NXR-800
11
2-6. Driver circuit
The driver circuit amplifi es the transmitter frequency sig-
nal to the level required for input to the Final Unit (X45-382
A/5).
This circuit consists of RF amplifiers Q201, Q202 and
Q203, switches Q204 and Q205, and operating amplifier
IC201.
DC switches Q204 and Q205, turns the power supply
voltage of RF amplifi ers Q201, Q202, and Q203 on and off.
The transmitter main PLL circuit output is attenuated by
attenuators R201, R202 and R203, by approximately 7dB.
So, the input level to Q201 is approximately -12dBm (63µW).
Q201 amplifi es it by approximately 12dB. So, the output
level is approximately 0dBm (1mW).
The Q201 output is amplifi ed by Q202 by approximately
10dB. Furthermore, it is amplifi ed by Q203 by approximately
10dB. The Q203 output is approximately +20dBm (100mW).
This output level is output from driver output connector
CN802 and is connected to the Final Unit (X45-382 A/5).
Q203 has an AGC (Auto Gain Control) circuit. D201 rec-
tifi es a part of the Q203 output and converts it into DC volt-
age. It is compared with the control voltage (D_PC) by the
operation amplifi er IC201. The Q203 Gate terminal voltage
is controlled for the stabilizing Q203 output (+20dBm).
Q201 Q203
TX main
PLL circuit
8V #1
Final
unit
D201
ATT
SW
368~
400MHz
D_PC
IC201
(A/2)
IC201
(B/2)
8V #1’
CN802
368~400MHz
+20dBm
8V #1’
Q204, 205
Q202
Fig. 6 Driver circuit
2-7. Modulation level adjustment circuit
The level adjustment circuit adjusts the modulation signal
level to provide the required level of modulation. This circuit
consists of IC301, IC304, IC305, and IC308.
The audio signal comes from the Control Unit (X53-413)
through pin 4. The modulating signal is input to IC304 from
this.
IC304 is an electronic volume control IC.
The modulation waveform balance adjustment, maximum
AF Dev. change, and adjustment are performed according
to data from the MPU using the FPU.
The modulation signal is produced by the modulating
low-pitched tone to the transmitter modulation 19.2MHz PLL
circuit and adds the high-pitched modulation to the transmit-
ter main PLL.
IC305 is an inverting amplifi er (B/2) for inverting the am-
plifi cation (A/2) of the modulating signal and synthesizing the
VCXO (X301) control voltage and modulating signal.
IC301 is a reference voltage generator (A/2) in modulat-
ing level adjusting circuit and non-inverting amplifi cation of
modulating signal with a cutoff signal of approximately 9kHz
(B/2).
Fig. 7 Modulation level adjustment circuit
CIRCUIT DESCRIPTION
Control
unit
TX Mod 19.2MHz
PLL circuit
VCXO_CV
TX main
PLL circuit
VCO_MOD
Mod
signal
CN804
4
1
IC304
IC308 (B/2)
5V #2
IC301
(B/2)
5V #2
IC305
(A/2)
IC305
(B/2)
5V #2
5V #2
5V #2
TX Mod 19.2MHz
PLL CP
3
2
10
4
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