Kenwood NXR-800 Service Manual page 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, Q205 and Q206, and operating am-
plifi er IC201.
DC switches Q204, Q205, and Q206 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).
450~
480MHz
TX main
PLL 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.
Control
unit
CIRCUIT DESCRIPTION
Q204~206
8V #1
SW
ATT
Q201 Q202
Fig. 6 Driver circuit
5V #2
Mod
3
signal
4 1
IC305
CN804
(A/2)
2
5V #2
IC304
10
IC308 (B/2)
Fig. 7 Modulation level adjustment circuit
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 amplified by Q203 by approxi-
mately 10dB. The Q203 output is approximately +20dBm
(100mW). This output level is output from driver output con-
nector CN802 and is connected to the Final Unit (X45-382
A/5).
Q203 has an AGC (Auto Gain Control) circuit. D201 recti-
fi 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).
8V #1'
Q203
D201
8V #1'
IC201
IC201
(A/2)
(B/2)
D_PC
The modulation signal is produced by the modulating low-
pitched tone to the transmitter modulation 19.2MHz PLL cir-
cuit and adds the high-pitched modulation to the transmitter
main PLL.
IC305 is an inverting amplifi er (B/2) for inverting the am-
plification (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).
TX Mod 19.2MHz
PLL CP
5V #2
5V #2
TX Mod 19.2MHz
5V #2
IC305
(B/2)
IC301
(B/2)
NXR-800
CN802
Final
unit
450~480MHz
+20dBm
PLL circuit
VCXO_CV
TX main
PLL circuit
VCO_MOD
11