Kenwood NX-800H Service Manual

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

NX-800/800H194. Transmitter System4-1. Audio Band CircuitThe signal from the microphone goes through the muteswitch (Q706), the Mic-Mute signal (MM) becomes Low,then mute switch (Q706) is turned off. The signal frommicrophone goes through Mic-AGC (Q704, Q705, D704,D705), and goes through switch IC (IC708), and amplified byMic-Amp IC706 (1/2), LPF IC706 (2/2) works as anti-aliasingfi lter.If an optional scrambler board is installed, the switch(IC708) adjusts the signal path so that the audio signal is in-put to the scrambler board.4-2. Base Band CircuitThe audio signal output from the base band circuit isconverted to digital data of a sampling frequency of 48kHz.This digital data is sent to the DSP (IC502), and voice signalsof 300Hz or lower and frequencies of 3kHz or higher arecut off and an audio range 300Hz to 3kHz is extracted. Theaudio signal is then pre-emphasized in FM mode and syn-thesized with the signals, such as QT and DQT, as required,and is then output from the IC510. In Digital mode, the au-dio signal is converted to the 4-Level FSK base band signaland output from the IC510. The DTMF and MSK base bandsignals are also generated by the DSP and output by theIC510.LPF (IC702) works as smoothing filter. The DAC (IC712)assigns the base band signal to the VCO and VCTCXO (X1).At this time, the level output according to the transmit car-rier is fi ne-adjusted according to each modulation method.CIRCUIT DESCRIPTIONSWQ707 IC708MMAMPIC706(1/2)LPFIC706(1/2)LPFIC702(1/2)AMP IC712IC709(1/2)IC510IC502DSPLPFIC702(2/2)AMPIC1AMPVCTCXOX1VCOIC5 (2/2)AGCD703,D704Q705,Q706SWSCSWOptional Scrambler BoardINT. MICFig. 5Fig. 64-3. Drive and Final amplifierThe transmit signal obtained from the TX VCO bufferamplifier Q9, is amplified to approximately +17dBm by thedriver amplifi ers Q10, Q101 and Q102.This amplified signal is passed to the power amplifiermodule (power module) IC102, which consists of a MOS-FET amplifi er and capable of transmission output power.4-4. APC circuitThe Automatic transmission power control (APC) circuitstabilizers the transmitter output power at a predeterminedlevel by detecting the power module output with a diodesD108, D109 and D110. Diodes D108, D109 and D110 applya voltage to DC amplifi er IC103 (1/2).IC103 (2/2) compares the APC control voltage (PC) gen-erated by microprocessor IC510 and DC amplifier IC101 (1/2,2/2) with the detection output voltage from IC103 (1/2) tocontrol the Vgg Pin of IC102, and stabilizes transmission out-put.The APC circuit is configured to protect over-current ofthe power module due to fluctuations of the load at theantenna end and to stabilize transmission output at voltageand temperature variations.TX VCOVCTCXO19.2MHz0dBm +17dBmDrive AMPQ10Buff AMPQ9Drive AMPQ101Drive AMPQ102Final AMPIC102MODMB DCAMPDCAMPPCMPSW ANT FilterD103*,D104,D106,D216DETD108ANT*D103: NX-800H onlyGatebiasIC101 IC103DETD109DETD110