Kenwood NXR-700 Service Manual page 19

5. Baseband Signal Processing Part
The baseband circuit is located on unit X53-413. This
circuit enables the selection of the Analog Signal Processing
mode and the Digital Signal Processing mode, and adjusts
the level of the baseband signals in each mode. This circuit
consists of IC2, IC3, IC5, IC8, IC9, IC12, IC14, IC19, IC20
and 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 the
operational amplifi ers (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 amplifi ed by IC5 (A/2), input into the AINR ter-
minal of CODEC IC (IC4), and then processed as an audio
signal by the DSP (IC37). The processed audio signal from
the AOUTR terminal of IC4 is amplifi ed to a suffi cient level
by IC12 (A/2), and is then passed through the anti-aliasing
fi 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 (X53-414
IC323), and voice decode processing is performed by TX_
VOCODER DSP (X53-414 IC324). The processed audio
signal from the AOUTL terminal of CODEC IC (X53-414
IC309) is amplifi ed to a suffi cient level by IC20 (D/4), and is
then passed through the anti-aliasing fi lter at IC20 (C/4).
The audio signal path is selected by multiplexer (IC14)
depending on the Analog mode (IC14 is setting Y=Y0) or
the NXDN mode (IC14 is setting Y=Y1). The audio signal
is then routed through an electronic volume (IC8) V3/V4 to
multiplexer IC (IC25), and is amplifi ed to a suffi cient level to
drive the loudspeaker using an audio power amplifi er (IC29).
5-2. Audio amplifi er aircuit
The audio amplifi er circuit is located in the control section
of the Control unit (X53-413).
The 3W output audio power is available from the pin 15
test connector "SPO, SPG" on the rear panel to the external
speaker in the case of a 13.2V power supply voltage and 4
ohm load.
5-3. Microphone circuit
The signal from the microphone is passed through the
AGC circuit located in the DISPLAY circuit (X56-311 B/3) so
that it may not saturate. This circuit consists of IC926, D933,
D934 Q931, and Q932. The AGC controls the amplifier
gains using the detected audio signal depending on the pos-
itive and negative peaks of the signal amplitude. The audio
signal goes to the control section of the Control unit (X53-413)
CIRCUIT DESCRIPTION
from the DISPLAY circuit (X56-311 B/3).
5-4. Modulation circuit
of the multiplexer IC (IC3) for microphone muting.
IC3 is setting X=X0), the audio signal is amplifi ed by IC9 (A/4),
input to the AINL terminal of the CODEC IC (IC4), and audio
processed by the DSP (IC37). The processed audio signal
from the the AOUTL terminal of IC4 is amplifi ed to a suffi -
cient level by IC9 (B/4), and is then passed through an anti-
aliasing fi lter at IC9 (C/4), and amplifi ed by the summing (TD)
amplifi er IC9 (D/4).
cessing mode (multiplexer IC3 is setting X=X1), the audio
signal is amplifi ed by IC20 (A/4), input to the AINL terminal
of the CODEC IC (X53-414 IC309), and processed by the
TX_VOCODER DSP (X53-414 IC324). The processed audio
signal from the AOUTR terminal of IC309 passes through
the anti-aliasing fi lter at IC19 (B/2).
6. Control Circuit
X53-414.
band signal path selection circuit (level adjustment is in-
cluded), analog mode voice codec circuit, and RF controller
circuit.
circuit, NXDN mode communication processing circuit, LAN
interface circuit, and Compact Flash interface circuit.
6-1. X53-413
■ RF control MPU
processor incorporating 256 kilobytes of ROM and 20 kilo-
bytes of RAM.
transmitter unit, and EEPROM of each unit, and the display
circuit, and has communication I/F with external devices.
■ DSP
and receiving signals, and the encoding and decoding of
sub-audible signals (encode: QT, DQT, DTMF, decode: QT,
DQT, DTMF).
and IC12.
digital by IC4 with a sampling frequency of 16.128kHz. The
digitized audio signal is sent to the DSP (IC37) to process
the sub-audible signal and audio signal. The processed digi-
tal audio signal is applied to CODEC IC4, and is converted
from digital to analog. The analog signal is output from pin
16 (AOUTR). The audio signal is then amplifi ed by IC12 (A/2),
passes through the low-pass fi lter at IC12 (B/2), is selected
by the multiplexer IC14 (Y0=Y) and is then input into an
(Analog/NXDN signal processing)
The transmitting audio signal goes to the input terminal
In case of the Analog Signal Processing mode (multiplexer
On the other hand, in the case of the NXDN Signal Pro-
The control circuit consists of two units, X53-413 and
Unit X53-413 mainly has the power supply circuit, base-
Unit X53-414 has the mode selection (analog or NXDN)
The IC34 RF control MPU is a 16-bit single chip micro-
This MPU controls the Flash memory, DSP, receiver unit,
The DSP circuit is in charge of the fi ltering of transmitting
This circuit consists of IC37, IC30, IC31, IC4, IC5, IC9,
The receiving signal, DET is converted from analog to
NXR-700
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