200 Service Manual

Also see for NEXEDGE NX-200: Brochure Instruction manual Instruction manual Specifications Instruction manual

NX-200(G)13CIRCUIT DESCRIPTION1. OverviewThe NX-200(G) is a VHF portable transceiver designedto operate in the frequency range of 136 to 174MHz. Theunit consists of receiver, transmitter, phase-locked loop (PLL)frequency synthesizer, base band parts, power supply, andcontrol circuits.2. Frequency ConfigurationThe receiver is a double-conversion superheterodyne us-ing the fi rst 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 circuitANTTX/RX: 136~174MHz136~174MHzMCFCF450kHz58.05MHz19.2MHz194.05~232.05MHzPAAMPTXAMPVCTCXOAFAMPMICAMP1st 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 (D104, D105, D209and D211) and then the bandpass filter (L220, L224). Thebandpass fi lter is adjusted by a variable capacitor. The inputvoltage to the variable capacitor is regulated by the voltageoutput from the D/A converter (IC703). The signal is ampli-fied by an RF amplifier (Q204), and passed through thebandpass fi lter (L212, L215). The resulting signal is appliedto the fi rst mixer (Q203), where it is mixed with the fi rst lo-cal oscillator 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 fi lter (XF200) to reject adjacent channel signals.The fi ltered fi rst IF signal is amplifi ed by the fi rst IF amplifi er(Q202) and then applied to the lF system IC (IC202). TheIF system IC provides a second mixer, AGC amplifi er, 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 fi lter(CF200) to reject the adjacent channel signal. The filteredsecond IF signal is amplified by the AGC amplifi er.The signal from the AGC amplifier is input to the ASIC(IC108) through the ceramic filter (CF201) and operationalamplifier (IC203).IC413INAMTIC713(2/2)IC409SWSWIC202MIX, AGCEXAMTIC704 IC707IC108ASICIC102DSPIC408IC203IC412IC703AMTVOLCF201IF AMPQ202MCFXF200Q2012nd OSCX119.2MHzVCTCXO x3 CF200INT. SPEXT. SPRF AMPQ204ANTANTSW1st MIXQ203L109,L110,L113 L212,L2151st PLL OSC (PLL)L220,L224D104,D105D209,D211