Kenwood NX-800 Service Manual page 35

The MCU controls the TXC signal to High during trans-
mission to supply power (80T) for transmission circuit. The
MCU controls the signals (RXC) to High during reception to
supply power (80R, 50R) for reception circuit.
When the MCU detects the PSW (Power switch) signal,
IGN (Ignition sense) signal or /BINT signal, it controls the
SBC signal to Low, and turns the transceiver power (SB) off.
When D401 and Q401 detect over-voltage condition, they
turns Q404 (SB SW) off. But the MCU still works.
If +B is not provided to the transceiver, the power is pro-
vided to SRAM and RTC through the secondary battery con-
nected with CN405.
8. Signaling Circuit
8-1. Encode (QT/DQT/LTR/DTMF/2-tone/MSK)
Each signaling data signal of QT, DQT, LTR, DTMF, 2-tone
and MSK is generated by the DSP circuit, superposed on
a modulation signal and output from IC510. The modula-
tion balance of the QT/DQT signal is adjusted by the D/A
converter (IC712) and the resulting signal is routed to the
modulation input of the VCO and VCTCXO (X1). The each
deviation of the TX QT, DQT, LTR, DTMF, 2-tone and MSK
tone is adjusted by changing the output level of the IC510
and the resulting signal is routed to VCO and VCXO. The
RX DTMF tone is routed to the receive audio signal system,
and is output from the speaker.
8-2. Decode (QT/DQT/LTR/DTMF/2-tone/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 transceiver contains DSP (IC502) to
perform this operation. The transceiver compander can be
turned on or off using the FPU.
CIRCUIT DESCRIPTION /
电路说明
发射期间， MCU 将 TXC 信号控制为高， 为发射电路供电 (80T)。
接收期间， MCU 将信号 (RXC) 控制为高， 为接收电路供电 (80R、
50R)。
当 M C U 检测 P S W ( 电源开关 ) 信号、I G N ( 点火感应 ) 信号
或 / B I N T 信号时，它将 S B C 信号控制为低，关闭车载对讲机
电源 ( S B )。当 D401 和 Q401 检测到过电压情况时，它们将关
闭 Q404(SB SW)。
但 M C U 仍然工作。如果没有对车载对讲机提供 + B，则通过
与 CN405 相连的备用电池对 SRAM 和 RTC 供电。
8. 信令电路
8-1. 编码 (QT/DQT/LTR/DTMF/2 音 /MSK)
QT、DQT、LTR、DTMF、2 音和 MSK 的各信令信号由 DSP 电
路产生，叠加到调制信号上并从 IC510 输出。QT/DQT 信号的
调制平衡由 D / A 转换器 ( I C712) 进行调整，产生的信号送入
VCO 和 VCTCXO (X1) 的调制输入。TX QT、DQT、LTR、DTMF、2
音和 MSK 音各自的频偏通过 IC510 输出电平的变化进行调整，
产生的信号被送入 VCO 和 VCXO。RX DTMF 音被送入接收音频
信号系统，从扬声器输出。
8-2. 解码 (QT/DQT/LTR/DTMF/2 音 /MSK)
音频信号从发送到 DSP 电路的 FM 检测信号中移除，产生的
信号被解码。
9. 压扩器电路
"compander"一词表示压缩器和扩展器。压扩器利用压缩
器和扩展器减低噪音。车载对讲机含有 D S P ( I C102)，用以执
行此操作。可用 FPU 打开或关闭车载对讲机的压扩器。
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