Kenwood NXR-700 Service Manual

Also see for NEXEDGE NXR-700: Brochure Instruction manual Service manual Instruction manual Instruction manual

Contents

NXR-700195. Baseband Signal Processing PartThe baseband circuit is located on unit X53-413. Thiscircuit enables the selection of the Analog Signal Processingmode and the Digital Signal Processing mode, and adjuststhe level of the baseband signals in each mode. This circuitconsists of IC2, IC3, IC5, IC8, IC9, IC12, IC14, IC19, IC20and IC21.The type of input modulation signals are local micro-phone terminal, low-speed data (LSD), high-speed data(HSD), external audio input (TA), and external data input (TD),and also the type of output demodulation signals are receiv-ing audio output (RA), and receiving data output (RD).The multiplexer (IC2, IC3, IC14) selects the signal path,the electronic volume (IC8) adjusts the signal level, and theoperational amplifiers (IC5, IC9, IC12, IC19, IC20, and IC21)amplify and sum various signals.5-1. Demodulation circuit(Analog/NXDN signal processing)In case of the Analog Signal Processing mode, the de-tected audio signal obtained from the IF SYSTEM IC (X55-307 IC8) is amplified by IC5 (A/2), input into the AINR ter-minal of CODEC IC (IC4), and then processed as an audiosignal by the DSP (IC37). The processed audio signal fromthe AOUTR terminal of IC4 is amplified to a sufficient levelby IC12 (A/2), and is then passed through the anti-aliasingfi lter at IC12 (B/2).In case of the NXDN Signal Processing mode, the de-tected audio/data signal obtained from the IF SYSTEM IC(X55-307 IC7) is input into the ADC (X53-414 IC312). Re-ceiving signal processing is performed by RX_DSP (X53-414IC323), and voice decode processing is performed by TX_VOCODER DSP (X53-414 IC324). The processed audiosignal from the AOUTL terminal of CODEC IC (X53-414IC309) is amplified to a sufficient level by IC20 (D/4), and isthen passed through the anti-aliasing filter at IC20 (C/4).The audio signal path is selected by multiplexer (IC14)depending on the Analog mode (IC14 is setting Y=Y0) orthe NXDN mode (IC14 is setting Y=Y1). The audio signalis then routed through an electronic volume (IC8) V3/V4 tomultiplexer IC (IC25), and is amplifi ed to a suffi cient level todrive the loudspeaker using an audio power amplifi er (IC29).5-2. Audio amplifier aircuitThe audio amplifier circuit is located in the control sectionof the Control unit (X53-413).The 3W output audio power is available from the pin 15test connector “SPO, SPG” on the rear panel to the externalspeaker in the case of a 13.2V power supply voltage and 4ohm load.5-3. Microphone circuitThe signal from the microphone is passed through theAGC circuit located in the DISPLAY circuit (X56-311 B/3) sothat it may not saturate. This circuit consists of IC926, D933,D934 Q931, and Q932. The AGC controls the amplifiergains using the detected audio signal depending on the pos-itive and negative peaks of the signal amplitude. The audiosignal goes to the control section of the Control unit (X53-413)from the DISPLAY circuit (X56-311 B/3).5-4. Modulation circuit(Analog/NXDN signal processing)The transmitting audio signal goes to the input terminalof the multiplexer IC (IC3) for microphone muting.In case of the Analog Signal Processing mode (multiplexerIC3 is setting X=X0), the audio signal is amplified by IC9 (A/4),input to the AINL terminal of the CODEC IC (IC4), and audioprocessed by the DSP (IC37). The processed audio signalfrom the the AOUTL terminal of IC4 is amplified to a suffi-cient level by IC9 (B/4), and is then passed through an anti-aliasing filter at IC9 (C/4), and amplified by the summing (TD)amplifi er IC9 (D/4).On the other hand, in the case of the NXDN Signal Pro-cessing mode (multiplexer IC3 is setting X=X1), the audiosignal is amplified by IC20 (A/4), input to the AINL terminalof the CODEC IC (X53-414 IC309), and processed by theTX_VOCODER DSP (X53-414 IC324). The processed audiosignal from the AOUTR terminal of IC309 passes throughthe anti-aliasing fi lter at IC19 (B/2).6. Control CircuitThe control circuit consists of two units, X53-413 andX53-414.Unit X53-413 mainly has the power supply circuit, base-band signal path selection circuit (level adjustment is in-cluded), analog mode voice codec circuit, and RF controllercircuit.Unit X53-414 has the mode selection (analog or NXDN)circuit, NXDN mode communication processing circuit, LANinterface circuit, and Compact Flash interface circuit.6-1. X53-413■ RF control MPUThe IC34 RF control MPU is a 16-bit single chip micro-processor incorporating 256 kilobytes of ROM and 20 kilo-bytes of RAM.This MPU controls the Flash memory, DSP, receiver unit,transmitter unit, and EEPROM of each unit, and the displaycircuit, and has communication I/F with external devices.■ DSPThe DSP circuit is in charge of the filtering of transmittingand receiving signals, and the encoding and decoding ofsub-audible signals (encode: QT, DQT, DTMF, decode: QT,DQT, DTMF).This circuit consists of IC37, IC30, IC31, IC4, IC5, IC9,and IC12.The receiving signal, DET is converted from analog todigital by IC4 with a sampling frequency of 16.128kHz. Thedigitized audio signal is sent to the DSP (IC37) to processthe sub-audible signal and audio signal. The processed digi-tal audio signal is applied to CODEC IC4, and is convertedfrom digital to analog. The analog signal is output from pin16 (AOUTR). The audio signal is then amplified by IC12 (A/2),passes through the low-pass filter at IC12 (B/2), is selectedby the multiplexer IC14 (Y0=Y) and is then input into anCIRCUIT DESCRIPTION