NXR-901
11
CIRCUIT DESCRIPTION
2-6. Modulation level adjustment circuit
The level adjustment circuit adjusts the modulation signal
level to provide the required level of modulation. This circuit
consists of IC203, IC206 and IC207.
The audio signal comes from the Control unit (X53-413)
through CN804 pin 4. The modulating signal is fed to IC207
from this pin. IC207 is an electronic volume control IC.
The modulation waveform balance adjustment and maxi-
mum deviation adjustment are performed according to data
from the MPU to IC207 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.
IC206 is an inverting amplifi er (B/2) for inverting the am-
plifi cation (A/2) of the modulating signal and synthesizing the
VCXO (X201) control voltage and modulating signal.
IC203 is a reference voltage generator (A/2) in the modu-
lating level adjusting circuit and non-inverting amplifi cation
(B/2) of the modulating signal with a cut off signal of approxi-
mately 9kHz.
CN804
PIN4
(MOD)
IC206 A/2
IC207
Electric
volume
control
TX 1
9
.2MHz
PLL circuit
Control
unit
IC203 B/2
TX main
PLL circuit
TX UNIT
Fig. 5 Modulation level adjustment circuit
2-7. AVR circuit
IC7, IC707, IC708, IC709, IC710, IC808, IC810, IC403
and IC809 are AVR ICs.
Each circuit contains its own power regulator IC to main-
tain isolation between circuits.
External DC
power supply
CN801
IC7
IC80
9
IC808
IC707
IC708
IC70
9
IC403
IC710
IC810
VCO
OCXO
Driver amplifiers
5V common #3
3.3V TCXO
5V common #4
5V common #1
5V common #2
3.3V PLL IC
Fig. 6 AVR circuit
2-8. Other circuits
In addition, IC202 is an EEPROM. The transmitter adjust-
ment data adjusted for each unit is written into the EEPROM.
If the unit is installed in another set, it is not necessary to ad-
just it again from the beginning; only fi ne-tuning is necessary
for each unit.
The temperature sensor (IC704) monitors the tempera-
ture of the Transmitter unit (X56-315 A/3).
The D/A converters (IC201 and IC705) convert the AGC
setting (D_PC) of the driver circuit, VCO tuning voltage set-
ting (CV_ADJ2) of transmitter main PLL circuit and control
voltage value (PWR_CONT, PA_BIAS) of the Final unit (X45-
387 A/4).
The A/D converter (IC703) converts the Transmitter unit
(X56-315 A/3) temperature, VCO and VCXO control voltage
(CVT, CVT-REF and CVT-MOD), Final unit (X45-387 A/4) PA
current (PA_CURR), fan current (FAN_CURR), output power
detection voltage (FWD_PWR, RFL_PWR), etc.
The shift register (IC701) controls each part of the Trans-
mitter unit (X56-315 A/3) based on serial data of the Control
unit (X53-413).
3. Final Unit
The RF final amplifier unit (X45-387 A/4) amplifies the
transmitter power to specifi ed levels.
This unit consists of the following circuits:
(1) Transmitter power amplifi er IC
(2) Forward power detector and isolator circuit
(3) Refl ected power detector circuit
(4) High pass fi lter and Harmonic fi lter circuit
(5) APC circuit
(6) High temperature detector circuit
(7) FAN action control circuit
(8) Current detector circuit
(9) AVR Circuit
(10) Other Circuits
Summary of Contents for NEXEDGE NXR-901
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