Kenwood NX-900 Service Manual page 22

NX-900
DCin CN401
(13.6V)
CN402
GND
CN403
8. Signaling Circuit
8-1. Encode (QT/DQT/DTMF/MSK)
Each signaling data signal of QT, DQT, DTMF and MSK
is generated by the DSP circuit, is superimposed onto the
modulation signal, and is output from the DSP (IC717) and
ASIC (IC510). The modulation balance of the QT/DQT signal
is adjusted by the D/A converter (IC719) and the resulting
signal is routed to the modulation input of the VCO and PLL
IC (IC3). Each deviation of the TX QT, DQT, DTMF and MSK
signal is adjusted by changing the output level of IC717 and
the resulting signal is routed to the VCO and PLL IC (IC3).
The RX DTMF tone is routed to the receive audio signal sys-
tem, and is output from the speaker.
22
CIRCUIT DESCRIPTION
F401
IC405
DC/DC
Q404
DC SW
SBC_2
IC401
/BINT
Detect
D401
Q401
Protect
SBC
/IGN
1
Q403
2
IC402
3.3V AVR
IC408
33A
3.3V AVR
Q416
SBC_2 33A_2
DC SW
Q412
50MC
DC SW
D408
33M
SBC_2
IC409
15M
1.5V AVR
SB
IC403
80C
8V AVR
Q407
80T
DC SW
TXC
Q408
80R
DC SW
SBC_2
RXC
IC404
5V AVR
Q409
DC SW
IC406
3.3V AVR
IC407
3.3V AVR
Fig. 8
8-2. Decode (QT/DQT/DTMF/MSK)
The audio signal is removed from the FM detection
signal sent to the DSP circuit and the resulting signal is de-
coded.
9. Compander Circuit
The term "compander" means compressor and expand-
er. The compander reduces noise by utilizing a compressor
and an expander. The NX-900 contains a DSP (IC717) to per-
form this operation. The NX-900 compander can be turned
on or off using the FPU.
+B
50M
33M
Q405
SCTAM1
DC SW
/BINT
Q411
33BU
DC SW
CN405
/RST
Backup Battery
IC506
/RST
RESET
50C
50R
RXC
33C
33GPS