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3-6. High temperature detector circuit
The high temperature detector circuit consists of a ther-
mal switch IC (IC7) and a switching FET (Q8).
This circuit stops the transmission when the Final unit
temperature is too high (83°C or higher).
IC21
Q15,Q22,Q2
DC switch
5V AVR
IC17
Fig. 10 High temperature detector circuit
3-7. FAN action control circuit
The FAN action control circuit consists of a FAN, current
detection resistors (R11, R915 to R917), a Differential ampli-
fi er (IC15), a Switching transistor (Q3), and a Switching FET
(Q14).
It detects the normal and abnormal state by monitoring
the current flowing FAN motor, and stops operation when
failure occurs.
VBATT
R11
R915~R917
Diff. AMP
IC12
AVR
Q3
SW
M
Fig. 11 FAN action control circuit
3-8. Current detector circuit
The current detector circuit monitors the current of the
PA MMIC. It consists of current detection resistors (R918 to
R921) and a current detection IC (IC1).
It detects the normal and abnormal state of the PA MMIC
by monitoring the current of the MMIC. If a failure occurs, it
stops operation.
R918~R921
sense IC
Fig. 12 Current detector circuit
CIRCUIT DESCRIPTION
Q8
IC7
DC switch
Temp. sens.
IC15
FAN_CURR
Q14
FAN_CONT
SW
IC1
Current
PA_CURR
3-9. AVR circuit
IC17 and IC18 are AVR ICs for PA MMIC. IC11 supplies
5V to the OP amp ICs. IC12 supplies 5V to the FAN.
They maintain isolation of each power supply.
CN2
External DC
IC18
power supply
IC11
IC12
Fig. 13 AVR circuit
3-10. Other circuits
IC9 is an EEPROM that saves various adjustment data of
the Final unit.
4. Receiver Unit
The Receiver unit (X55-312) consists of the following cir-
cuits:
(1) Front-end circuit
(2) 1st-Mixer circuit
(3) 1st-IF circuits
(4) Demodulator circuits
(5) Squelch circuit
(6) Receiver PLL circuits
(7) AVR circuit
(8) Other circuits
There are three demodulating modes that can receive
Analog_Narrow, Digital_Narrow, and Digital_Very-Narrow. In
addition, there are 2 mixed modes.
4-1. Front-end circuit
The front-end circuit consists of L203 dielectric BPF,
Q201 Low Noise Amplifi er (LNA), L210 dielectric BPF and
IC202 variable attenuator. The dielectric BPFs cover from
896 to 902MHz.
The collector current of Q201 is monitored by the IC201
current detection circuit. The detected DC voltage is input to
pin 15 of IC811 (ADC).
The IC202 variable attenuator is used for the RF AGC.
The controlled attenuation value of IC202 is at its minimum
when the input level is lower than –20dBm.
4-2. 1st-Mixer circuit
The 1st mixer consists of IC205, L215, L218 and L221.
The mixer device is doubly balanced and it has local oscilla-
tor amplifi er and IF amplifi er.
The 1st local buffer stage consists of a BPF, amplifier
Q10 and frequency doubler Q11. The frequency doubler pro-
duces a 823 to 829MHz local oscillator signal from the VCO.
The BPF attenuates the 411.5 to 414.5MHz signal and 1234
to 1244MHz signal.
73.05MHz is produced as the 1st Intermediate Frequency
(IF1).
NXR-901
IC17
PA
APC,
Temp. sens.
Q3
DC
FAN
switch
13
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