Service Manual
9.1.8 Temperature Protection
86
to the heat sink pad of the final-stage amplifier, and is used to detect the current
certain level, the fan will stop running.
is above , the control unit will send an alarm signal. If the temperature rises ć
falls
9.1.9 Low-voltage and Over-voltage Protection
age of system power supply in a real time way. When the voltage is
The thermistor is close
temperature of the heat sink. When the temperature of heat sink rises to the default value, the fan will
run; when the temperature drops to a
When the temperature
continuously, the temperature protection circuit (U407B) will output a control voltage, to reduce the
power level Vset, thus reducing the transmitter power and protecting the PA. When the temperature
below 85 , Vset and transmitter power will restore to their normal levels. Naturally, the alarm will ć
dissolve.
The control unit detects the volt
below 12V, the control unit will reduce the TX power to 30W, ensuring no damage to the driver amplifier
of transmitter. When the voltage is above 14.6V, it will reduce the power level to 40W, ensuring no
damage to the final-stage amplifier of transmitter.
9.2 RX Circuit
12
Figure 9-2 Block Diagram of Receiver Circuit
The receiver circuit mainly comprises the RF band-pass filter, low-noise amplifier, mixer, IF filter, IF
amplifier and IF processor.
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