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7. Signaling Circuit
7-1. Encode
• Low-speed data (QT, DQT)
Low-speed data is output from pin 1 of the MCU. The
signal passes through a low-pass CR fi lter, and goes to the
summing amplifi er (IC305 1/2). The signal is mixed with the
audio signal and goes to the VCO and TCXO (X1) modulation
input after passing through the D/A converter (IC307) for
BAL adjustment.
• High-speed data (DTMF)
High-speed data is output from pin 2 of the MCU. The
signal passes through a low-pass fi lter consisting of IC304,
and provides a TX DTMF tone and a RX DTMF tone TX
DTMF deviation making an adjustment by MCU is passed
through the D/A convertor (IC307), and then applied to the
audio processor (IC500).
The signal is mixed with the audio signal and goes to the
VCO and TCXO, the RX DTMF tone is passed a summing
amplifier (IC305 2/2), the D/A converter (IC307) for audio
control, audio power amplifi er and then to the speaker.
• FFSK
ESN utilizes 1200bps FFSK signal. FFSK signal is output
from pin 6 of IC500. The signal passes through the D/A
converter (IC307) for the FFSK deviation adjustment. and is
routed to the VCO. When encoding FFSK, the microphone
input signal is muted.
LSD
OUT
1
7-2. Decode
• Low-speed data (QT, DQT)
The demodulated signal from the IF IC (IC200) is ampli-
fied by IC300 (2/2) and passes through a low-pass filter
(IC306) to remove audio components. The signal is input to
pin 95 of the MCU.
The MCU digitizes this signal, performs processing such
as DC restoration, and decodes the signal.
CIRCUIT DESCRIPTION /
IC309
MCU
IC305(2/2)
IC304
2
HSD
LPF
OUT
SUM
IC305(1/2)
Fig. 10 Encode / 图 10 编码
电路说明
7. 信令电路
7-1. 编码
• 低速率数据 (QT，DQT)
M C U 的管脚 1 输出低速率数据。信号通过低通陶瓷滤波器
进入总和放大器 (IC305 1/2)。此信号与音频信号混合，通过
数 / 模转换器 (IC307) 进行 BAL 调整后进入 VCO 和 TCXO(X1)
调制输入。
• 高速率数据 (DTMF)
M C U 的管脚 2 输出高速率数据。信号通过 I C304 组成的低
通滤波器，并提供 T X D T M F 音频和 R X D T M F 音频。通过 M C U
调整 TX DTMF 频偏并进入数 / 模转换器 (IC307)，然后提供给
音频处理器 (IC500)。
此信号与音频信号混合后进入 VCO 和 TCXO，RX DTMF 通过
总和放大器 (IC305 2/2)，数 / 模转换器 (IC307) 进行音频控
制，音频功率放大器，然后进入扬声器。
• FFSK
ESN 使用 1200bps FFSK 信号。 IC500 的管脚 6 输出 FFSK 信号。
此信号通过数 / 模转换器 (IC307) 进行 FFSK 频偏调整，然后
进入 VCO。当编码 FFSK 时，话筒输入信号为静音。
RX Audio
I6
O6
AF
SUM
AMP
IC307
D/A (ADJ)
I3
O3
I5
O5
I2
O2
IC302
O1 BUFF
AMP
7-2. 解码
• 低速率数据 (QT，DQT)
来自于中频芯片 (IC200) 的已解调的信号被 IC300(2/2) 放
大，然后通过低通滤波器 ( I C306) 消除音频成分。此信号被
输入到 MCU 的管脚 95。
M C U 使信号数字化，执行诸如直流恢复和解码信号这样的
步骤。
TK-3148
IC500
SUM
MIC IN
MD
VCO
X1
MB
TCXO
17
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