NXR-810
19
2-3. Transmitter Main PLL circuit (SUB unit)
■
VCO
The TX VCO circuit consists of two VCOs (VCO A X58-
510: Q352, VCO B X58-510: Q353). Those VCOs generates
a transmit carrier. VCO A Q352 produces a transmitter fre-
quency from 400.000MHz to 434.995MHz. VCO B Q353
produces a transmitter frequency from 435.000MHz to
470.000MHz.
Those VCO oscillation frequencies are determined by two
systems of voltage control terminals: “CV” and “TXASSIST”.
The voltage control terminals, “CV” and “TXASSIST”, are
controlled by the PLL IC (X58-510: IC300) and MCU (X53-
449: IC20) and the output frequency changes continuously
according to the applied voltage. For the modulation input
terminal, “MO”, the output frequency changes according to
the applied voltage.
Fig. 3 Transmitter VCO circuit /
图 3 发射机 VCO 电路
D355
D352
D358
D359
SW Q350
TXVCOA
TX_CV
TXASSIST
TXVCOB
MO
80C
80C
VO
VCO_A
Q352
Buffer
Q354
SW Q351
D357
D353
D360
D361
VCO_B
Q353
■
PLL IC (X58-510: IC300)
The PLL IC compares the differences in phases of the
VCO oscillation frequency and the transmitter PLL reference
signal (16.8MHz), returns the difference to the VCO CV ter-
minal and realizes the “Phase Locked Loop” for the return
control. This allows the VCO oscillation frequency to accu-
rately match (lock) the desired frequency.
When the frequency is controlled by the PLL, the fre-
quency convergence time increases as the frequency dif-
ference increases when the set frequency is changed. To
supplement this, the MCU is used before control by the
PLL IC to bring the VCO oscillation frequency close to the
desired frequency. As a result, the VCO CV voltage does not
change and is always stable at approx. 3.0V.
CIRCUIT DESCRIPTION /
电路说明
2-3. 发射机主 PLL 电路 (SUB 单元 )
■ VCO
TX VCO 电路由两个 VCO(VCO A X58-510:Q352,VCO B X58-
510:Q353) 组成。这些 VCO 生成发射载波。VCO A Q352 产生
从 400.000MHz 到 434.995MHz 的发射机频率。VCO B Q353 产
生从 435.000MHz 到 470.000MHz 的发射机频率。
这些 V C O 振荡频率由电压控制端子的两个系统 :“C V”和
“TXASSIST”决定。
电 压 控 制 端 子“C V” 和“T X A S S I S T” 由 P L L I C ( X58-
510:IC300) 和 MCU(X53-449:IC20) 控制，并根据施加的电压
连续输出频率变化。对于调制输入端子“M O”
，输出频率根据
施加的电压改变。
■ PLL IC(X58-510: IC300)
PLL IC 对比 VCO 振荡频率和发射机 PLL 基准信号 (16.8MHz)
的相位差，将相位差返回 VCO CV 端子，实现返回控制的“锁
相环路”
。这可以使 V C O 震荡频率与所需的频率精确匹配 ( 锁
定 )。
频率由 P L L 控制时，频率锁定时间将随着设定频率改变时
频率差的增大而增加。为对此进行补充，在由 PLL IC 控制之
前使用 M C U 以使 V C O 振荡频率接近所需的频率。因此，V C O
CV 的电压不变，始终稳定在约 3.0V。
