Service Manual
power.
265
amplifier, and is used to detect the
re of the heat sink. When the temperature of heat sink rises to the default value, the
m signal. If the temperature rises
falls
ower will restore to their normal levels. Naturally, the alarm will dissolve.
mage to the driver amplifier
the voltage is above 14.6V, it will reduce the power level to 40W, ensuring no
Temperature Protection
The thermistor RT402 is close to the heat sink pad of the final-stage
current temperatu
fan will run; when the temperature drops to a certain level, the fan will stop running.
When the temperature is above ć, the control unit will send an alar
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 ć, Vset and transmitter p
Low-voltage and Over-voltage Protection
The control unit detects the voltage of system power supply in a real time way. When the voltage is
below 12V, the control unit will reduce the TX power to 30W, ensuring no da
of transmitter. When
damage to the final-stage amplifier of transmitter.
12.2 RX Circuit
12
Figure 12-2 Block Diagram of Receiver Circuit
ly comprises the RF band-pass filter, low-noise amplifier, mixer, IF filter, IF The receiver circuit main
amplifier and IF processor.
Front-end Circuit
The HF signal from the low-pass filter passes through the electrically tunable band-pass filter controlled
via TV level, to remove out-of-band interference signal and to send wanted band-pass signal to the
low-noise amplifier (U402). The amplified signal goes to a band-pass filter controlled via TV level, to
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