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307 IC7) is input into the ADC (X53-414 IC312). Receiving
signal processing is performed by RX_DSP (X53-414 IC323),
and voice decode processing is performed by TX_VOCOD-
ER DSP (X53-414 IC324). The processed audio signal from
the AOUTL terminal of CODEC IC (X53-414 IC309) is ampli-
fi 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 circuit
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 pin15
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 ampli-
fi er gains using the detected audio signal depending on the
positive and negative peaks of the signal amplitude. The
audio signal 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 terminal of
the multiplexer IC (IC3) for microphone muting.
In case of the Analog Signal Processing mode (multiplexer
IC3 is setting X=X0), the audio signal is amplified 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 AOUTL terminal of IC4 is amplifi ed to a suf-
fi 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).
On the other hand, in the case of the NXDN Signal Pro-
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
The control circuit consists of two units, X53-413 and
X53-414.
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 controller
circuit.
CIRCUIT DESCRIPTION /
电路说明
获得的已检测音频 / 数据信号被输入到 ADC(X53-414 IC312)。
接收信号的处理由 R X _ D S P ( X53-414 I C323) 执行，语音解
码处理由 TX_VOCODER DSP(X53-414 IC324) 执行。CODEC
I C ( X53-414 I C309) 的 A O U T L 端 子 的 已 处 理 音 频 信 号 由
IC20(D/4) 放大到足够的电平，然后通过 IC20(C/4) 的抗混叠
滤波器。
音频信号路径由多路器 ( I C14) 根据模拟模式 ( I C14 设置
Y=Y0) 或 NXDN 模式 (IC14 设置 Y=Y1) 作出选择。然后，音频
信号经由 (IC8) V3/V4 发送到多路器 IC(IC25)，然后被放大
到足够的电平，用音频功率放大器 (IC29) 驱动扬声器。
5-2. 音频放大器电路
音频放大器电路位于控制单元 (X53-413) 的控制部分。
在电源电压 13.2V、负载 4 o h m 的情况下，从后面板上的
针脚 15 测试连接器"SPO,SPG"到外部扬声器可获得 3W 输出
功率。
5-3. 麦克风电路
麦克风的信号通过位于 DISPLAY 电路 (X56-311 B/3) 内的
A G C 电路，因此它不会饱和。该电路由 I C926、D933、D934
Q931 和 Q932 组成。A G C 利用检测的音频信号，根据信号振幅
的正负峰值控制放大器增益。音频信号从 DISPLAY 电路 (X56-
311 B/3) 进入控制单元 (X53-413) 的控制部分。
5-4. 解调电路
( 模拟 /NXDN 信号处理 )
发射音频信号进入用于麦克风静音的多路器 I C ( I C3) 的输
入端子。
在模拟信号处理模式中 ( 多路器 I C3 设置 X = X0)，音频信
号由 IC9(A/4) 放大，输入到 CODEC IC(IC4) 的 AINL 端子，
由 DSP(IC37) 进行音频处理。IC4 的 AOUTL 端子的已处理音频
信号由 I C9( B /4) 放大到足够的电平，然后通过 I C9( C /4) 的
抗混叠滤波器，并由加法 (TD) 放大器 IC9(D/4) 进行放大。
另 一 方 面， 在 N X D N 信 号 处 理 模 式 中 ( 多 路 器 I C3 设 置
X=X1)，音频信号由 IC20(A/4) 放大，输入到 CODEC IC(X53-
414 I C309) 的 A I N L 端子，由 T X _ V O C O D E R D S P ( X53-414
I C324) 进行处理。I C309 的 A O U T R 端子的已处理音频信号通
过 IC19(B/2) 的抗混叠滤波器。
6. 控制电路
控制单元由 X53-413 和 X53-414 两个单元组成。
单元 X53-413 主要包括电源电路、基带信号路径选择电路
( 包括电平调整 )、模拟模式语音编解码电路以及 R F 控制器
电路。
NXR-700H
29
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